Herschel-PACS photometry of faint stars
Ulrich Klaas, Zoltan Balog, Markus Nielbock, Thomas Muller, Hendrik Linz, Csaba Kiss
AAstronomy & Astrophysics manuscript no. klaas_firfaintstars_pacs_astroph c (cid:13)
ESO 2018November 8, 2018
Herschel -PACS (cid:63) photometry of faint stars for sensitivityperformance assessment and establishment of faint FIR primaryphotometric standards
U. Klaas , Z. Balog , M. Nielbock , , T.G. Müller , H. Linz , and Cs. Kiss Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germanye-mail: [email protected] Haus der Astronomie, MPIA-Campus, Königstuhl 17, 69117 Heidelberg, Germany Max-Planck-Institut für extraterrestrische Physik (MPE), PO Box 1312, Giessenbachstraße, 85741 Garching, Germany Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 1121 Budapest,Konkoly Thege Miklós út 15-17, HungaryReceived 23 August 2017 / Accepted 7 December 2017
ABSTRACT
Aims.
Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux fromintermediately bright ( (cid:46) (cid:38)
Herschel exposure-time calculation tool.
Methods.
We obtain aperture photometry from
Herschel -PACS high-pass-filtered scan maps and chop / nod observations of the faintstars. The issues of detection limits and sky confusion noise are addressed by comparison of the field-of-view at di ff erent wavelengths,by multi-aperture photometry, by special processing of the maps to preserve extended emission, and with the help of large-scaleabsolute sky brightness maps from AKARI . This photometry is compared with flux-density predictions based on photospheric modelsfor these stars. We obtain a robust noise estimate by fitting the flux distribution per map pixel histogram for the area around the stars,scaling it for the applied aperture size and correcting for noise correlation.
Results.
For 15 stars we obtain reliable photometry in at least one PACS filter, and for 11 stars we achieve this in all three PACS filters(70, 100, 160 µ m). Faintest fluxes, for which the photometry still has good quality, are about 10 – 20 mJy with scan map photometry.The photometry of seven stars is consistent with models or flux predictions for pure photospheric emission, making them goodprimary standard candidates. Two stars exhibit source-intrinsic far-infrared excess: β Gem (Pollux), being the host star of a confirmedJupiter-size exoplanet, due to emission of an associated dust disk, and η Dra due to dust emission in a binary system with a K1 dwarf.The investigation of the 160 µ m sky background and environment of four sources reveals significant sky confusion prohibiting thedetermination of an accurate stellar flux at this wavelength. As a good model approximation, for nine stars we obtain scaling factorsof the continuum flux models of four PACS fiducial standards with the same or quite similar spectral type. We can verify a lineardependence of signal-to-noise ratio (S / N) with flux and with square root of time over significant ranges. At 160 µ m the latter relationis, however, a ff ected by confusion noise. Conclusions.
The PACS faint star sample has allowed a comprehensive sensitivity assessment of the PACS photometer. Accuratephotometry allows us to establish a set of five FIR primary standard candidates, namely α Ari, ε Lep, ω Cap, HD 41047 and 42 Dra,which are 2 – 20 times fainter than the faintest PACS fiducial standard ( γ Dra) with absolute accuracy of < Key words.
Space vehicles: instruments – Methods: data analysis – Techniques: photometric – Infrared: stars – Stars: atmospheres– Radiation mechanisms: thermal
1. Introduction
The photometric calibration of the PACS photometer (Poglitschet al. 2010) on-board the
Herschel
Space Observatory (Pilbrattet al. 2010) is based on celestial standard stars (Balog et al.2014; Nielbock et al. 2013). These primary standard stars havewell-modelled spectral energy distributions (SEDs) of their pho-tospheric emission and an accurate absolute calibration in theK-band (Dehaes et al. 2011). They are still relatively bright inthe far-infrared (in the range 1 - 10 Jy) to achieve high signal-to-noise ratios (S / N) within reasonable measurement times. Be- (cid:63)
Herschel is an ESA space observatory with science instruments pro-vided by European-led Principal Investigator consortia and with impor-tant participation from NASA. sides repeated measurements of these standard stars, a set offainter secondary standard stars was repeatedly measured byPACS as part of the calibration program during the
Herschel
Per-formance Verification and Routine Operations periods. This in-cluded sources down to a few mJy. The PACS photometer is lin-ear over a flux range exceeding the primary standard fluxes, withan optimized detector set-up for the flux background from thetelescope. Flux nonlinearity is therefore an issue for consider-ably brighter sources and has been addressed elsewhere (Mülleret al. 2016). However, including fainter sources with well knownflux predictions allows to us address the following questions:1) How does the sensitivity scale with flux and time?
Article number, page 1 of 42 a r X i v : . [ a s t r o - ph . S R ] D ec & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Table 1.
Faint secondary standards observed by
Herschel -PACS. Source fluxes from Gordon et al. (2007) are for an e ff ective wavelength of71.42 µ m and have been colour-corrected to the PACS central wavelength of 70 µ m by dividing by the factor 0.961 (cf. Müller et al. 2011) for aRayleigh-Jeans-tail-type SED. 100 and 160 µ m fluxes for these sources are then extrapolated values for this adopted SED. Model flux prediction (mJy) Spectral type ReferenceHD Other name f f f β Gem 2457 ( ± ± ± a α Ari 1707 ( ± ± ± a ε Lep 1182 ( ± ± ± a ω Cap 857.7 ( ± ± ± a η Dra 479.5 ( ± ± ± b δ Dra 428.9 ( ± ± ± a θ Umi 286.2 ( ± ± ± a ± ± ± a ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± b δ Hyi 22.9 ± ± ± /
2V Gordon et al. (2007)156729 e Her 12.0 ( ± ± ± b ± ± ± b Notes.
Source flux models are from ( a ) http: // general-tools.cosmos.esa.int / iso / users / expl_lib / ISO / / isoprep / cohen / extraps / ( b ) http: // general-tools.cosmos.esa.int / iso / users / expl_lib / ISO / / isoprep / gbpp /
2) How does the finally achieved sensitivity compare with pre-dictions by the PACS exposure-time calculator of the
Her-schel observation planning tool?3) What is the impact and consistency of the applied data re-duction scheme on the resulting source flux for fainter andfainter flux contributions on top of the telescope backgroundlevel?4) What is the impact of background confusion noise on theresulting fluxes and the sensitivity limit?Ultimately, some of the faint sources may be characterized wellenough to become primary standard sources for future pow-erful and sensitive FIR space telescopes, such as SPICA (e.g.Sibthorpe et al. 2015), Millimetron (e.g. Smirnov et al. 2012) orthe Origins Space Telescope (Meixner et al. 2017).Most of the observations have been done in mini-scan-mapmode, but we have included also a valuable set of complemen-tary chop / nod point-source photometry. We first report the scanmap photometry including the sensitivity verification. Then wepresent the chop / nod photometry and compare it with the scanmap results. Finally, we analyse the source spectral energy dis-tributions (SEDs) by comparison with model SEDs and establishwhich sources are suitable as accurate celestial standards.
2. Source selection
In preparation of the PACS in-flight photometric calibration, sec-ondary standard source lists with stars described in Cohen et al.(1996), Hammersley et al. (1998), and Gordon et al. (2007) wereprepared by the PACS Instrument Control Centre (ICC) team.Depending on the source visibility during the Herschel mission,a subset of sources from these lists were observed to cover theflux range from 0.5 - 2.5 Jy down to 2 - 10 mJy over the threephotometer wavelengths 70, 100, and 160 µ m. The finally ob-served 17 sources are listed in Table 1.
3. Scan map photometry
Fifteen out of the 17 sources were observed in the PACS mini-scan-map point-source observing mode. This was the recom-mended scientific observing mode for point sources after
Her-schel’s
Science Demonstration Phase (SDP), because it had abetter sensitivity and allowed a better characterization of thesource vicinity and larger-scale structures of the backgroundthan chop / nod photometry. The satellite scans were mostly donewith the nominal 20 (cid:48)(cid:48) / s speed; a few early ones were done withthe originally adopted speed of 10 (cid:48)(cid:48) / s. The scan map dimensionparameters are usually 3 (cid:48) leg length and ten legs with a separa-tion of 4 (cid:48)(cid:48) with scan angles in array coordinates of 70 ◦ and 110 ◦ (along the diagonal of the bolometer arrays). Only a few earlymeasurements had di ff erent parameters from these values, whenstill probing for the optimum parameter set. In the case of repe-tition factors larger than 1, in particular for our faintest targets,the whole scan map was repeatedly executed according to thespecified factor. We note that a repetition factor may have beenoptimized for the short wave filter measurement and is hence lessoptimal for the 160 µ m filter, where the star is fainter. The obser-vations were usually done in high gain mode. There are a fewexceptions taken for comparative performance checks. Selectedobserving parameters are listed for all individual scan map ob-servations in Tables A.3 to A.5. The data reduction and calibration performed in HIPE (Ott2010) followed the description in Balog et al. (2014), apply-ing the high-pass filter (HPF) algorithm to remove the f -noise HIPE is a joint development by the Herschel Science Ground Seg-ment Consortium, consisting of ESA, the NASA Herschel Science cen-ter, and the HIFI, PACS and SPIRE consortia.Article number, page 2 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Table 2.
Relevant scan map parameters for photometry and noise determination. r phot aper is the radius of the aperture used for the point-sourcephotometry, c aper is the corresponding correction factor to scale the flux to its total value, cc( λ ref ) is the colour-correction factor to derive the sourceflux at the reference wavelength λ ref of the filter (Müller et al. 2011), HPF is the abbreviation for high pass filter, pixfrac is the ratio of drop sizeto input pixel size used for the drizzling algorithm (Fruchter & Hook 2002) within the photProject() mapper, outpix is the output pixel size in thefinal map, N aper is the number of output pixels inside the photometry aperture with r phot aper , and f corr is the correlated noise correction factor dependingon the combination of HPF radius / pixfrac / outpix. Filter r phot aper c aper cc star ( λ ref ) HPF radius a pixfrac outpix N aper f corr ( µ m) (") (")70 5.6 1.61 1.016 15 1.0 1.1 81.42 3.13100 6.8 1.56 1.033 20 1.0 1.4 74.12 2.76160 10.7 1.56 1.074 35 1.0 2.1 81.56 4.12 Notes. ( a ) This parameter determines the elementary section of a scan over which the high-pass filter algorithm computes a running median value.Its unit is "number of read-outs". The spatial interval between two readouts is α ro = v scan ν ro . For the standard ν ro =
10 Hz read-out scheme in PACSprime mode, and a scan speed v scan = / s, the spatial interval α ro between two read-outs corresponds to 2". The entire width of the HPF window(") = [(2 × HPF radius) + × α ro . from the scan data of the bolometer detectors. A few recentdevelopments in PACS data reduction (gyro correction and up-dated pointing products, refined focal plane geometry calibrationand more precise timing of the detector readouts) have been in-cluded.The source flux is determined by aperture photometry. Therelation between the final stellar flux at the reference wavelengthof the respective filter (70, 100 and 160 µ m), f star ( λ ref ), and theintegrated background subtracted map flux inside the aperture,f aper , is given by f star ( λ ref ) = c aper ( λ ref ) × f aper ( λ ref ) cc star ( λ ref ) , (1)where c aper is the aperture correction factor to get the total non-colour-corrected source flux, f tot . Since the PACS calibrationscheme yields a flux related to a SED ν × f = const . the colour-correction factor cc star ( λ ref ) provides the appropriate correctionfor the stellar SED (5000 K blackbody). The aperture and colour-correction factors are listed in Table 2.For the investigation of background contamination we alsoused the JScanam algorithm (Graciá-Carpio et al. 2015), whichbetter preserves extended emission. For the final projection of alldata, the HIPE algorithm photProject() was applied; the selectedmapping parameters pixfrac and output pixel size are listed inTable 2. For the faint star photometry we have selected smaller apertures(cf. Table 2) than were used for the fiducial star photometry inBalog et al. (2014) (12 (cid:48)(cid:48) , 12 (cid:48)(cid:48) , 22 (cid:48)(cid:48) , respectively). These are thesame aperture sizes as for chop-nod photometry.These smaller apertures, which are adapted to the PSFFWHM in the respective filter, result in a much higher flux re-producibility among the individual measurements and hence asmaller standard deviation of the mean source flux, as well asmore reliable and consistent (with regard to the relative spectralshape) source flux measurements for the faintest sources. Thisis shown in Table A.1 in Appendix A.1, where photometry withthe large standard apertures is compared with the photometryapplying the smaller apertures. For the cases with ≥ Table 3.
Average photometric reproducibility and its standard deviationfor the six brightest stars with at least eight individual measurementsper filter.
