Refining the asteroseismic model for the young delta Scuti star HD 144277 using HARPS spectroscopy
Konstanze Zwintz, Tatiana Ryabchikova, Patrick Lenz, Alosha Pamyatnykh, Luca Fossati, T. Sitnova, Michel Breger, Ennio Poretti, Monica Rainer, Markus Hareter, Luciano Mantegazza
aa r X i v : . [ a s t r o - ph . S R ] J un Astronomy&Astrophysicsmanuscript no. hd144277sp-new-lang c (cid:13)
ESO 2018July 9, 2018
Refining the asteroseismic model for the young δ Scuti starHD 144277 using HARPS spectroscopy ⋆ K. Zwintz , T. Ryabchikova , P. Lenz , A. A. Pamyatnykh , , , L. Fossati , T. Sitnova , , M. Breger , E. Poretti , M.Rainer , M. Hareter , and L. Mantegazza Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgiume-mail: : [email protected] Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya Str 48, 109017 Moscow, Russia Copernicus Astronomical Centre, Bartycka 18, 00-716 Warsaw, Poland University of Vienna, Institute of Astronomy, T¨urkenschanzstrasse 17, A-1180 Vienna, Austria Argelander-Institut f¨ur Astronomie der Universit¨at Bonn, Auf dem H¨ugel 71, 53121 Bonn, Germany Moscow M.V. Lomonosov State University, Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119992 Russia Dept. of Astronomy, University of Texas at Austin, Austin, TX 78712, USA INAF-Osservatorio Astronomico di Brera, Merate, ItalyReceived / Accepted
ABSTRACT
Context.
HD 144277 was previously discovered by Microvariability and Oscillations of Stars (MOST) space photometry to be ayoung and hot δ Scuti star showing regular groups of pulsation frequencies. The first asteroseismic models required lower than solarmetallicity to fit the observed frequency range based on a purely photometric analysis.
Aims.
The aim of the present paper is to determine, by means of high-resolution spectroscopy, fundamental stellar parameters requiredfor the asteroseismic model of HD 144277, and subsequently, to refine it.
Methods.
High-resolution, high signal-to-noise spectroscopic data obtained with the HARPS spectrograph were used to determinethe fundamental parameters and chemical abundances of HD 144277. These values were put into context alongside the results fromasteroseismic models.
Results.
The e ff ective temperature, T e ff , of HD 144277 was determined as 8640 + − K, log g is 4.14 ± υ sin i , is 62.0 ± − . As the υ sin i value is significantly larger than previously assumed, we refined the firstasteroseimic model accordingly. The overall metallicity Z was determined to be 0.011 where the light elements He, C, O, Na, and Sshow solar chemical composition, but the heavier elements are significantly underabundant. In addition, the radius of HD 144277 wasdetermined to be 1.55 ± R ⊙ from spectral energy distribution (SED) fitting, based on photometric data taken from the literature. Conclusions.
From the spectroscopic observations, we could confirm our previous assumption from asteroseismic models thatHD 144277 has less than solar metallicity. The fundamental parameters derived from asteroseismology, T e ff , log g , L / L ⊙ and R / R ⊙ agree within one sigma to the values found from spectroscopic analysis. As the υ sin i value is significantly higher than assumed inthe first analysis, near-degeneracies and rotational mode coupling were taken into account in the new models. These suggest thatHD 144277 has an equatorial rotational velocity of about 80km s − and is seen equator-on. The observed frequencies are identified asprograde modes. Key words. stars: variables: δ Sct - stars: oscillations - stars: individual: HD 144277 - techniques: photometric
1. Introduction
High-precision time-series photometry obtained by theMicrovariability and Oscillations of Stars (MOST; Walker et al.2003) space telescope during two consecutive years discovered δ Scuti pulsations in HD 144277 (Zwintz et al. 2011; PaperI, hereafter). The twelve independent pulsation frequenciesidentified lie in four distinct groups, i.e., they show regularfrequency patterns. The first asteroseismic analysis was basedon limited additional knowledge of the physical parameters ofHD 144277. The star was only known to have a spectral typeof A1V with a respective e ff ective temperature of 9230 K (both Send o ff print requests to : K. Zwintz,e-mail: [email protected] ⋆ This work is based on ground-based observations made withthe 3.6m telescope at La Silla Observatory under the ESO LargeProgramme LP185.D-0056 taken from the Tycho-2 Spectral Type Catalog; Wright et al.2003), and a parallax of 7.00 ± δ Scuti instability strip wasdetermined by dedicated Str¨omgren photometry (see Paper I formore details).The asteroseismic analysis conducted in Paper I found evi-dence of two radial modes of sixth and seventh overtones underthe assumption of slow rotation. The models calculated in PaperI needed slightly less than solar metallicity and a moderate en-hancement of the helium abundance compared to the standardsolar chemical composition.With the lack of high-resolution spectroscopy forHD 144277, it was not possible to test if the non-solarabundances required from asteroseismology for the excitationof the observed δ Scuti frequencies could also be found inthe atmosphere of the star. The asteroseismic models would of
1. Zwintz et al.: Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy course also be di ff erent, if the υ sin i were significantly largerthan assumed in Paper I. We obtained high-resolution spectra forHD 144277 in order to test the validity of the first asteroseismicmodels and the assumptions needed to explain the observedfrequencies.We present here the results of our spectral analysis forHD 144277 that lead to a refinement of the asteroseismic modelsfirst presented in Paper I.
