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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Bright OB stars in the Galaxy. IV. Stellar and wind parameters of early to late B supergiants
Context: B-type supergiants represent an important phase in theevolution of massive stars. Reliable estimates of their stellar and windparameters, however, are scarce, especially at mid and late spectralsubtypes. Aims: We apply the NLTE atmosphere code FASTWIND toperform a spectroscopic study of a small sample of GalacticB-supergiants from B0 to B9. By means of the resulting data andincorporating additional datasets from alternative studies, weinvestigate the properties of OB-supergiants and compare our findingswith theoretical predictions. Methods: Stellar and wind parametersof our sample stars are determined by line profile fitting, based onsynthetic profiles, a Fourier technique to investigate the individualcontributions of stellar rotation and “macro-turbulence” andan adequate approach to determine the Si abundances in parallel withmicro-turbulent velocities. Results: Due to the combined effectsof line- and wind-blanketing, the temperature scale of GalacticB-supergiants needs to be revised downward, by 10 to 20%, the lattervalue being appropriate for stronger winds. Compared to theoreticalpredictions, the wind properties of OB-supergiants indicate a number ofdiscrepancies. In fair accordance with recent results, our sampleindicates a gradual decrease in v_? over the bi-stability region,where the limits of this region are located at lower T_eff than thosepredicted. Introducing a distance-independent quantity Q' related towind-strength, we show that this quantity is a well defined,monotonically increasing function of T_eff outside this region. Insideand from hot to cool, dot M changes by a factor (in between 0.4 and 2.5)which is much smaller than the predicted factor of 5. Conclusions: The decrease in v_? over the bi-stability region isnot over-compensated by an increase of dot M , as frequently argued,provided that wind-clumping properties on both sides of this region donot differ substantially.
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Statistical properties of a sample of periodically variable B-type supergiants. Evidence for opacity-driven gravity-mode oscillations
Aims.We have studied a sample of 28 periodically variable B-typesupergiants selected from the HIPPARCOS mission and 12 comparison starscovering the whole B-type spectral range. Our goal is to test if theirvariability is compatible with opacity-driven non-radialoscillations. Methods: .We have used the NLTE atmosphere codeFASTWIND to derive the atmospheric and wind parameters of the completesample through line profile fitting. We applied the method to selectedH, He, and Si line profiles, measured with the high resolution CESspectrograph attached to the ESO CAT telescope in La Silla, Chile.Results: .From the location of the stars in the (log T_eff, log g)diagram, we suggest that variability of our sample supergiants is indeeddue to the gravity modes resulting from the opacity mechanism. We findnine of the comparison stars to be periodically variable as well, andsuggest them to be new α Cyg variables. We find marginal evidenceof a correlation between the amplitude of the photometric variabilityand the wind density. We investigate the wind momentum-luminosityrelation for the whole range of B spectral type supergiants, and findthat the later types (>B5) perfectly follow the relation for Asupergiants. Additionally, we provide a new spectral type - T_effcalibration for B supergiants. Conclusions: .Our results imply thepossibility of probing internal structure models of massive stars ofspectral type B through seismic tuning of gravity modes.Figures of the spectral line fits and discussion of the individualobjects, Appendices A, B and Table 6 are only available in electronicform at http://www.aanda.org
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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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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New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
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Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
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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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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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Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
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Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
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A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
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OB Stellar Associations in Crux. II. Analysis and Discussion
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..306T&db_key=AST
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OB Stellar Associations in Crux. I. Observations With the Glazar Space Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..299T&db_key=AST
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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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A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
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An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
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Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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The diffuse interstellar bands
The structure of diffuse interstellar bands is examined using spectraobtained in La Silla, Chile with the ESO coude echelle spectrographcombined with the coude auxiliary telescope. Emphasis is given to thestructural characteristics of the yellow and a few of the red bands.Also, the relationship between the diffuse interstellar bands and otherinterstellar features is discussed.
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The volume filling factor of the infrared cirrus IS 0.2
The filling factor of the infrared cirrus in which luminous stars areembedded is estimated. The stars are assumed to be randomly situatedwith respect to the cirrus. A direct ratio of the number of stars withassociated cirrus emission to those which in principle could be detectedindicates that the cirrus filling factor is roughly 0.2.
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The maximum amplitude of the optical micro-variations of massive O-F type stars (or Alpha Cygni variables, including LBV's or S DOR variables) across the HR diagram
The maximum light amplitude (MLA) of the microvariations of nearly 100massive stars with spectral type O 3-F8 are collected from theliterature and unpublished material. These variables, called the AlphaCygni variables, also include the LBVs or S Dor type variables. The SDor type variables must be in a quiescent stage to detect theirintrinsic variations properly. The log T(eff)/MLA diagram exhibits aclear separation between S Dor type variables and the normal Alpha Cygnivariables (the majority). The results suggest that the outer layers ofboth types of stars where gravity waves presumably occur, differphysically from each other.