Filter Photometric reproducibility( µ m) (%)70 0.23 ± ± ± µ m, respectively, af-ter correction for evaporator temperature e ff ects and initial sig-nal drifts after cooler recycling and photometer switch-on. Ourphotometry includes the evaporator temperature correction andpractically all measurements are outside phases with noticeableinitial signal drifts. The mean reproducibility of the 70 µ m stellarfluxes comes close to the standard deviation of the bolometer re-sponse. At 100 and 160 µ m the mean reproducibility is less goodand shows a larger scatter, firstly because the sources are weakerand secondly because the uncertainties in background subtrac-tion are higher. A flux histogram has been constructed for all output pixels ofthe image map, where the corresponding coverage map indi-cates that cover pix (cid:38) cover max . This is justified, since the starsare located in the central part of the map around the highest cov-erage. A Gauss fit has been performed to the histogram but re-stricted to the part with fluxes below the bin associated with themaximum number, representing in first approximation the back-ground level, and hence avoiding contamination of the derived The coverage map gives the sum of all complete ( = < & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph noise per pixel, σ pix , by flux of faint sources (to optimize thequality of the fit, actually about 10 bins above the bin with themaximum number are included in the fit). An example of thisprocedure is shown in Fig. 1. This method provides very reliableand homogeneous noise figures. Fig. 1.
Illustration of the histogram method to determine the backgroundnoise. The example shows the number of pixels per flux bin of the 70 µ mmap of OBSID 1342242772 ( β Gem on OD 1051) for all pixels with acoverage value > cover max ( > ff towards higher fluxes. The red curve is the Gaussian fit to thishistogram. For this fit we took all bins left of the distribution maximuminto account, but limited the right fitting range to ten bins beyond thedistribution maximum in order to avoid a bias of the fitted width by truesource flux. The vertical and horizontal red dashed lines indicate themean background level and the FWHM = (cid:112) log (2) σ pix , respectively.For fluxes per pixel above ≈ For our photometric measurements, the noise inside the mea-surement aperture must be determined from the noise per pixel σ pix . This is given by σ aper = (cid:112) N aper × σ pix , (2)with N aper being the number of map output pixels inside the mea-surement aperture. The respective numbers of N aper are listed inTable 2.The high pass filtering and map projection lead to correlatednoise which must be corrected to reconstruct the real detectornoise (Popesso et al. 2012). This is achieved by applying thecorrelated noise correction factor f corr f corr = n = (cid:88) ≤ i + j + k ≤ n c i jk hp f i outpix j pix f rac k (3) k = , n ; j = , ( n − k ); i = , ( n − k − j ) . Hence, the noise corrected for correlated noise inside themeasurement aperture is σ aper , corr = (cid:112) N aper × f corr × σ pix . (4)The S / N of the measurement is then determined as SN = f aper σ aper , corr , (5) c ijk is related to the 20 parameters P(0) . . . P(19) in Table 9 of Popessoet al. (2012) by running three nested DO-loops with (from outer to in-ner) k =
0, n; j =
0, (n-k); and i =
0, (n-k-j).
Table 4.
RMS noise values f σ, s , the 1 σ ( SN =
1) flux level beingachievable with an integration time of 1 s, used in HSpot for S / N calcu-lation.
Filter f σ, s ( µ m) (mJy)70 30.6100 36.0160 68.5 Table 5.
Central coverage time of a source during a scan map execu-tion depending on the scan map parameters (scan leg length, scan legseparation and number of scan legs) as calculated by HSpot. The com-bination in bold face is the default combination used for the majority ofthe measurements.
Scan map parameters Map angle t obscovercent (" / " / / s150 / /
10 70 /
110 80 / / /
110 90210 / /
20 90 220210 / /
25 90 275240 / / /
117 9690 / / /
110 45210 / / / s120 / /
21 80 /
100 252150 / / /
95 144210 / /
20 90 440210 / /
25 90 55090 / / /
120 90120 / / /
100 108210 / / aper is the part of the source flux measured inside the aper-ture. The measured S / Ns are compared with the S / N predictions of theexposure time calculation tool in the
Herschel
Observatory Plan-ning Tool HSpot (Herschel-Spot (HSpot) User’s Guide: HerschelObservation Planning Tool 2013). HSpot calculates the S / Nsbased on an rms noise due to telescope thermal noise emissionand the electrical noise of the read-out electronics, cf. Table 4: SN HSpot = f star f σ, s (cid:112) n rep t obscover , (6)with f star using the colour- and aperture-corrected total stellarflux.This S / N scales with the square root of the coverage time ofthe source during one scan map, t obscover and the number of scanmap repetitions, n rep . For mini-scan-maps, t obscover is maximumat the map centre and decreases towards the boarders. In anal-ogy to the noise determination in the final maps, as describedin Sect. 3.3, we use t obscover = t obscovercent .The value of t obscover depends on the scan map parameters (scan leg length, scan legseparation and number of scan legs) and is listed in Table 5 forall scan map parameter combinations used for our observations. Article number, page 4 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Figure 2 shows the dependence of the achieved S / Ns on time,represented as number of scan repetitions, and the comparisonwith the HSpot prediction. This includes combined maps of scanand cross-scans, which have the sum of the scan repetitions ofthe individual maps.For 70 and 100 µ m measurements we find S / N ∝ √ n rep .There are deviations from this relation in that respect that theS / N of the combined maps is higher than the expected factorof √ / Nto the HSpot prediction is 1.14–1.22 at 70 µ m and 1.03–1.09 at100 µ m, respectively. Given the fact that the HSpot predictionis for half maximum coverage and the noise determination inthe maps is above a threshold of half maximum coverage, themeasured S / N can be considered as consistent with the HSpotprediction.For the 160 µ m measurements we find for small repetitionnumbers ( n rep ≤
12) that the S / N increases with the √ n rep forsingle and combined maps. For higher repetition numbers it isobvious that the increase of the measured S / Ns is flatter. Thisflattening is caused by confusion noise, which will be discussedin the following Section. The ratio of the average measured S / Nto the HSpot prediction is around 0.80. We note, however, thatthere is some margin in achievable S / N depending on the se-lection of the high-pass filter (HPF) radius. We calculate a de-crease of the resulting noise by ≈
23% between HPF radius = =
15 read-outs for pixfrac = (cid:48)(cid:48) . µ m observations of ε Lep from OD 1377, to check the performance relative to full ar-ray observations. With regard to comparable observations fromODs 502, 833, and 1034 (cf. Table A.5), we find the following:The coverage is 0.51 of the full array map, but the noise is in-creased by only a factor of 1.21.In the case of η Dra the performance of scan speeds 10" / sand 20" / s can be inter-compared. While the coverage time of the10" / s scan speed maps is always greater than or equal to twicethe coverage time of the 20" / s scan speed (cf. configurations inTables A.3 to A.5 and corresponding coverage times in Table 5),the measured S / N of the 20" / s scan speed is above the HSpot pre-diction at 70 and 100 µ m, while the measured S / Ns of all 10" / sscan speed combinations are below the HSpot prediction. Thisis a clear demonstration that the 20" / s scan speed maps are rela-tively more sensitive than their 10" / s scan speed counterparts. At160 µ m this is even more pronounced; the S / N of the 20" / s scanspeed map with half of the coverage time is better than that of the10" / s scan speed map with otherwise identical map parameters.Figure 3 shows the dependence of the achieved S / Ns on flux.For the 70 and 100 µ m filters we can verify that the S / N scaleslinearly with flux over two decades of flux and at least down tototal (aperture corrected) source fluxes of 30 mJy and 18 mJy,respectively. For the 160 µ m filter the linearity with flux can beverified over about one decade in flux down to a total (aperturecorrected) source flux of 85 mJy for repetition factors 1 – 12. Forfainter fluxes measurements with higher ( ≥
20) repetition factorsare necessary to achieve a S / N which is su ffi ciently above val-ues close to the detection limit (S / N (cid:46) / N that is smaller than expected, which we explain in the following Section as be-ing due to a confusion noise contribution. Since the confusionnoise contribution is not the same in the di ff erent source fields,the linearity of the S / N with flux cannot be verified any morestraightforwardly in the 160 µ m flux range below 85 mJy. Impact on S / N by background confusion noise
In particular at 160 µ m, there may be another relevant noisesource, which is FIR background confusion noise. This is com-posed of a cosmic infrared background component and a galac-tic cirrus component. Examples of background confusion, whichalso a ff ects the source photometry, are shown in Figs. 5 and 6.The confusion noise is independent of on-source observationtime, that is, in the case of approaching the confusion noise limit,the S / N does not improve anymore with on-source observationtime. SN HSpot , conf = f star (cid:114) f σ, s n rep t obscover + f . (7)This leads to the e ff ect that the S / N curve with time flattensout as observed for the 160 µ m S / Ns in Fig. 2. For our sourcefields, HSpot returns a 160 µ m point source equivalent confusionnoise estimate f confnoise between 1.3 and 1.5 mJy. The typical on-source observation time for repetition factor 1 is 45 s, resultingin a 160 µ m noise level of 10 mJy. This is about a factor of 7higher than the estimated confusion noise and only for large scanmap repetition factors ( > HD 181597 and HD 15008 ( δ Hyi) are good examples for non-detections at 160 µ m, because the expected source flux is belowthe detection limit. Both sources have a clear detection at 70 µ m(S / N =
30 and 15, respectively), which allows to identify the ex-pected source position on the 160 µ m maps (see Fig. 4). Table 6lists the determined S / Ns, which are < / Nmeasurement in the map is actually higher by the factor f corr = / N detection limit of 5– 6). This is in accordance that no source can be detected at thelocation of the star in the 160 µ m map. Table 6. S / N determination at 160 µ m for HD 181597 and HD 15008,which are below the detection limit (S / N (cid:46) HD f predict f aper σ aper , corr SN ( µ m) (mJy) (mJy) (mJy)181597 5.2 3.3 2.6 1.315008 4.4 2.8 3.2 0.9 The fainter the star, the higher the probability, in particular at 100and 160 µ m, that nearby sources confuse the source flux insidethe measurement aperture.A clear case of confusion by neighboring sources is shownin Fig. 5 for the star HD 159330. While at 70 µ m the star is moreor less the only visible source inside the field, at 100 µ m a small Article number, page 5 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Fig. 2.
Measured S / Ns for mini-scan-map photometry depending on the number of repetitions. Blue, green, and red symbols represent measure-ments in the three filters, 70, 100, and 160 µ m, respectively. Diamond symbols indicate a scan speed of 20" / s, triangles a scan speed of 10" / s. Thedotted lines in the respective colours show the S / N prediction by the PACS exposure time calculator of the
Herschel observation planning toolHSpot for the measured colour corrected stellar flux. Long dashed red lines indicate the S / N prediction including confusion noise. An exceptionis the panel of η Dra, where the sets of four dotted, dashed, and dashed-dotted lines represent the sensitivity predictions for four di ff erent mapparameter combinations; the upper three are with 10" / s scan speed, the lowest one is with 20" / s scan speed. For more details, see text.Article number, page 6 of 42. Klaas et al.: Herschel -PACS photometry of faint stars
Fig. 2. continued. Measured S / Ns for mini scan map photometry depending on the number of repetitions. Article number, page 7 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Fig. 3.
Measured S / Ns for mini-scan-map photometry depending on the source flux (Note: fluxes measured inside the aperture are used here). Forbetter comparability only measurements with an observational set-up identical with the final mini-map set-up (ten 180 (cid:48)(cid:48) scan legs with 4 (cid:48)(cid:48) separationand scan speed 20 (cid:48)(cid:48) / s) are considered. Lighter colour tones are measurements with higher scan map repetition factors. We note that here the dotted,dashed, and dashed dotted lines in di ff erent colour tones do not represent the S / N prediction by the PACS exposure time calculator of the
Herschel observation planning tool HSpot, but are empirical adjustments to the average measured S / N for the respective scan map repetitions. In the 160 µ mpanel, numbers in parentheses mark measurements with high repetition factors whose S / N is degraded by confusion noise. This is also indicatedby two S / N with flux lines for repetition factor 90, where the lower one includes additional confusion noise (cn) of 0.8 mJy.Article number, page 8 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Fig. 4.
