|The Ultraviolet and Optical Spectra of Luminous B-Type Stars in the Small Magellanic Cloud|
We present ultraviolet spectra from the Space Telescope ImagingSpectrograph (STIS) of 12 early B-type stars in the Small MagellanicCloud (SMC), composed of nine supergiants and three giants. Amorphological comparison with Galactic analogs is made using archivaldata from the International Ultraviolet Explorer (IUE). In general, theintensity of the P Cygni emission in the UV resonance lines is greaterand is seen to later spectral types in the Galactic spectra than intheir metal-deficient SMC counterparts. We attribute these effects asmost likely arising from weaker stellar winds in the SMC targets, aspredicted by radiatively driven wind theory. We also include unpublishedSTIS observations of two late O-type stars in the SMC. In combinationwith published O-type STIS data, we now have an extensive ultravioletspectral library of metal-deficient stars to use in the study ofunresolved starbursts and high-redshift star-forming galaxies. In thiscontext, we present empirical measurements for the B-type spectra of thenew ``1978 index'' suggested by Rix et al. as a probe of metallicity insuch systems.
|The 74th Special Name-list of Variable Stars|
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
|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.
|Cross-correlation characteristics of OB stars from IUE spectroscopy|
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
|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.
|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.
|Deep Hα survey of the Milky Way. II. The l=328deg area.|
The detailed velocity field of the ionized hydrogen over an area ofabout 4x3deg around galactic longitude 328deg has been obtained in theframe of an Hα Survey of the galactic plane carried out at ESO LaSilla. The detailed analysis of the Hα profiles shows that thereare several layers of ionized hydrogen with different velocities.Besides individual HII regions there are two diffuse nebular emissionsdetected all over the studied area with velocities -20km/s and -40km/s.The HII regions exhibit complex structures; according to theirvelocities they can be divided into two groups around -40km/s and-47km/s. We have studied in detail the structure and velocities of thebright HII regions. The well known narrow lines of RCW94 are confirmed.The distances of the O-B3 stars in this area have been calculated fromthe literature data, and combined with radio data and our Hα dataallow us to determine the distances of the nebular components. We findthat the faint ionized gas layer at -20km/s, never detected before,neither at optical nor at radio wavelengths, is at about 1kpc anddefines the Sagittarius Carina arm at longitude 328deg. This impliesthat the main HII regions in this area and the diffuse ionized hydrogenin which they are immersed belong to a second arm (probably the ScutumCrux arm). This arm appears split at this longitude with two groups at2.3 and 3kpc. The radiosource 327.759-0.351 at H109αV_LSR_=-72km/s (d_kin_=4.5kpc) has been detected at Hα wavelengthbehind the other Hα emissions.
|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.
|Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry|
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
|Carbon and nitrogen abundances in the BN supergiant HD 93840, and their implications for normal Galactic supergiants|
It is demonstrated how carbon and nitrogen abundances of luminous Bstars can be determined by a combined analysis of their UV photosphericand wind lines. It is shown that HD 93840 has nearly the sametemperature and surface gravity as the normal B1 Ib star Zeta Per. Thesetwo stars are compared on the basis of their UV photospheric siliconspectra and the differences in their photospheric CNO and metallic linesare discussed. A quantitative comparison between the wind profiles ofthe two stars is made. A simple model for the compositions of bothatmospheres is used to derive the fraction of material in eachatmosphere which has undergone CNO processing. It is argued that theenriched material must have resided in a nuclear burning core for only avery short time. Best estimates of 0.09 + or - 0.07 and 0.90 + or - 0.1are made for the carbon abundances relative to cosmic ones for HD 93840and Zeta Per, respectively.
|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.