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Diffuse interstellar bands - an observational review (Review)
This paper presents a review of observational data concerning theunidentified diffuse interstellar bands (DIBs). The history of theinvestigation of these fascinating spectral features is presentedtogether with very recent results obtained with the aid of solid statedetectors. The high signal-to-noise spectra allowed to divide diffusebands into at least 3 families defined as sets of these featurescharacterized by constant intensity ratios in every observed spectrum.'Intrinsic' profiles of DIBs, i.e., profiles that originated in singleinterstellar clouds free of any Doppler splitting were derived from highresolution spectra. The same observations revealed convincingly theDoppler structures inside DIB profiles observed in distant objects. Itis shown that DIBs may originate in clouds of very low opacity - theiragent(s) being thus resistant against diffuse UV radiation. The agent(s)seems not to be the dust causing the visual extinction as the bands maybe absent in some of reddened spectra. Relations between DIBs and otherinterstellar absorptions are also briefly reviewed.
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High-resolution profiles of diffuse interstellar bands as functions of the structure of the interstellar medium
High-resolution spectra (0.05 A) are used to illustrate the influence ofthe physical parameters of the intervening clouds, as well as of theDoppler shifts, on the observed diffuse interstellar band (DIB)profiles. The results suggest that the DIBs at 5780 and 5797 may becaused by different carriers. It is noted that the ability of singleinterstellar clouds to produce DIBs varies from cloud to cloud and fromone DIB to another. DIB profiles observed in distant stars depend uponboth the optical properties of all clouds along the line-of-sight andtheir radial velocities.
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The structure of the diffuse interstellar bands
It is shown that the diffuse interstellar bands (DIB) at 5780, 5797,6196, and 6203 A are composed of Doppler-shifted components ofappreciable widths in those directions where several interstellar sodiumclouds have been identified. The optical properties of the interveningclouds may differ appreciably; some of the clouds are more likely tocontain the carrier(s) of one DIB family than that of another. The DIBsobserved in the spectra of distant objects are therefore generallyill-defined averages over a number of clouds along the line-of-sight. Asevery component also introduces its particular radial velocity, asubstantial widening of some of the profiles is observed. In some cases,a resolution of the bands into a number of Gaussian components has beenpossible. In general 'intrinsic bands', defined with the aid of nearbystars, have been successfully fitted to complex bands observed indistant stars. These 'intrinsic' bands are presented as normalizedprofiles in the case of the 5780- and 5797-bands.
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An investigation of the micro-variations of highly luminous OBA type stars. V
The optical microvariations of eight high luminous stars, five of typeO, two of type B, and one of type A are analyzed. The reddening,temperatures, gravities, and characteristic periods for the stars areestimated. The changes in the light and color curves are discussed. Theamplitude-wavelength relation is studied. It is observed that seven ofthe stars are variable and characteristic periods for only three of thestars are detected in the light curve. The data reveal that theamplitudes of light variations are largest in the ultraviolet for BAtype supergiants; for some O type stars there is little differencebetween the amplitudes at short and long wavelengths.
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An investigation of the micro variations of highly luminous OBA type stars. IV
VBLUW photometry of eight OBA type stars of high luminosity, M(001) lessthan -7, is presented. The mean errors of the nightly averages amount toless than or equal to + or - 0.002 mag. All but presumably one appear tobe variable, of which the maximum light amplitude amounts up toapproximately 0.1 mag. The variability of brightness and colors, andtheir time scales (days to weeks) increase with decreasing temperature.
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On the intrinsic UVBY colours of early-type supergiants
The present photoelectric uvby observations of 43 late O-type to earlyA-type supergiants are combined with published results to extend theZhang (1983) determination of the intrinsic color lines in the(b-y)/c(1) diagram. Zhang's conclusion that the H-beta index is wellcorrelated with luminosity class is reaffirmed by the results obtained,although the degree of separation found here is less clear. It is notfound, however, that beta has a significant minimum between the B1 andB3 spectral types.
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A study of B-type supergiants with the uvby,beta photometric system
The applicability of the uvby,beta photometric system to theclassification and study of B-type supergiants (BTS) is investigatedusing published data on 157 BTS and observations of 17 BTS made with the36-in. reflector at McDonald Observatory. The results are presented intabular form and analyzed to produce preliminary calibrations ofluminosity class vs. beta index and of absolute magnitude (Mv) vs. beta(or delta Mv vs. delta beta) for four associations of stars. Theeffectiveness of various color indices as temperature indicators isdiscussed. It is shown that there is good correspondence between MK anduvby,beta classifications of B-type main-sequence stars, giants, andBTS, confirming the usefulness of the uvby,beta system in furtherresearch on BTS.
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New UBVRI photometry for 900 supergiants
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
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INHABITED SKY
