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Herbig Ae/Be Stars in nearby OB Associations
We have carried out a study of the early-type stars in nearby OBassociations spanning an age range of ~3-16 Myr, with the aim ofdetermining the fraction of stars that belong to the Herbig Ae/Be class.We studied the B, A, and F stars in the nearby (<=500 pc) OBassociations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1,with membership determined from Hipparcos data. We also included in ourstudy the early-type stars in the Trumpler 37 cluster, part of the CepOB2 association. We obtained spectra for 440 Hipparcos stars in theseassociations, from which we determined accurate spectral types, visualextinctions, effective temperatures, luminosities and masses, usingHipparcos photometry. Using colors corrected for reddening, we find thatthe Herbig Ae/Be stars and the classical Be (CBe) stars occupy clearlydifferent regions in the JHK diagram. Thus, we use the location on theJHK diagram, as well as the presence of emission lines and of strong 12μm flux relative to the visual, to identify the Herbig Ae/Be stars inthe associations. We find that the Herbig Ae/Be stars constitute a smallfraction of the early-type stellar population even in the youngerassociations. Comparing the data from associations with different agesand assuming that the near-infrared excess in the Herbig Ae/Be starsarises from optically thick dusty inner disks, we determined theevolution of the inner disk frequency with age. We find that the innerdisk frequency in the age range 3-10 Myr in intermediate-mass stars islower than that in the low-mass stars (<1 Msolar) inparticular, it is a factor of ~10 lower at ~3 Myr. This indicates thatthe timescales for disk evolution are much shorter in theintermediate-mass stars, which could be a consequence of more efficientmechanisms of inner disk dispersal (viscous evolution, dust growth, andsettling toward the midplane).
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| On the Expansion of Stellar Association Per OB2
Not Available
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| Photoelectric minima of 30 eclipsing binary systems
Not Available
| 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.
| AG Persei: Absolute dimensions and membership of Perseus OB2
Accurate physical parameters for the B-type eclipsing binary AG Per (HD25833; B4 V, V = 6.7, P = 2.03 days) have been determined for a completere-analysis of available light curves and recent spectrscopic elements(Popper & Hill 1991). The components have masses of 5.36 +/- 0.16and 4.90 +/- 0.13 solar mass and radii of 2.99 +/- 0.07 and 2.60 +/-0.07 solar radii, respectively, and they are among the least evolved Bstars with well-determined dimensions. Effective temperatures of 18 200+/- 800 K and 17b 400 +/- 800 K are derived. The orbit is slightlyeccentric (e = 0.0710 +/- 0.0010) and shows apsidal motion with awell-established period of U = 75.6 +/- 0.6 yr. Comparison with stellarevolution models based on the latest opacity library by Rogers &Iglesias (1992) and including a moderate amount of convectiveovershooting (Claret & Gimenez 1992) shows AG Per to be young; anage of about 4-6 107 yr is derived from the scale independentmasses and radii. AG Per is too little evolved to provide anyconstraints on the amount of convective overshooting. The mean densityconcentration coefficient determined from the apsidal motion parameters,log k2 = -2.14 +/- 0.04, agrees well with that computed forthe models, provided a relativistic correction based on the generalrelativity theory is included. In its present formulation andcalibration the alternative non-symmetric gravitational theory proposedby Moffat (1989) is not supported. AG Per is generally accepted as amember of Per OB2. We find a distance of 355 +/- 30 pc for the binary,compared to 330-420 pc given by various authors for the association. Newstellar models and calibrations indicate a photometric age of about1-1.5 107 yr for Per OB2, larger than previously obtained butstill well below that of AG Per (4-6 107 yr. This weakens thestatus of AG as a member. New observations of (potential Per OB2members, including fainter stars, are clearly needed.
| Interstellar extinction in the direction of the open cluster IC 348 and the Per OB2 association
The relationship between interstellar extinction and distance in thedirection of dark clouds in the areas around the open cluster IC 348 andthe association Per OB2 is determined using the results of photoelectricphotometry of 189 stars in the Vilnius photometric system. Two absorbinglayers are found. The nearest layer, covering the whole area around IC348, shows the mean extinction A(V) of about 0.7 mag. It begins at thedistance of 160 pc and probably is an extension of the Taurus darkclouds to the northwest. The second absorbing layer has the form of achain of dark condensations named L1468, L1470, and L1471 and is at 260pc distance. This layer has a higher density, its mean extinction beingabout 2.0 mag. The cluster IC 348 is at about the same distance and isphysically related to the dark cloud L1470. The distance of the Per OB2association is found to be 340 pc and the mean extinction of its membersis 0.95 mag. A model of the spatial distribution of the Perseus andTaurus dark clouds based on photometric distance determinations in thisand previous papers is proposed. Six stars in the IC 348 area aresuspected to have emission in the H-alpha line.
| 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.
| Catalogue of Hydrogen Line Spectral Profiles of 236 B-Stars A-Stars and F-Stars
Not Available
| Atlas of extinction curves derived from ultraviolet spectra of the TD-1 satellite
The collection of 166 extinction curves derived from the publishedlow-resolution spectra acquired with the aid of the spectrometer onboard the TD-1 satellite is presented. The observed variety ofextinction laws is apparently due to the varied physical parameters ofinterstellar clouds; for example, the bright stars, included in thesample of TD-1 material, are very likely to be obscured by single clouds(interstellar or circumstellar). The system of standards constructedwith the aid of a special procedure allowing the possible effects ofspectral mismatch to be avoided and making possible the derivation ofextinction curves even in cases of very small E(B-V)S, was applied. Thecurves are presented in the form of plots, normalized to E(B-V) = 1.
| Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature
A new determination of the visual absolute magnitude of Be stars iscarried out. For this, a new calibration of visual absolute magnitudesof B stars of luminosity classes, V, IV, and III is first obtained froma sample of 215 stars. The absolute luminosity excess in the visual isdetermined for a sample of 49 Be stars. It is found that this excess iscorrelated with the effective temperature of the underlying stars. Awell defined correlation between this excess and the emission in thefirst two Balmer lines is established. From these results, using asimple model of circumstellar envelope, it is inferred that the zones ofthe circumstellar envelope contributing to the emission in the continuumand in the lines have to be rather small. It is also deduced that theemission measure of the envelope is correlated with the temperature ofthe central star and that the irregular photometric variations of Bestars are an envelope-opacity phenomenon.
| 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.
| On the period and nature of the light and radial-velocity variations of HD 25799
Reanalysis of the published radial velocities of the supposedspectroscopic binary HD 25799 shows that its period is 0.9121679 dayrather than the 10.67 days found by Blaauw and van Albada (1963). Newphotometric observations of this star were obtained during the period1981-87. Comparison of light curves formed from these observations witheach other and with light curves formed from archival data shows thatthe amplitude and possibly the shape of the light curve are variable.These changes cannot be explained by a binary star model. The similarityof the light and velocity variations to those of B stars that arebelieved to be nonradial pulsators argues that HD 25799 is a member ofthis group.
| Two-colour diagrams for differentially rotating stars
Not Available
| Apsidal rotation in the eclipsing binary AG Persei
New three-filter light curves of AG Per are given. These yield times ofminimum light in accord with the known rate of apsidal rotation but donot improve that rate. These light curves and all other publishedhistorical ones have been treated with the code EBOP and are shown togive largely consistent geometric and photometric parameters no matterwhich orientation of the orbit is displayed to the observer.
| The vicinity of Omicron Per
The region around the B1 III star Omicron Per (HD 23180) in the emissionof the J = 1-0 and J = 2-1 lines of C-12O and C-13O with about 1 arcminresolution. The molecular cloud morphology suggests the presence of awarm hole near the position of the star. It is tempting to think thatOmicron Per is the cause of this molecular gap. However, the observedheating of the cloud edge, as well as optical, infrared (IRAS) andcarbon recombination line data, all suggest that the local ultravioletfield is enhanced only by a factor 10-100. Therefore Omicron Per must belocated at least a few parsecs away from the cloud, and the precisealignment of the observed hole with the star is probably mainly due tochance. Furthermore, other neighboring OB stars could contributeappreciably (even more than Omicron Per) to the ultraviolet enhancementwhich seems to extend over several degrees on the north-east edge of thePerseus local molecular cloud.
| Helium abundance in the atmospheres of B stars in open clusters
The model-atmosphere method is applied to 6-m telescope spectrograms of46 B stars in the Per OB2 and Sco-Cen associations and in the alpha Percluster and the Pleiades to determine effective temperatures, surfacegravities, and helium abundances log epsilon(He). To within the erorrs,each cluster has the same mean epsilon(He).
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| Peculiar stars in the association Per OB2.
Not Available
| 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.
| Radial velocities for early type stars in six galactic regions
Coudespectroscopy has been carried out for 353 stars of spectral typesB0-A0 and V magnitudes between 6.5 and 10.8 m, selected in six regions(three northern and three southern) close to the galactic plane at thegalactic longitudes 135, 175, 315 and 350 deg. The radial velocitieswere obtained by cross-correlating each spectrogram with a referencespectrogram giving an internal error of 1.4 km/s.
| Four-color and H-beta photometry for O-A0 type stars in three regions near the galactic equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...49..561W&db_key=AST
| Spectrophotometry of massive eclipsing binary stars
Normalized flux distributions have been measured for U Oph, AG Per,Lambda Tau, and V356 Sgr. Light curves at 4700 A for U Oph and AG Perare used to check published eclipsing-binary-system parameters, and theparameters given by Koch and Koegler (1977) and Popper (1974) areemployed for the analysis of U Oph and AG Per, respectively. No evidenceof circumstellar matter is found for U Oph and AG Per. The resultsindicate that the spectra of Lambda Tau from phase 0.77 to 0.90 arecharacteristic of spectral type B4, that the spectra of V356 Sgr matchB3 and A0 spectra except at isolated phases exhibiting UV excess light,and that the excess-light spectrum is characteristic of hydrogenfree-bound emission. Color excesses and component-star temperatures andabsolute visual magnitudes are determined for U Oph and AG Per.
| Seven-Colour Photometry of the Variable HD 25539
Not Available
| Spectroscopic studies of stars in Per OB2.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..598G&db_key=AST
| Dynamical evolution of the subsystem of bright stars in the ζ Persei association
Not Available
| Evidence for a rotational reddening in early B-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&A....42..471M&db_key=AST
| Interstellar Matter in the Region of the Perseus II Association
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969PASP...81..496L&db_key=AST
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