The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
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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
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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.
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The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
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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.
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Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
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A photometric survey of the bright southern Be stars
Repeated UBV photometric measurements were made of the 86 bright Bestars south of declination -20 deg, and a network of comparison starswas set up. From a statistical study of the differential photometry itwas found that short- or intermediate-term variability seems to beoccurring in about half of the Be stars, and to be more evident in thestars of earlier spectral type. It was also possible to identify 11individual short- or intermediate-term variables. Four of these (all ofearly B spectral type) appear to exhibit significant variability on atime-scale of a day or less. More intensive observations of one of thesestars, 28 Omega CMA, indicate short-term variations consistent with thepublished spectroscopic period of 1.37 day.
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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.
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Extinction distance to the planetary nebula He 2-131.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985RMxAA..10..199M&db_key=AST
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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.
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The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
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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
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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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Intermediate band photometry of early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..205E&db_key=AST
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A search for stellar soft X-ray sources
A sensitive soft X-ray survey of about one-tenth of the sky, carried outas part of the Skylab program and flown on 1973 July 28, revealed noevidence for soft X-ray emission from stellar sources. We present upperlimits to the soft X-ray luminosity of about 50 nearby stars. Withnominal assumed values for stellar space densities, we show it unlikelythat emission from giants, main sequence stars, white dwarfs, or starsin known binary systems can account for the soft X-ray diffusebackground.
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The Scorpio-Centaurus Association: II. Spectral types and luminosities of 220 O, B and a stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961MNRAS.122..325M&db_key=AST
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On the individual parallaxes of the brighter galactic helium stars in the southern hemisphere, together with considerations on the parallax of stars in general.
Not Available
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