|The UV silicon spectra of early B stars|
Equivalent widths of UV silicon lines obtained from high dispersion IUESWP spectra for a sample of 37 mid- to early B stars are presented.These are compared to other atmospheric diagnostics and to modelatmosphere calculations. It is found that some of the UV silicon linesare extremely sensitive to stellar temperature and luminosity over therange B5-B0.5, or roughly a factor of two in effective temperature. Thepotential usefulness of these lines is stressed, and it is demonstratedthat they could determine temperatures and surface gravities to the sameaccuracy as other commonly used diagnostics once adequate models becomeavailable. Although the available models fail to predict thequantitative behavior of the line strengths, they do, in most instances,describe their qualitative behavior. Since the existing models aresomewhat out of date, the results suggest that models based upon morecomplete opacity tables may be quite reliable.
|The UV silicon spectra of early B stars|
The UV silicon spectra of mid to early B stars are examined and comparedto models. It is found that lines are extremely sensitive to stellartemperature and luminosity. Although the models fail to predict thequantitative behavior of the line strengths, they do, in most instances,describe their qualitative behavior.
|Low dispersion spectrophotometry of bright early-type stars|
Intensity distributions for 79 stars of spectral types O9 to A3, plus anF3 star and 7 standard stars, are presented. The observations cover awavelength range from 3300 to 6000 A. The internal errors are discussed.Synthetic uby colors are obtained for all the stars observed, and arecompared with observed published data.
|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.
|A study of visual double stars with early type primaries. IV Astrophysical data|
Astrophysical parameters (MK class, color excess, absolute magnitude,distance, effective temperature, mass, and age) are derived fromcalibrations of the uvby-beta indices for the members of 253 doublestars with O or B type primaries and faint secondaries. The photometricspectral classification is compared to the MK classes, and the agreementis very good. The derived data together with spectroscopic and JHKL dataare used for deciding which pairs are likely to be physical and whichare optical, and it is shown that 98 (34 percent) of the secondaries arelikely to be members of physical systems. For 90 percent of the physicalpairs the projected separation between the components is less than25,000 AU. A majority of the physical secondaries are late-type stars,and 50 percent of them are contracting towards the zero-agemain-sequence. Also presented are new uvby-beta data for 43 secondariesand a computer program for determining astrophysical parameters fromuvby-beta data.
|White Dwarf Candidates for Trigonometrical Parallax Determination|
|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.
|Photographic observations of visual double stars|
The results of photographic observations of 199 visual double stars,obtained at the Bosscha Observatory at Lembang, Indonesia, in the years1958-1975 (with one 1953 plate) are presented. The material comprises708 plates with an average of 37 images measured per plate. A shortdescription of the program is given (cf. van Albada-van Dien, 1958).
|A study of visual double stars with early type primaries. II - Photometric results|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&AS...51..161L&db_key=AST
|A study of visual double stars with early type primaries. I - Spectroscopic results|
Attention is given to spectral peculiarities found in data on thespectral classes of 486 stars in 254 visual doublet or multiplet systemswith O or B type primaries, in order to isolate a group of very youngstars that may serve for the study of early stellar evolutioncharacteristics. It is noted that the material contains a substantialfraction of secondaries that are likely to be physical, and that severalof these may be in the premain-sequence phase of stellar evolution, orhave reached the zero-age main sequence.
|The interstellar 2200 A band - A catalogue of equivalent widths|
|Erratum - Discordances Between SAO and HD Numbers for Bright Stars|
|Comparison of proper motions obtained by means of rectilinear trajectories of optical double stars with those given by the SAO catalog|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&A....71...55D&db_key=AST
|UVBY photometry of wide visual double stars with B, A and F spectral type- I.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..453O&db_key=AST
|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.
|Equivalent widths and rotational velocities of southern early-type stars|
|The Balmer discontinuities of O9-B2 supergiants.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975ApJ...196..503S&db_key=AST
|Wavelength dependence of interstellar polarization and ratio of total to selective extinction|
A multichannel polarimeter-photometer which uses dichroic filters toseparate the (UBVR) spectral regions is described. The instrument wasused with a 24-inch rotatable tube telescope for polarimetricobservation of nearby stars. Polarization data for 364 nearby stars aretabulated, together with the wavelength dependence of linear andinterstellar polarization.