Examples of detection at 70 µ m and non-detection at 160 µ m. The red cross (arm length equal to 5 (cid:48)(cid:48) ) indicates the common Herschel position. We note that for both sources there exists only one scan map orientation which leads to some residual scan artefacts, in vertical anddiagonal direction, respectively; see Table A.3 for details. Top: HD 181597, OBSID 1342185451 on OD 146. The bright point source at the rightis KIC 11555225. Bottom: HD 15008 ( δ Hyi), OBSID 1342189130 on OD 241. cluster of sources around the star starts to pop up, but the staris still the dominant source inside the field. At 160 µ m, all sur-rounding sources are brighter than the star, which appears onlyas an appendix of the source located north-west of it. Also thelocal brightness maximum is not as well located on the cross asis the case for the stellar images at 70 and 100 µ m. It is there-fore not possible to obtain reliable photometry for HD 159330 at160 µ m. The compactness of the surrounding sources both in theHPF and the JScanam image points to an extragalactic nature ofthe confusing sources. This is di ffi cult to verify in the optical,since HD 159330 is a 6.2 mag (V band) bright star.An example of likely cirrus confusion is shown in Fig. 6around the star η Dra (HD 148387). There is relatively signifi-cant similarity between the HPF and JScanam processed mapconcerning the brighter spots and features, while on the low levelthere are di ff erences, because the HPF algorithm is not designedto preserve faint extended emission. Nevertheless both maps in-dicate a filamentary emission around the star. Indeed, η Dra, withl = o and b = + o , is located at the edge of the Draco neb-ula (cf. e.g. Fig. 3 in Herbstmeier et al. 1998, w.r.t. its location),a pronounced cirrus cloud. The extract of the AKARI
Wide-L(140 µ m) all sky map (Doi et al. 2015) reveals that η Dra is lo-cated at the southern edge of a cirrus knot with an extension of AKARI
Far-infrared All-Sky Survey maps query servicehttp: // / AKARI / Archive / Images / FIS_AllSkyMap / search / We use the
AKARI
WIDE-L (140 µ m) maps instead of the N160 it passing north-west into the PACS map area. The cirrus confu-sion a ff ects the derived 160 µ m flux noticeably, as is discussedin Sect. 5.2. Other cases of suspected cirrus confusion are alsodiscussed there. Results of individual photometric measurements are given inAppendix A, Sect. A.3 in Tables A.3 to A.5. Here we report thecombined aperture and colour-corrected photometry of all mea-surements in Table 7. This is identical with the phot_s photome-try in Table A.1. The quoted uncertainties of the measurementsin Table 7 include the absolute calibration uncertainty of 5%, dueto the fiducial star model uncertainties, which is quadraticallyadded to the rms of the mean flux value as quoted in Table A.1.For 11 stars we obtain reliable photometry in all three PACSbands. There is no 70 µ m flux for HD 41047, since there areonly measurements in the 100 and 160 µ m filters. There is no160 µ m detection for HD 159330 because of confusion noise.For HD 181597 and HD 15008 we obtain reliable fluxes only at70 µ m, since there are no 100 µ m scan map measurements and at160 µ m the stars are too faint for the applied repetition numbers.Faintest fluxes, for which the photometry has still good quality(accuracy ≤ (160 µ m) maps, because the latter ones do not have su ffi cient S / N overthe whole field for illustration of the background structure.Article number, page 9 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Fig. 5.
Example of background confusion noise around the star HD 159330 (OBSIDs 1342213583-86 on OD 628, see Tables A.3 and A.4 fordetails) by comparing maps in the three filters 70, 100 and 160 µ m. At 160 µ m both the high-pass filtered (HPF) and the JScanam maps are shownto explore the nature of the background sources. The red cross (arm length equal to 5 (cid:48)(cid:48) ) indicates the best common Herschel position of the starafter frame centering at RA = = + Fig. 6.
Example of cirrus confusion noise around the star HD 148387 ( η Dra, OBSIDs 1342186146, ..47, ..55, ..56 from OD 160). The left panelshows the high-pass filter processed map used for the photometry, the photometric aperture with 10 (cid:48)(cid:48) . AKARI
WIDE-L (140 µ m) background emission around the source (red cross), the AKARI map area is about four times as largeas the PACS map area, which is indicated by the red dashed square.
In Appendix Section A.2, we conduct a qualitative inter-comparison of the high-pass filter (HPF) photometry with threeother
Herschel mapper softwares for HD 152222, the fainteststar at 160 µ m with reliable photometry in all three filters. As-pects like noise behaviour and shape of the intensity profiles areinvestigated and discussed. The main conclusion is that for theother mappers adapted aperture correction factors need to be es-tablished which will be determined on the basis of the high S / Nfiducial standard star observational database in a forthcoming pa-per (Balog et al., 2018, in preparation).The evaluation of the correspondence with the models isdone in Sect. 5.
4. Chop-nod photometry
Thirteen out of the 17 sources were observed in the PACS chop-nod point source observing mode. This was the originally recom-mended PACS photometer observing mode for point and com-pact sources. This mode used the PACS chopper to move thesource on-array by about 50 (cid:48)(cid:48) , corresponding to the size of aboutone blue / green bolometer matrix (16 pixels) or the size of abouthalf a red matrix (8 pixels), with a chopper frequency of 1.25 Hz.The nodding was performed by a satellite movement of the sameamplitude but perpendicular to the chopping direction. On eachnod position the chopper executed 3 ×
25 chopper cycles. Thethree sets of chopper patterns were either on the same array po-sition (no dithering) or on three di ff erent array positions (ditheroption). In the latter case the chopper pattern was displaced par- Article number, page 10 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Table 7.
Combined mini-scan-map photometry. Model fluxes are listed in Table 1. The quoted uncertainties of the measurements include theabsolute calibration uncertainty of 5%. In the case of only one observation for a specific source, the statistical error of this flux measurementis used in the uncertainty determination, and in the case of more than one observation for a source, as given in columns n , n , and n , thestandard deviation of the weighted mean as given in Table A.1, column phot_s, is used in the uncertainty calculation. HD Name n f star (70 µ m) f star (70 µ m ) f model n f star (100 µ m) f star (100 µ m ) f model n f star (160 µ m) f star (160 µ m ) f model (mJy) (mJy) (mJy)62509 β Gem 8 2649 ±
132 1.08 ± ±
64 1.08 ± ±
25 1.09 ± α Ari 8 1664 ±
83 0.97 ± ±
41 0.99 ± ±
17 1.02 ± ε Lep 8 1166 ±
58 0.99 ± ±
28 0.99 ± a ±
11 1.00 ± ω Cap 8 845 ±
42 0.99 ± ±
21 0.99 ± ± ± η Dra 8 506 ±
25 1.06 ± ±
13 1.07 ± ± ± δ Dra 12 436 ±
22 1.02 ± ±
11 1.03 ± ± ± θ Umi 4 284 ±
14 0.99 ± ± ± b ± f ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± c ± ± ± ± ± ± ± ± ± ± d ± ± ± ± ± ± e ± ± ± ± δ Hyi 1 22 ± ± ( a ) OBSIDs 1342205202 & 1342263904 excluded ( b ) OBSIDs 1342184574, 1342184575, 1342184585, 1342184586 excluded ( c ) OBSIDs 1342185446, 1342185448, 1342185447, 1342185449, 1342191986 excluded ( d ) OBSIDs 1342240702, 1342240703, 1342227973 & 1342227974 ( e ) Only OBSIDs 1342198537 & 1342198538 ( f ) Due to cirrus confusion, a background subtraction uncertainty of 10% must be added: 62 ± Table 8.
Combined chop-nod photometry. Model fluxes are listed in Table 1. Values in italics are uncertain. The quoted uncertainties of themeasurements include the absolute calibration uncertainty of 5%. In the case of only one observation for a specific source, the statistical error ofthis flux measurement is used in the uncertainty determination, in case of more than one observation for a source, as given in columns n , n ,and n , the standard deviation of the weighted mean from the individual chop / nod fluxes listed in Tables B.1 to B.3 is used in the uncertaintycalculation. HD Name n f star (70 µ m) f star (70 µ m ) f model n f star (100 µ m) f star (100 µ m ) f model n f star (160 µ m) f star (160 µ m ) f model (mJy) (mJy) (mJy)62509 β Gem 1 2570 ±
129 1.05 ± ±
65 1.07 ± ±
25 1.09 ± ε Lep 2 1181 ±
59 1.00 ± ±
31 0.97 ± ±
12 0.92 ± η Dra 1 509 ±
31 1.06 ± ±
19 1.01 ± ±
10 1.13 ± δ Dra 5 440 ±
22 1.03 ± ±
12 1.03 ± ± ± θ Umi 10 282 ±
14 0.98 ± ± ± a ± ± ± ± ±
15 0.77 ± ± ± ± ± b ± ± ± ± ± ± ± ± δ Hyi 4 20 ± ± ( a ) ( b ) OBSIDs 1342185441 & 1342185442 excludedallel to the chopper deflection by 8 (cid:48)(cid:48) . blue pixels or 1 redpixels). Most of the faint star observations were performed withthe dither option on; Tables B.1 to B.3 indicate for each ob-servation the selection of the respective dither / no-dither mode. Each chopper plateau lasted for 0.4 s (16 readouts on-board) pro-ducing four frames per plateau in the telemetry down-link. Thefull 3 ×
25 chopper cycles per nod position were completed inless than 1 minute. In the case of repetition factors larger than
Article number, page 11 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Fig. 7.
Ratio of the observed and colour-corrected (cc) scan map photometry fluxes with either the photometric standard model flux or the Gordonet al. (2007) 70 µ m flux prediction and Rayleigh-Jeans extrapolation (red diamonds). The uncertainty of the models is shown by the light bluerange, the uncertainty of the flux prediction and the Rayleigh-Jeans extrapolation by the dark blue range. The uncertainty of the flux ratio includesthe absolute photometric error of the measurement.
1, in particular for our faintest targets, the nod-cycles were re-peated in the following way (example for 4 repetitions): nodA-nodB-nodB-nodA-nodA-nodB-nodB-nodA to minimize satelliteslew times. Selected repetition factors are given in Tables B.1to B.3. We note that a repetition factor may have been optimizedfor the short-wave filter measurement and is hence less optimalfor the 160 µ m filter, where the star is fainter. The observationswere usually done in high gain mode, but there were a few ex-ceptions taken for comparative performance checks. The data reduction and calibration performed in HIPE (Ott 2010)followed the description in Nielbock et al. (2013). For the reduc-tion of our faint star targets we adjusted a few aspects and usedvery recent software developments for PACS photometer obser-vations (gyro correction and updated pointing products and re-fined focal plane geometry calibration). These new correctionsare meanwhile part of the Standard Product Generation (SPG)pipelines version 13.0 and higher. For the stellar flux derivationthe same procedures and parameters as for scan map photometry,and as summarized in Eq. 1 and Table 2, are applied.The photometric uncertainty was estimated with the his-togram method with a coverage threshold as described in detail in Sect. 3.3 for the scan maps. Correlated noise is corrected forvia an empirical function to obtain a conservative upper limitfor the measurement uncertainties. The applied correction fac-tors f corr are 6.33, 4.22, and 7.81 for the 70, 100, and 160 µ mfilters, respectively. Results of individual measurements are given in Appendix Bin Tables B.1 to B.3. We note that there are observations ofHD 138265 on OD 146 for which the noise does not seem toscale with the number of repetitions. The reason is that for thesemeasurements the basic length of the nod period was varied andcompensated by the corresponding number of nod cycle repeti-tions.Here we report the combined photometry of all measure-ments in Table 8. The quoted uncertainties of the measurementsinclude the absolute calibration uncertainty of 5%, due to thefiducial star model uncertainties, which is quadratically added tothe the rms of the mean flux value.For six stars we obtain reliable photometry in all three PACSbands. There is no 70 µ m flux for HD 41047, since there areonly measurements in the 100 and 160 µ m filters. There is no160 µ m detection for HD 159330 because of confusion noise. Article number, page 12 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Table 9.
Evaluation of correspondence of PACS photometry with models or flux predictions (C = Cohen, H = Hammersley, G = Gordon). Column"mode" specifies the PACS observing mode (s = scan map, c = chop / nod). Column "Reason for deviation" gives a short summary of the discussionin the reference sections. HD Other name Model Mode Correspondence with model Reason for deviation Sect.62509 β Gem C s,c no, excess of ≈ +
8% dust disk in planetary system 5.2.112929 α Ari C s yes, better than ± ε Lep C s,c yes, better than ± ω Cap C s yes, better than ± η Dra H s,c no, excess of ≈ +
8% dust in binary system 5.2.1180711 δ Dra C s,c partially, ≈ +
3% o ff set for λ ≤ µ m +
7% @160 µ m cirrus confusion 5.2.2139669 θ Umi C s,c partially, ≈ +
3% o ff set for λ ≤ µ m +
16% @160 µ m cirrus confusion 5.2.241047 HR 2131 C s,c yes, better than ± ≈ −
4% o ff set138265 HR 5755 G s,c partially, ≈ −
2% o ff set for λ ≤ µ m +
40% @160 µ m cirrus confusion 5.2.2159330 HR 6540 G s,c partially, better than ±
1% for λ ≤ µ mno flux determination @160 µ m source confusion 3.7152222 SAO 17226 G s,c yes, better than ± µ m +
19% @100 µ m, + µ m background confusion 5.2.2181597 HR 7341 H s,c yes, better than 4% @70 µ mno flux determination @160 µ m below detection limit 3.615008 δ Hyi G s,c yes, better than 4% @70 µ mno flux determination @160 µ m below detection limit 3.6156729 e Her H c no below detection limit168009 HR 6847 H c no below detection limitFor HD 15008 we only obtain a reliable flux at 70 µ m, sinceat 100 and 160 µ m the star is too faint for the applied repe-tition numbers. HD 181597, HD 156729 and HD 168009 havenon-detections despite a high repetition factor of 50. The non-detection is likely due to a not-yet-perfect knowledge of the op-timum observing strategy early in the mission (the observationswere Astronomical Observation Template (AOT) test cases).Faintest fluxes, for which the photometry has still good quality(accuracy ≤ / nod and scan map stellar photometry. In summary theresults are very consistent and confirm each other. A few caseswith larger discrepancy are due to only a small number of mea-surements or low S / N in chop / nod mode.
