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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.
| The Chandra Variable Guide Star Catalog
Variable stars have been identified among the optical-wavelength lightcurves of guide stars used for pointing control of the Chandra X-rayObservatory. We present a catalog of these variable stars along withtheir light curves and ancillary data. Variability was detected to alower limit of 0.02 mag amplitude in the 4000-10000 Å range usingthe photometrically stable Aspect Camera on board the Chandraspacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains827 stars, of which 586 are classified as definitely variable and 241are identified as possibly variable. Of the 586 definite variable stars,we believe 319 are new variable star identifications. Types of variablesin the catalog include eclipsing binaries, pulsating stars, and rotatingstars. The variability was detected during the course of normalverification of each Chandra pointing and results from analysis of over75,000 guide star light curves from the Chandra mission. The VGUIDEcatalog represents data from only about 9 years of the Chandra mission.Future releases of VGUIDE will include newly identified variable guidestars as the mission proceeds. An important advantage of the use ofspace data to identify and analyze variable stars is the relatively longobservations that are available. The Chandra orbit allows forobservations up to 2 days in length. Also, guide stars were often usedmultiple times for Chandra observations, so many of the stars in theVGUIDE catalog have multiple light curves available from various timesin the mission. The catalog is presented as both online data associatedwith this paper and as a public Web interface. Light curves with data atthe instrumental time resolution of about 2 s, overplotted with the databinned at 1 ks, can be viewed on the public Web interface and downloadedfor further analysis. VGUIDE is a unique project using data collectedduring the mission that would otherwise be ignored. The stars availablefor use as Chandra guide stars are generally 6-11 mag and are commonlyspectral types A and later. Due to the selection of guide stars entirelyfor positional convenience, this catalog avoids the possible bias ofsearching for variability in objects where it is to be expected.Statistics of variability compared to spectral type indicate theexpected dominance of A-F stars as pulsators. Eclipsing binaries areconsistently 20%-30% of the detected variables across all spectraltypes.
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