A survey for low-mass stellar and substellar members of the Hyades open cluster
AAstronomy & Astrophysics manuscript no. aa30134-16˙12Jan2018 © ESO 2018January 16, 2018
A survey for low-mass stellar and substellar members of theHyades open cluster.
Stanislav Melnikov , and Jochen Eisl¨o ff el Th¨uringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany Ulugh Beg Astronomical Institute, Astronomical str. 33, 700052 Tashkent, UzbekistanReceived / Accepted
ABSTRACT
Context.
Unlike young open clusters (with ages <
250 Myr), the Hyades cluster (age ∼
600 Myr) has a clear deficit of very low-massstars (VLM) and brown dwarfs (BD). Since this open cluster has a low stellar density and covers several tens of square degrees on thesky, extended surveys are required to improve the statistics of the VLM / BD objects in the cluster.
Aims.
We search for new VLM stars and BD candidates in the Hyades cluster to improve the present-day cluster mass function downto substellar masses.
Methods.
An imaging survey of the Hyades with a completeness limit of 21 . m R band and 20 . m I band was carried outwith the 2k ×
2k CCD Schmidt camera at the 2m Alfred Jensch Telescope in Tautenburg. We performed a photometric selection ofthe cluster member candidates by combining results of our survey with 2MASS
JHK s photometry. Results.
We present a photometric and proper motion survey covering 23.4 deg in the Hyades cluster core region. Using optical / IRcolour-magnitude diagrams, we identify 66 photometric cluster member candidates in the magnitude range 14 . m < I < . m
5. Theproper motion measurements are based on several all-sky surveys with an epoch di ff erence of 60-70 years for the bright objects. Theproper motions allowed us to discriminate the cluster members from field objects and resulted in 14 proper motion members of theHyades. We rediscover Hy 6 as a proper motion member and classify it as a substellar object candidate (BD) based on the comparisonof the observed colour-magnitude diagram with theoretical model isochrones. Conclusions.
With our results, the mass function of the Hyades continues to be shallow below ∼ . M (cid:12) indicating that the Hyadeshave probably lost their lowest mass members by means of dynamical evolution. We conclude that the Hyades core represents the‘VLM / BD desert’ and that most of the substeller objects may have already left the volume of the cluster.
Key words. stars: low-mass stars, brown dwarfs — stars: mass function — open cluster: individual: the Hyades
1. Introduction
The accurate initial mass function (MF) of Galactic open clus-ters allows us to build up a picture of the initial conditions ofcluster formation and to investigate their further evolution. Thebright end of the mass function has been analysed in many de-tailed studies of bright clusters. In the last decades, on the otherhand, deep photometric surveys of open clusters were focused onthe faint MF end reaching out to the lowest mass members. Thenearby open clusters are very convenient targets for this goal. Inthe solar neighbourhood there are a number of open clusters in-cluding the Pleiades, the Hyades, Praesepe (M44), and the ComaBerenices open cluster (Melotte 111). Extensive deep surveys ofthe Pleiades (age ∼
120 Myr) have led to the discovery of a largepopulation of very low-mass stars (VLM) and substellar mem-bers known as brown dwarfs (BDs) (Stau ff er et al. 2007; Lodieuet al. 2012a; Zapatero Osorio et al. 2014; Bouy et al. 2015). Aconsiderable low-mass population has also been discovered insome other younger stellar clusters ( α Per: Lodieu et al. 2012b; σ Ori: Pe˜na Ram´ırez et al. 2012). These surveys showed that theinitial conditions of star formation in stellar clusters were e ff ec-tive in creating low-mass members.However, the proximity of a cluster also has the disadvan-tage of a large extension on the sky, which renders surveysfor cluster membership di ffi cult. Moreover, with cluster evo- Send o ff print requests to : Stanislav Melnikov, e-mail: [email protected] lution the lowest mass members may escape from a clustercore (‘evaporate’ from the cluster) due to dynamical encoun-ters and mix-up with the field objects (Terlevich 1987; Kroupa1995; de La Fuente Marcos & de La Fuente Marcos 2000).Therefore, detection of these objects will be more complicated.De La Fuente Marcos & de La Fuente Marcos (2000) suggestedthat this e ff ect can already be noticeable in the clusters with agesof ≥
200 Myr. The first surveys of the intermediate-age clusters,which covered only a small percent of the cluster core areas,did not find any significant population of low-mass members,similar to what was found for the Pleiades. The first studies ofthe Coma open cluster (age ∼
500 Myr) showed that this clus-ter has a deficit of low-mass stars in comparison to the youngerclusters (Deluca & Weis 1981; Odenkirchen et al. 1998). Therecent and deeper surveys of this cluster covered a larger fieldand were reaching into the substellar domain. They confirmedthat this deficit seems to be intrinsic and this finding (Casewellet al. 2006; Melnikov & Eisl¨o ff el 2012) supports the idea thatthe depletion is caused by dynamical evolution. Recent studiesof Praesepe ( ∼
600 Myr), another open cluster of similar age,based on the analysis of all-sky surveys UKIDSS (Boudreaultet al. 2012) and 2MASS, PPMXL, Pan-STARRS (Wang et al.2014) found conflicting results. Boudreault et al. (2012) foundthat the Praesepe MF is consistent with that of the Galactic diskpopulation down to 0 . M (cid:12) , whereas Wang et al. (2014) con-cluded that the cluster MF shows a deficit of members below0 . M (cid:12) . Therefore, deep wide-field surveys of intermediate-aged a r X i v : . [ a s t r o - ph . S R ] J a n tanislav Melnikov and Jochen Eisl¨o ff el: The VLM / BDs in the Hyades cluster open clusters (with ages of 450–600 Myr) are required to im-prove the comparison of their mass functions with those of theyounger clusters and construct a more reliable scenario of howopen clusters evolve with age.The Hyades open cluster (d =
46 pc) with age ∼
600 Myr(age =
625 Myr, Perryman et al. 1998), which has a Pleiades-likestellar population, is one of the most studied open clusters lo-cated in the solar neighbourhood. The earliest wide-field searchfor Hyades members covering ∼
110 deg discovered a deficitof M-type dwarfs in this cluster (Reid 1992, 1993) with respectto the solar neighbourhood mix. From these observations Reid(1992) derived a gravitational binding radius of ∼ M (cid:12) . Deeper imaging surveys,which covered only small areas to reach fainter members didnot lead to a discovery of any significant population of such ob-jects (Reid & Hawley 1999; Reid & Mahoney 2000; Gizis et al.1999). A survey covering 10.5 deg by Dobbie et al. (2002) alsofailed to find any new low-mass members and recovered onlythe known stellar member RHy 29 (Reid 1993). A wide-fieldstudy of the Hyades based on the recent proper motion cata-logue PPMXL, 2MASS, and Carlsberg Meridian Catalogue 14(CMC14; Copenhagen University et al. 2006) photometry hasenabled a full census of the kinematic cluster members downto masses of ∼ M (cid:12) in a region up to 30 pc from the clus-ter centre (R¨oser et al. 2011). Combining these three surveys,R¨oser et al. (2011) carried out a three-dimensional analysis ofthe cluster population and found that the Hyades have a tidal ra-dius of ∼ . M (cid:12) . Based on the deepest surveyover 16 deg of the