5. Comparison with model fluxes or flux predictions
Since all detected stars are observed in scan map mode and wehave more and better S / N measurements in this mode, we re-strict the following inter-comparison with the models to scanmap photometry. For each star a quantitative comparison per fil-ter is given in Table 7. Figure 7 shows a graphical comparisonof the measured fluxes with the model and Table 9 provides asummary of the correspondence evaluation.We find an excellent correspondence with the model or fluxprediction over the full PACS wavelength range for α Ari, ε Lep, ω Cap, HD 41047, 42 Dra and HD 152222. We find a partial cor-respondence up to 100 µ m for δ Dra, θ Umi, HD 138265 andHD 159330, while the 160 µ m flux exceeds the model flux or,as in the latter case, cannot be determined due to confusion bynearby sources. For HD 39608, the 70 µ m flux still corresponds excellently with the flux prediction, but at 100 and 160 µ m anoticeable flux excess is discovered. β Gem and η Dra both ex-hibit a significant o ff set above the model for all wavelengths. ForHD 181597 and HD 15008 we can prove a good correspondenceat 70 µ m, but have no means to do so at longer wavelengths,since our measurements are not above the detection limit.We discuss now the origin of the excess emission for δ Dra, θ Umi, HD 138265, HD 39608, β Gem and η Dra.
A FIR excess can be an intrinsic source property or be caused byconfusing background sources, as already addressed in Sect. 3.7.Cohen et al. (2005) and Dehaes et al. (2011) discuss possiblechromospheric emission or thermal emission from an ionizedwind which gives noticeable excess at sub-mm wavelengths, butmay already set in at FIR wavelengths, as intrinsic emissionmechanisms. Groenewegen (2012) investigated the phenomenonof infrared excess around red giant branch stars assuming massloss arising from chromospheric activity.One other aspect to consider in this context is possible sourcevariability; we investigate this for the case of β Gem: The Cohenet al. (1996) FIR model SED is an extension of an absolutelycalibrated 1.2 – 35 µ m model Cohen et al. (1995). In Fig. 8 weshow both model parts represented by the orange and red lines.No inconsistency between both parts can be recognised. Be-sides the PACS photometry we show the colour-corrected
IRAS
FSC (Moshir et al. 1989) and SPIRE PSC (Schulz et al. 2017) http: // general-tools.cosmos.esa.int / iso / users / expl_lib / ISO / / isoprep / cohen / composites / Article number, page 13 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph photometry spanning the wavelength range from 12 to 500 µ m.All measured photometry was taken between 1983 and 2009 –2013 and is clearly above the model, meaning that variability ofthe source is an unlikely explanation, since a major part of thephotometric input for the Cohen model was obtained in-between(but IRAS
12 and 25 µ m photometry was not considered).Another explanation for an intrinsic FIR excess can be aresidual dust disk from a stellar- or planetary-system-formationprocess. One of the first giant stars, for which an infrared excesswas reported, is the K3 giant δ And (Judge et al. 1987). The giantis the brightest star in a triple or quadruple system and is itself aspectroscopic binary with a companion that is most likely a mainsequence K-type star (Bottom et al. 2015). Judge et al. (1987) ar-gued that the infrared excess appears to be caused by a detachedprimordial dust shell around the giant. Plets et al. (1997) con-cluded for a larger sample of giants with infrared excess, thatthis phenomenon is most likely related to the Vega phenomenonaround first-ascent giants. β Gem is another good candidate for having a residual debrisdisk, since it is the host star of a confirmed (Hatzes et al.2006) Jupiter-sized planet (HD 62509 b, M = ± J , a = ± ). A rough estimate (assuming a Jupiter diameterand T =
300 K) gives a contrast of > between star and planet,meaning that the planet cannot account for the FIR excess of ≈ β Gem are based on T e ff ≈ ff ective temperature T e ff of giant stars are determined in theultraviolet to near-infrared wavelength range, either from photo-metric indices (e.g. Lyubimkov & Poklad 2014), colours andmetallicities (e.g. Alonso et al. 1999), or integrated fluxes andinterferometric measurements of the stellar diameters (e.g. Dycket al. 1996). Other references give T e ff = ±
18 K (Jofré et al. 2015) and thus confirm thevalue used by Cohen. We have scaled a continuum model ofthe PACS fiducial standard star α Boo, a K2III star, by calcu-lating the Selby et al. (1988) K n narrow band photometry ratio10 − . · ( − . − ( − . = β Gem FIR photometry, but to demonstrate thatthe SED of the cooler source with T e ff = > µ m given by the IRAS , PACS, and SPIRE pho-tometry argues for a flat blackbody dust disk (see e.g. Chiang& Goldreich 1997; Beckwith 1999, for a discussion of the dustdisk SED shape depending on its geometry). α Ari and 42 Dra are also host stars of confirmed Jupiter-sized planets (alf Ari b, M = ± J , a = ; 42 Dra b, M = ± J , a = ) , but for these stars any possible debris disk emis- http: // irsa.ipac.caltech.edu / cgi-bin / Gator / nph-scan?submit = Select&projshort = HERSCHEL;for SPIRE colour correction, see SPIRE Handbook, Table 5.7http: // herschel.esac.esa.int / Docs / SPIRE / spire_handbook.pdf The Extrasolar Planet Encyclopediahttp: // exoplanet.eu / catalog / HD 62509_b / This model can be found underhttp: // archives.esac.esa.int / hsa / legacy / ADP / StellarModels / The Extrasolar Planet Encyclopediahttp: // exoplanet.eu / catalog / alf Ari_b / http: // exoplanet.eu / catalog / / Fig. 8.
Investigation of the discrepancy of the β Gem Cohen et al. (1996)model and measured FIR photometry. For a better zoom-in over a largewavelength range, log ( λ · f λ ) is displayed. The orange and red linesare the Cohen et al. (1995) absolutely calibrated 1.2 – 35 µ m spectralmodel and the Cohen et al. (1996) FIR extension, respectively. Theblack line represents a scaled ( × α Boo (Dehaes et al. 2011). The scaling factor has been derived fromthe Selby et al. (1988) K n narrow band photometry ratio 10 − . · ( − . + . and the position of the scaling wavelength (2.205 µ m) is indicated bythe violet square symbol. We note that the K n zero point is ≈
3% higherthan that for the Cohen models (cf. file header of α Boo model (refer-ence, see text) vs. Table 1 in Cohen et al. (1992)). Dark-blue squares,light-blue diamonds and green triangles represent
IRAS
FSC, PACS andSPIRE photometry and their respective uncertainties. This photometryhas been colour-corrected for a 4500 K blackbody spectrum. sion is much fainter than for β Gem. The observed SED shapeof α Ari is a little bit shallower than the model prediction (cf.Table 7), but the measurement and model uncertainties do notallow any detection. For 42 Dra, no deviation from a pure pho-tospheric emission SED can be found from our photometry. Wetherefore keep both stars in our standard star list.In Sect. 3.7 we have shown the 160 µ m map of η Dra (Fig. 6)as a representative example for cirrus confusion. Indeed, fromTable 10, f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr = f f model = (cid:48)(cid:48) . µ m fluxes are o ff by + + IRAS
FSC (Moshir et al. 1989) photometry andISOPHOT (Lemke et al. 1996) HPDP (Highly Processed DataProducts photometry (c.f. Appendix. D, Table D.1). It is obvi-ous that all photometric measurements are consistently above themodel, irrespective of whether the observations were obtainedduring the
IRAS , ISO , or
Herschel missions (1983 – 2013). Theexcess is a clear hint of an additional emission component be-sides the photospheric emission of the star, whereby the risein flux beyond 100 µ m is likely caused by cirrus emission. TheG8 giant η Dra (also identified as CCDM J16239 + + (cid:48)(cid:48) . o NE.The origin of the excess emission could then be dust inside thisbinary system.
Article number, page 14 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Table 10.
Input data for the investigation of 160 µ m photometric flux contamination of faint stars by background confusion. The determination ofB IS M is described in the text. The OBSID combinations of the deepest maps are used for this investigation. f , excess is estimated as the di ff erenceof the measured f minus model f model flux from Table 7. Listed fluxes f aperture radius160 , corr are not colour corrected. Uncertainties of the flux estimatesinclude a 1% uncertainty of the aperture correction to obtain the total flux, which is quadratically added to σ aper (c.f. Eq. 2). HD l b B
IS M
OBSIDs f , excess f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr ( o ) ( o ) (MJy sr − ) (mJy) (mJy) (mJy) (mJy)148387 92.6 + ± + ..47 + ..55 + ..56 8.5 106.7 ± ± ± + ± + .498 + .499 + .500 5.5 87.4 ± ± ± + ..48 + ..49 + ..50 90.8 ± ± ± + ..72 + ..73 + ..74 92.0 ± ± ± + ..94 + ..95 + ..96 87.2 ± ± ± + ..88 + ..89 + ..90 86.2 ± ± ± + ± + ..83 8.0 61.3 ± ± ± + ± +
42 9.0 30.1 ± ± ± − ± + ..36 + ..37 + ..38 6.0 10.7 ± ± ± + ± + ..74 – 8.2 ± ± ± Fig. 9.
Investigation of the discrepancy of the η Dra Hammersley et al.(1998) model and measured FIR photometry. For a better zoom-inover a large wavelength range, log ( λ · f λ ) is displayed. The redline is the model, absolutely calibrated at 2.208 µ m (K n magnitude = ± IRAS
FSC, PACS, and ISOPHOTHPDP photometry and their respective uncertainties. This photometryhas been colour-corrected for a 5000 K blackbody spectrum.
In Table 10 we have compiled crucial information for thosesources whose 160 µ m fluxes may be contaminated by back-ground confusion. All sources are at relatively high galactic lati-tudes in the range 23 o ≤ | b | ≤ o . The 160 µ m brightness of theISM, B IS M , was derived from
AKARI -FIS WIDE-L (140 µ m) all-sky survey maps (Doi et al. 2015) in the following way: B IS M = B AKARI
WIDE − L − B CFIRB cc ν cc ν . BB ( T = K ) K FIS − PACS ν . BB ( T = K ) , (8)with B AKARI
WIDE − L being the measured AKARI µ m flux (we high-light that we have transformed the original 6 deg × CFIRB = / sr being the cosmic far-infrared background level (cf.Juvela et al. 2009), cc ν = ν . BB ( T = K ) = AKARI -FIS WIDE-L colour-correction factors (Shirahata et al.2009) for the indexed SEDs and K
FIS −− PACS ν . BB ( T = K ) = AKARI -FISWIDE-L and the PACS 160 µ m filter (Müller et al. 2011) for themodified blackbody SED ν . BB(T =
20 K), which is typical forIR cirrus emission according to latest results (Planck Collabora-tion et al. 2014; Bianchi et al. 2017). The listed surface bright-ness of B
IS M is associated with the 15 (cid:48)(cid:48) × (cid:48)(cid:48) pixel covering thestar position, the uncertainty was computed as the standard de-viation of the eight neighboring pixel values with regard to thecentral one. B IS M are between 1.3 and 6.0 MJy sr − , with a gra-dient with | b | .Kiss et al. (2005) parameterized the sky confusion noise(1 σ ) for FIR measurements with ISOPHOT depending on wave-length and background reference configuration geometry as N PHTconf ( θ, k , λ )1 mJy = C ( θ, k , λ ) + C ( θ, k , λ ) (cid:104) B ( λ ) − B CFIRB ( λ )1 MJy sr − (cid:105) η ( θ, k ,λ ) . (9)The ISOPHOT C200 measurement configuration P / C / (cid:48)(cid:48) inTable 4 of Kiss et al. (2005) is closest to our PACS mini-scan-map measurement configuration, except that aperture size andbackground ring radius have to be scaled down by a factor of ≈ (cid:48)(cid:48) ISOPHOT C200 pixel size vs. 19 (cid:48)(cid:48)
PACS "pixel"size corresponding to a circular aperture with 10 (cid:48)(cid:48) . (cid:48)(cid:48) vs. 40 (cid:48)(cid:48) background ring radius). This means that the PACSsky confusion noise, N PACSconf , has to be scaled down by a factorof 0.22 . (Kiss et al. 2005) due to the better spatial resolutionof PACS. For computation of a point-source representative skyconfusion noise we multiply with the aperture correction factorc aper (160 µ m ) = N PACSconf , PS mJy = .
