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Kepler observations of the variability in B-type stars
The analysis of the light curves of 48 B-type stars observed by Kepleris presented. Among these are 15 pulsating stars, all of which show lowfrequencies, characteristic of slowly pulsating B (SPB) stars. Seven ofthese stars also show a few weak, isolated high frequencies and theycould be considered as SPB/? Cephei (? Cep) hybrids. In allcases, the frequency spectra are quite different from what is seen fromground-based observations. We suggest that this is because most of thelow frequencies are modes of high degree which are predicted to beunstable in models of mid-B stars. We find that there are non-pulsatingstars within the ? Cep and SPB instability strips. Apart from thepulsating stars, we can identify stars with frequency groupings similarto what is seen in Be stars but which are not Be stars. The origin ofthe groupings is not clear, but may be related to rotation. We findperiodic variations in other stars which we attribute to proximityeffects in binary systems or possibly rotational modulation. We find noevidence for pulsating stars between the cool edge of the SPB and thehot edge of the ? Sct instability strips. None of the stars showsthe broad features which can be attributed to stochastically excitedmodes as recently proposed. Among our sample of B stars are twochemically peculiar stars, one of which is a HgMn star showingrotational modulation in the light curve.
| Characterization of Kepler early-type targets *
Context. Stellar pulsation offers a unique opportunity to constrain theintrinsic parameters of stars and unveil their inner structure. TheKepler satellite is collecting an enormous amount of data of unprecedentphotometric precision, which will allow us to test theory and obtain avery precise tomography of stellar interiors. Aims: We attempt todetermine the stars' fundamental parameters (Teff, log g, vsin i, and luminosity) needed for computing asteroseismic models andinterpreting Kepler data. We report spectroscopic observations of 23early-type Kepler asteroseismic targets, 13 other stars in the Keplerfield, that had not been selected to be observed. Methods: Wemeasured the radial velocity by performing a cross-correlation withtemplate spectra to help us identify non-single stars. Spectralsynthesis was performed to derive the stellar parameters of our targetstars, and the state-of-the-art LTE atmospheric models were computed.For all the stars of our sample, we derived the radial velocity,Teff, log g, v sin i, and luminosities. For 12 stars, weperformed a detailed abundance analysis of 20 species, for 16, we couldderive only the [Fe/H] ratio. A spectral classification was alsoperformed for 17 stars in the sample. Results: We identify twodouble-lined spectroscopic binaries, HIP 96299 and HIP 98551, the formerof which is an already known eclipsing binary, and two single-linedspectroscopic binaries, HIP 97254 and HIP 97724. We also report twosuspected spectroscopic binaries, HIP 92637 and HIP 96762, and thedetection of a possible variability in the radial velocity of HIP 96277.Two of our program stars are chemically peculiar, namely HIP 93941,which we classify as B2 He-weak, and HIP 96210, which we classify as B6Mn. Finally, we find that HIP 93522, HIP 93941, HIP 93943, HIP 96210 andHIP 96762, are very slow rotators (v sin i < 20 km s-1)which makes them very interesting and promising targets forasteroseismic modeling.Based on observations collected with the telescope at the M.G.Fracastoro station of the INAF - Osservatorio Astrofisico diCatania.Reduced spectra are only available in electronic form atthe CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/517/A3
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