Hyades core, Bouvier et al. (2008) reportedthe discovery of the first two BDs and confirmed membershipof 19 low-mass stellar members. Analysing the statistically sig-nificant number of Hyades members found in the previous stud-ies, Bouvier et al. (2008) concluded that the present-day massfunction of the Hyades is clearly deficient in the VLM / BD do-main compared to the initial MF of the Pleiades, which havea similar population structure, but are much younger than theHyades. Another study based on the all-sky surveys UKIDSSand 2MASS (Hogan et al. 2008) and following spectroscopicanalysis (Casewell et al. 2014; Lodieu et al. 2014) added severalBDs to the substellar domain of the cluster. Nevertheless, theupdated MF still shows the apparent deficit of the lowest massmembers (Lodieu et al. 2014).In this paper, we present the results of a new deep imag-ing survey of the Hyades open cluster obtained with the wide-field Schmidt camera at the 2m Alfred Jensch Telescope ofthe Th¨uringer Landessternwarte in Tautenburg, Germany (TLS).Details of the photometric observations and data reduction aredescribed in Sect. 2. In Sect. 3 we introduce the photometric se-lection procedure of VLM objects and BD candidates; we thencompute proper motions of our optically selected candidates bycombining the TLS astrometric calibration with earlier epochall-sky surveys, and describe the results. In Sect. 4 we reporton the comparison of our photometric selection with the resultsof previous surveys of the Hyades; we also discuss the updatedmass function of the cluster combining our new cluster membercandidates with those from the previous studies. h m h m h m h m h m RA13 O O O O O Hyades D E C Fig. 1.
Area of the Hyades cluster mapped by our TLS imag-ing survey. The total size of the surveyed area is ∼ .Star symbols are photometrically selected Hyades member can-didates, which are listed in Table A.1.
2. TLS photometric survey and basic CCDreduction
We have carried out a new wide and deep imaging survey ofthe Hyades open cluster (RA = h m DEC =+ ◦ (cid:48) ) in the RI bands using the 2k x 2k CCD camera in the Schmidt focus of the2m Alfred Jensch Telescope in Tautenburg. A short descriptionof the RI photometric system of the CCD camera can be foundin Melnikov & Eisl¨o ff el (2012). The Hyades are a very closeopen cluster and its core area ( r ∼ . ∼
50 deg . Our photometricsurvey obtained in October-November 2006 covers 23.4 deg inits central area, i.e. about 47% of the cluster core (see Fig. 1).The total exposure time per filter (one frame) was 600 s, andfor this exposure time the limiting magnitude of the frames wasestimated to be 22 . I band. To avoid saturated stellar pro-files, we ensured that I -magnitudes were in general > ∼ s ( ∼ (cid:48) ) in rightascension and ∼ . (cid:48) ; this procedure included overscan correction, bias sub-traction, and dome flat-fielding. The I -band images contained a IRAF is distributed by National Optical Astronomy Observatories,which is operated by the Association of Universities for Research inAstronomy, Inc., under contract with the National Science Foundation.2tanislav Melnikov and Jochen Eisl¨o ff el: The VLM / BDs in the Hyades cluster prominent interference fringe pattern caused by night sky emis-sion. These fringe strips were removed with a fringe mask con-structed from the whole set of the I -band images. The R - and I -band images were then aligned where necessary and all wereastrometrically calibrated using the Graphical Astronomy andImage Analysis Tool software (GAIA) and the Hubble GuideStar Catalog (GSC v.1.2) as reference. The GSC contains po-sitions for most of the field stars down to magnitude V = . (cid:48)(cid:48) RI frames of the same sky field into one image and reject-ing cosmics. The images also had several di ff erent kinds of arte-facts and extended objects which had to be discriminated fromstar-like objects. A description of these various artefacts and themethod allowing us to clean the images is described in Melnikov& Eisl¨o ff el (2012).Instrumental magnitudes of all extracted sources were thenextracted based on the measurement of the point spread func-tion (PSF) using the daophot package of IRAF. Finally, we con-verted the instrumental magnitudes into RI -band magnitudes us-ing photometric standards observed in Landolt Selected Areas(Landolt 1992). Photometric errors for the RI bands depend onmagnitude: in the range of 14 −
18 the errors gradually increasefrom 0 . m
01 to 0 . m
04, but for objects with R >
18 and I > . m R ≈
20. For the I − ( I − J ) and I − ( I − K ) CMDs, the I -errors are combined with theinfrared photometry errors provided in the 2MASS catalogue.
3. Selection of very low-mass stellar and browndwarf candidates
All 65 CCD cluster fields together contain about 290 000 ob-jects that were detected by SExtractor (Bertin & Arnouts 1996)in the R , I bands. We plot the I − ( R − I ) colour-magnitude di-agram (CMD) for the extracted sources (Fig. 2) and comparetheir diagram position with the model isochrones for low-massobjects, shifted to the distance of the Hyades ( m − M = . ff e et al. 1998), DUSTY (Chabrier et al. 2000), and COND(Bara ff e et al. 2003) isochrones (e.g. Dobbie et al. 2002; Bouvieret al. 2008). NextGen evolutionary models for solar metallic-ity based on non-grey dust-free atmosphere models describedvarious observed properties of M dwarfs down to the bottomof the main sequence (CMDs, spectral types, etc.), whereas theDUSTY and COND models try to reproduce the same propertiesfor BDs, taking into account the possible formation and opacityof dust grains in the atmosphere of objects with T e ff (cid:46) ff erent in that the latterinclude e ff ects of rapid gravitational settling of the grains in thelower atmospheric layers below the photosphere. Chabrier et al.(2000) predict that this process will occur at a temperature of T e ff (cid:46) M ≈ . M (cid:12) .The BT-Settl models (Allard et al. 2012) are a further devel-opment of evolutionary models which account for the forma-tion of dusty clouds via a parameter-free cloud model (basedon the cloud microphysics from Rossow 1978). Compared toDUSTY, the BT-Settl models include, among other microphys-ical processes, gravitational settling of the dust in the cool BDatmospheres. The BT-Settl models, based on a solar abundance from Ca ff au et al. (2011, CIFIST2011) were already employedfor the Hyades member selection in Goldman et al. (2013), whoused the wide global surveys such as Pan-STARRS1 and SDSScombined with 2MASS and WISE infrared survey. The BT-Settlmodel grid allows a good reproduction of near-infrared (NIR)spectral energy distribution of cool VLMs and BDs (Allard2014). The current BT-Settl model grid (Bara ff e et al. 2015;Allard 2016) covers the stellar parameter range for the low-massobjects with T e f f = − . m
12 fainter or brighter than the centralcluster isochrone. Moreover, the main sequence of the Hyadesin the R − ( R − I ) CMD constructed from the previously knownmembers from Reid (1993) shows that it is not just a thin line,but has a width of ∼ . − . ff ect on M V − ( V − I ), but it is also ob-servable in M I − ( I − K ). Reid (1993) suggested that this e ff ectcan be a sequence of natural dispersion of stellar parameters,where the high rate of unresolved binaries amongst the clustermembers (Gri ffi n et al. 1988; Reid 1993) can be partly responsi-ble for this scatter. Thus, we used the additional colour strip of0 .
