|B Stars as a Diagnostic of Star Formation at Low and High Redshift|
We have extended the evolutionary synthesis models by Leitherer et al.by including a new library of B stars generated from the IUEhigh-dispersion spectra archive. We present the library and show how thestellar spectral properties vary according to luminosity classes andspectral types. We have generated synthetic UV spectra for prototypicalyoung stellar populations varying the IMF and the star formation law.Clear signs of age effects are seen in all models. The contribution of Bstars in the UV line spectrum is clearly detected, in particular forgreater ages when O stars have evolved. With the addition of the newlibrary we are able to investigate the fraction of stellar andinterstellar contributions and the variation in the spectral shapes ofintense lines. We have used our models to date the spectrum of the localsuper-star cluster NGC 1705-1. Photospheric lines of C III λ1247,Si III λ1417, and S V λ1502 were used as diagnostics todate the burst of NGC 1705-1 at 10 Myr. Interstellar lines are clearlyseen in the NGC 1705-1 spectrum. Broadening and blueshifts of severalresonance lines are stronger in the galaxy spectrum than in our modelsand are confirmed to be intrinsic of the galaxy. Si II λ1261 andAl II λ1671 were found to be pure interstellar lines with anaverage blueshift of 78 km s-1 owing to a directed outflow ofthe interstellar medium. We have selected the star-forming galaxy1512-cB58 as a first application of the new models to high-z galaxies.This galaxy is at z=2.723, it is gravitationally lensed, and its highsignal-to-noise ratio Keck spectrum shows features typical of localstarburst galaxies, such as NGC 1705-1. Models with continuous starformation were found to be more adequate for 1512-cB58 since there arespectral features typical of a composite stellar population of O and Bstars. A model with Z=0.4 Zsolar and an IMF with α=2.8reproduces the stellar features of the 1512-cB58 spectrum.
|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.
|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
|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.
|Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. IV - Further IUE detections|
We have obtained IUE spectra for 31 middle and late-type giant andsupergiant stars whose TD-1 fluxes or ground-based spectra indicate thepresence of a hot component, or whose radial velocities indicate anunseen component. Stellar components earlier than type F1 were detectedin 22 cases. While 20 of the hot secondaries are seen weakly in opticalspectra, two are UV discoveries: HD 58134 and HD 183864. The hotcompanions are classified accurately by temperature class from theirfar-UV spectra. The interstellar extinction of each system and therelative luminosities of the components are derived from the UV andoptical fluxes, using a new grid of UV intrinsic colors for hot dwarfs.We find that many giant stars apparently have companions which are toohot and hence too luminous for consistency with the primary's spectralclassification.
|Photometric monitoring of O-type stars|
A photometric survey of 16 bright O-type stars was conducted in order todetermine the incidence of low-order nonradial pulsation or othervariability among them. For each star, several observations wereobtained per night so that periodicities as short as one hour can bedetected. The results show that microvariability with a time-scale ofthe order of days is present in all the O supergiants and in somedwarfs. Except for Zeta Oph, no periodicity characteristic of nonradialpulsation could be found in any of the stars. However, high-order modeswould not have been detected. One O-type star is a previously unknowneclipsing binary. In the process of this study, two new B-type eclipsingbinaries were discovered.
|Spectral synthesis in the ultraviolet. IV - A library of mean stellar groups|
A library of mean UV stellar energy distributions is derived from IUEspectrophotometry of 218 stars. The spectra cover 1230-3200 A with aspectral resolution of about 6 A. They have been corrected forinterstellar extinction and converted to a common flux and wavelengthscale. Individual stars were combined into standard groups according totheir continuum colors, observed UV spectral morphology, MK luminosityclass, and metal abundance. The library consists of 56 groups: 21dwarf(V), 8 subgiant(IV), 16 giant(III), and supergiant(I + II) groups,covering O3-M4 spectral types. A metal-poor sequence is included,containing four dwarf and two giant groups, as is a metal-enhancedsequence with a single dwarf, subgiant, and giant group. Spectralindices characterizing the continuum and several strong absorptionfeatures are examined as temperature, luminosity, and abundancediagnostics. The library is intended to serve as a basis forinterpreting the composite UV spectra of a wide variety of stellarsystems, e.g., elliptical galaxies, starburst systems, and high-redshiftgalaxies.
|Observations that link infrared cirrus and ultraviolet extinction|
Results are presented of UV extinction measurements of 17 stars in theopen cluster IC 4665 and of four stars in the open cluster NGC 1647,showing that the UV extinctions of the two clusters stars have differentproperties. Whereas the stars in NGC 1647 cluster are typical of generalinterstellar space, the stars in IC 4665 have a small 'linear' termwhich is typical of stars found near regions of active star formation.Using data from the IRAS satellite to study the emission by the'infrared cirrus' for each of the regions and to measure theI(60-micron)/I(100-micron) ratio for the two regions, it was found that,when the linear term component is present, it dominates the 100-microncirrus emission. When it is absent, the 100-micron emission is from therelatively hot particles that are responsible for the 60-micronemission. It is suggested that the 60-micron emitters are smallcarbonaceous grains that are major contributors to all parts of the UVextinction except the linear term.
|The orbit and colors of the Cepheid S MUSCAE|
A new orbit has been computed for the binary Cepheid S Mus combining newdata from Mount John Observatory with previous data. Corrections to thecolors and reddening due to the light from the companion are derived.The spectral type determined from IUE low-dispersion spectra is used forthese corrections. The corrections are small, even though the companionis one of the hottest (B5 V) known for a Cepheid.