54 10 − × [ C + C (cid:104) B ( λ ) − B CFIRB ( λ )1 MJy sr − (cid:105) η ] . (10)Applied parameters are C = ± = ± η = ± term represents the confusion noise due to cosmic in-frared background fluctuations and amounts to 0.33 ± σ c = Article number, page 15 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph cosmological fields in the
Herschel -PEP survey (obtained for q = f lim σ c = value equal to 26.0 mJy.The C (cid:104) B IS M (cid:105) η term represents the cirrus confusion noise,which depends on the surface brightness of the emitting cirrusmaterial. With the range 1.3 ≤ B IS M ≤ − , we predict acirrus confusion noise 0.18 ± ≤ N PACScirrconf , PS ≤ ± µ m excess f , excess in Table 10 fully tosky confusion and compare with our confusion noise prediction,we note the following: For our small sample of 160 µ m excessstars we do not see any dependence on B IS M , in particular forHD 138265 with the lowest B
IS M = − , the highestf , excess = σ sky confusion noise de-rived via Eq. 10 underestimates the actually measured noise byfactors 3 – 25 (1.9 – 21 accounting for the maximum positiveuncertainty).The confusion noise predictions are average numbers basedon a statistical analysis. Peaks and depressions in the sky noisecan significantly deviate from the average. The spatial resolu-tion of the AKARI µ m all-sky survey maps is ≈ (cid:48)(cid:48) (Takitaet al. 2015). The PACS maps reveal much finer structures. Theirweight to the noise is much higher than to the average surfacebrightness. Therefore, calculating the cirrus noise from the sur-face brightness of a larger area will always underestimate the lo-cal cirrus noise. Another possibility is that the PSF of a discretefew-mJy source coincides - accidentally to a large percentage -with the PSF of the star. Di ff erential number counts in cosmolog-ical fields, as in Fig. 7 of Berta et al. (2011), suggest that thereare 9.2 × background sources / deg for f lim ≥ (cid:48)(cid:48) .
7, hence an al-ready high likelihood that such a source can blend the photome-try of our faint stars. We cannot exclude either that in some mapssome amount of the 160 µ m excess is produced by the data re-duction scheme itself by reducing the background level in someof the background reference areas (this can vary from map tomap depending on the actual detector drift behaviour along thetime-line and the level of reduction).To some extent a contribution by an underlying source canbe disentangled via multi-aperture photometry which includesaperture sizes as small as the PSF FWHM. From multi-aperturephotometry of the deepest maps (OBSIDs combinations are indi-cated in Table 10) with aperture radii 5 (cid:48)(cid:48) .
35, 10 (cid:48)(cid:48) . (cid:48)(cid:48) .
0, we see that the flux in-crease is usually greater than the associated uncertainties, whichis a hint of flux contribution by another source. As a reference,we also include the multi-aperture photometry of HD 152222which does not show any flux increase (rather a flux decrease dueto increasing uncertainties in the background subtraction withlarger aperture size).In Fig. 10 we investigate the nature of the 160 µ m sky back-ground structure, both on an absolute level and larger scale withthe help of the AKARI -FIS WIDE-L (140 µ m) all-sky surveymaps (Doi et al. 2015) and on the PACS scale by parallel JS-canam processing of the maps which tends to preserve more re-liably small-scale structured extended emission, while the larger-scale background is subtracted. In the following, we discuss thesources δ Dra, θ Umi, HD 138265, HD 39608 and HD 152222 in-dividually with regard to level and nature of their backgroundconfusion.For δ Dra the scan map photometry in Table 10 gives on av-erage f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr = f f model = µ m fluxes are 2– 3% above the model. The AKARI -map in Fig. 10 shows that the source is located at the wing of a cirrus knot. The JScanammap reveals filamentary structure around the source, which in-dicates that the small excess in the order of 4% is likely by IRcirrus contamination. One out of the five cases investigated inTable 10 does not indicate any excess and the measured 10 (cid:48)(cid:48) . θ Umi the scan map photometry gives f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr = f f model = µ m photometry in the small aperture is quiteclose to the model flux. The AKARI -map in Fig. 10 shows thatthe source is located on a cirrus filament. The JScanam map re-veals filamentary structure, too, coinciding in direction with the
AKARI -map feature, which supports that the excess found for thedefault photometric aperture of 10 (cid:48)(cid:48) . µ m only,which makes it a potential background-contaminated source,too. The AKARI -map in Fig. 10 shows that it is located on thewing of a small faint cirrus knot. The JScanam processed map in-dicates filamentary knotty structure mostly east, south, and westof the source, which fits to its location on the knot. The morphol-ogy of the filamentary structure resembles cirrus emission ratherthan compact sources. We derive f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr = f f model = µ m excess, with f f model = f (cid:48)(cid:48) . , corr f (cid:48)(cid:48) . , corr = AKARI -map in Fig. 10 shows that it is located onthe wings of two brighter cirrus knots with a depression southof it. The JScanam map reveals that there is extended filamen-tary structure mainly north of the source, in agreement with thelarger-scale feature of the
AKARI -map. This also a ff ects the areawhere the background is determined. Given that the source is oneof the faintest in our sample, with an expected photospheric fluxof only about 6 mJy, any inaccuracy in the background determi-nation has a severe impact on the resulting source flux. Further-more, the source looks elongated in the north-south direction,which indicates contaminating emission inside the measurementaperture. From Fig. 7, we see that there is already a noticeableexcess of 19% at 100 µ m. Unfortunately we cannot investigatethis properly on a JScanam processed map, since there existsonly one map in one scan direction (the cross-scan map was erro-neously executed in the 70 µ m filter). HD 39608 has the secondstrongest ISM sky background B IS M (c.f. Table 10), meaningthat it is very likely that already at 100 µ m there can be signifi-cant sky background contamination. The deep combined 70 µ mmap shows an elongated emission feature underneath the source,too.For comparison we also show the environment of HD 152222in Fig. 10, which is only slightly brighter than HD 39608. The AKARI -map shows that it is located outside a cirrus ridge closeto a depression in the cirrus emission. The JScanam map re-veals that the area around it is also crowded, but the sourcesare discrete compact sources, which argues for an extragalac-tic nature, and besides the star itself appears isolated inside themeasurement aperture. The derived flux is quite consistent with
Article number, page 16 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Fig. 10.
Investigation of the 160 µ m sky background structure around the sources δ Dra (OD 934), θ UMi (OD 160), HD 138265 (OD 233),HD 39608 (OD 400) and HD 152222 (OD 843) from top to bottom. The deepest available maps were used, see Table 10 for the OBSID combina-tion and Table A.5 for the observation details. The left panel shows the high-pass filter processed map used for the photometry, the photometricaperture with 10 (cid:48)(cid:48) . δ Dra shows the superposition of all five sets of OBSIDs inTable 10 (ODs 607, 751, 934, 1198 and 1328) as the deepest image of this field. The right panel shows the
AKARI
WIDE-L (140 µ m) backgroundemission around the source (red cross), the AKARI map area is about four times as large as the PACS map area, which is indicated by the reddashed square. the model flux which argues against a systematic backgroundunderestimate in this source flux range.HD 39608 is hence no longer qualified as a potential cali-bration standard. θ Umi and HD 138265 can be considered assuitable standards up to 100 µ m.
6. Establishment of new faint FIR primary standards
Primary flux standards are used for absolute flux calibration.Their SED is assumed to be known and stable or predictable.Absolute calibration of these sources is achieved either by a di-
Article number, page 17 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Table 11.
K-band and PACS 100 µ m photometry and a selection of stellar parameter information for the PACS fiducial primary standards (status:"f") and PACS faint star primary standard candidates (status: "c") with nearly identical spectral type. Fiducial primary standards and relatedcandidates are grouped together. V-band photometry is given for completeness and for the conversion of the K magnitude between the (Selby et al.1988) K n narrow band photometric system and the Johnson K-band photometric system. Name Status SpType V K K n p3 K s , p4 f p5 T e ff Θ d (mag) (mag) (mag) (mag) (mJy) (K) m (cid:48)(cid:48) α Boo f K2III -0.04 -3.07 ± ±
375 4320 ± s1 ± s1 α Ari c K1IIIb 2.01 -0.63 ± p1 ±
41 4636 ± s2 ± s5
42 Dra c K1.5III 4.82 1.95 ± p2 ± ± s2 ± s5 HD 159330 c K2III 6.21 2.787 ± ± ± ± α Tau f K5III 0.85 -2.94 ± ±
345 3850 ± s1 ± s1 γ Dra f K5III 2.23 -1.38 ± ±
80 3960 ± s1 ± s1 ε Lep c K4III 3.18 -0.20 ± p1 ±
28 4243 ± s2 ± s5 HD 41047 c K5III 5.52 1.740 ± ± ± s4 θ Umi c K5III 4.98 1.33 ± p2 ± ± s5 HD 138265 c K5III 5.90 2.38 ± p2 ± ± s3 ± s3 β And f M0III 2.06 -1.93 ± ±
137 3880 ± s1 ± s1 ω Cap c M0III 4.12 0.21 ± p1 ±
21 3760 ± s4 ± s5 ( ) Star is a proven reliable standard only up to 100 µ m due to background confusion ( p1 ) Ducati (2002, catalogue of stellar photometry in Johnson’s 11-colour system) ( p2 ) Neugebauer & Leighton (1969, two-micron sky survey) ( p3 ) Selby et al. (1988) ( p4 ) Cutri et al. (2003, 2MASS all-sky catalogue of point sources) Note: For K s , < ( p5 ) For the fiducial standards we use the continuum model flux with an uncertainty of 5%; for the candidate stars we use the fluxfrom scan map photometry. ( s1 ) Dehaes et al. (2011) ( s2 ) Jofré et al. (2015) ( s3 ) Baines et al. (2010) ( s4 ) Tsuji (1981) ( s5 ) Cohen et al. (1999)rect method, like comparison against a blackbody source, or bya indirect method, for example stellar or planetary atmospheremodels. Deustua et al. (2013) give a detailed description of abso-lute calibration of astronomical flux standards. Primary flux stan-dards in the far-infrared wavelength range are, with decreasingbrightness, planets (Müller et al. 2016), asteroids (Müller et al.2014), and stars (Dehaes et al. 2011), which are all calibratedvia the indirect method and verified by independently calibratedmulti-wavelength flux measurements. The best achievable un-certainties are currently 5 – 7%.The Cohen et al. (1996) models of α Ari, ε Lep, ω Cap, δ Draand HD 41047 are well confirmed by our PACS photometry andare thus adequate representations of the stellar FIR photosphericemission. These stars together with 42 Dra and HD 152222 aregood candidates to establish fainter FIR primary standards. Thislist is complemented by θ Umi, HD 159330, and HD 138265 forwhich we can confirm a reliable FIR spectrum only up to 100 µ mdue to neighbouring source- or cirrus confusion at longer wave-lengths.As already discussed earlier, the Cohen et al. (1996) modelsare FIR extensions of absolutely calibrated 1.2 – 35 µ m templatespectra Cohen et al. (1995, 1999). Another set of models rang-ing from 0.7 µ m to 7 cm was developed by Dehaes et al. (2011)for the Herschel -PACS fiducial primary standards. Several of our faint primary standard candidates have the same or similar spec-tral type as one of the PACS primary standard stars. As a firstmodel approximation we can scale these fiducial standard starmodels to the flux levels of our primary standard candidates. Foran accurate model one would have to run a flux model code tak-ing into account the stellar parameter information of each star, aproject which is beyond the scope of this paper. δ Dra with spectral type G9III has no suitable counterpartamong the
Herschel -PACS fiducial primary standards, since theearliest spectral type is K2III. But we note that it was modelledearlier by (Decin et al. 2003) as
ISO -SWS calibrator. We do notinclude δ Dra in Table 11, but refer to Table 3 in Decin et al.(2003) which gives its stellar properties.In Table 11 we have compiled photometry and stellar prop-erties of the fiducial primary standards and our primary stan-dard candidates which match in spectral type. Jofré et al. (2015)provide essential stellar parameters for α Ari, ε Lep, and 42 Dra,therefore a dedicated flux model code could be run.In Table 12 we compile the K-magnitude ratio and the100 µ m flux ratio for matching pairs of fiducial primary stan-dards and primary standard candidates. From both ratios wecompute the scale factor for the fiducial star model as a weightedmean. We apply the following transformations between the dif-ferent K-band photometric systems: (1) V-K = -0.020 + × Article number, page 18 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars (V-K n ) (Selby et al. 1988) and (2) K = K s , + α Booand still about 80 times fainter than the faintest fiducial primarystandard, γ Dra. Table 12 also gives the percentage of the uncer-tainty of the scaling. We estimate the uncertainty due to variationin stellar parameters, such as the e ff ective temperature, by scal-ing the fiducial model of α Tau to the level of γ Dra, which areboth K5III stars. The di ff erence over the wavelength range 2 –250 µ m is less than 0.8%. We therefore adopt an uncertainty of1% due to variations in stellar parameters. Given, that the fidu-cial primary standards have an absolute accuracy of 5%, then theabsolute uncertainty of the scaled model approximation, as listedin the last column of Table 12, can be determined as the sum ofthe three uncertainty terms described above.Figure 11 shows the scaling of the fiducial standard star mod-els to the flux levels of our primary standard candidates and averification with available photometry. K-band and PACS pho-tometry are supplemented by IRAS
FSC photometry (Moshiret al. 1989) and in some cases by ISOPHOT HDPD photome-try (Lemke et al. 1996, see Appendix D).For α Ari, ε Lep, ω Cap, HD 41047 and 42 Dra the derivedabsolute photometric uncertainty is in the range 5–6%, hencethey are well suited new FIR primary standards, which are about2 – 20 times fainter than our faintest fiducial primary standard γ Dra. Only for the faintest star, HD 152222, does the higher un-certainty of the scaling factor result in a derived absolute uncer-tainty of 13%. A major driver for this high scaling uncertaintyis the high uncertainty of the publicly available K-band photom-etry (cf. Table 11, footnote p4), meaning that the K-magnituderatio and the 100 µ m flux ratio do not match well. From Fig. 11it is obvious that a more accurate K-band photometry would cer-tainly help to bring this star into a similar absolute photometricuncertainty range to the brighter ones.For θ Umi, HD 138265 and HD 159330, which are substan-tially a ff ected by neighbouring source- or cirrus confusion at160 µ m (Sects. 3.7 and 5.2), clean photometry can be obtainedup to 100 µ m with a telescope of angular resolution similar to Herschel , which leads to an equally good absolute photometricuncertainty in the range 5 – 7%. Also, for HD 159330, improvedK-band photometry can further reduce its resulting absolute pho-tometric uncertainty. We therefore keep these three sources asreliable standards up to 100 µ m, but with the strong caveat notto use them beyond this wavelength. Only with a considerablyhigher angular resolution than Herschel could the confusion is-sues of these sources be overcome at 160 µ m.HD 138265, HD 159330, and HD 152222 will be observablewith the James Webb Space Telescope
MIRI Imager at 20 µ m inbright source mode with the 64 ×
64 sub-array (Bouchet et al.2015).