15 mag width in order to take into consideration this disper-sion and increase the detection probability of real members. Asa result, we started with all objects within a strip that takes intoaccount the cluster depth, the dispersion of colour indices, plus a1 . σ wide strip due to photometric uncertainty (PSF photomet-ric errors only). The strips are shown in the I − ( R − I ) CMDin Fig. 2 as the two dashed curves on both sides of the BT-Settlisochrone which are getting wider due to increasing photometricerrors with growing magnitude.When we use the BT-Settl model for analysis of the I − ( R − I )CMD, we can roughly split the procedure into two parts. For thebright objects with I <
18, the BT-Settl isochrone is separatedfrom the bulk of the field dwarfs quite well and we have foundonly several tens of photometric candidates within the photomet-ric errors. There are also a number of objects located redwardof our red uncertainty boundary which we included in our ini-tial sample, especially in the upper part between I = − . I − ( R − I )CMD, all these reddish objects were initially included in our listas potential cluster members. As a result, we identified severaltens of low-mass cluster member candidates in the magnituderange 14 < I <
18, covering from 0.15 M (cid:12) to about 0.075 M (cid:12) .These sources were then cross-identified with JHK I > .
5, the BT-Settl model predicts thatthe R − I isochrone has a turnover and fainter objects will havebluer colour indices. Therefore, for the candidates with massesbelow 0 . M (cid:12) , one can see that the model coverage signifi- ff el: The VLM / BDs in the Hyades cluster
15 16 17 18 19 20 0.5 1 1.5 2 2.5 3 3.5 I R-IVLM/BD candidatesPM candidatesBT-Settl 625 Myrs 0.110.100.090.080.070.06photom. uncertaintyBDs boundaryLithium limit
14 15 16 17 18 19 20 1.5 2 2.5 3 3.5 4 I I-J BT-Settl 20150.150.130.110.100.090.080.07
14 15 16 17 18 19 20 2.5 3 3.5 4 4.5 5 I I-K BT-Settl 20150.150.130.110.100.090.080.07
13 14 15 16 17 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 J J-K BT-Settl 20150.130.110.100.090.080.070.06
Fig. 2. I − ( R − I ) (top left), I − ( I − J ) (top right), I − ( I − K ) (bottom left), and J − ( J − K ) (bottomright) colour-magnitude diagrams of opticallyselected candidates (points) from the TLS and2MASS / UKIDSS surveys; the proper motioncandidates are indicated by filled circles. In allCMDs, we show 625 Myr BT-Settl isochronesshifted to the distance of the Hyades cluster( m − M = .
33) as solid lines. The verticalline labelled with stellar mass ( M (cid:12) ) is the massscale according to this model. The two dashedlines outline the selection area (see text). Theupper horizontal line at I = . / substellar boundary and the lower line in-dicates the lithium burning limit. The BT-Settlisochrone in the J − ( J − K ) CMD agrees wellwith the colour indices of the faintest membercandidates. cantly overlaps with the field dwarfs at the I − ( R − I ) CMD(Fig. 2). Using the BT-Settl isochrone has led to a selectionof several thousand objects. These sources were then cross-identified against sources in 2MASS and the UKIRT InfraRedDeep Sky Survey (Galactic Clusters Survey, UKIDSS). TheUKIDSS survey has a deeper detection limit, but its photometricselection contained only the K band for the Hyades. We discussthis photometric selection in the following section. As the next step of the photometric selection, we used threeNIR CMDs of I − ( I − J ), I − ( I − K ), and J − ( J − K ) (seeFig. 2). As for the I − ( R − I ) diagram, the 625 Myr BT-Settlisochrones from Allard (2016) are shown on these IR CMDsin Fig. 2 as solid lines. The two dashed lines at both sides ofthe isochrones indicate the selection area defined by parametersadopted for I − ( R − I ) CMD such as the photometric uncertainty,the cluster depth, and the natural photometric dispersion. AllCMDs in Fig. 2 also represent a scale of stellar mass according tothe model. Using the CMDs, we then selected all the photomet-ric candidates which agree with the theoretical NIR isochroneswithin defined selection areas. Contrary to I − ( R − I ), the BT-Settlisochrones in the I − ( I − J ) and I − ( I − K ) CMDs predict a grad-ual increase in the colour indices with decreasing stellar massat least down to 0.05 M (cid:12) . The BT-Settl J − ( J − K ) isochrone is almost vertical for J < .
5, but for fainter J the colour index be-comes considerably redder. This behaviour agrees well with thecolour indices of the faintest member candidates, which showvery red colour indices on this CMD (Fig. 2).Goldman et al. (2013) note that the discrimination betweenthe Hyades cluster sequence and the bulk of the background starsis better when the wavelength di ff erence between the bands isgreater. Thus, the I − ( I − K ) CMD is a good one for this pre-liminary discrimination. First, we cross-identified all our initialcandidates selected from the I − ( R − I ) CMD in the Two MicronAll-Sky Survey (2MASS, Skrutskie et al. 2006). Using a match-ing radius of 2 . (cid:48)(cid:48)
5, we derived
JHK s photometry for all our can-didates up to I ≈ .
3. We combined the derived NIR photom-etry with our I -magnitudes into the three additional CMDs (seeFig. 2). For our targets with I (cid:38) .
