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|A high-resolution spectroscopy survey of β Cephei pulsations in bright stars|
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
|An empirical temperature calibration for the Δ a photometric system . I. The B-type stars|
We establish an empirical effective temperature calibration of mainsequence, luminosity class V to III B-type stars for the Δ aphotometric system which was originally developed to detect magneticchemically peculiar objects of the upper main sequence (early B-type toearly F-type) at 5200 Å. However, this system provides the index(g_1-y) which shows an excellent correlation with (B-V) as well as (b-y)and can be used as an indicator of the effective temperature. This issupplemented by a very accurate color-magnitude diagram, y or V versus(g_1-y), which can be used, for example, to determine the reddening,distance and age of an open cluster. This makes the Δ aphotometric system an excellent tool to investigate theHertzsprung-Russell-Diagram (HRD) in more detail. Using thereddening-free parameters and already established calibrations withinthe Strömgren uvbyβ, Geneva 7-color and Johnson UBV systems, apolynomial fit of third degree for the averaged effective temperaturesto the individual (g_1-y)0 values was derived. For thispurpose, data from the literature as well as new observations were takenresulting in 225 suitable bright normal B-type objects. The statisticalmean of the error for this sample is 238 K which is sufficient toinvestigate the HRD of distant galactic open clusters as well asextragalactic aggregates in the future.
|A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: II. Results and Interpretation|
We have carried out a sensitive high-latitude (|b| > 15?) HI 21cm-line absorption survey towards 102 sources using the GMRT. With a3σ detection limit in optical depth of ?0.01, this is the mostsensitive HI absorption survey. We detected 126 absorption features mostof which also have corresponding HI emission features in the LeidenDwingeloo Survey of Galactic neutral Hydrogen. The histogram of randomvelocities of the absorption features is well-fit by two Gaussianscentered at Vlsr ?0 km s1 with velocity dispersions of 7.6± 0.3 km s-1 and 21±4 km s-1respectively. About 20% of the HI absorption features form the largervelocity dispersion component. The HI absorption features forming thenarrow Gaussian have a mean optical depth of 0.20±0.19, a mean HIcolumn density of (1.46 ± 1.03) × 1020cm2, and a mean spin temperature of 121 ± 69 K. TheseHI concentrations can be identified with the standard HI clouds in thecold neutral medium of the Galaxy. The HI absorption features formingthe wider Gaussian have a mean optical depth of 0.04±0.02, a meanHI column density of (4.3±3.4)×1019cm-2, and a mean spin temperature of 125±82 K. The HIcolumn densities of these fast clouds decrease with their increasingrandom velocities. These fast clouds can be identified with a populationof clouds detected so far only in optical absorption and in HI emissionlines with a similar velocity dispersion. This population of fast cloudsis likely to be in the lower Galactic Halo.
|High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds|
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
|Interstellar Silicon Abundance|
We present 34 measurements of silicon gas phase column densities in theinterstellar medium. We have used spectra containing the SiII 1808 Angline which were obtained with the Goddard High Resolution Spectrograph(GHRS) aboard the Hubble Space Telescope (HST). Extinction curveparameters are determined for analyzed lines of sight and relationbetween Si/H ratio and extinction parameters is discussed. We find theabundance of gas phase silicon in diffuse clouds to be lower than thesolar value by a factor of four.
|Detection of a variable interstellar absorption component towards δ Orionis A|
Observations of δ Ori A made with the UHRF in its highestresolution mode (R~900000) have revealed the presence of a cool(Tk<=350K) variable absorption component at a heliocentricvelocity of +21.3kms-1. The component is detected in NaiD1, where clear hyperfine splitting is seen, and Caii K.Comparison of our data with existing spectra suggests that the componenthas consistently increased in strength from 1966 to 1994, andsubsequently reduced in intensity by 1999. Following a discussion of thepossible origins of this component it is concluded that an interstellar,rather than circumstellar, origin is most likely. This is one of veryfew detections of variable interstellar absorption reported in theliterature, and we suggest an origin within filamentary materialassociated with the expanding Hi shell surrounding the Orion-Eridanussuperbubble.