2. High-resolution spectroscopy: observations anddata reduction
Fundamental parameters and abundances for HD 144277 weredetermined from spectra obtained during five nights between2011 June 28 and July 3 with the HARPS spectrograph (Mayoret al. 2003) at the 3.6 m telescope of ESO La Silla Observatory.HD 144277 was used as a backup target for the ESO LP185.D-0056 to extend the physical scenario of the δ Sct stars observedwith CoRoT. In the adopted EGGS configuration the fiber-fedhigh-resolution ´echelle spectrograph has a resolving power of80 000. Each spectrum covers the wavelength range of 3781 –6913 Å.The 18 single spectra of HD 144277 were observed for ex-posure times of 1100 (15 spectra), 1200 (two spectra) and 1300(one spectrum) seconds and have mean pixel-by-pixel signal-to-noise ratios (S / N) between 143 and 248 calculated in the wave-length range of 5805 to 5825 Å. The HARPS spectra, in theadopted configuration, cover the hydrogen Balmer lines H α , H β ,H γ , H δ , and H ǫ . Since the 18 single spectra were obtained dur-ing five di ff erent nights and since the pulsation periods discov-ered earlier are shorter than 24 minutes, the data could not beused as a spectroscopic time series to study line profile varia-tions. Figure 1 shows that both the radial velocity variations andthe line profile variations are much smaller than the rotationalbroadening. The 18 single spectra were therefore combined toincrease the S / N of the combined spectrum that then amounts to363 computed again in the wavelength range of 5805 to 5825 Å.The spectra were reduced using both the ESO pipeline anda semi-automatic MIDAS pipeline (Rainer 2003). They werethen normalized by fitting a low-order polynomial to carefullyselected continuum points. The resulting normalized combinedhigh-resolution spectrum was thereafter used to determine thefundamental stellar parameters presented in this article.
3. Atmospheric parameters determination andabundance analysis
The starting values for determining the fundamental parametersand chemical abundances of HD 144277 were taken from multi-color photometry. For HD 144277 Str¨omgren colors (Paper I)without β -parameter, and usual broad-band photometric data areavailable. With three di ff erent calibrations of Str¨omgren photo-metric indices (Moon & Dworetsky 1985, Balona 1994, Ribas etal. 1997) included in the TEMPLOGG package (Kaiser 2006),and with a proper range of assumed β -parameters, we estimated T e ff = ±
150 K, log g = M of -0.28from photometry.A comparison between the observed spectrum of HD 144277and the synthetic spectrum, calculated for an atmospheric modelwith the above mentioned parameters, shows a rather high ro-tational velocity, and, as a consequence, strong line-blending.This led us to use spectral synthesis and employ the SME(Spectroscopy Made Easy) package to derive the atmospheric F l u x Velocity (km s -1 ) Fig. 1.