3, the 2MASS survey did notcontain IR photometry and thus we cross-identified these againstsources in the UKIDSS survey. Although the Hyades are coveredby this survey, it provides only K -magnitudes ( K ) for this clus-ter. Finally, we used the transformation equation from Hewettet al. (2006) to convert UKIDSS K magnitudes to 2MASS K s .The analysis of the large candidate set on the I − ( I − K )CMD showed that almost all UKIDSS and 2MASS sources with I > . I − K bluer than is predicted by the BT-Settl I − ( I − K ) isochrone, and thus they are probably field dwarfs.Therefore, we excluded all the objects from the further analysis.In our results, we identified only seven photometric candidates ff el: The VLM / BDs in the Hyades cluster with I > .
5. For I < . An estimate of the number of contaminating field stars can beobtained from the Besanc¸on Galaxy model (Robin et al. 2003),which gives star counts depending on their brightness, colour,and Galactic coordinates. Using this model, Goldman et al.(2013) have found that the contamination by field stars is negli-gible ( < J − H ) − ( H − K ) diagram to weed outpossible background giants from our sample. This type of con-taminating objects probably experiences interstellar extinctionand tends to populate the top left side of the diagram above thesequence of the dwarf stars (Goldman et al. 2013). In Melnikov& Eisl¨o ff el (2012) we tried to find giants as background con-taminants projected onto the Coma open cluster with the help ofthe analysis of narrowband spectral indices (Jones 1973), whichallowed us to distinguish genuine low-mass members from thefar red giants with similar colour indices. However, no giantswere found in the background of the Coma cluster. The Hyades(at l = b = − .
3) are located in the opposite directionto the Galactic centre and quite high above the Galactic plane.Therefore, we do not expect to find a large amount of distantbackground M-type giants in the direction of the Hyades either,given that this cluster is located at high Galactic latitude as well.As a result of this NIR two-colour analysis, we found nineobjects that are located in the CMD region with high extinction.To double check, we calculated proper motions of these targets(see Sect. 3.4). Most of these objects have proper motions aroundzero which seems to favour the idea that they might be back-ground objects. Finally, we excluded these objects from our listof photometric VLM candidates.
To determine the spectral types of the VLM candidates, we ex-ploited the method of luminosity–spectral type calibration byKraus & Hillenbrand (2007). This method is based on a largesample of stellar spectral energy distributions (SEDs) and allowsus to estimate the spectral type (SpT) of a star using only its op-tical / NIR photometry. The results of this classification are pre-sented in Table A.1. The second to last column holds the spec-tral type derived from the TLS I -band magnitudes and the lastcolumn is the average of the three SpT values determined from2MASS JHK s . Spectral type sequences based on 2MASS pho-tometry are self-consistent and the SpT estimates derived fromthese bands agree very well: the SpT values are equal to or liewithin one spectral subclass. At the same time, the spectral typederived from 2MASS is systematically later than those calcu-lated from the TLS I band. Moreover, this di ff erence increasestowards later SpT objects. This may imply that our I -band cali-bration has some bias with respect to the 2MASS JHK s -system.Considering this result in more detail, one can say that the SpTdetermined from the two methods agree well (with the di ff er-ence of a SpT subclass) for most objects whose spectral indiceswere derived from the 2MASS photometry (58 of the 66 ob-jects), whereas for 8 objects, SpT (2MASS) values are later by Fig. 3.
PM diagram of photometrically selected objects in theHyades region as a vector diagram of µ α cos δ and µ δ . The greybox plotted following Bouvier et al. (2008) and Bryja et al.(1994) defines the region of PMs expected for the cluster. Takinginto account rms errors, 14 objects of 66 optically selected can-didates (empty circles) were classified as PM members (filledcircles).two subclasses and larger than those derived from the TLS pho-tometry.We should note that this luminosity–spectral calibration se-quence is based on the stellar SEDs of VLMs only and is validfor stellar objects with K < . (cid:38) . M (cid:12) ). Therefore,this calibration method may not be reliable for BD candidatesand it may not provide the proper spectral classification for ob-jects with SpT about and later than L0. The mean proper motion (PM) of the Hyades cluster is ∼ − (Bouvier et al. 2008), which is quite di ff erent from thatof Galaxy field stars and therefore can be used for the separationof genuine cluster members from background and foregroundobjects. It was found that the faint Hyades members are locatedwithin the octant of PM space between PA =
90° and PA = ∼ ff ected the measurements. Thesame shortcomings are found in the PPMXL, which combinesUSNO-B1.0 and 2MASS astrometry. Therefore, we decided tomeasure our own precise positions for our selected candidates toderive more reliable PM results, especially for the faint objects.Therefore, we measured the (X-Y) location of our opticallyselected candidates on the astrometrically calibrated TLS RI im-ages and determined their sky coordinates (J2000). To com-pute the PMs from several epochs, we then cross-referenced ff el: The VLM / BDs in the Hyades cluster our candidates with the following surveys: POSS1 ( R ), POSS2( R + I ), 2MASS, UKIDSS K band, and WISE; we then obtainedastrometry for seven independent epochs (TLS RI − averaged)from 1950 to 2010. Most objects fainter than I =
17 could notbe detected on the POSS1-R plates. These objects were mea-sured on the WISE 3.4 and 4.6 µ m bands, where they were alldetected, and were small enough to provide high-quality astrom-etry. These objects therefore only have an epoch di ff erence from1990 to 2010. We note that all objects could be measured onthe downloaded 2MASS images, even those that are not in the2MASS catalogue, while UKIDSS covers the Hyades only in its K band.The equatorial coordinates were extracted from all photo-metric surveys for the same epoch J2000 and thus a changeof object positions should only depend on its PM. Finally, thePM of every target was derived from linear fitting the positionchanges over the epochs spanned by our data. The typical er-rors of the measurements are σ ( µ α cos δ ) = . − and σ ( µ δ ) = . − for the PMs measured within 1950–2010and σ ( µ α cos δ ) = . − and σ ( µ δ ) = . − forthe 1990–2010 epochs.One source that can a ff ect our PM results is a visual binarysystem. Reid (1993) found that the Hyades may have a substan-tial fraction of the binaries, from 25% to 60% depending on themodel. If we measure the position of an unresolved binary, webelieve that we derive the motion of the system as a whole, butif we measure the motion of an object which is actually a com-panion of a visual binary system, the measured PM can di ff erfrom that of the system because the components are involved inmotion around their centre of mass. We inspected all selectedmember candidates and if they had signs of binarity, we markedthem in Tables 1 and A.2 as ‘VB’ for probable visual binaries(visual partially resolved systems) or as ‘VB?’ for wide stel-lar pairs with lower probability (resolved systems). One can seethat the binary fraction in our selection set is not as high as pre-dicted by Reid (1993). This is probably due to the source detec-tion method used; the method used the shape of stellar imagesto separate single stellar objects from extended sources such asgalaxies or artefacts. As a result, the many partially resolved sys-tems whose components were not resolved during the detectionprocess seem to have been excluded.The resulting measured PMs for all 66 objects are shown as avector diagram of µ α cos δ and µ δ in Fig. 3. The objects with PMssatisfying Hyades membership were selected using the same PMbox as in Bouvier et al. (2008); Bryja et al. (1994). Four other ob-jects are located outside of this box, but can also be classified asHyades members within their error bars. In total, 14 objects wereselected as Hyades PM members (Table 1). Two objects havebeen selected as possible components of visual binaries TLS-Hy-2 and -8; both have also been classified as Hyades membersin previous studies as LH 234 (Leggett & Hawkins 1988) andRH 230 (Reid 1992). However, both objects are mentioned inthese studies as single stars without counterparts. Therefore, itis possible that these visual pairs are not physical binaries, butwere classified as such due to projection e ff ects. The opticallyselected candidates whose PMs do not satisfy Hyades member-ship are listed in Table A.2. Their PMs are listed with individualrms errors and actual epoch range.