|The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way|
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
|Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant|
We present high-resolution (R~75,000), high signal-to-noise (S/N~100) CaII λ3933.663 and Na I λλ5889.951, 5895.924 spectraof 68 stars in the direction of the Vela supernova remnant. The spectracomprise the most complete high-resolution, high S/N optical survey ofearly-type stars in this region of the sky. A subset of the sight lineshas been observed at multiple epochs, 1993/1994 and 1996. Of the 13stars observed twice, seven have spectra revealing changes in theequivalent width and/or velocity structure of lines, most of which arisefrom remnant gas. Such time variability has been reported previously forthe sight lines toward HD 72089 and HD 72997 by Danks & Sembach andfor HD 72127 by Hobbs and coworkers. We have confirmed the ongoing timevariability of these spectra and present new evidence of variability inthe spectra of HD 73658, HD 74455, HD 75309, and HD 75821. We havetabulated Na I and Ca II absorption-line information for the sight linesin our sample to serve as a benchmark for further investigations of thedynamics and evolution of the Vela SNR. Based on observations obtainedat the European Southern Observatory, La Silla, Chile.
|Evidence of Interstellar NA I Structure at Scales Down to 15 AU in Low-Density Gas|
We present high-resolution Hubble Space Telescope/Space TelescopeImaging Spectrograph and multiepoch KPNO coudé feed observationsof multiple interstellar lines toward the binary system HD 32039/40.Comparisons of the Na I profiles observed over a period of 4.25 yrreveal significant temporal variation in the Na I column in at least onecomponent, implying that there is structure at scales on the order ofthe proper motion (~15-21 AU). Large differences are also observed amongmultiple components in the profiles of the neutral species between thebinary sight lines (5060 AU separation). In addition, significantdifferences in the S II profile are seen between the stars-the firstoptical/UV detection of small-scale variations in a dominant ion.Measurements of the C I fine-structure excitation in the variablecomponents suggest that the densities in these components are ~20-200cm-3, significantly lower than the densities inferred in pastH I 21 cm and Na I studies. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association for Research inAstronomy, Inc., under NASA contract NAS5-26555.
|Studies of the ISM in the Vela Supernova Remnant|
Recent observations of the Vela SNR in the ISM species Ca II and Na Iare presented and discussed in the context of the ``break-down'' of theSpitzer-Routly effect. Variations in line profiles with time aredemonstrated, eventually through a statistical approach a description ofcloud structure will be possible. The IS lines in ~ 70 sightlines areused to determine an accurate distance to the Vela SNR of 250 +/- 30 pc.Finally a discussion of future observations are given relatinginformation obtained from measurements of near-by ISM to more distantintergalactic medium.
|UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars|
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
|An extensive Delta a-photometric survey of southern B and A type bright stars|
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 18.104.22.168 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|Ultra--High-Resolution Observations of Interstellar Na I and Ca II K toward the High Galactic Latitude Star HD 28497|
We present very high resolution (0.32 km s-1) spectra of interstellar NaI D1, D2, and Ca II K absorption toward HD 28497 obtained with theUltra--High-Resolution Facility at the 3.9 m Anglo-Australian Telescope.The star is located in projection in a highly disturbed interstellarregion close to a number of identified features including the highgalactic latitude molecular cloud MBM 20, the large Orion-Eridanusshell, seen in H alpha and H I 21 cm maps, and a filamentary loopstructure between vLSR = -12 and -4 km s-1 in the Berkeley H I 21 cmsurvey and visible on the IRAS 100 mu m map. Toward HD 28497 we detect13 absorption components in the Na I spectra, to a column density limitof 2 x 1010 cm-2, and 10 in Ca II K over a velocity range of ~70 km s-1.Four absorption components in the Na I spectra show s-resolved hyperfinestructure with b-values from 0.31 to 0.40 km s-1 and column densitiesfrom 4.0 to 14 x 1010 cm-2. If we assume the clouds represented by thesecomponents have no internal turbulent velocities, their temperatureswould range between 134 and 227 K. One of these hyperfine split (hfs)components, at vLSR = -11.1 km s-1, shows significant temporal variationin equivalent width compared to earlier (1977) observations, making thisthe first interstellar sight line outside the Vela supernova remnant toshow a time-varying component. The feature may be associated with thefilamentary loop structure seen in this region. There is poorcorrespondence between the Na I and Ca II profiles: we do not detectnarrow Ca II profiles to the four hfs Na I components, and only three ofthe well-resolved components have the same Ca II and Na I radialvelocities and consistent b-values. One of these components, at vLSR =-30.0 km s-1, has a low Na I/Ca II ratio and arises in a region whereturbulent motions dominate---properties consistent with the hypothesisthat the cloud lies close to HD 28497. In general, however, the Na I andCa II occupy different gaseous phases in the ISM. We have compared ourdata with 21 cm emission profiles obtained from the recentLeiden/Dwingeloo H I survey. Based on agreement in the velocities, theNa I/Ca II ratio, and the kinetic temperatures, we conclude that thecomponent at vLSR = -7.5 km s-1 is associated with the front side of thelarge, expanding Orion-Eridanus shell. Unexpectedly, the molecular cloudMBM 20 is not detected either in our absorption spectra or in the H Iprofiles, indicating that HD 28497 lies away from the core of MBM 20.Apart from the two features at -11 and -7.5 km s-1 there is almost noagreement between the H I profiles and the optical spectra. Although wecannot rule out the possibility that most of the H I lies behind thestar, this explanation seems unlikely because many of the H I featureshave previously been attributed to foreground phenomena. The beam sizesof the H I and the optical studies are quite different and this suggestsa different explanation, namely that the physical sizes of theinterstellar structures we detect in Na I and Ca II are not extensiveenough to be detected in H I. If so, this raises questions about theusefulness in general of combining results obtained from H I 21 cmstudies with results obtained from optical (or ultraviolet) studies ofthe interstellar gas.
|A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
|The LS stars at 25 years|
Since its publication in 1971, Stephenson and Sanduleak's Luminous Starsin the Southern Milky Way has served as a starting point for a wholegeneration of investigations of galactic structure and thecharacteristics of massive, early-type stars. This paper presents asilver-anniversary review of the Stephenson-Sanduleak "LS" stars: theirdistribution on the sky, observed magnitudes, colors and spectral types,their distribution in space, and the characteristics of some of the moreunique individual objects. While much has been learned of and from theseobjects, much fundamental data remain to be acquired.
|Interstellar Abundances from Absorption-Line Observations with the Hubble Space Telescope|
The Goddard High-Resolution Spectrograph (GHRS) aboard the Hubble SpaceTelescope (HST) has yielded precision abundance results for a range ofinterstellar environments, including gas in the local medium, in thewarm neutral medium, in cold diffuse clouds, and in distant halo clouds.Through GHRS studies, investigators have determined the abundances ofelements such as C, N, 0, Mg, Si, S, and Fe in individual interstellarclouds. These studies have provided new information about thecomposition of interstellar dust gains, the origin of the Galactichigh-velocity cloud system, and the processes that transport gas betweenthe disk and the halo. Precision measurements of the interstellar D to Hratio and of the abundances of r- and s-process elements have alsoprovided fiducial reference values for cosmological and stellarevolutionary observations and theoretical models.
|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.