Mean line profiles for each of the 18 single spectra ob-tained for HD 144277 on di ff erent nights. Spectral intensities (incontinuum units) on the y-axis are arbitrarily shifted for bettervisibility. Spectra are in chronological order from bottom to top.parameters for HD 144277. The SME software was developedby Valenti & Piskunov (1996) and, for example, was success-fully applied to determine the atmospheric parameters of FGKstars (Valenti & Fischer 2005). SME allows to derive e ff ectivetemperature, surface gravity, overall metallicity, individual ele-ment abundances, and the microturbulent, macroturbulent, rota-tional, and radial velocities of a star by fitting synthetic spectrato the observed ones. Spectral synthesis calculations may be per-formed for di ff erent grids of model atmospheres and are interpo-lated between the grid nodes. We used a model grid calculatedwith the LL models stellar model atmosphere code (Shulyak et al.2004) for microturbulent velocity υ mic = − , which rangesfrom 4500–22000 K in e ff ective temperature, from 2.5–5.0 dexin surface gravity, and from -0.8 – 0.8 dex in metallicity (seeTable 5 in Tkachenko et al. 2012). The corresponding steps are0.1 in log g , 0.1 dex in metallicity, 100 K in the e ff ective tem-perature region from 4500–10000 K and 250 K for higher T e ff values.The following spectral regions were chosen for the fittingprocedure of HD 144277: 4140-4410 Å, 4411-4705 Å, 4750-4963 Å, 4963-5298 Å, 5257-5620 Å, 6100-6250 Å, 6340-6465 Å and 6480-6580 Å. These ranges include the threeBalmer lines H α , H β , and H γ . Atomic parameters were extracted
2. Zwintz et al.: Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy from the Vienna Atomic Line Database (VALD). We chose threedi ff erent steps to derive the star’s parameters: (i) we used onlythe three Balmer lines as input for SME, (ii) we took the spectralregions without the Balmer lines, and (iii) all above-mentionedspectral regions were selected at the same time. The correspond-ing solutions are 8558 K / / -0.56 (i), 9035 K / / -0.33(ii) and 8641 K / / -0.54 (iii) for T e ff , log g , and metallicity[Fe / H]. All three solutions give υ sin i values close to 62 km s − .Microturbulent velocity varied around 2.5 km s − . In the tem-perature region of the assumed position of HD 144277, the hy-drogen lines are rather insensitive to variations in T e ff and moresensitive to variations in log g , while the ionization balance forFe i / Fe ii is sensitive both to T e ff and log g . The use of the ion-ization balance requires accurate transition probabilities for Fe i and Fe ii lines as well as non-local thermodynamic equilibrium(NLTE) line formation.We applied an extensive model atom of Fe i and Fe ii fromMashonkina (2011a). NLTE level populations were calculatedusing a revised version of the DETAIL code developed by Butlerand Giddings (1985). NLTE leads to a weakening of the Fe i lines, and the NLTE abundance corrections vary from 0.00 to + ii lines, the NLTE abundance correctionsare negative and do not exceed 0.01 dex in absolute value. Theiron abundance computed from the Fe ii lines depends on theadopted system of the oscillator strengths. Fig. 2 shows theabundances derived from NLTE calculations of the Fe i andFe ii lines with di ff erent oscillator strengths taken from VALDand from Mel´endez & Barbuy (2003). While both sets providereasonable agreement for the lines with the excitation poten-tial < ff erence ∼ > T e ff = + − K, log g = ± υ mic = ± − , and υ sin i = ± − . Errors for T e ff are computed with SME us-ing di ff erent spectral regions and for log g by allowing ± ff erence in the Fe i / Fe ii ionization balance. A comparison be-tween the observed and calculated line profiles for H α , H β , andH γ is shown in Fig. 3. A zoom into the Mg I line at 4702Å(Fig. 4) illustrates the accuracy of the υ sin i determination. l og ( F e / N t o t ) Fe I (VALD)Fe II (VALD)Fe II (MB)
Fig. 2.
Iron abundance based on NLTE calculations versus lowerlevel energy. Individual abundances from Fe i (open circles), Fe ii (VALD oscillator strengths – filled circles) and Fe ii (Mel´endez& Barbuy 2003 oscillator strengths – asterisks) are shown.Horizontal lines indicate the mean Fe abundance with ± Fig. 3.
Region of the H α (left), H β (middle), and H γ (right) linesfor HD 144277: observed spectra (black solid line), syntheticspectra with the final adopted stellar parameters ( T e ff = g = T e ff and log g values derived from fitting the spectral regions exclud-ing the Balmer lines (i.e., T e ff = g = ff erences (in %) betweenobserved and synthetic spectra for the three Balmer line regions. Fig. 4.