4. Results and discussion
Our RI survey covered 23.4 deg in the core area of the Hyades(Fig. 1). We estimated the completeness and the limiting magni-tude of the survey in the RI bands as described in Caballero et al. (2007). Our calculation shows that our survey is complete to 21.5in the R band and 20.5 in the I band. The limiting magnitude ofthe RI survey is about 1.5–2 mag fainter than the completenessmagnitude, i.e. the limiting magnitude is 23 for the R band and22.5 for I . Since we used the same CCD camera, these valuesare similar to those of our Coma imaging survey (Melnikov &Eisl¨o ff el 2012), but the Hyades ( m − M = .
3) are closer to theSun than the Coma open cluster ( m − M = .
7) and therefore wecan detect objects in the Hyades with an absolute magnitude thatis ∼ RI − photometry with 2MASS IR we haveselected 66 photometric candidates (Fig. 2 and Table A.1) us-ing the modern BT-Settl theoretical model (Bara ff e et al. 2015;Allard 2016). The photometric candidates span magnitudes from I ∼ . . M (cid:12) to0 . M (cid:12) (67 Jupiter masses). The objects with I = . − . I > .
7) should have spec-tral types later than L0. At the adopted distance, the boundarybetween stellar and substellar objects lies at I ∼ . RI photometry of the objects as well as their PM values.Coordinates of the objects extracted from the TLS frames arebased on the J2000 epoch of the Guide Star Catalog v1.2. Onlyone PM member (TLS-Hy-7) is located well under the substellarborderline ( I > .
1) and we classify it as a photometric BD.
Several studies of the Hyades during the last years were focusedon improving the census of its lowest mass members. Some ofthe surveys tried to cover as much area as possible around theHyades core using new all-sky surveys. For example, the R¨oseret al. (2011) and Goldman et al. (2013) studies are based onthe PPMXL / Pan-STARRS1 surveys and did all-sky searches forHyades members in a very wide region covering ∼ around the cluster centre (a radius of ∼
30 pc). Other surveyswere focused on the core area of this cluster trying to registersubstellar members towards the lowest masses, e.g. the Bouvieret al. (2008) survey. In our survey we used the same approachand tried to discover the faintest RI objects in the Hyades core.Nevertheless, our TLS and Bouvier et al. (2008) surveys do notcover the same area. A comparison of our survey with the spatialcoverage of Bouvier’s study (16 deg ) shows that they overlapover ∼
60% ( ∼ . Thus it is complementary to the Bouvier etal. study.The R¨oser et al. (2011) and Goldman et al. (2013) surveysboth used the same technique of kinematic selection (the con-vergent point method), and Goldman et al. (2013) published alist of 63 additional candidates not included in the R¨oser et al.(2011) list. Since the upper mass limit of our TLS survey is ∼ M (cid:12) , it does not overlap with the lower mass limit of theR¨oser et al. (2011) survey (0 . M (cid:12) ). To check this we tried tocross-reference both our PM candidates and photometric candi-dates with the R¨oser et al. (2011) list, but, as expected, we foundno common objects. The Goldman et al. (2013) survey has alower mass limit of 0 . M (cid:12) so that there could be some commonsources. However, since the surface density of low-mass Hyades ff el: The VLM / BDs in the Hyades cluster
Table 1.
Hyades PM member candidates.
Object RA
TLS
DEC
TLS
I R − I µ α cos δ µ δ epoch mass notesTLS-Hy-.. (J2000) (mag) (mas yr − ) ( M (cid:12) )1 04 17 31.3 15 23 01 14.88 1.61 95.1 ± − . ± . ± − . ± ± − . ± ± − . ± ± − . ± ± − . ± + ± − . ± ± − . ± ± − . ± ± − . ± ± − . ± ± − . ± ± − . ± + ± − . ± = a visual binary (partially resolved system), Cross-identification: CFHTHy = Bouvier et al. (2008); Hy = Hogan et al. (2008); LH = Leggett& Hawkins (1988); LHD = Leggett et al. (1994); RH = Reid (1992). candidates in the survey is quite low in the core region, only 3of 62 candidates from the Goldman et al. (2013) list are locatedwithin the area covered by our TLS fields. Nevertheless, we wereable to cross-identify two objects with this survey: TLS-Hy-8 = + = + R = .
