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The Discordance of Mass-Loss Estimates for Galactic O-Type Stars
We have determined accurate values of the product of the mass-loss rateand the ion fraction of P+4, M˙q(P+4), for asample of 40 Galactic O-type stars by fitting stellar wind profiles toobservations of the P V resonance doublet obtained with FUSE, ORFEUSBEFS, and Copernicus. When P+4 is the dominant ion in thewind [i.e., 0.5<~q(P+4)<=1], M˙q(P+4)approximates the mass-loss rate to within a factor of <~2. Theorypredicts that P+4 is the dominant ion in the winds of O7-O9.7stars, although an empirical estimator suggests that the range O4-O7 maybe more appropriate. However, we find that the mass-loss rates obtainedfrom P V wind profiles are systematically smaller than those obtainedfrom fits to Hα emission profiles or radio free-free emission bymedian factors of ~130 (if P+4 is dominant between O7 andO9.7) or ~20 (if P+4 is dominant between O4 and O7). Thesediscordant measurements can be reconciled if the winds of O stars in therelevant temperature range are strongly clumped on small spatial scales.We use a simplified two-component model to investigate the volumefilling factors of the denser regions. This clumping implies thatmass-loss rates determined from ``ρ2'' diagnostics havebeen systematically overestimated by factors of 10 or more, at least fora subset of O stars. Reductions in the mass-loss rates of this size haveimportant implications for the evolution of massive stars andquantitative estimates of the feedback that hot-star winds provide totheir interstellar environments.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Stellar and wind parameters of Galactic O-stars. The influence of line-blocking/blanketing
We have re-analyzed the Galactic O-star sample from \citet{puls96} bymeans of line-blanketed NLTE model atmospheres in order to investigatethe influence of line-blocking/blanketing on the derived parameters. Theanalysis has been carried out by fitting the photospheric and wind linesfrom H and He. In most cases we obtained a good fit, but we have alsofound certain inconsistencies which are probably related to a stillinadequate treatment of the wind structure. These inconsistenciescomprise the line cores of Hγ and Hβ insupergiants (the synthetic profiles are too weak when the mass-loss rateis determined by matching Hα) and the ``generalizeddilution effect'' (cf. \citealt{vo89}) which is still present in He I4471 of cooler supergiants and giants.Compared to pure H/He plane-parallel models we found a decrease ineffective temperatures which is largest at earliest spectral types andfor supergiants (with a maximum shift of roughly 8000 K). This findingis explained by the fact that line-blanketed models of hot stars havephotospheric He ionization fractions similar to those from unblanketedmodels at higher Teff and higher log g. Consequently, anyline-blanketed analysis based on the He ionization equilibrium resultsin lower Teff-values along with a reduction of either log gor helium abundance (if the reduction of log g is prohibited by theBalmer line wings). Stellar radii and mass-loss rates, on the otherhand, remain more or less unaffected by line-blanketing.We have calculated ``new'' spectroscopic masses and compared them withprevious results. Although the former mass discrepancy \citep{h92}becomes significantly reduced, a systematic trend for masses below 50Msun seems to remain: The spectroscopically derived valuesare smaller than the ``evolutionary masses'' by roughly 10Msun. Additionally, a significant fraction of our samplestars stays over-abundant in He, although the actual values were foundto be lower than previously determined.Also the wind-momentum luminosity relation (WLR) changes because oflower luminosities and almost unmodified wind-momentum rates. Comparedto previous results, the separation of the WLR as a function ofluminosity class is still present but now the WLR for giants/dwarfs isconsistent with theoretical predictions.We argue that the derived mass-loss rates of stars withHα in emission are affected by clumping in the lowerwind region. If the predictions from different and independenttheoretical simulations (\citealt {Vink00, Paul03, puls03a}) that theWLR should be independent of luminosity class were correct, a typicalclumping factor <ρ2>/<ρ>2 ≈5 should be derived by ``unifying'' the different WLRs.Based upon observations obtained at the INT and the European SouthernObservatory, La Silla, Chile. The INT is operated on the island of LaPalma by the ING in the Spanish Observatorio de El Roque de losMuchachos of the Instituto de Astrofísica de Canarias.Appendix A in only available in electronic form athttp://www.edpsciences.org