|A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars|
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
|Interstellar Lines in HD 72127A and B: A Binary Star behind the VELA Supernova Remnant|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..590W&db_key=AST
|An HST study of galactic inerstellar zinc and chromium|
We present a survey of interstellar Zn II and Cr II absorption extractedfrom the Hubble Space Telescope Goddard High Resolution Spectrograph(HST GHRS) data archive. We find clear evidence for an enhanceddepletion of Zn from the gas phase with increasing fractional abundanceof molecular hydrogen f(H2). Our lower limit to the Galacticinterstellar metallicity is approximately 65% of the solar value asdetermined by the measured Zn abundances in the lowest f(H2) sightlines,(N(Zn)/N(H0tot) = -0.19 +/- 0.04. Thecorrespondingly high depletion of Cr with respect to solar(N(Cr/N(H0tot) = -1.44 +/- 0.26 indicates thatthere are significant amounts of dust present in these lines of sight.The Galactic abundances of Zn and Cr in the ISM provide a fundamentalreference point which is used to understand the metal enrichment anddust formation history of damped Lyman alpha QSO absorption-linesystems, normally believed to arise from intervening precursors tomodern disk galaxies. Although the spread in Zn abundances is large forboth the local ISM and in damped Lyman alpha systems, we still find asubstantial difference (factor of 4-10) in metallicity between the twosets. This survey and future observations of more distant objects whichprobe the full extent of the Milky Way halo provide a more completepicture of the enrichment and depletion characteristics of present-daygalaxies.
|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.
|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.
|Variable interstellar absorption toward HD 72127A. II - 1981-1988|
The present study examines eight new echelle spectra of HD 72127A foundbetween 1981 and 1988 near the Ca II K line, along with four similarspectra near the Na I D lines. In addition to the unrivaled intensityand width of this interstellar K line formed at a distance of not morethan 500 pc, which were previously discovered by Thackeray (1974), thespectra show clearly the unique temporal variability of the interstellarabsorption along this light path, which was reported in an earlier studyby Hobbs et al. (1982). The new results strengthen further thehypothesis that the interstellar absorption toward this star occurspredominantly in the disturbed gas located within the SNR, in which theinterstellar grains have been largely destroyed. The variableinterstellar lines were found to consist of at least 120 components atthe K line and of at least eight generally corresponding components atthe D lines. The total column densities summed over all of theseinterstellar clouds varied irregularly by about 45 percent in five andabout 38 percent in ten years, respectively.
|Broad-band photometry of selected southern ultraviolet-bright stars.|
|Long Slit Observations of Emitting Gas in the VELA Supernova Remnant|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.245..701W&db_key=AST
|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.
|An atlas of 12 rather subtle composite spectra|
True composite spectra, at MK classification dispersion, have beenobtained from the components of close visual binaries. From an availableset of 46 composites, 12 are presented in photographic montages with thespectra of their component stars for comparison. These 12, ranging inspectral type from B2 to G5, illustrate mainly the less easilyrecognized composite spectra. An analysis of their peculiaritiesgenerates seven typical clues which can alert the classifier to thecomposite nature of a spectrum under examination.
|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.
|Close visual binaries. I - MK classifications|
Each component of 170 close visual binaries has been classified with newprocedures for controlling contamination problems. These classificationsare presented and are shown to be on the MK system. Two sources of areascanner UBV photometry were compared in order to establish homogeneousphotometric as well as spectroscopic data. From a consideration ofsystematic errors in the V magnitude difference (Delta V) betweencomponents the photometry of Hurly and Warner (1983) is to be preferred.Absolute magnitudes for each binary are derived from Delta V via atested MK - M(v) map.
|Close visual binaries. II - Quantitative test of isochrones|
Homogeneous and accurate color-magnitude data are available from Paper Ifor each component of 56 close visual binaries, 30 with evolvedcomponents. The 21 binaries with main-sequence primaries are comparedwith new Yale isochrones to determine the appropriate isochronecomposition: Y = 0.25, Z = 0.04. Explanations are given for eightbinaries found to be inconsistent with this isochrone. Some of theremaining binaries suggest a decrease by 0.5 in the mixing lengthparameter for the reddest main-sequence stars, and either a smallerdecrease or mass loss in the subgiant and giant phase of evolution. Ingeneral, the mean apparent age difference between binary components (0.0+ or - 0.1 Gyr) shows stellar evolution to be well modeled by the newYale isochrones.
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