364 was too bright for the TLS survey.Bouvier et al. (2008) selected 22 low-mass probable mem-bers based on their photometry and PM. Ten of the objects arebrighter than I =
14 and two BD candidates have I > . = CFHTHy-16, TLS-Hy-11 = CFHTHy-14,and TLS-Hy-12 = CFHTHy-12. Four of the objects were not de-tected because of special observing conditions: CFHTHy-15 and-17 are components of a close double source (RHy 240AB, Reid1992), which was not resolved in our survey photometry, and wetherefore removed these objects from our lists. The remainingtwo objects (CFHTHy-18 and -19) are located in the vicinity ofvery bright stars with spikes and strong halos, and therefore themethod used was not able to detect and derive photometry forthese objects. A comparison of our PM values of the objects incommon with those of Bouvier et al. (2008) shows that they arein agreement within the rms errors.We also searched for our objects in several earlier surveyscovering the Hyades core region: Leggett & Hawkins (1988),Reid (1992), Leggett et al. (1994), and Hogan et al. (2008).The cross-identification is indicated in the ‘Notes’ column ofTable 1. In addition to Bouvier et al. (2008), TLS-Hy-11 wasalso identified as a Hyades member in Reid (1992) (RHy 281)and TLS-Hy-10 was selected as a photometric members inLeggett & Hawkins (1988) (LH 91) and Leggett et al. (1994)(LHD0426 + ff erence agree well with other Hyades member can-didates. According to the photometric distance obtained fromUKIRT JHK -photometry (Leggett & Hawkins 1988) LH 222is located outside the Hyades core. However, the UKIRT
JHK -magnitudes of LH 222 are considerably di ff erent from 2MASS JHK -photometry ( > RI and the 2MASS photometry, a location of LH 222 on both I − ( R − I ) and NIR CMDs agrees well with the BT-Settl theoret-ical sequence for the Hyades distance. LH 68 was also selectedas a probable member in Bouvier et al. (2008) based on the cri-teria of photometry and PM (CFHTHy-12).We have selected only one object (TLS-Hy-7) lying nearthe substellar domain ( M ≤ . M (cid:12) ) and cross-identified itwith Hy 6 from Hogan et al. (2008). Since the photometricerror is large at these magnitudes, we are unable to ascertainwhether the object is lying above or below this boundary. Thus,this candidate may be a BD or instead the lowest mass stel-lar member known. Casewell et al. (2014) observed this ob-ject with medium-resolution NIR spectroscopy and classifiedTLS-Hy-7 as a Hyades BD member with spectral type of M8–L2. This spectral classification agrees with our estimation (M9–L0) obtained from the spectro-photometric calibration (Kraus &Hillenbrand 2007).In total, ten previously selected Hyades members are redis-covered in our TLS survey (marked in the ‘Notes’ column inTable 1). Thus only four member candidates from our list arenot identified in any of the previous surveys and no new BDcandidates have been found. The object TLS-Hy-153 (RA = h m s DEC = + ◦ (cid:48) (cid:48)(cid:48) , I = . R − I = .
72) was selected as a photometric candi-date, and it is located in the BD region on the I − ( R − I ) CMD.Since this object is quite faint, it was not cross-identified witha 2MASS source, but only with a UKIDSS object. After trans-formation from K (UKIDSS) to K S (2MASS) this object wasplaced on the I − ( I − K ) CMD, but it was rejected from the listof photometric candidates due to its inconsistent colour index( I − K S = . I -band image of the TLS survey. At the same time, an in-spection of WISE images shows that this object is quite brightat 3.4 and 4.6 µ m (Fig. 4) and at UKIDSS K band (2.2 µ m).Moreover, the WISE images reveal a bright companion (markedby an arrow) with a similar brightness. At 4.6 µ m this objectis brighter than at 3.6 µ m and it is brighter than TLS-Hy-153(comparing the peak flux of the central pixels). This IR com- ff el: The VLM / BDs in the Hyades cluster
TLS I
WISE 3.4 nm
WISE 4.6 nm
WISE 12.1 nm
Fig. 4.
TLS and WISE images of TLS-Hy-153 region. The IRcompanion of TLS-Hy-153 (empty arrow) is invisible in the TLS I -band image, but bright in the WISE 3.4 µ m and 4.6 µ m bands.This IR object is also visible at the WISE 12.1 µ m, whereas TLS-Hy-153 is not visible at the wavelengths.panion (hereafter TLS-Hy-153-IR) can even be seen at 12.1 µ m.This IR object is also detected on the UKIDSS K -band image:J041652.01 + K -mapis ∼ (cid:48)(cid:48) , which is ∼
500 AU at the distance to the Hyades.To estimate the temperature of the objects we constructedtheir SEDs from the available data: the TLS photometry, theWISE, and the UKIDSS surveys. The TLS-Hy-153 SED is basedon the five data points measured in the R , I bands; the UKIDSS K band; and WISE W1,W2; whereas photometry data for TLS-Hy-153-IR are available from three WISE bands, W1, W2, and W3(Fig. 5), and from the UKIDSS K band. The fluxes of the closecompanion on the W1,W2 images were separated and calculatedusing PSF-photometry ( IRAF.daophot ), whereas the W3 flux ofTLS-Hy-153-IR was estimated using aperture photometry; thefluxes were then converted to magnitudes with zero points pro-vided by the WISE survey. Both objects are well resolved onthe high-resolution UKIDSS K -map and therefore we used theirphotometric magnitudes from the survey.One can see that TLS-Hy-153 shows a maximum brightnessat 2.2 µ m. We estimate the TLS-Hy-153 temperature by fittingits SED with a Planck function for a black body. If we assumethat the radiation from the R , I band comes from the stellar ob-ject, the best solution that fits the blue cut-o ff and the SED slopearound the bands gives a flux distribution at T = K and W1–2corresponds to a Planck function with a temperature of ∼
800 K,whereas the W3 emission fits better with a black body at 300 K.This implies that the estimate of the TLS-Hy-153-IR tempera-ture using a single Planck function may not be reliable becauseat these wavelengths di ff erent sources with di ff erent tempera-tures can contribute to the resultant flux. Indeed, measurementsof the diameter of the TLS-Hy-153-IR image in di ff erent WISEbands show that the FWHM of its stellar profile in the W3 bandis larger than in W1 or W2. Therefore, we suggest that TLS-Hy-153-IR represents an extremely faint object (an ultra-cold BD or K W3W2W1R I TLS-Hy-153TLS-Hy-153-IRT = 1380 KT = 800 KT = 300 K f l u x ( m a g ) μ m)1 10 Fig. 5.
