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Preparing the COROT Space Mission: New Variable Stars in the Galactic Anticenter Direction
The activities related to the preparation of the asteroseismic,photometric space mission COROT are described. Photoelectricobservations, wide-field CCD photometry, uvbyβ calibrations, andfurther time series have been obtained at different observatories andtelescopes. They have been planned to complete the COROT program in thedirection of the Galactic anticenter. In addition to suitableasteroseismic targets covering the different evolutionary stages betweenzero-age main sequence and terminal-age main sequence, we discoveredseveral other variable stars, both pulsating and geometric. We comparedresults on the incidence of variability in the Galactic center andanticenter directions. Physical parameters have been obtained, andevolutionary tracks fitting them have been calculated. The peculiaritiesof some individual stars are pointed out.Based on observations collected at the San Pedro Martír, SierraNevada, Teide, La Silla, Haute-Provence, and Roque de Los Muchachos(Telescopio Nazionale Galileo and Mercator telescopes) observatories.
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Binary systems with post-T Tauri secondaries
The identification of post-T Tauri (pTT) stars selected throughspectroscopic criteria by Pallavicini et al. (\cite{Pallavicini92}) andby Martín et al. (1992) among the candidates belonging to visualbinary systems is revisited in the present paper by studying theirposition in the HR diagram. These stars belong to the so-called Lindroosbinary sample (Lindroos \cite{Lindroos85}), i.e. to systems withearly-type primaries and late-type companions. If these binaries arephysical and not simply optical pairs, similar ages must be found forthe early-type primary and the late-type component of each system. Theages of these systems have been derived by Lindroos in 1986, by usingcalibrations of the uvbyβ indices. In this paper, we revisit theseages through the position of these stars among new evolutionary tracksin the HR diagram for pre- and post-main sequence stars. We derive newestimations of the ages of each system component, as well as theirmasses, using parallaxes of the early-type component derived fromHipparcos data and by forcing the late-type companion to be at the samedistance. Teff and log g of the early-type components havebeen computed using the calibrations of two independent photometricsystems: the uvbyβ photometry and the Geneva system. TheTeff of the late-type stars have been determined by usingvarious calibrations of several photometric systems: uvbyβ, UBV andVRI, in order to determine the uncertainties and systematic errors onthese parameters and consequently on the ages. Differences in the agesand masses obtained by using various sources of recent evolutionarymodels are considered and discussed. The consistency of the age of thelate type component with that of its early type primary is examined; thevalidity of this criterion for a selection of physical pairs isdiscussed. The accuracy of the observational and theoretical data arenot sufficient to assign stringent values to the age for several of theexamined systems. Nevertheless, in spite of the large error bars, wehave established that we could select a number of systems which,according to their position in the HR diagram, may be physicallyassociated. The selection of possible physically bounded systemsobtained with the present approach and that made by Pallavicini et al.(\cite{Pallavicini92}) or Martín et al. (1992) on the basis ofspectroscopic criteria are not always coincident. Spectroscopiccriteria, for example the presence of a strong Li feature, are morestringent conditions than that of coherent ages of primaries andsecondaries; however the Li I 6708 doublet is expected to fade in thelatest stages of the pre-main sequence life of a star, so that the``oldest" pTTs may not be detected by spectroscopy only. The differentresults so obtained are discussed for each system and we conclude thatthe present approach may be used as a powerful criterion to select newpTT candidates in visual binaries to be observed and analyzed with highresolution spectrographs and to select candidates that have almostreached the main sequence. Partly based on data from the ESA Hipparcosastrometric satellite. Tables 2, 5, 7 and 9 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/162
| X-ray emission from Lindroos binary systems
We present a study of the X-ray emission from binary systems extractedfrom the Lindroos catalogue (Lindroos 1986) based on the ROSAT All-Skysurvey as well as ROSAT PSPC and HRI pointings. The studied sampleconsists of visual binary systems comprised of early-type primaries andlate-type secondaries. The ages of the systems were determined byLindroos (1985) from uvbybeta photometry of the primaries. These agesrange between 33 and 135 Myr, so if the late-type secondaries arephysically bound to the early-type primaries, they could be Post-T Tauristars (PTTS). We have found strong X-ray emission from severalsecondaries. This fact together with their optical and IR data, makethem bona fide PTTS candidates. We have also detected X-ray emissionfrom several early-type primaries and, in particular, from most of thelate-B type stars. Because their HRI hardness ratios are similar tothose from resolved late-type stars, the presence of an unresolvedlate-type companion seems to be the cause of this emission.
