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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.
| uvby? photometry of early type open cluster and field stars
Context. The ? Cephei stars and slowly pulsating B (SPB) stars aremassive main sequence variables. The strength of their pulsationaldriving strongly depends on the opacity of iron-group elements. As manyof those stars naturally occur in young open clusters, whosemetallicities can be determined in several fundamental ways, it islogical to study the incidence of pulsation in several young openclusters. Aims: To provide the foundation for such aninvestigation, Strömgren-Crawford uvby? photometry of opencluster target stars was carried out to determine effectivetemperatures, luminosities, and therefore cluster memberships. Methods: In the course of three observing runs, uvby? photometryfor 168 target stars was acquired and transformed into the standardsystem by measurements of 117 standard stars. The list of target starsalso included some known cluster and field ? Cephei stars, as wellas ? Cephei and SPB candidates that are targets of theasteroseismic part of the Kepler satellite mission. Results: Theuvby? photometric results are presented. The data are shown to beon the standard system, and the properties of the target stars arediscussed: 140 of these are indeed OB stars, a total of 101 targets liewithin the ? Cephei and/or SPB star instability strips, and eachinvestigated cluster contains such potential pulsators. Conclusions: These measurements will be taken advantage of in a numberof subsequent publications.Based on measurements obtained at McDonald Observatory of the Universityof Texas at Austin.Tables 3-6 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A148
| Spectral analysis of Kepler SPB and ? Cephei candidate stars
Context. For asteroseismic modelling, analysis of the high-accuracylight curves delivered by the Kepler satellite mission needs support byground-based, multi-colour and spectroscopic observations. Aims:We determine the fundamental parameters of SPB and ? Cep candidatestars observed by the Kepler satellite mission and estimate the expectedtypes of non-radial pulsators. Methods: We compared newlyobtained high-resolution spectra with synthetic spectra computed on agrid of stellar parameters assuming LTE, and checked for NLTE effectsfor the hottest stars. For comparison, we determined Teffindependently from fitting the spectral energy distribution of the starsobtained from the available photometry. Results: We determineTeff, log g, microturbulent velocity, v sin i, metallicity,and elemental abundance for 14 of the 16 candidate stars. Two stars arespectroscopic binaries. No significant influence of NLTE effects on theresults could be found. For hot stars, we find systematic deviations inthe determined effective temperatures from those given in the KeplerInput Catalogue. The deviations are confirmed by the results obtainedfrom ground-based photometry. Five stars show reduced metallicity, twostars are He-strong, one is He-weak, and one is Si-strong. Two of thestars could be ? Cep/SPB hybrid pulsators, four SPB pulsators, andfive more stars are located close to the borders of the SPB instabilityregion.Based on observations with the 2-m Alfred Jensch telescope at theThüringer Landessternwarte (TLS) Tautenburg.
| 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
| Four-colour and H-beta photometry of blue stars selected from a balloon-ultraviolet survey and other sources
New uvby and/or H-beta photometry is obtained at the Chiranhigh-altitude outstation for 105 stars. Certain of the program stars areselected from a comparison of the SCAP 2000 balloon-ultraviolet skysurvey of the Laboratoire d'Astronomie Spatiale with the correspondingblue and red prints of the Palomar Observatory sky survey. Only a smallportion of these stars turn out to be B stars, whereas, the rest of thestars, which are selected from a variety of other sources, are mostly Bstars and if of normal luminosity are in many cases many Population Iscale heights from the galactic plane. It is shown that theidentification of B stars is practicable only at a good observing siteand that if H-beta photometry is also obtained, sdOB, sdB, and hothorizontal branch B stars can be distinguished from normal stars bytheir position in the beta/c(0) diagram.
| Optical observations of ultraviolet objects. II - Classification and photometry /l = 0 to 145 deg/
UBV photometry and MK spectral classification are presented for a sampleof stars originally selected as UV objects from satellite photometrywith the S2/68 experiment. Although most stars of the sample arespectroscopically normal, a number of hot, subluminous stars were alsofound. Radial velocities are given for some of the stars observed. It isproposed that the majority of the apparently normal early B stars athigh galactic latitudes which are not runaway stars are subluminousdisc-population analogues of horizontal branch B stars of Population II.
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