SEDs of TLS-Hy-153 and its IR companion. The TLS-Hy-153 SED is fitted with a single Planck function correspond-ing to the flux distribution of a black body with a temperature of1380 K ( dashed line ). The fit is based on the best solution for theblue cut-o ff and the SED slope around the R , I bands at which thestellar object irradiates. The TLS-Hy-153-IR SED is fitted withtwo Planck functions, with a black body at 800 K and 300 K.a planet-like object) surrounded by a lower temperature structuresuch as a dust envelope or a circumstellar disk.There are two possibilities to consider for the location ofthis binary object. The first is that this is a wide binary sys-tem located in the Hyades; however, as noted above, becauseof its faintness the PM of this object could only be obtained overthe epoch di ff erence 1997–2010 and does not support its clus-ter membership. On the other hand, the rms of the PM valuesare quite high. Therefore, we repeated the imaging of this areaat the TLS 2m telescope with a longer exposure (2 ×
20 min) inthe I band in 2015. The astrometry of the brighter companion onthese images confirms the previous estimate of its PM direction,while the fainter companion is still not visible on these expo-sures. However, if the system is indeed a wide physical pair, themotion of TLS-Hy-153 around the common mass centre maya ff ect the PM determination. Therefore, we cannot exclude thecluster membership of these objects.A second possibility is that we are looking at a young, moredistant system in the Taurus star-forming region (SFR). Since theHyades are located in front of the Taurus SFR, objects in the SFRcan be mixed up with genuine Hyades members. We note that theWISE images show a mini-cluster of bright IR objects aroundthe young stellar object (YSO) 2MASS J04220042 + R - and I -band images, but four objects (TLS-Hy-107, -108, -109, -110) have been selected as photometric candidates inthis area; however, they were all rejected after the PM selection.Since these objects are projected on the dim area (comparing thisregion with adjacent ones), all the IR objects might be membersof the Taurus SFR. The TLS-Hy-153 system is located 2 . ◦ ff el: The VLM / BDs in the Hyades cluster riphery of the Taurus SFR. For the Taurus distance of 140 pc, thespatial distance between the objects will be very high: 1540 AU.On the other hand, the star density around TLS-Hy-153 is higherthan around this IR cluster which means that the extinction is notstrong in this area. However, isolated YSOs located near SFRsin an area without signs of dust clouds with strong extinctionare a known phenomenon. Therefore, we neglect the interstel-lar extinction which is probably low in this area. Unfortunately,we do not know a value of the circumstellar extinction for thisobject which might be considerable in the case of YSOs. If weadopt a distance to the SFR as 140 pc (Kenyon et al. 1994) andits age as 2 Myr (Kenyon & Hartmann 1995), according to theBT-Settl model TLS-Hy-153 is a very low-mass substellar ob-ject with M ∼ . M (cid:12) (10 M jup ) and T ∼ µ α cos δ = . ± . − , µ δ = − . ± . − ) obtained from the shortepoch di ff erence coincides within our rms with the PM of othermembers of the Taurus region (e.g. 5 . , − . − : Grankin2013; Ducourant et al. 2005). However, it is very unusual to findsuch an object so far from the core of the Taurus SFR. If we takethe position of the dust cloud where many young stars such asDF Tau and DG Tau are located, α = h m , δ =+ ◦ (cid:48) , theangular distance between TLS-Hy-153 and this potential birth-place would be ∆ α ≈ ◦ and ∆ δ ≈ . ◦ . To reach the currentplace within 2 Myr, the di ff erence in velocity between the objectand the mean Taurus SFR should be about 4 mas yr − and 22mas yr − for α and δ , respectively, which led to µ α cos δ = . − and µ δ = −
42 mas yr − for TLS-Hy-153. If we take theposition of T Tau, which is also associated with a dust cloud andclose to our target, the di ff erence in the velocity will be less than µ α cos δ = . − and µ δ = −
31 mas yr − . Unfortunately,the PM uncertainty for TLS-Hy-153 is quite high, which doesnot allow us to draw a conclusion on its birthplace. Nonetheless,TLS-Hy-153 and the accompanying IR object might representan interesting wide system: one of the elements may be a BDand the other a planet-like object (or an ultra-cold BD). The previous studies found that the Hyades are probably a moremassive cluster than the similarly aged open cluster in Coma.R¨oser et al. (2011) estimated a cluster tidal radius of 9 pc, whichis about twice that of Melotte 111 (5–6 pc, Odenkirchen et al.1998). Within this tidal radius R¨oser et al. (2011) found 364 stel-lar systems with the total mass of 275 M (cid:12) . Reid (1992) estimatedthe Hyades gravitational binding radius to be as large as ∼ M (cid:12) .The present-day mass function (PDMF) was investigated indetail by Bouvier et al. (2008) based on a large member sam-ple compiled in the Prosser & Stau ff er database (Bouvier et al.2008). This database, combined from many studies, lists morethan 500 probable Hyades members and allowed them to build aPDMF spanning a range of stellar masses of 0 . − M (cid:12) . Bouvieret al. (2008) showed that the Hyades and Pleiades mass functionsare similar in shape for masses ≥ M (cid:12) and agree with a Salpeterslope ( α = .
35, Salpeter 1955). However, for the lower massesthe Hyades MF becomes shallower than for Pleiades and for arange of M = . − . M (cid:12) the Hyades MF agrees with a powerlaw index of α = − .
3, whereas the Pleiades show α = . N ( l o g m ) Mass(M ⊙ ) Fig. 6.
Present-day mass function of the Hyades between 0.05 M (cid:12) and 3 M (cid:12) . This MF is combined from our new TLS sur-vey, the Bouvier et al. (2008) survey and the Prosser & Stau ff erdatabase (solid line). The dashed histogram corresponds to thedata shown in Bouvier et al. (2008). The data derived from oursurvey added objects to the Hyades MF in the two lowest massbins, 0.048–0.12 M (cid:12) and 0.12–0.19 M (cid:12) . The error bars take intoaccount the Poissonian error and the photometric uncertaintiesas well. For comparison, the Pleiades MF ( dashed histogram)adopted from Bouvier et al. (2008) is overplotted. Both the TLSand the Pleiades MFs are normalised to the mass distribution ofthe Prosser & Stau ff er database as described in Bouvier et al.