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New beta Cephei and SPB Stars Discovered in Hipparcos Photometry
We discuss 34 stars for which we detected new frequencies in HipparcosHp magnitudes. 13 of these stars are variables discovered in this paper.For 20 stars, we derive log T_eff and log g from Stromgren or Genevaphotometry.We classify one new beta Cep star, HIP 88352, two new beta Cep suspects,HIP 54753 and 88123, four new SPBs, HIP 1030, 39206, 46192 and 111147,and two SPB suspects, HIP 75787 and 98778. We find the last star to betriply-periodic and we show that the frequencies detected in Hpmagnitudes are present in the photoelectric observations of Hill etal(1976).Finally, we discover the hottest variable of the SPB type, namely, HIP1030.
| 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).
| The Ultraviolet Extinction Curve of Intraclump Dust in Taurus (TMC-1): Constraints on the 2175 Å Bump Absorber
Ultraviolet extinction curves for three early-type stars that sampledust in the Taurus dark cloud in the vicinity of TMC-1 are analyzed toexamine the contribution of internal (intraclump) dust to the totalline-of-sight extinction. One of our selected targets samples only dustin the ``diffuse-screen'' component of the cloud, where the dust grainslack ice mantles and have optical properties similar to average``diffuse-ISM'' dust. Comparison with data for more heavily reddenedstars that also sample dust within TMC-1 (where grains are mantled)allows us to determine the intraclump extinction. Our principal resultis that the 2175 Å ``extinction bump'' is extremely weak or absentinside the clump. The feature present in the observed extinction curvesappears to arise almost entirely in the diffuse screen. This dramaticreduction in bump amplitude in the high-density environment isconsistent with the prediction of the graphite model that the feature issuppressed by hydrogenation. Amplitude reduction is accompanied by amore subtle change in the profile of the bump, specifically, an increasein width. Comparison of Taurus and other clouds strongly suggests thatthe increase in width results from accumulation of surface coatings onthe carrier grains rather than from particle clustering.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Photoelectric Photometry of Stars in the Orion Standard Region
Magnitudes and color indices in the Vilnius seven-color photometricsystem are given for 108 stars in the Orion standard region around theOrion Belt and the star lambda Orionis. New spectral and luminosityclasses, estimated from the photometric data, are given for some of thestars.
| Far-Ultraviolet (912--1900 Angstrom ) Energy Distribution in Early-Type Main-Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..280C&db_key=AST
| 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.
| 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.
| The small scale structure of the interstellar medium in the Orion association: The flotsam of star formation
The small scale dynamics and structure of the interstellar medium of theOrion OB1b, c association was studied using IUE high dispersion SWP andLWR/LWP spectra. The area surveyed centers on the Belt and encompassesthe Orion Cloak. The dynamics and abundances of the ionized and warmneutral gas surrounding the central parts of the association aredetermined using 35 B stars. Results are compared with the picture ofthe Orion interstellar medium gained using COPERNICUS, especially forthe structure and dynamics of the Orion Cloak.
| IUE observations of the broad continuum feature at 1400 A in the silicon and related stars
The upper main sequence chemically peculiar stars have previously beenstudied spectrophotometrically using low-resolution TD-1 spectra. Theseshow that the broad continuum feature at 1400 A is a useful indicator ofSi anomaly. In this paper the observations are extended to IUElow-resolution spectra and it is shown that this feature is indeed wellcorrelated with Si and also with optical chemical peculiarity indices.Its utility in selecting silicon stars is further demonstrated. Thisfeature is likely due to autoionization of Si II and is the bestavailable discriminator of the overabundance of a key element in the Apstars.
| Kinematical studies of open clusters and OB-associations from relative radial velocity observations. II - The Orion Belt region
Relative radial velocities have been obtained for 66 stars of theclustering Cr 70 in the Orion Belt region. The peculiar frequencydistribution of the radial velocities is discussed. Their conspicuoussystematical spatial distribution corresponds perfectly to the gradientof distance moduli found by Hardie et al. (1964). Therefore the presenceof two additional subgroupings in the Ori OB 1 association is proposed.Comparison with the radial velocities in the various subgroups of theOri OB 1 complex as defined by Blaauw (1964) does not yet reveal aconsistent kinematical picture.
| A photometric study of the Orion OB 1 association. III - Subgroup analyses
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...36..497W&db_key=AST
| A photometric study of the Orion OB 1 association. I - Observational data.
A catalog of observational data is presented for stars in the region ofthe young stellar association Orion OB 1. Photoelectric observationsobtained in the uvby-beta and UBV systems are compiled along withprevious photoelectric and spectroscopic data for all these stars aswell as for several bright members of the association with availablephotometric indices. Mean weighted values are computed for thephotometric data and summarized in tables expected to be reasonablycomplete for association members earlier than spectral type A0.Membership criteria are derived, and qualitative membershipprobabilities summarized, for the 526 stars in the final program. Theanalytical procedures are discussed for association stars of B,intermediate, and AF types. Effects of the nebular environment andvarious calibrations of Balmer-line and four-color indices areconsidered for the determination of absolute magnitudes for the B-typestars.
| Evidence of helium abundance differences between young groups of stars
Seven groups of B-type stars - Sco-Cen, NGC 6231, LacOBI,OriOBIb, h + chi Per, CepOBIII, and field stars - wereinvestigated photoelectrically to determine whether helium abundance isuniform in the solar neighborhood and in a region of the spiral arm ofthe Galaxy. Observations were performed using an echelle spectrometer inthe narrow band index of the I (4026) of the He I-4026 line. Amodel-atmosphere analysis of I (4026) and the beta index of the H betaline shows that in the spectral range B O-B 2, the relation between I(4026) and beta is insensitive to differences in the surface gravity butsensitive to differences in the helium to hydrogen ratio. It is foundthat stars in the two groups most distant from the sun - h + chi Per andCepOBIII - have a lower helium abundance than stars in the solarneighborhood.
| Spectral classification in the belt of ORI OB1.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..537G&db_key=AST
| Rotational velocities in the ORI association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79.1073S&db_key=AST
| A search for He-weak stars in very young clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....19..482B&db_key=AST
| Energy Distributions and Spectra of Orion B Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...169..529S&db_key=AST
| Far-Ultraviolet Interstellar Absorption in Orion and Monoceros
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...166..543W&db_key=AST
| Photoelectric Hbeta photometry for B stars in the Orion belt region
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..610C&db_key=AST
| The Meridian Proper Motions of 161 Stars in the Region of the Belt of Orion.
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