7. Conclusions
The PACS faint star sample with 14 giant and 3 dwarf starshas allowed a comprehensive sensitivity assessment of the PACSphotometer and provided accurate photometry for detailed SEDinvestigation and establishment of a set of faint FIR primarystandard candidates for use by future space missions.For PACS scan maps, the recommended scientific observa-tion mode for the PACS photometer, we have described a con-sistent method for how to derive S / Ns, based on a robust noisemeasurement with the help of a flux histogram restricted to theapplicable map coverage value range. The comparison with the S / N predictions of the exposure time calculation tool in the
Her-schel
Observatory Planning Tool HSpot has resulted in verygood consistency, proving the tools for PACS photometry ob-servation planning as very reliable. We have demonstrated thatthe underlying assumptions of the tool, that the S / N scales lin-early with flux and with the square root of the observing time, arevalid over large ranges of flux and time. A restriction appears forthe 160 µ m filter, where source confusion often limits the gainin S / N with increasing observing time. We could also show thatscan maps obtained with the recommended scan speed of 20 (cid:48)(cid:48) / syield a higher S / N than scan maps with 10 (cid:48)(cid:48) / s, the scan speedfavoured pre-flight.We have shown that in the case of faint sources, small aper-ture sizes (with a radius of the size of the PSF FWHM) reducesbackground noise inside the aperture and optimizes the accuracyof the flux determination.We have obtained reliable photometry for 11 stars in allthree PACS filters (at 70, 100, 160 µ m). For one further starwe have obtained reliable 100 and 160 µ m photometry. For onemore star we have obtained reliable 70 and 100 µ m photome-try only, 160 µ m photometry being limited here by confusionof neighbouring sources. For two other stars we have obtainedreliable photometry only at 70 µ m, a detection at longer wave-lengths being limited by sensitivity limitations and confusionnoise. The two faintest sources observed in chop / nod mode havenot been detected at all despite high repetition factors of the ba-sic chop / nod pattern. The non-detection is likely due to a not-yet-perfect knowledge of the optimum observing strategy earlyin the mission. Faintest fluxes, for which the photometry has stillgood quality, are about 10 – 20 mJy for the scan map observa-tions and 30 mJy for the available chop / nod observations.For the faintest star at 160 µ m with reliable photometry in allthree filters, HD 152222, we have conducted an inter-comparisonof the high-pass filter (HPF) photometry from the deepest mapwith the results of three additional Herschel mapper softwares,namely JScanam, Scanamorphos and Unimap. All four mappersallow us to obtain sound photometry in all three filters. We haveidentified the level of qualitative consistency as well as some sys-tematic di ff erences with regard to photometry, noise, and beamprofiles among the four mappers. A more systematic and quanti-tative photometric performance comparison of the four mapperswill be the subject of a dedicated publication.For the 12 stars with reliable photometry out to 160 µ m wecan prove that 7 stars are consistent with models or flux predic-tions for pure photospheric emission. δ Dra has a slight 160 µ mexcess due to cirrus contamination of the order of 4%, but thisis still within the overall uncertainty margin. Two stars show ex-cess emission over the whole ( > µ m) FIR range. For β Gem(Pollux), which is the host star of a confirmed Jupiter-sized ex-oplanet, we conclude from our photometry results that it has inaddition a flat blackbody dust disk. The G8 giant η Dra has aK1 dwarf companion, therefore the origin of the excess emis-sion likely arises from dust inside this binary system. For threestars with 160 µ m fluxes below 60 mJy we find 160 µ m excessesin the order 6 to 9 mJy. Investigation of the 160 µ m absolute skybrightness with the help of AKARI -maps, the filamentary emis-sion structure in the environment of the source on the PACSmaps, and multi-aperture PACS photometry strongly support anexplanation of this excess as being due to sky background con-fusion. This is a combination of cirrus confusion a ff ecting thebackground subtraction and faint underlying objects inside thephotometric aperture around the star a ff ecting the source profile.The faintest star at 70 µ m with reliable photometry in all three fil-ters, HD 39608, is heavily a ff ected by sky confusion noise from Article number, page 19 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Table 12.
Determination of the scale factor to adjust the related fiducial primary standard star model to the flux level of the candidate primarystandard. The last two columns list the uncertainty percentage of the scale factor and the absolute uncertainty of the scaled model approximation,the latter being the Gaussian error propagation of the scale uncertainty, 1% uncertainty in the stellar parameters and 5% uncertainty of the models.
Primary candidate Primary standard Kmag ratio f ratio Scale factor % scale uncert. % abs. uncert. α Ari α Boo 1.11 ± − ± − ± − α Boo 1.03 ± − ± − ± − α Boo 2.07 ± − ± − ± − α Boo 4.58 ± − ± − ± − ε Lep α Tau 8.49 ± − ± − ± − ε Lep γ Dra 3.56 ± − ± − ± − α Tau 1.37 ± − ± − ± − γ Dra 5.73 ± − ± − ± − θ Umi α Tau 2.07 ± − ± − ± − θ Umi γ Dra 8.71 ± − ± − ± − α Tau 7.88 ± − ± − ± − γ Dra 3.31 ± − ± − ± − ω Cap β And 1.48 ± − ± − ± − ( ) Star is a proven reliable standard only up to 100 µ m due to background confusion. Fig. 11.
Scaling of PACS fiducial star continuum models (black and purple lines) to the flux level of the primary standard candidates applying thescale factors of Table 12. For a better zoom-in over a large wavelength range, log ( λ · f λ ) is displayed. Blue squares are the K-band photometry,green squares are colour-corrected IRAS
FSC photometry (Moshir et al. 1989), orange squares are ISOPHOT HPDP photometry (Lemke et al.1996, see Appendix D) and red squares are PACS photometry. In the middle panel the scaled models of both α Tau (black) and γ Dra (purple) areplotted. Dashed parts of the SEDs of HD 159330, θ Umi, and HD 138265 indicate that these stars are proven reliable standards only up to 100 µ mdue to background confusion. µ m onwards and has therefore to be excluded as a primarystandard candidate.The seven stars with pure photospheric emission over the fullPACS wavelength range, α Ari, ε Lep, ω Cap, δ Dra, HD 41047,42 Dra and HD 152222, are promising primary standard candi-dates. The stars θ Umi, HD 138265 and HD 159330 prove to begood primary standard candidates, too, but only up to 100 µ m due to significant source confusion at 160 µ m at the spatial res-olution of PACS. For three of the new primary standard can-didates essential stellar parameters are known, meaning that adedicated flux model code could be run. As a good model ap-proximation for nine of our primary standard candidates we canscale the continuum flux models of four PACS fiducial standardswith the same or quite similar spectral type. Only for δ Dra is
Article number, page 20 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars there no suitable counterpart among the fiducial standard stars.This allows us to establish a set of five FIR primary standardcandidates up to 160 µ m, which are 2 – 20 times fainter than thefaintest PACS fiducial standard ( γ Dra) with absolute accuracy of < γ Dra), is currently limited to13% by the accuracy of the existing K-band photometry. A set ofthree primary standard candidates up to 100 µ m with an absoluteaccuracy of <
7% complements the list of proven flux standards.
Acknowledgements.
PACS has been developed by a consortium of insti-tutes led by MPE (Germany) and including UVIE (Austria); KUL, CSL,IMEC (Belgium); CEA, OAMP (France); MPIA (Germany); IFSI, OAP / AOT,OAA / CAISMI, LENS, SISSA (Italy); IAC (Spain). This development has beensupported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium),CEA / CNES (France), DLR (Germany), ASI (Italy), and CICYT / MCYT (Spain).ZB acknowledges funding by DLR for this work. TM receives funding from theEuropean Union’s Horizon 2020 Research and Innovation Programme, underGrant Agreement no. 687378. This research has made use of the SIMBAD database and the VizieR catalogue access tool, operated at CDS, Strasbourg, France.This research has made use of SAOImage DS9, developed by Smithsonian As-trophysical Observatory. This research has made use of the NASA / IPAC InfraredScience Archive, which is operated by the Jet Propulsion Laboratory, CaliforniaInstitute of Technology, under contract with the National Aeronautics and SpaceAdministration. We thank the referee for constructive comments.
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Appendix A: Scan map photometry
Appendix A.1: Comparison of different aperture sizes foroptimization of photometric aperture
Table A.1.
Comparison of mini scan map photometry for di ff er-ent aperture sizes. phot_l is the photometry with the large aperturesizes 12" / / / / star are determined as the colour-corrected weighted average of aperture corrected fluxes f tot from ≥ σ aper , corr (Eq. 4) for = Star Filter µ m) (mJy) (mJy) (mJy) β Gem 70 8 2649.4 ± ± ± ± ± ± α Ari 70 8 1668.3 ± ± ± ± ± ± ε Lep 70 8 1157.1 ± ± ± ± ± ± ω Cap 70 8 839.0 ± ± ± ± ± ± η Dra 70 8 517.8 ± ± ± ± ± ± δ Dra 70 12 433.6 ± ± ± ± ± ± θ Umi 70 4 278.7 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± δ Hyi 70 1 7.7 ± ± Appendix A.2: Dependence on applied mapper software
For the faintest star at 160 µ m with reliable photometry in allthree filters, HD 152222, we conduct an inter-comparison of thehigh-pass filter (HPF) photometry from the deepest map with theresults of three additional Herschel mapper softwares, namely JScanam (Graciá-Carpio et al. 2015), Scanamorphos (Roussel2013) and Unimap (Piazzo et al. 2015). The data analysis wasdone by applying the standard HIPE ipipe (interactive pipeline)scripts of these mappers and selecting the same output pixelsizes as defined in Table 2.For the Scanamorphos processing release version 25 of thesoftware was applied, the "mini-map" option was selected, andthe software was set to correct for the PACS distortion flat-field.For the JScanam processing version 14.2.0 (analogue to HIPEversion) was applied and the "galactic" option was switched on.For the Unimap processing, version 6.5.3 was applied with theparameter pixelNoise (gain to apply to the estimated pixel noisein the GLS pixel noise compensation ) set to zero. For the com-parison with the other mappers we used the weighted GLS (Gen-eralized Least-Squares) L2.5 map product, corresponding to theFITS XTENSION "Image". Table A.2.
Comparison of the photometric results of HD 152222 fromdi ff erent mapper softwares: HPF (High Pass Filter, default reductionscheme of this work), JScanam (Graciá-Carpio et al. 2015), Scanamor-phos (Roussel 2013) and Unimap (Piazzo et al. 2015). Used OBSIDsare the combinations of 1342240702 +
03 at 70 µ m and 1342227973 + µ m. Listed fluxes are the colour-corrected total stellarfluxes f star . Mapper Filter r aper f star σ aper f mapper star f HPF star ( µ m) ( (cid:48)(cid:48) ) (mJy) (mJy)HPF 70 5.6 37.7 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± star de-rived from aperture photometry with 5 (cid:48)(cid:48) .