Zoom into the region of the Mg I line at 4702 Å: ob-served spectrum (black solid line), synthetic spectrum with thebest fitting υ sin i value of 62 km s − (red solid line) and two syn-thetic spectra calculated by increasing and decreasing υ sin i by2km s − (dashed blue and green lines).Table 1 lists the element abundances in the atmosphere ofHD 144277 with their standard deviations. The most realistic es-timate of the error comes from the Fe lines because it is the onlyelement with a statistically significant number of lines. For afew elements other than Fe, abundances were also derived takingNLTE e ff ects into account. For example, the oxygen abundancewas calculated following the procedure described by Sitnova etal. (2013).
3. Zwintz et al.: Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy
Our model provides us with an ionization equilibrium for Fe(see above), Mg and Ca. The Mg abundance from Mg i lines wasderived using NLTE calculations by Mashonkina (2013). TheMg abundance in LTE computed from the Mg ii lines was de-rived using the two lines at 4390.5 and 4481.2 Å.The NLTE formation of Mg ii lines in the atmospheres ofthree A-type stars was studied by Przybilla et al. (2001); twomodels were computed for supergiants, and the third model isfor a main sequence star of T e ff = g = ff ective temperature of this 1D model is hotter by 900 K thanthat of HD 144277, but model atmospheres for both stars havecomparable gravity and metallicity. Hence, we can apply thesetheoretical calculations to estimate possible NLTE correctionsfor HD 144277.In the model atmosphere of a star with T e ff = g = ff ected by NLTE whilethe NLTE correction is -0.2 dex for the 4481.2 Å line (Przybillaet al. 2001). The Mg abundance inferred from the 4390 Å line islog( Mg / N tot ) = -4.88. Applying this correction to log( Mg / N tot ) = -4.75 derived from the 4481.2 Å line, we estimate an average Mgabundance of -4.92 ± i lines.The Ca i , Ca ii abundances were calculated for the atmo-sphere of HD 144277 in NLTE with the model atom fromMashonkina, Korn & Przybilla (2007). For the Cr ii lines we usedthe most recent transition probability calculations by Kurucz that provide reasonable agreement with the abundances derivedfrom Cr i lines. Table 1.
LTE atmospheric abundances in HD 144277 with theerror estimates based on the internal scattering from the numberof analyzed lines, n . Ion HD 144277 Sunlog( N el / N tot ) n [( N el ] log( N el / N tot )He i − − i − ± − i * − ± − i * − ± − ii * − ± − ii − ± − i − ± − i * − ± − ii * − ± − ii − ± − ii − ± − i − ± − ii − ± − i * − ± − ii * − ± − i − ± − ii − ± − ii − ± − ii − ± − Notes.
Elements treated in NLTE are marked by asterisks. [( N el / N tot )]is the abundance of a certain element relative to the total abundance ofall elements, which is set to be equal to 1. For purpose of comparison,the last column gives the abundances of the solar atmosphere calculatedby Asplund et al. (2009). http: // kurucz.harvard.edu / atoms / / HD 144277 has solar chemical composition for the light ele-ments C, O, Na, and S, but shows underabundances in the heav-ier elements. The average metallicity calculated from the ele-ments Si to Ba is M = − . ± .
14. If we include in the metallic-ity calculations all those species (C to Ba) for which we derivedabundances, then we get a Z value of 0.011. The He abundancewas measured only from a single line (see Table 1), but seems tobe slightly higher than the solar value, i.e., by 0.04. In turn, thisa ff ects the X value to be 0.72 instead of 0.74 as in the solar case(see Table 2). Fig. 5.
Comparison between LL models theoretical fluxes (thickblack line), calculated with the fundamental parameters de-rived for HD 144277 ( T e ff = g = ±
63 pc was taken from Kharchenko & Roeser(2009) and the interstellar reddening E ( B − V ) = R = ± ⊙ ; the relatively large error is mainlycaused by the large uncertainty in distance.For T e ff = g of 4.14 an increase in gravity onthe order of 0.15 dex results in a violation of the Fe i / Fe ii ion-ization balance exceeding the expected NLTE e ff ects by a fac-tor of two. We therefore take log g = T e ff = R ⊙ , we estimate HD 144277’s luminosity tobe log L / L ⊙ = . + . − . . The uncertainties in luminosity can onlybe used as formal errors that take into account the uncertainty ofthe distance fully. As HD 144277 is certainly not a sub-dwarf, itsradius must at least be larger than the solar radius. This woulddecrease the real lower error bar on the radius to 0.56 R ⊙ and onthe luminosity to 0.41.A summary of the observationally determined values can befound in the third column of Table 2.