| Bright OB stars in the Galaxy. I. Mass-loss and wind-momentum rates of O-type stars: A pure H\alpha analysis accounting for line-blanketing
We study mass-loss and wind momentum rates of 29 Galactic O-type starswith luminosity classes I, III and V by means of a pure H\alpha profileanalysis and investigate to what extent the results compare to thoseoriginating from a state-of-the-art, complete spectral analysis. Ourinvestigation relies on the approximate method developed by\citet{Puls96} which we have modified to account for the effects ofline-blanketing. Effective temperatures and gravities needed to obtainquantitative results from such a simplified approach have been derivedby means of calibrations based on most recent spectroscopic NLTEanalyses and models of Galactic stars by \citet{Repo03} and\citet{Martins02}. Comparing (i) the derived wind-densities to thosedetermined by \citet{Repo03} for eleven stars in common and (ii) theWind-momentum Luminosity Relationship (WLR) for our sample stars tothose derived by other investigations, we conclude that our approximateapproach is actually able to provide consistent results. Additionally,we studied the consequences of ``fine tuning'' some of the direct andindirect parameters entering the WLR, especially by accounting fordifferent possible values of stellar reddening and distances. Combiningour data set with the corresponding data provided by \citet{Herrero02}and \citet{Repo03} we finally study the WLR for the largest sample ofGalactic O-type stars gathered so far, including an elaborate errortreatment. The established disagreement between the theoreticalpredictions and the ``observed'' WLRs being a function of luminosityclass is suggested to be a result of wind clumping. Different strategiesto check this hypothesis are discussed, particularly by comparing theH\alpha mass-loss rates with the ones derived from radio observations.
| A study of RV in Galactic O stars from the 2MASS catalogue
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 185 O stars, using J, H,Ks photometry from the 2MASS project. The results arecombined with data from the literature of 95 stars where RVhas been derived with the same technique, 22 of which in common with ourpresent sample from the 2MASS project catalogue. The averageRV from these 258 O stars is of 3.19 +/- 0.50. All objectswhose RV departs from this value by more than 2 sigma havebeen recognized. Ten objects have RV higher than this valueand two lower. It is found that anomalous RV can scarcely beassociated with anomalies in the general interstellar medium, e.g. withdifferent behaviour in different spiral arms. They are clearly linked tolocal cloud effect. In the Cygnus region RV values follow thebehaviour of the general interstellar medium, while in the Carina arm,in spite of the relatively larger distance, local cloud effects prevail.An explanation for this is suggested. The relatively few stars of oursample whose Hipparcos parallaxes are reliable, are found to havedistances systematically smaller than the distances derived by thespectroscopic parallaxes. We argue that this effect is consistent withthe recently claimed discovery of grey extinction towards OB stars.This publication makes use of data products from the Two Micron All SkySurvey (2MASS), which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center/CaliforniaInstitute of Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/905
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Revised Stellar Temperatures for Magellanic Cloud O Supergiants from Far Ultraviolet Spectroscopic Explorer and Very Large Telescope UV-Visual Echelle Spectrograph Spectroscopy
We have undertaken quantitative analysis of four LMC and SMC O4-9.7extreme supergiants using far-ultraviolet FUSE, ultraviolet IUE/HubbleSpace Telescope, and optical Very Large Telescope UV-Visual EchelleSpectrograph spectroscopy. Extended, non-LTE model atmospheres thatallow for the consistent treatment of line blanketing, developed byHillier & Miller, are used to analyze wind and photosphericsspectral features simultaneously. Using Hα to constrain mass-lossrates, He I-He II photospheric lines reveal stellar temperatures thatare systematically (5-7.5 kK) and substantially (15%-20%) lower thanpreviously derived from unblanketed, plane-parallel, non-LTEphotospheric studies. We have confidence in these revisions sincederived temperatures generally yield consistent fits across the entire912-7000 Å observed