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The Classification of Kepler B-star Variables
The light curves of 252 B-star candidates in the Kepler database areanalyzed in a similar fashion to that done by Balona et al. to furthercharacterize B-star variability, increase the sample of variable B starsfor future study, and to identify stars whose power spectra includeparticularly interesting features such as frequency groupings. Stars areclassified as either constant light emitters, ? Cep stars, slowlypulsating B stars (SPBs), hybrid pulsators, binaries or stars whoselight curves are dominated by rotation (Bin/Rot), hot subdwarfs, orwhite dwarfs. One-hundred stars in our sample were found to be eitherlight constants or to be variable at a level of less than 0.02 mmag. Weincrease the number of candidate B-star variables found in the Keplerdatabase by Balona et al. in the following fashion: ? Cep starsfrom 0 to 10, SPBs from eight to 54, hybrid pulsators from seven to 21,and Bin/Rot stars from 23 to 82. For comparison purposes, approximately51 SPBs and six hybrids had been known prior to 2007. The number of? Cep stars known prior to 2004 was 93. A secondary result of thisstudy is the identification of an additional 11 pulsating white dwarfcandidates, four of which possess frequency groupings.
| Kepler Input Catalog: Photometric Calibration and Stellar Classification
We describe the photometric calibration and stellar classificationmethods used by the Stellar Classification Project to produce the KeplerInput Catalog (KIC). The KIC is a catalog containing photometric andphysical data for sources in the Kepler mission field of view; it isused by the mission to select optimal targets. Four of the visible-light(g, r, i, z) magnitudes used in the KIC are tied to Sloan Digital SkySurvey magnitudes; the fifth (D51) is an AB magnitude calibrated to beconsistent with Castelli & Kurucz (CK) model atmosphere fluxes. Wederived atmospheric extinction corrections from hourly observations ofsecondary standard fields within the Kepler field of view. For thesefilters and extinction estimates, repeatability of absolute photometryfor stars brighter than magnitude 15 is typically 2%. We estimatedstellar parameters {T eff, log (g), log (Z), E B - V} using Bayesian posterior probability maximization to matchobserved colors to CK stellar atmosphere models. We applied Bayesianpriors describing the distribution of solar-neighborhood stars in thecolor-magnitude diagram, in log (Z), and in height above the galacticplane. Several comparisons with samples of stars classified by othermeans indicate that for 4500 K <=T eff <= 6500 K, ourclassifications are reliable within about ±200 K and 0.4 dex inlog (g) for dwarfs, with somewhat larger log (g) uncertainties forgiants. It is difficult to assess the reliability of our log (Z)estimates, but there is reason to suspect that it is poor, particularlyat extreme T eff. Comparisons between the CK models andobserved colors are generally satisfactory with some exceptions, notablyfor stars cooler than 4500 K. Of great importance for the Keplermission, for T eff <= 5400 K, comparison withasteroseismic results shows that the distinction between main-sequencestars and giants is reliable with about 98% confidence. Larger errors inlog (g) occur for warmer stars, for which our filter set providesinadequate gravity diagnostics. The KIC is available through the MASTdata archive.
| 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
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| First Kepler results on compact pulsators - I. Survey target selection and the first pulsators
We present results from the first two quarters of a survey to search forpulsations in compact stellar objects with the Kepler spacecraft. Thesurvey sample and the various methods applied in its compilation aredescribed, and spectroscopic observations are presented to separate theobjects into accurate classes. From the Kepler photometry we clearlyidentify nine compact pulsators and a number of interesting binarystars. Of the pulsators, one shows the strong, rapid pulsations typicalof a V361 Hya-type sdB variable (sdBV); seven show long-period pulsationcharacteristics of V1093 Her-type sdBVs; and one shows low-amplitudepulsations with both short and long periods. We derive effectivetemperatures and surface gravities for all the subdwarf B stars in thesample and demonstrate that below the boundary region where hybrid sdBpulsators are found, all our targets are pulsating. For the stars hotterthan this boundary temperature a low fraction of strong pulsators(<10 per cent) is confirmed. Interestingly, the short-period pulsatoralso shows a low-amplitude mode in the long-period region, and severalof the V1093 Her pulsators show low-amplitude modes in the short-periodregion, indicating that hybrid behaviour may be common in these stars,also outside the boundary temperature region where hybrid pulsators havehitherto been found.
| 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
| A survey for pulsating subdwarf B stars with the Nordic Optical Telescope
Context. A search programme for pulsating subdwarf B stars was conductedwith the Nordic Optical Telescope on La Palma over 59 nights between1999 and 2009. Aims: The purpose of the programme was tosignificantly extend the number of rapidly pulsating sdB stars to betterunderstand the properties of this new group of variable compact stars. Methods: Candidates were selected initially from the HS and HEsurveys, but were supplemented with additional objects from othersurveys. Short sequences of time-series photometry were made on thecandidates to determine the presence of rapid pulsations. Results: In total twenty new pulsators were found in this survey, mostof which have already been published and some extensively studied. Wepresent four new short period pulsators, bringing the total of suchpulsators up to 49. We also give limits on pulsation amplitudes for 285objects with no obvious periodic variations, summarise the results ofthe survey, and provide improved physical parameters on the compositepulsators for which only preliminary estimates were published earlier.Full Table 5 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/513/A6
| A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
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