B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
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Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
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Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
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Surface abundances of light elements for a large sample of early B-type stars - I. Spectral observations of 123 stars; measurements of hydrogen and helium lines; infrared photometry
High-resolution spectral observations of 123 B0-B5 stars in the mainsequence evolutionary phase were obtained at two observatories, namelythe McDonald Observatory (McDO) and the Crimean AstrophysicalObservatory (CrAO). Accurate equivalent widths W of two Balmer lines,Hβ and Hγ, and ten Hei lines were obtained for all the stars,as well as of the Heiiλ4686 line for the hottest ones. A carefulanalysis of the measured equivalent widths was performed. It is shownthat there is a very good agreement between the W values derived fromthe McDO and CrAO spectra for 14 common stars. A comparison withpublished data leads to the conclusion that the W values measuredearlier by some authors for strong Hei lines are very likely to beunderestimated. Infrared photometric observations in the J, H, and Kbands were performed for 70 programme stars. All these data will be usedin other papers: in particular for the Teff and loggdetermination and for the He, C, N and O abundance analyses.
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The HB Narrowband Comet Filters: Standard Stars and Calibrations
We present results concerning the development and calibration of a newset of narrowband comet filters, designated the HB filter set, which wasdesigned and manufactured to replace aging IHW filters. Information isalso presented about the design and manufacturing of the filters,including the reasoning that was used for deciding the final wavelengthsand bandpasses. The new filters are designed to measure five differentgas species (OH, NH, CN, C2, C3), two ions(CO+, H2O+), and four continuum points.An improved understanding of extended wings from emission bands in cometspectra, gained since the development of the IHW filters, wasincorporated into the new design, so that contamination from undesiredspecies is significantly reduced compared to previous filters. Inaddition, advances in manufacturing techniques lead to squarertransmission profiles, higher peak transmission and UV filters withlonger lifetimes. We performed the necessary calibrations so that dataobtained with the filters can be converted to absolute fluxes, allowingfor, among other things, accurate subtraction of the continuum from thegas species. Flux standards and solar analogs were selected andobserved, and the data were used to establish a magnitude system for theHB filters. The star measurements were also used to evaluate which solaranalogs were best representatives of the Sun and to explore how the fluxstandards differed in the UV with respect to their spectral type. Newprocedures were developed to account for the non-linear extinction inthe OH filter, so that proper extrapolations to zero airmass can beperformed, and a new formalism, which can account for mutualcontaminations in two (or more) filters, was developed for reducingcomet observations. The relevant equations and reduction coefficientsare given, along with detailed instructions on how to apply them. Wealso performed a series of tests involving factors that can affecteither the filter transmission profiles or the distribution of theemission lines in the gas species to determine how these effectspropagate through to the calibration coefficients. The results indicatethat there are only two factors that are a concern at a level of morethan a few percent: f-ratios smaller than f/4, and a few individualfilters whose transmission profiles are significantly different from thefilters used in the calibrations.
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Helium peculiar stars in the red spectral region
Based upon 33 A/mm dispersion spectroscopic material we examine ifequivalent widths of H and He lines can be used for the detection of newhelium-peculiar stars. The answer is affirmative and we present some newcandidates discovered this way. We have also investigated if the use ofdifferent helium lines than those of the (3) D series (4026, 4471)modifies the assignments of helium peculiar stars. This is not the case,since the use of lambda 6678 ((1) D) and lambda 7065 (3S) gives the sameresults. Based on observations obtained at the Haute ProvenceObservatory (CNRS)
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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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Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
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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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A list of MK standard stars
Not Available
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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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ICCD speckle observations of binary stars. I - A survey for duplicity among the bright stars
A survey of a sample of 672 stars from the Yale Bright Star Catalog(Hoffleit, 1982) has been carried out using speckle interferometry onthe 3.6-cm Canada-France-Hawaii Telescope in order to establish thebinary star frequency within the sample. This effort was motivated bythe need for a more observationally determined basis for predicting thefrequency of failure of the Hubble Space Telescope (HST) fine-guidancesensors to achieve guide-star lock due to duplicity. This survey of 426dwarfs and 246 evolved stars yielded measurements of 52 newly discoveredbinaries and 60 previously known binary systems. It is shown that thefrequency of close visual binaries in the separation range 0.04-0.25arcsec is 11 percent, or nearly 3.5 times that previously known.