4. Zwintz et al.: Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy
Table 2.
Parameters of asteroseismic models of HD 144277 andcomparison with the results from spectroscopy.
Model 2 Model 3 Spectroscopy(Paper I)X 0.70 0.70 0.72Z 0.010 0.011 0.011M / M ⊙ T e ff ± / L ⊙ . + . − . R / R ⊙ ± ± rot [km s − ] 15.0 79.7 ( υ sin i :) 62.0 ±
4. Refinement of the asteroseismic model
The asteroseismic model presented in Paper I was mainly de-rived based on information extracted from the observed fre-quency spectrum. With our new spectroscopic observations, wegained additional constraints on the fundamental parameters ofthe star. Consequently, the asteroseismic model can now betested and possibly refined.The new observations could confirm a lower metallicitycompared to solar composition, which was predicted by the as-teroseismic models in Paper I in order to explain the pulsa-tional instability of the observed modes. The spectroscopicallydetermined temperature, luminosity, and radius agree within onesigma to the values derived from asteroseismology, whereas thetheoretical and spectroscopical log g values match only within2 σ (see Table 2). On the other hand, spectroscopy indicates thatwith v sin i = . ± . − the rotational velocity of HD144277 is higher than assumed in the asteroseismic models inPaper I, where an equatorial rotation velocity of 15 km s − wasadopted. Since most fundamental parameters of the original as-teroseismic model are in good agreement with the new observa-tions, we used Model 2 from Paper I as a reference model (seeTable 2) and increased its rotational velocity to study the influ-ence on the predicted frequencies and mode instability.To estimate the e ff ects of rotation on the frequencies we useda second-order perturbation theory, which is su ffi cient only forreasonably slow rotators. Increasing the rotational velocity at theequator from 15 km s − to 60 km s − implies that the e ff ects ofnear-degeneracies gain importance. As shown in, e.g., Goupil etal. (2000) modes can couple if (i) they are close in frequency, (ii)their spherical degree di ff ers by 2, and (iii) their azimuthal ordersare equal. We therefore also considered the e ff ects of rotationalmode coupling according to the formalism presented in Soufi,Goupil & Dziembowski (1998) and Daszy´nska-Daszkiewicz etal. (2002). In our study we considered the rotational couplingof up to three modes and conducted tests thereby adopting vari-ous values for the rotational velocity. The adopted evolutionaryand pulsational codes were the same as those used in Paper I.We again used OPAL opacities (Iglesias & Rogers, 1996) andthe Asplund et al. (2009) proportions in the heavy element abun-dances to be consistent with Paper I.We find that the best agreement between observational andtheoretical frequencies is found if we assume a rotational ve-locity at the equator between 60 and 80 km s − . For higher ro-tation there are no clear patterns in the theoretical frequencyspectra that can be matched to the very regular pattern of theobserved frequencies. This finding implies a nearly equator-onview. As can be seen in Fig. 6, the observed groups of frequen-cies at 60 and 67 d − correspond to prograde and zonal dipole l o g L / L s u n eff sun sun sun sun sun Fig. 7.