6, 6 (cid:48)(cid:48) . (cid:48)(cid:48) . µ m, respectively.We also list the noise inside the measurement aperture, σ aper (cf. Eq. 2), which was determined from all maps with the his-togram method described in Sect. 3.3. We note that here onlythis noise term can be used for inter-comparison, not the onecorrected for correlated noise, σ aper , corr , since correlated noise Herschel user contributed softwarehttps: // / web / herschel / user-contributed-software Herschel data processing overviewhttps: // / web / herschel / data-processing-overviewin particular PACS Data Reduction Guide PhotometryArticle number, page 22 of 42. Klaas et al.: Herschel -PACS photometry of faint stars
Fig. A.1.
Inter-comparison of HD 152222 photometric maps for di ff erent mapper softwares for 70, 100, and 160 µ m (top to bottom). First column:HPF (High Pass Filter, default reduction scheme of this work), second column: JScanam, third column: Scanamorphos and 4th column: Unimap.Used OBSIDs are the combinations of 1342240702 +
03 at 70 µ m and 1342227973 +
74 at 100 and 160 µ m. The red circle indicates the photometricaperture. correction factors f corr were only derived for the high-pass fil-tered data reduction (one may argue that the final corrected noise σ aper , corr should be about the same for all mappers, since it ismainly determined by the detector noise). A σ tot for the totalflux can be calculated as σ tot = c aper × σ aper .The noise determined from the JScanam maps is slightlylarger than that of the HPF maps. This finding indicates thatthe noise correlation is slightly less for the JScanam mapper.The noise determined from the Scanamorphos maps is slightlysmaller than that of the HPF maps, indicating a slightly highernoise correlation. The noise determined from the Unimap mapsis a factor of 1.5 – 2.1 higher than that of the HPF maps. Thisis explained by Unimap using the Generalized Least-Squares(GLS) algorithm to remove the correlated f -noise (Piazzo et al.2015). The Unimap noise is hence closer to the real noise level,and the above scaling factors do not exceed the correlated noisecorrection factors f corr to be applied to the HPF noise (cf. Eq. 4and Table 2) for calculation of the correlation-free noise level.At 70 µ m, with an expected source flux in the order of40 mJy, the fluxes of all four mappers correspond to each otherwithin 4 – 6%. At 100 µ m, with an expected source flux in theorder of 20 mJy, the correspondence is still better than 15%. At160 µ m, with an expected source flux of only ≈ / N (cid:46)
10, the scatter is naturally larger. Jscanam photometry showsthe best correspondence with the HPF photometry, being within4% for all filters. This can be expected, since both mappers usethe same projection algorithm photProject() . Unimap photom-etry shows the second best correspondence with HPF photom-etry, with the tendency that the Unimap fluxes are larger (at70 and 160 µ m). Scanamorphos photometry gives systematicallysmaller fluxes than HPF photometry, with the deviation increas-ing with wavelength and a 160 µ m flux which is noticeably o ff .The PACS photometric calibration scheme (Balog et al.2014) was established with HPF analysis, in particular also thederivation of the aperture photometry correction factors c aper from the PACS Point Spread Function (Lutz 2015), by deter-mining the Encircled Energy Fractions with radius. Therefore,one aspect a ff ecting the aperture photometry depending on theselected mapper software was not considered in the evaluationscheme described above, namely the shape of the point spreadfunction. From the inspection of the stellar intensity profilesand their close surrounding in Fig. A.1, in particular from the70 and 100 µ m images, it is obvious that there are systematicdi ff erences in the resulting profile shapes of the star depend-ing on the applied mapper. The HPF processing shows the typ-ical tri-lobe pattern of the PACS point spread function (Lutz Article number, page 23 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph f mapper tot , cc f HPF tot , cc in Table A.2 should not beused as general scaling factors between the various mappers,since they are based on the evaluation of a single map of a veryfaint star implying quite some uncertainty. Accurate scaling fac-tors for photometry with the various mappers do not exist yetand will be determined on the basis of the high signal-to-noisefiducial standard observational database in a forthcoming paper(Balog et al., 2018, in preparation). Appendix A.3: Photometry results of individualmeasurements
Individual photometric results for the 70, 100, and 160 µ m filtersare compiled in Tables A.3 to A.5. The applied radius for thephotometric aperture was 5.6, 6.8 and 10.7 (cid:48)(cid:48) for the 70, 100 and160 µ m filter, respectively. The number of output pixels (1 (cid:48)(cid:48) . (cid:48)(cid:48) .
4, and 2 (cid:48)(cid:48) . aper = corr = aper = µ m filter, respec-tively. Proper motion correction was applied throughout.The tables contain the following information: Col. 1: Uniqueobservational identifier (OBSID) of the PACS observation;Col. 2: Herschel Observational Day (OD); Col. 3: Target name;Col. 4: Applied gain (G) of the PACS bolometer electronics:h(igh) / l(ow); Col. 5: Scan speed: low = (cid:48)(cid:48) / s, medium = (cid:48)(cid:48) / s,high = (cid:48)(cid:48) / s; Col. 6: Number of repetitions (rep.) of the ba-sic scan map with the parameters given in next column; Col. 7:Parameters of the scan map: scan leg length( (cid:48)(cid:48) ) / scan leg sepa-ration ( (cid:48)(cid:48) ) / number of scan legs; Col. 8: Scan angle of the map,in case of co-added maps all angles of the individual maps aregiven; Col. 9: Measured flux inside the photometric aperture ofthis filter, f aper ; Col. 10: Noise per pixel, σ pix ; Col. 11: Noisecorrected for correlated noise inside the measurement aperture, σ aper , corr , according to Eq. 4. Col. 12: Achieved signal-to-noiseratio according to Eq. 5; Col. 13: Stellar flux f star according toEq. 1; Cols. 14 - 16: Maximum and minimum Full Width (W)Half Maximum (in (cid:48)(cid:48) ) of the source PSF of the source PSF andits uncertainty determined by an elliptical fit to the intensity pro-file. Article number, page 24 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e b l u e ( µ m fi lt e r) . P r o ce ss i ngp r o cee d e d fr o m SP G v13 . . l e v e l r odu c t s w it h H I P E v e r s i on15bu il d165 . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . ε L e ph201180 / / . . . . . . . ε L e ph201180 / / . . . . . . . + ε L e ph202180 / / + . . . . . . . ε L e ph201180 / / . . . . . . . ε L e ph201180 / / . . . . . . . + ε L e ph202180 / / + . . . . . . . ε L e ph201180 / / . . . . . . . ε L e ph201180 / / . . . . . . . + ε L e ph202180 / / + . . . . . . . ε L e ph201180 / / . . . . . . . ε L e ph201180 / / . . . . . . . + ε L e ph202180 / / + . . . . . . . Article number, page 25 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e b l u e ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . η D r a h101120 / / . . . . . . . η D r a h101120 / / . . . . . . . + η D r a h102120 / / + . . . . . . . η D r a h10190 / / . . . . . . . η D r a h10190 / / . . . . . . . + η D r a h10290 / / + . . . . . . . η D r a h20190 / / . . . . . . . . η D r a h20190 / / . . . . . . . . + η D r a h20290 / / + . . . . . . . η D r a h101150 / / . . . . . . . η D r a h101150 / / . . . . . . . + η D r a h102150 / / + . . . . . . . δ D r a h201240 / / . . . . . . . δ D r a h201240 / / . . . . . . . . + δ D r a h202240 / / + . . . . . . . δ D r a h203180 / / . . . . . . . δ D r a h203180 / / . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . δ D r a h203180 / / . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . δ D r a h203180 / / . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . δ D r a h203180 / / . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . δ D r a h203180 / / . . . . . . . + δ D r a h206180 / / + . . . . . . . Article number, page 26 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e b l u e ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) θ U m i h101210 / / . . . . . . . . θ U M i h201210 / / . . . . . . . . θ U m i h206150 / / . . . . . . . θ U m i h206150 / / . . . . . . . + θ U m i h2012150 / / + . . . . . . . D r a h2020180 / / . . . . . . . D r a h2020180 / / . . . . . . . + D r a h2040180 / / + . . . . . . . D r a h2020180 / / . . . . . . . D r a h2020180 / / . . . . . . . + D r a h2040180 / / + . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . HD / / . . . . . . . + HD / / + . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . δ H y i h209240 / / . . . . . . . . Article number, page 27 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e g r ee n ( µ m fi lt e r) . P r o ce ss i ngp r o cee d e d fr o m SP G v13 . . l e v e l r odu c t s w it h H I P E v e r s i on15bu il d165 . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . β G e m h203180 / / . . . . . . . β G e m h203180 / / . . . . . . . + β G e m h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . α A r i h203180 / / . . . . . . . α A r i h203180 / / . . . . . . . + α A r i h206180 / / + . . . . . . . ε L e ph201150 / / . . . . . . . ε L e ph201150 / / . . . . . . . + ε L e ph202150 / / + . . . . . . . ε L e ph203180 / / . . . . . . . ε L e ph203180 / / . . . . . . . + ε L e ph206180 / / + . . . . . . . ε L e ph203180 / / . . . . . . . ε L e ph203180 / / . . . . . . . + ε L e ph206180 / / + . . . . . . . ε L e ph203180 / / . . . . . . . ε L e ph203180 / / . . . . . . . + ε L e ph206180 / / + . . . . . . . ε L e ph203180 / / . . . . . . . ε L e ph203180 / / . . . . . . . + ε L e ph206180 / / + . . . . . . . ε L e ph203180 / / . . . . . . . ε L e ph203180 / / . . . . . . . + ε L e ph206180 / / + . . . . . . . Article number, page 28 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e g r ee n ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . ω C a ph203180 / / . . . . . . . ω C a ph203180 / / . . . . . . . + ω C a ph206180 / / + . . . . . . . η D r a h101120 / / . . . . . . . . η D r a h101120 / / . . . . . . . . + η D r a h102120 / / + . . . . . . . . η D r a h10190 / / . . . . . . . . η D r a h10190 / / . . . . . . . . + η D r a h10290 / / + . . . . . . . . η D r a h20190 / / . . . . . . . . η D r a h20190 / / . . . . . . . . + η D r a h20290 / / + . . . . . . . . η D r a h101150 / / . . . . . . . . η D r a h101150 / / . . . . . . . . + η D r a h102150 / / + . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . + δ D r a h206180 / / + . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . + δ D r a h206180 / / + . . . . . . . Article number, page 29 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e g r ee n ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) θ U m i h101210 / / . . . . . . . . θ U m i h201210 / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . + D r a h2040180 / / + . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . + D r a h2040180 / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . Article number, page 30 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) . P r o ce ss i ngp r o cee d e d fr o m SP G v14 . . l e v e l r odu c t s w it h H I P E v e r s i on15bu il d1480 . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . .. + + + β G e m h2012180 / / + . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . .. + + + β G e m h2012180 / / + . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . .. + + + β G e m h2012180 / / + . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . β G e m h203180 / / . . . . . . . . .. + + + β G e m h2012180 / / + . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h303180 / / . . . . . . . . .. + + + α A r i h2012180 / / + . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . .. + + + α A r i h2012180 / / + . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . .. + + + α A r i h2012180 / / + . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . α A r i h203180 / / . . . . . . . . . + + + α A r i h2012180 / / + . . . . . . . . Article number, page 31 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) ε L e ph201150 / / . . . . . . . . ε L e ph201150 / / . . . . . . . . + ε L e ph202150 / / + . . . . . . . . ε L e ph201180 / / . . . . . . . . ε L e ph201180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . .. + + + ε L e ph208180 / / + . . . . . . . . ε L e ph203180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . + ε L e ph206180 / / + . . . . . . . . ε L e ph201180 / / . . . . . . . . ε L e ph201180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . + + + ε L e ph208180 / / + . . . . . . . . ε L e ph201180 / / . . . . . . . . ε L e ph201180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . ε L e ph203180 / / . . . . . . . . .. + + + ε L e ph208180 / / + . . . . . . . .
28 13422639021377 ε L e ph203180 / / . . . . . . . .
20 13422639031377 ε L e ph203180 / / . . . . . . . .
22 13422639041377 ε L e ph201180 / / . . . . . . . .