|Spectral synthesis in the ultraviolet. III - The spectral morphology of normal stars in the mid-ultraviolet|
The morphology of 218 mid-UV spectra of stars ranging from O through Kin spectral type is examined. Several new line and continuum indices aredefined and their usefulness as temperature, luminosity, and metallicitydiscriminants is discussed. Mid-UV stellar continua are found to bemarkedly affected by abundance. A UV excess, delta(2600-V), is computedwhich is more sensitive by a factor of 10 to (Fe/H) than is delta(U-B).The relative strength of spectral lines in the mid-UV is not as stronglyaffected by abundance. Mid-UV spectra are much more sensitive to thetemperature of the stellar population than to either metallicity or thedwarf/giant ratio. Mg II 2800 shows unexpected behavior, displaying nosensitivity to abundance for cool stars and a reversed sensitivity in FGdwarfs such that metal-poor stars have stronger Mg II strengths at thesame temperature than more metal-rich stars.
|Mass to line-strength relations from IUE spectra of early-type stars|
An extensive survey of the 1200-1900 A region in OB type stellar spectraobtained from the IUE archives has been used to establish line-strengthversus spectral-type relationships. One hundred and sixty-threelow-resolution IUE spectra of 124 well-classified O3 to B5 stars wereexamined. Earlier results that the equivalent width of Si IV (1400 A)and C IV (1550 A) features are well correlated with optical spectraltype are confirmed. The equivalent width/spectral type/luminosity classrelations for these features are then established.
|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.
|HR 3562 and 3600 - Two short-period B-type variables|
Fron intensive photometric observations of the early B stars HR 3562 andHR 3600, it is shown that they are both singly periodic variables. Themultiple periods previously proposed are not confirmed, and anexplanation in terms of nonradial oscillations need not be invoked. Itis suggested that they be classified as ellipsoidal variables ratherthan 53 Per stars. One of the comparison stars, HR 3527, is an eclipsingbinary.
|Intensities of the resonance lines of neutral and ionized magnesium in stellar spectra|
Empirical curves giving the dependence of the equivalent widths of thedoublet 2800 Mg II and the line 2852 Mg I on the spectral class havebeen plotted. Some features of the behavior of these lines in thespectra of stars of the spectral classes A-K have been analyzed. Thelines 2795 Mg II and 2852 Mg I have been used to determine the meanelectron concentration ne(Mg) in the atmospheres of 87 stars of thespectral classes B8-K4.
|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.
|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.
|The ultraviolet spectrum of the center of M31|
A total of twelve long-exposure low-resolution IUE images have been usedto study the spectrum and surface brightness distribution of theultraviolet radiation within the central 50 pc of M31. The presence ofweak absorption features near 1300 A demonstrates that the radiation ofthe well-known spectral upturn below 2000 A does not originate in youngmetal-rich stars. The most likely sources are considered to be hot,highly evolved stars. The energy distribution is bluer than thatmeasured by experiments with larger entrance apertures, and below 2000 Athe surface brightness gradient near the nucleus increases. Thesefindings indicate that the blue stars are more centrally concentratedwithin the bulge of M31 than the more metal-rich red giants. The energydistribution measured by IUE appears to be much bluer at shortwavelengths than that of the metal-rich globular cluster 47 Tucanae, yetit also differs from those of clusters having more populous bluehorizontal branches.
|Ultraviolet observations of hot stars with circumstellar dust shells|
Absolute fluxes over the wavelength range 1200-3200 A are presented for13 normal early-type stars and 12 early-type stars known to have largeIR excess; the data were obtained to study the UV spectral modificationsproduced by absorbing circumstellar dust particles. It is found that allthe Be/shell stars whose spectral types are later than B6 exhibitgreatly enhanced line absorption due to circumstellar Fe II. Thecircumstellar gaseous line absorption in stars cooler than B6 severelycomplicates the study of circumstellar dust absorption. However, those Band A stars that exhibit the circumstellar 9.7-micron emission featurehave a very large increase in circumstellar absorption for 1800 A; suchabsorption is expected from circumstellar silicate particles.
|The fundamental physical parameters of main-sequence and near main-sequence B type stars as derived from uvby,beta photometry|
From spectrophotometric measurements of hydrogen line intensities, uvbyphotometry and photoelectrically determined H-beta and H-gamma indicesof 75 B2-B6 main-sequence stars, effective temperature and surfacegravity are derived by using the model atmospheres computed by Kurucz(1974). Comparisons between the g values and the MK luminosityclassification show good agreement for the MK standard stars but ratherserious disagreement for the average stars in such a way that most ofthe stars classified in luminosity class V really belong to class IV.Using the evolutionary model sequences calculated by Hejlesen et al.(1972) the stellar mass, age and luminosity are determined from the uvbyand beta data through effective temperature and surface gravity. Thetheoretically derived luminosities are in excellent agreement with theluminosities derived by calibrations.
|On the anomaly of the far UV extinction in the 30 Doradus region|
Area-integrated ultraviolet observations made with the NetherlandsAstronomical Satellite (ANS) of about 800 fields in a 0.7 square degreeregion around the giant H II region 30 Doradus in the Large MagellanicCloud are discussed. The five-channel ANS photometric system is shown tobe information-redundant in the present application: the LMCobservations can be discussed in terms of only two parameters, i.e., theextrapolated visual brightness and a temperature parameter (color). Acolor-brightness diagram for about 600 fields with good qualitymeasurements is given, and it is concluded that most of the spread incolor is caused by differential extinction. By various independentmethods it is found that the 2200 A-feature is deficient by a factor ofthree, on a logarithmic scale, relative to the average galacticextinction law.
|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.
|New kinematical data for bright southern OB-stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..129L&db_key=AST
|Four-color and H-beta photometry for bright B-type stars in the southern hemisphere.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..621C&db_key=AST
|MK Spectral Types for Bright Southern OB Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157..313H&db_key=AST
|A Survey of Southern Be Stars|