HD 144277 in the HR-diagram: post-main sequence evo-lutionary tracks (solid lines) for 1.5 to 1.9 M ⊙ in steps of 0.1 M ⊙ computed for the same chemical composition (X, Z) as indicatedby spectroscopy and by asteroseismology, refined asteroseismicmodel (solid diamond), and observational position (open square)of HD 144277.modes, while the other two groups are related to the radial andquadrupole modes.Table 2 presents a comparison between the fundamental pa-rameters of Model 2 from Paper I and the new model presentedin this paper (denoted as Model 3). The position of the model inthe Hertzsprung-Russell (HR)-diagram is shown in Fig. 7. Forthe refined asteroseismic model a small increase in the metallic-ity was adopted to improve the agreement between the instabilityof theoretical modes and observed unstable modes (see Fig. 8).However, with Z = =
5. Summary & Conclusions
Our first asteroseismic model for HD 144277 was based solelyon the observed pulsation frequency spectrum (see Paper I) sinceno high-resolution spectroscopy was available. This first modelpredicted a slightly less than solar metallicity and assumed a ro-tational velocity at the equator of only 15 km s − .Using the high-resolution, high S / N HARPS spectra we con-firmed the slightly less than solar metallicity needed to excite theobserved δ Scuti frequencies in the range 59.9 to 71.1 d − (seePaper I). The fundamental parameters T e ff , log g , log L / L ⊙ andR / R ⊙ determined by spectroscopy agree within one sigma withthe values found by asteroseismology.The major di ff erence between the assumptions used in ourfirst asteroseismic models and the spectroscopically derived val-ues for HD 144277 is the rotational velocity. While we assumeda rotational velocity at the equator of 15 km s − in our firstanalysis, the projected rotational velocity, υ sin i , is significantlyhigher at 62.0 ± − . In the present study we therefore
5. Zwintz et al.: Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy
55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75Frequency (c/d)02468 observed a m p li t u d e s ( mm a g ) retrogradezonalprograde
55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75frequency (c/d) spherically symmetriclinear splittingnon-sphericaldistortion3-mode coupling ℓ=0ℓ=1ℓ=2
Fig. 6.
Top panel: observed modes.
Middle panel: theoretical modes with ℓ ≤
2: retrograde (light grey), zonal (dark grey), andprograde (black) modes.
Lower panel:
Stepwise addition of various rotational e ff ects on the mode frequencies in near-degeneratemode perturbation theory (spherical symmetry, linear splitting, non-spherical distortion, and three-mode coupling). Only ℓ = frequency (c/d) −0.10−0.050.000.050.100.15 η Fig. 8.
Instability parameter, η = R R ( dW / dr ) dr / R R | dW / dr | ,vs. mode frequency. Positive η corresponds to driven modes.Observed modes are shown with vertical lines. The two (red)lines show the value of the instability parameter for ℓ = ff ects of near-degeneracies and rotational mode cou-pling of up to three modes.As the best agreement between the observed and theoreti-cal pulsation frequencies is found for a rotational velocity at theequator of about 80 km s − , the star has to be seen equator-on.A near equator-on view implies that zonal modes have lowervisibility than prograde and retrograde modes for geometricalreasons (see, e.g., Fig. 6 in Breger & Lenz 2008). Our astero- seismic model indicates that the observed frequencies are pro-grade modes. Consequently, the following question arises: whyare the retrograde dipole modes not observed, despite their hav-ing a similar geometrical visibility to the prograde modes? Astriking feature that may be the key to the physical mechanismof mode selection in the special case of HD 144277 is that weparticularly see those modes that are very close in frequency anda ff ected by rotational mode coupling. These modes are in thecenter panel of Fig. 6 so that a better comparison can be madewith the theoretical mode distribution shown in the panel be-low and observations on top. This good agreement indicates thatHD 144277 may give us a valuable hint as to how the mode se-lection works in young δ Scuti stars.
Acknowledgements.
The authors would like to thank our referee, Torsten B¨ohm,for his valuable comments that helped to improve the paper significantly. Wethank L. Mashonkina for providing us with the departure coe ffi cients for the MgNLTE analysis.The research leading to these results has received funding from theEuropean Research Council under the European Community’s SeventhFramework Programme (FP7 / / ERC grant agreement No 227224(PROSPERITY). This research is (partially) funded by the Research Councilof the KU Leuven under grant agreement GOA / / Fonds zur F¨orderung derwissenschaftlichen Forschung (project P21830-N16). TR acknowledges partialfinancial support from Basic Research Program of the Russian Academy ofSciences “Origin and Evolution of Stars and Galaxies”. AAP acknowledges par-tial financial support from the Polish NCN grant No. 2011 / / B / ST9 / Asteroseismology: looking inside the stars with space- and ground-based observations.
MR also acknowledges financial support from the FP7project
SPACEINN: Exploitation of Space Data for Innovative Helio- and
6. Zwintz et al.: Refining the asteroseismic model for the young δ Scuti star HD 144277 using HARPS spectroscopy
Asteroseismology . MH acknowledges support from the Austrian
Fonds zurF¨orderung der wissenschaftlichen Forschung (project P22691-N16).
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