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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.
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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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Be stars in binaries
The known companions to 80 Be stars and 355 B stars listed in the BrightStar Catalogue in the range B1-B7 III-V and north of delta = -30 deg areconsidered. The known near-absence of Be binaries with periods less than1/10 yr is confirmed. For longer periods up to the limit of 10,000 AU ofthis survey, the Be and B stars do not differ in binary frequencies.This result implies that during pre-main-sequence contraction, the tidalbraking in binaries wider than 0.5 AU was inadequate to prevent theformation of stars with nearly the break-up rotational velocities. Thefraction of Be and B stars that have companions is higher in clustersand associations (38 percent) than among field stars (25 percent),confirming that escapees from clusters tend to be single stars. There issome evidence that the companions of Be stars that occur in the sameluminosity range tend also to be Be stars; that result was expectedbecause in visual binaries there is a known tendency for rapidlyrotating primaries to have rapidly rotating secondaries.
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The interstellar 2200 A band - A catalogue of equivalent widths
Not Available
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Spectral classification from the ultraviolet line features of S2/68 spectra. V - Supplement series
The paper presents the ultraviolet classification of more than 450 B-Aand F spectra obtained with the sky survey telescope mounted on the TD1satellite. Concerning abnormal objects, attention is given to the Bestars, the binary stars, the helium weak stars, and the lambda Booobjects. With regard to Be stars, it is concluded that the 1930 Awavelength feature is linked to the existence of either shell structuresor Fe II emission lines in the visual spectral range. In addition, it issuggested that stellar spectra at wavelengths of 1410, 1610-20 and 2400A are equivalent to the He-weak group in the classical range.
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Space velocities and ages of nearby early-type stars
Photometric distances and space velocities have been calculated for 458B0-A0 stars with apparent magnitudes not exceeding 6.5. UsingStromgren's ubvy-beta photometry the effective temperature and theposition in bolometric magnitude over the zero-age main sequence of thestars were derived. These quantities were used to obtain age and massfor 423 of the stars by interpolation in the models of stellar evolutionfor the chemical composition (X Z) = (0.7, 0.03). A relation forderiving interstellar reddening for normal stars in the intermediategroup is given.
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Infrared spectra of the WN stars HD 50896 and HD 151932
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..541B&db_key=AST
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Structure and age of the local association /Pleiades group/
Intermediate-band indices are used to derive luminosities for some 500early-type stars with well-determined proper motions and radialvelocities. Space motion vectors and galactic coordinates are computedfor the stars considered. It is found that the local association membersare mainly concentrated in the Sco-Cen region in the Southern Hemisphereand the Cas-Tau region in the north.
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Catalogue of early-type stars measured in a narrow-band photometric system
A compilation of the photoelectric measurements in the Barbier-Morguleffsystem is presented. The catalogue includes data for 773 stars ofspectral type 08 to F6. 706 stars have been measured at least twice.
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The helium-to-hydrogen ratio in B stars, as determined from photoelectric observations of a narrow-band index of the He I lambda 4026 line
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&A....36...57N&db_key=AST
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UV excess stars and radio sources in the Aquila ring.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&A....31..207I&db_key=AST
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On the energy distributions of main sequence stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971MNRAS.153..501S&db_key=AST
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Four-color, Hbeta, and UBV photometry for bright B-type stars in the northern hemisphere
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76.1058C&db_key=AST
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On the reality of the stellar ring in Aql.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....13...71P&db_key=AST
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Lichtelectrische Untersuchungen eines nahen Sternringes in Aql.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969A&A.....3..210I&db_key=AST
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Spectral Classifications of 239 Early-Type Stars
Not Available
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The Kinematics of the Gould Belt: an Expanding Group?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJS...17..371L&db_key=AST
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INHABITED SKY