36 13422639051377 ε L e ph201180 / / . . . . . . . . .. + + + ε L e ph208180 / / + . . . . . . . . A f t e r OD a l f o f t h e r e dpho t o m e t e r a rr a y w a s l o s t , r e s u lti ng i n i n c r ea s e dno i s ea nd r e du ce d S / Nw r t . p r e - OD s e r v a ti on s Article number, page 32 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . .. + + + ω C a ph2012180 / / + . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . .. + + + ω C a ph2012180 / / + . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . .. + + + ω C a ph2012180 / / + . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . ω C a ph203180 / / . . . . . . . . .. + + + ω C a ph2012180 / / + . . . . . . . . η D r a h101120 / / . . . . . . . . η D r a h101120 / / . . . . . . . . η D r a h101120 / / . . . . . . . . η D r a h101120 / / . . . . . . . . .. + + + η D r a h104120 / / + . . . . . . . . η D r a h10190 / / . . . . . . . . η D r a h10190 / / . . . . . . . . η D r a h10190 / / . . . . . . . . η D r a h10190 / / . . . . . . . . .. + + + η D r a h10490 / / + . . . . . . . . η D r a h20190 / / . . . . . . . . η D r a h20190 / / . . . . . . . . η D r a h20190 / / . . . . . . . . η D r a h20190 / / . . . . . . . . .. + + + η D r a h20490 / / + . . . . . . . . η D r a h101150 / / . . . . . . . . η D r a h101150 / / . . . . . . . . η D r a h101150 / / . . . . . . . . η D r a h101150 / / . . . . . . . . .. + + + η D r a h104150 / / + . . . . . . . . Article number, page 33 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) δ D r a h201240 / / . . . . . . . . δ D r a h201240 / / . . . . . . . . + δ D r a h202240 / / + . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . .. + + + δ D r a h2012180 / / + . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . .. + + + δ D r a h2012180 / / + . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . .. + + + δ D r a h2012180 / / + . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . .. + + + δ D r a h2012180 / / + . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . δ D r a h203180 / / . . . . . . . . .. + + + δ D r a h2012180 / / + . . . . . . . . θ U m i h101210 / / . . . . . . . . θ U m i h101210 / / . . . . . . . . + θ U m i h102210 / / . . . . . . . . θ U M i h201210 / / . . . . . . . . θ U m i h201210 / / . . . . . . . . + θ U m i h202210 / / . . . . . . . . θ U m i h206150 / / . . . . . . . . θ U m i h206150 / / . . . . . . . . + θ U m i h2012150 / / + . . . . . . . . Article number, page 34 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e A . . S ca n m a ppho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) c on ti nu e d . O B S I DOD T a r g e t G S p ee d R e p . M a pp a r a m s S ca n A ng l e s f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ∆ W ( (cid:48)(cid:48) / s )( (cid:48)(cid:48) / (cid:48)(cid:48) / no . )( d e g )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . .. + + + D r a h2080180 / / + . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . D r a h2020180 / / . . . . . . . . .. + + + D r a h2080180 / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . + HD / / + . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . HD / / . . . . . . . . .. + + + HD / / + . . . . . . . . Article number, page 35 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Appendix B: Chopped photometry
Appendix B.1: Photometry results of individualmeasurements
Individual photometric results for the 70, 100, and 160 µ m fil-ters are compiled in Tables B.1 to B.3. The applied radius for thephotometric aperture was 5.6, 6.8 and 10.7 (cid:48)(cid:48) for the 70, 100 and160 µ m filter, respectively. The number of output pixels (1 (cid:48)(cid:48) . (cid:48)(cid:48) .
4, and 2 (cid:48)(cid:48) . aper = corr = aper = µ m filter, respec-tively. Proper motion correction was applied throughout.The tables contain the following information: Col. 1: Uniqueobservational identifier (OBSID) of the PACS observation;Col. 2: Herschel Observational Day (OD), including its phase;Col. 3: Target name; Col. 4: Applied gain (G) of the PACSbolometer electronics: h(igh) / l(ow); Col. 5: Chopper dither pat-tern: y(es) / n(o); Col. 6: Number of repetitions (rep.) of the basicchop / nod cycle; Col. 7: Fitted peak flux intensity of the source;Col. 8: Measured flux inside the photometric aperture of this fil-ter, f aper ; Col. 9: Noise per pixel, σ pix ; Col. 10: Noise correctedfor correlated noise inside the measurement aperture, f aper , ac-cording to Eq. 4. Col. 11: Achieved signal-to-noise ratio ac-cording to Eq. 5; Col. 12: Stellar flux f star according to Eq. 1;Cols. 13 +
14: Maximum and minimum Full Width (W) HalfMaximum (in (cid:48)(cid:48) ) of the source PSF.
Article number, page 36 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e B . . C hop - nodpho t o m e t r y m ea s u r e m e n t s i n t h e b l u e ( µ m fi lt e r) . P r o ce ss i ngp r o cee d e d fr o m SP G v11 . . l e v e l r odu c t s w it h H I P E v e r s i on13bu il d2768 . G y r o c o rr ec ti on w a s a pp li e d f o r m o s t o f t h eca s e s . O B S I DOD T a r g e t GD it h R e p . F it P ea k f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ( m J y )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) . β G e m hy353 . . . . . . . . ε L e p l y127 . . . . . . . . ε L e phy128 . . . . . . . . η D r a hy210 . . . . . . . . δ D r a hy29 . . . . . . . . δ D r a hn29 . . . . . . . . δ D r a l y210 . . . . . . . . δ D r a hy210 . . . . . . . . δ D r a hy49 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy15 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy16 . . . . . . . . θ U m i hy205 . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . Article number, page 37 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e B . . C hop - nodpho t o m e t r y m ea s u r e m e n t s i n t h e g r ee n ( µ m fi lt e r) . P r o ce ss i ngp r o cee d e d fr o m SP G v11 . . l e v e l r odu c t s w it h H I P E v e r s i on13bu il d2768 . G y r o c o rr ec ti on w a s a pp li e d f o r m o s t o f t h eca s e s . O B S I DOD T a r g e t GD it h R e p . F it P ea k f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ( m J y )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) . β G e m hy330 . . . . . . . . ε L e phy115 . . . . . . . . ε L e phy213 . . . . . . . . η D r a hy26 . . . . . . . . δ D r a hy25 . . . . . . . . δ D r a hn25 . . . . . . . . δ D r a l y25 . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy13 . . . . . . . . . θ U m i hy14 . . . . . . . . . θ U m i hy13 . . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . Article number, page 38 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars T a b l e B . . C hop - nodpho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) . P r o ce ss i ngp r o cee d e d fr o m SP G v11 . . l e v e l r odu c t s w it h H I P E v e r s i on13bu il d2768 . G y r o c o rr ec ti on w a s a pp li e d f o r m o s t o f t h eca s e s . O B S I DOD T a r g e t GD it h R e p . F it P ea k f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ( m J y )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) . β G e m hy310 . . . . . . . . β G e m hy310 . . . . . . . . ε L e phy15 . . . . . . . . . ε L e p l y15 . . . . . . . . . ε L e phy15 . . . . . . . . . ε L e phy24 . . . . . . . . . η D r a hy22 . . . . . . . . . η D r a hy22 . . . . . . . . . δ D r a hy21 . . . . . . . . . δ D r a hn22 . . . . . . . . . δ D r a hy21 . . . . . . . . . δ D r a hn22 . . . . . . . . . δ D r a l y21 . . . . . . . . . δ D r a l y21 . . . . . . . . . δ D r a hy21 . . . . . . . . . δ D r a hy41 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy12 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy12 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy12 . . . . . . . . . θ U m i hy11 . . . . . . . . . θ U m i hy12 . . . . . . . . . θ U m i hy201 . . . . . . . . Article number, page 39 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph T a b l e B . . c on ti nu e d . C hop - nodpho t o m e t r y m ea s u r e m e n t s i n t h e r e d ( µ m fi lt e r) . O B S I DOD T a r g e t GD it h R e p . F it P ea k f a p e r σ p i x σ a p e r , c o rr S / N f s t a r W m a x W m i n ( m J y )( m J y )( m J y )( m J y )( m J y )( (cid:48)(cid:48) )( (cid:48)(cid:48) ) . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . . HD . . . . . . . . Article number, page 40 of 42. Klaas et al.:
Herschel -PACS photometry of faint stars
Appendix C: Comparison scan map with chop/nodphotometry
In Table C.1 we list the flux ratios of scan map photometryand chop / nod photometry for ten sources, which were observedin both modes. The comparison between the two photometrymodes gives the following result:For 70 µ m photometry, the consistency of the fluxes is bet-ter than 3% for seven out of nine sources. The two excursions,HD 159330 and HD 15008, are consistent within the larger errormargin which is caused by a larger uncertainty because of onlyone chop / nod measurement (HD 159330) or the faintness of thesource (HD 15008).For 100 µ m photometry, the consistency of the fluxes is bet-ter than 2% for five out of eight sources. For HD 138265 the fluxconsistency is ≈ η Dra and HD 41047 there is only one chop / nod measurement,which introduces a high uncertainty, but fluxes are consistentwithin the error margin.For 160 µ m photometry, the consistency of the fluxes is bet-ter than 3% for four out of seven sources. For ε Lep the scan mapflux is 9% higher than the chop / nod one. There is only a small (4)number of chop / nod measurements versus a large (18) numberof scan map measurements. We therefore consider the scan mapmode result as the more reliable one. The opposite is the case forthe number of photometric measurements of θ Umi, with 2 scanmap measurements versus 16 chop / nod measurements. Here thescan map flux is 13% higher than the chop / nod one. However, the2 scan map measurements, each with 6 repetitions, have the bestS / N of all measurements and are therefore quite reliable. Fifteenout of 16 chop / nod measurements have a repetition factor of only1. They still allow a reasonable detection of the source at theexpected location but show considerable scatter in the resulting(colour-corrected) fluxes between 35.5 and 91.6 mJy (expectedflux according to the model: 53.9 mJy). Only one chop / nod mea-surement has 20 repetitions with a S / N comparable to the twoscan maps. Its resulting flux of 52.8 mJy is 13% lower than theaverage 60.9 mJy from the two scan maps. Here we should notethat the annulus used for background determination is closer tothe source and narrower for chop / nod aperture photometry (ra-dius 24 – 28 (cid:48)(cid:48) , Nielbock et al. (2013)) than for scan map pho-tometry (radius 35 – 45 (cid:48)(cid:48) , Balog et al. (2014)). As we discussin Sect. 5.2, the scan map measurements prove contaminationof the source flux by FIR cirrus emission in the order of 10%explaining the excess over the model flux. The maps also showthat there is additional emission around the source which is muchmore picked up by the background annulus of the chop / nod pho-tometry, resulting in a higher subtracted background value. Thisleads to the result that the chop / nod photometry is close to theexpected model flux, because the underlying cirrus emission isby chance properly compensated for by the background subtrac-tion, while the scan map photometry reveals the extra emissioninside the aperture. The photometric result must therefore be as-sociated by an additional uncertainty of 10%, because the back-ground subtraction strongly depends on the selected backgroundarea geometry (c.f. Table 7). For HD 41047 there is only onechop / nod measurement with a very high assigned flux uncer-tainty, so that also the flux ratio of scan map to chop / nod pho-tometry is highly uncertain. Table C.1.
Ratios of fluxes obtained in scan map mode photometry (Ta-ble 7) versus chop / nod mode photometry (Table 8) as a measure of con-sistency between the two photometry modes. Values in italics have ahigh uncertainty. HD Name R S / C R S / C R S / C β Gem 1.031 ± ± ± ε Lep 0.987 ± ± ± η Dra 0.993 ± ± ± δ Dra 0.992 ± ± ± θ Umi 1.009 ± ± ± ± ± ± ± ± ± ± ± δ Hyi 1.110 ± Article number, page 41 of 42 & A proofs: manuscript no. klaas_firfaintstars_pacs_astroph
Appendix D: ISOPHOT Highly Processed DataProduct (HPDP) photometry
Table D.1.
ISOPHOT (Lemke et al. 1996) Highly ProcessedData Product (HPDP) photometry of P22 mini-maps of nor-mal stars (https: // / web / iso / highly-processed-data-products: Moór et al., 2003, "Far-infrared observations of normal starsmeasured with ISOPHOT in mini-map mode"). The values in column f ν are the original HPDP fluxes (for SED ∝ ν − ). They have to be dividedby the colour-correction factor cc, which is for a 5000 K BB SED. Star Filter λ c ISO TDT no. f ν cc( µ m) (mJy) α Ari C_180 180 79001902 314 ±
19 1.10 ε Lep C_60 60 65701315 1779 ±
71 1.06C_50 65 65701312 1835 ±
65 1.29C_70 80 65701309 1113 ±
46 1.23C_90 90 65701318 918 ±
64 1.17C_100 100 65701306 692 ±
36 1.10C_105 105 65701303 601 ±
44 1.05C_120 120 65002709 507 ±
43 1.21C_135 150 65002103 292 ±
21 1.10C_160 170 65002406 225 ±
21 1.20 ω Cap C_60 60 72701415 1232 ±
65 1.06C_50 65 72701412 1258 ±
45 1.29C_70 80 72701409 779 ±
32 1.23C_90 90 72701418 543 ±
38 1.17C_100 100 72701406 490 ±
25 1.10C_105 105 72701403 441 ±
32 1.05C_120 120 73401709 337 ±
28 1.21C_135 150 73401603 221 ±
16 1.10C_160 170 73401706 219 ± η Dra C_90 90 78300677 365 ±
26 1.17C_160 170 35800501 123 ±