| A Search for Star Clusters from the HIPPARCOS Data
We present results of a search for nearby star clusters and associationsusing Hipparcos Catalogue data, restricting the sample to stars withparallaxes above 2 mas (d <~ 500 pc). Two new OB associations havebeen identified in the Carina-Vela and Cepheus-Cygnus-Lyra-Vulpecularegions. A very probable new open cluster has been discovered in Carina.The cluster, a Car, named after its brightest member, is young (60 Myr)and nearby (d = 132 pc). However, only seven bona fide members can bedrawn from the Hipparcos data. We report a detection of nine opencluster candidates in the distance range of 150 to 400 pc, and sixpossible associations almost all located within the Gould belt, althoughslightly older than the known nearby associations. In all cases, wepresent Yale theoretical isochrone fits to the color-magnitude diagrams,which indicate a moderate spread of ages between 60 to 200 Myr.Evidently, these young open cluster and association candidates arerelated to the overall distribution of young OB and A-type stars in thesolar neighborhood.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Far-ultraviolet stellar photometry - A field in Monoceros
FUV photometry of stars in a field in Monoceros in the wavelength rangefrom 1230 to 1600 A has been carried out using data from anelectrographic Schmidt camera carried on a sounding rocket. Ultravioletmagnitudes were extracted for 602 objects in the field. Fifty-eightpercent were tentatively identified with visible stars using the SIMBADdata base while another 25 percent are blends of objects too closetogether to separate with our resolution. Eleven of the UV objectscoincide with parts of the star clusters NGC 2169, NGC 2244, and NGC2264 in which individual stars cannot be resolved. As in previousstudies, the majority of the identified ultraviolet sources areidentified with early-stars. However, there are a significant number forwhich no such identification was possible, and we suggest that many ofthese are nearby white dwarfs.
| A study of visual double stars with early-type primaries. V - Post-T Tauri secondaries
In an ongoing study of companions of O and B type primaries, themajority of the secondaries are found to be of spectral type F, G, or K.Their properties are investigated in relation to their evolutionarystatus. The ages of the systems have been determined from uvby-betaphotometry of the primaries and it is found that all are younger than150 million years and half are less than 30 million years old.Thirty-seven secondaries have ages less than the expected contractiontime to the zero-age-main sequence (ZAMS). More than 50 percent of theF, G, and K secondaries exhibit spectroscopic features (Ca II H, K andH-alpha emission and strong Li absorption) typical of young stars andreminiscent of T Tauri stars although not as conspicuous. It isappropriate to classify them as post-T Tauri stars. The lifetime of somefeatures characteristic of early stellar evolution is discussed.
| Visual multiples. VIII - 1000 MK types
A total of 1000 new classifications are given for stars brighter than B= 8.0 mag in the Aitken double star catalog. The classificationssupplement 865 classifications obtained in 1981 and 1984. Among thenewly discovered stars are 12 new Ap stars, eight Lambda Bootis stars,one Ba II star, and 60 Am stars. A detailed list of the newclassifications is given.
| A study of visual double stars with early type primaries. IV Astrophysical data
Astrophysical parameters (MK class, color excess, absolute magnitude,distance, effective temperature, mass, and age) are derived fromcalibrations of the uvby-beta indices for the members of 253 doublestars with O or B type primaries and faint secondaries. The photometricspectral classification is compared to the MK classes, and the agreementis very good. The derived data together with spectroscopic and JHKL dataare used for deciding which pairs are likely to be physical and whichare optical, and it is shown that 98 (34 percent) of the secondaries arelikely to be members of physical systems. For 90 percent of the physicalpairs the projected separation between the components is less than25,000 AU. A majority of the physical secondaries are late-type stars,and 50 percent of them are contracting towards the zero-agemain-sequence. Also presented are new uvby-beta data for 43 secondariesand a computer program for determining astrophysical parameters fromuvby-beta data.
| A study of visual double stars with early type primaries. II - Photometric results
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&AS...51..161L&db_key=AST
| A study of visual double stars with early type primaries. I - Spectroscopic results
Attention is given to spectral peculiarities found in data on thespectral classes of 486 stars in 254 visual doublet or multiplet systemswith O or B type primaries, in order to isolate a group of very youngstars that may serve for the study of early stellar evolutioncharacteristics. It is noted that the material contains a substantialfraction of secondaries that are likely to be physical, and that severalof these may be in the premain-sequence phase of stellar evolution, orhave reached the zero-age main sequence.
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| קבוצת-כוכבים: | אוריון |
| התרוממות ימנית: | 06h15m30.24s |
| סירוב: | +03°57'29.5" |
| גודל גלוי: | 6.999 |
| מרחק: | 307.692 פארסק |
| תנועה נכונה: | -3.6 |
| תנועה נכונה: | -2.9 |
| B-T magnitude: | 6.845 |
| V-T magnitude: | 6.987 |
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