(2008).assuming that the radial distribution of BDs and VLM stars isthe same and equals r C = r BD (cid:39) r BD = ff erence between the MFs (Bouvier et al. 2008).This finding confirms that the low-mass MF of the Hyades ismuch more poorly populated than in the Pleiades cluster, whichis much younger than the Hyades.In order to build an updated PDMF of the Hyades, wecombined our new results with the stellar mass statistics pre-sented by Bouvier et al. (2008). In order to calculate the massesfor our cluster member selection, we used the mass–magnituderelationships defined by the BT-Settl 625 Myr model (Allard2014). Since the isochrones are available for both R - and I -magnitudes, we estimated the masses from both bands indepen-dently. A comparison of the two estimates shows good agree-ment, within 0.01–0.02 M (cid:12) . Therefore, we averaged the two val-ues (see Table 1).Figure 6 represents the resulting new, more complete HyadesPDMF including our data, the compiled published data for M (cid:63) > . M (cid:12) from the Prosser and Stau ff er Open Cluster database,and the data from Bouvier et al. (2008). Since ten of our ob-jects were rediscoveries from previous studies, only four of ournew candidates have been added to update the known PDMF.The TLS member set was extrapolated to the whole cluster areaby a factor, taking into account the ratio of the covered areas inthe TLS and Bouvier surveys. The renormalised numbers havebeen added to the final MF. The error bars are based on thePoissonian statistics and also take into account the mass mea-surement errors converted from the photometric uncertainties.Only one object in our new sample falls within the lowest mass ff el: The VLM / BDs in the Hyades cluster bin (0.048–0.12 M (cid:12) ), whereas three objects have been added tothe 0.12–0.19 M (cid:12) bin. Adding our sample to the Bouvier et al.sample makes the mass spectrum a bit flatter over 0.05–0.20 M (cid:12) and the di ff erence between the Hyades and the Pleiades MFsis still clearly apparent (Fig. 6). We should take into accountthat this bin not only includes BDs, but also the low-mass stellarmembers. If our selected objects are genuine cluster members,the population in the lowest mass bin is more consistent withthe core radius of 7 pc for BDs in the Hyades cluster (Bouvieret al. 2008), i.e. r C (cid:39) r C (cid:39) α = − . ± . , which is close to the value fromBouvier et al. (2008).This result can be explained as a sequence of the contin-uing dynamical evolution of the Hyades, which are older thanthe Pleiades. Agekian & Belozerova (1979) showed that duringthe evolution of an open cluster, its members can escape fromthe cluster and form an extended halo around it. Comparing theshapes of the Hyades and Pleiades MFs, Bouvier et al. (2008)estimated that the Hyades must have lost >
90% of their ini-tial substellar population ( M < . M (cid:12) ). However, they con-cluded that currently ∼ higherthan in Bouvier et al. (2008). Modern numerical simulations ofthe Hyades cluster predict that during the dynamical evolution,‘evaporated’ BDs and other low-mass members will form elon-gated tails out of the main cluster core (Chumak et al. 2005).The modelling in Ernst et al. (2011) shows that the tidal tail oflost objects can reach a length of 800 pc after 625 Myr of evo-lution. Simple calculations show that if the escaping velocity isa few km / sec (for instance, ∼ / s, Chumak et al. 2005), theformer VLM member can recede from the cluster core on sev-eral tens of parsecs after 625 Myr of evolution and will be outof our selection criteria. Therefore, we cannot exclude that theobserved VLM / BD desert might be a sequence of the situationwhen almost all the VLM / BD members have left the cluster coreand even its halo.Therefore, our results support the conclusion that theVLM / BDs deficiency in the Hyades is a consequence of thegradual removal of low-mass cluster members due to weak grav-itational encounters during the continuous dynamical evolutionof the cluster (Bouvier et al. 2008). Moreover, the general resultfrom our survey combined with several previous wide surveysshows a lack of any considerable substellar population, whichimplies that the Hyades core has already lost most of these ob-jects. The most foreground VLM members probably mixed withforeground dwarfs and migrated so that they are no longer pro-jected on the cluster core. The background evaporated membersthat are projected onto the core are probably much fainter thanthose that are still located within the cluster volume, and thedeeper imaging survey is required to detect such objects.
5. Conclusion
We have carried out a wide imaging survey of 23.4 deg aroundthe core of the Hyades which partially overlaps with a similaroptical survey by Bouvier et al. (2008). Analysis of the TLS R , I photometry, together with 2MASS JHK s and derived PMs, led to a final list of 14 objects which satisfy the membership cri-teria for the Hyades. We identify four new low-mass membercandidates, while a further ten stars from our list can be cross-identified with objects discovered in earlier studies. No new pho-tometric substellar objects (BD) were discovered for the distanceof the Hyades core. We rediscovered only Hy 6 (Hogan et al.2008) as a PM member and classified it as a photometric sub-stellar object candidate (BD) based on the comparison of the ob-served CMD with theoretical model isochrones. With our fournew candidates added to the present-day mass function of theHyades below 0 . M (cid:12) , the updated mass function is close tothat of Bouvier et al. (2008). However, low-resolution spectra ofthe objects in the red and near-infrared spectral domain are de-sirable in order to check their ages, which should coincide withthe cluster age. In the case of a cluster membership, the objectsshould exhibit signs of relative youth, such as H α in emission(Bouvier et al. 2008; Melnikov & Eisl¨o ff el 2012). Acknowledgements.
J.E. and S.M. acknowledge support from the AmericanAstronomical Society under the 2005 Henri Chr´etien International ResearchGrant. This publication has made use of data products from the Two MicronAll-Sky Survey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center / California Institute of Technologyand the United Kingdom Infrared Deep Sky Survey. This research has made useof the SIMBAD database, operated at CDS, Strasbourg, France, and of the IRAFsoftware distributed by NOAO.
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Appendix A: Hyades photometric member candidates
In Table A.1, we provide a list of 66 optically selected Hyades member candidates inferred from an I − ( R − I ) CMD that wereselected for follow-up based on 2MASS JHK s photometry. Table A.1. RI - and 2MASS JHK s photometry of Hyades member candidates. Object 2MASS RA
TLS
DEC
TLS
I R − I J H K s SpT SpTTLS-Hy-.. (J2000) (mag) (mag) 2MASS
I JHK s
101 04170259 + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± > L0105 04193697 + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± ff el: The VLM / BDs in the Hyades cluster
Table A.1. continued.
Object 2MASS RA
TLS
DEC
TLS
I R − I J H K s SpT SpTTLS-Hy-.. (J2000) (mag) (mag) 2MASS
I JHK s
144 04323779 + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± + ± ± Table A.2.
Proper motion of Hyades probable non-members.
Object µ α cos δ µ δ epoch Notes Object µ α cos δ µ δ epoch Notes(mas yr − ) (mas yr − ) (mas yr − ) (mas yr − )101 50 . ± − . ± . ± − . ± . ± − . ± − . ± − . ± − . ± − . ± . ± − . ± − . ± − . ± . ± − . ± . ± . ± − . ± − . ± . ± − . ± − . ± − . ± − . ± − . ± − . ± . ± − . ± . ± − . ± − . ± − . ± − . ± . ± − . ± − . ± . ± . ± − . ± . ± − . ± . ± − . ± − . ± − . ± . ± − . ± . ± − . ± . ± − . ± . ± . ± − . ± − . ± − . ± . ± . ± − . ± − . ± − . ± − . ± − . ± . ± − . ± − . ± − . ± − . ± − . ± . ± . ± − . ± − . ± − . ± . ± − . ± . ± − . ± − . ± − . ± . ± − . ± − . ± . ± − . ± . ± − . ± . ± − . ± − . ± − . ± . ± − . ± . ± − . ± . ± − . ± . ± . ± − . ± − . ± − . ± − . ± = a visual binary (partially resolved system), VB? = a possible visual binary (resolved system)a possible visual binary (resolved system)