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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A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
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The interstellar Ca II distance scale
Aims: We attempt to extend the relation between the strengths of theinterstellar Ca II lines and the distances to early-type stars toobjects beyond 1 kiloparsec, with the line saturation taken intoaccount. Methods: We measure the Ca II K and Ca II H equivalentwidths, and compute Ca II column densities for 262 lines of sighttowards early-type stars with available Hipparcos parallaxes (?). Thetargets are located within a few hundred parsecs of the Galactic plane,and span all the range of Galactic longitudes. We fit the NCaII - parallax relation with a function of the form ? = 1 / (a\cdot NCa II + b), using a maximum-likelihood approach totake account of errors in both variables. We use the resultant formulato estimate distances to stars in OB associations and clusters, andcompare them to those found in the literature, usually estimated byspectrophotometric methods. Results: For lines of sight withEW(K)/EW(H) > 1.3, we obtain the following approximate formula forthe distance: DCa II = 77 + (2.78 + {2.60}/{{EW(K)}/{EW(H)} -0.932}) EW(H), where the equivalent widths EW(K) and EW(H) are inmÅ, and the distance DCa II in parsecs. The errors inDCa II, resulting from the uncertainty in the fit parametersand errors in the equivalent widths, are typically about 15% of thedistance. We can also expect the equation not to hold for objectssituated farther than a few hundred parsecs from the Galactic plane. Wefind several cases of significant column density differences betweenassociation or cluster members, especially notable in theTrumpler 16 cluster, indicating either a localcontribution to the Ca II column density, or background/foreground starsbeing confused with members. The ratio DCa II/D_assoc appearsto depend on the Galactic longitude, being highest in the range 70°< l < 120° and lowest for 200° < l < 300°. Thiseffect may be due to large-scale structure being present in the Ca IIlayer, or to the nonmember confusion being enhanced in these directions.Table 1 is only available in electronic form at http://www.aanda.org
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New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
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Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
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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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Atlas of Interstellar Extinction Curves of OB Stars Covering the Whole Available Wavelength Range
The paper presents a collection of 436 extinction curves covering thewhole available range of wavelengths from satellite UV to near-IR. Thedata were taken from the ANS photometric catalogue and from thecompilations of IR photometric measurements. The data curves have beenobtained with the aid of ``artificial standards": Papaj et al. (1993)and Wegner (1994, 1995). The visual magnitudes and spectralclassifications of O and B type stars with EB-V>= 0.05were taken from the SIMBAD database. The curves are given in the form ofplots and tables E{lambda - V} / EB-V versus1/λ. The observed variety of extinction laws among slightlyreddened stars is apparently due to the various physical parameters ofinterstellar clouds.
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Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
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The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
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Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
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UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
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Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
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Rotational Velocity Determinations for 164 Be and B Stars
Rotational velocities, v sin i, have been obtained for 96 Be and 68normal B stars by measurements of the FWHM of the He I lambda-4471 line(for spectral types B0-B4.5) and Mg II lambda-4481 (for types B5-B9.5).The consistency of various published sources is examined. (SECTION:Stars)
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Extinction law survey based on UV ANS photometry
The paper presents an extensive survey of interstellar extinction curvesderived from the ANS photometric measurements of early type starsbelonging to our Galaxy. This survey is more extensive and deeper thanany other one, based on spectral data. The UV color excesses aredetermined with the aid of 'artificial standards', a new techniqueproposed by the authors which allows the special check of Sp/L match ofa target and the selected standard. The results indicate that extinctionlaw changes from place to place.
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The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
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Rotationally extended stellar envelopes. IV. The detached shell of HD187399.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.155..357H&db_key=AST
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Be stars and galactic rotation.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..338C&db_key=AST
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Emissions-B-Sterne und Galaktische Struktur.
Not Available
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Photoelectric 4430 A observations of 506 O, B and A stars.
Not Available
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Die galaktischen Emissions-B-Sterne : (Spectralklassifikation, Photometrie, Entwicklung und Verteilung in der Milchstraszenebene)
Not Available
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Catalogue of stellar spectra classified in the Morgan-Keenan system
Not Available
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Luminous Stars in the Northern Milky Way
Not Available
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Photoelectric measures of the 4430 A diffuse interstellar band
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.125..141W&db_key=AST
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Photometric, Polarization, and Spectrographic Observations of O and B Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956ApJS....2..389H&db_key=AST
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Studies in Galactic STRUCTURE.II.LUMINOSITY Classification for 1270 Blue Giant Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2...41M&db_key=AST
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Polarization of Stellar Radiation. III. The Polarization of 841 Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1951ApJ...114..241H&db_key=AST
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A Finding List of O and B Stars of High Luminosity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1951ApJ...113..141N&db_key=AST
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Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1933ApJ....78...87M&db_key=AST
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INHABITED SKY