spectral range. In particular, we are able toresolve the UV-optical temperature discrepancy identified for AzV 232(O7 Iaf+) in the SMC by Fullerton and coworkers. Thetemperature and abundance sensitivity of far-ultraviolet, UV, andoptical lines are discussed. ``Of'' classification criteria are directlylinked to (strong) nitrogen enrichment (via N III λ4097) and(weak) carbon depletion (via C III λλ4647-4651), providingevidence for mixing of unprocessed and CNO-processed material at theirstellar surfaces. Oxygen abundances are more difficult to constrain,except via O II lines in the O9.7 supergiant, for which it is also foundto be somewhat depleted. Unfortunately, He/H is very difficult todetermine in individual O supergiants because of uncertainties inmicroturbulence and the atmospheric scale height. The effect of windclumping is also investigated, for which P V λλ1118-1128potentially provides a useful diagnostic in O star winds, unlessphosphorus can be independently demonstrated to be underabundantrelative to other heavy elements. Revised stellar properties affectexisting calibrations of (1) Lyman continuum photons-a factor of 2 lowerfor the O4 supergiant-and (2) kinetic energy released into the ISM by Osupergiants. Our results also have importance for the calibration of thewind momentum-luminosity relationship for OB stars, particularly sincethe stars studied here are among the visually brightest OB stars inexternal galaxies. Based on observations made with the NASA-CNES-CSA FarUltraviolet Spectroscopic Explorer. FUSE is operated for NASA by JohnsHopkins University under NASA contract NAS 5-32985. Also based in parton observations collected at the European Southern Observatory VeryLarge Telescopes in programs 65.H-0705 and 67.D-0238, plus archival dataobtained with the NASA-ESA Hubble Space Telescope and NASA-ESA-PPARCInternational Ultraviolet Explorer.
| 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
| The Ionization in the Winds of O Stars and the Determination of Mass-Loss Rates from Ultraviolet Lines
Empirical ionization fractions of C IV, N V, Si IV, and empiricalionization plus excitation fractions of C III* and N iv^* in the windsof 34 O stars and one B star have been derived. We combine the mass-lossrates derived from radio measurements and Hα with the line fittingof ultraviolet resonance lines and subordinate lines using the Sobolevplus exact integration (SEI) method. The dependence of the empiricalionization fractions, q, on the stellar effective temperature and on themean wind density is discussed. This sets constraints for the models ofionization in the winds of hot stars. The ionization and excitationfractions can be expressed in terms of an empirical radiationtemperature. This radiation temperature scales with T_eff, and we deriveempirical relations for T_rad as a function of T_eff. The radiationtemperatures are on the order of 0.5-0.9 T_eff, with significantdifferences between the ions. The derived relations between theionization fractions and the stellar parameters have an uncertainty of0.2 dex forSi IV, N V, and C iii^*, and about 0.26 dex for N iv^*. For CIV, we can only derive an expression for the mean ionization fraction inthe wind if the mass-loss rate is small, M<10^-6 M_solar yr^-1,because the C IV lines are usually saturated for higher mass-loss rates.The resulting expressions for T_rad can be used to derive the mass-lossrates from studies of ultraviolet P Cygni profiles in the range ofstellar parameters studied here: 30,000 K<~T_eff<~50,500 K,5.2<~logL/L_*<~6.4, and -7.5 M_solar<~logM<~-4.6 M_solaryr^-1. An accuracy of about a factor of 2 or better can be reached,depending on the lines that are used and the accuracy of the line fitsand the stellar parameters. The Si IV lines give the most reliablemass-loss rates, because the abundance is about the same for all Ostars, the lines saturate only for high mass-loss rates, the doubletlines only partly overlap, and the mass-loss rate is proportional to thesquare root of the column density. The radiation temperature of N Vshows a surprisingly strict relation with T_eff, with a scatter of onlyDeltaT_rad/T_eff=0.01. The mass-loss rate cannot be derived from the N Vlines, because the column density of the N V ions in the wind isindependent of M. A consistency check and a test of the method for thestars HD 14749 and HD 190429 show that the mass-loss rate derived fromthe UV lines with the ionization fractions of this paper agree very wellwith the mass-loss rate derived from new radio flux measurements.
| 1-m spectroscopy of normal OB stars
We have obtained spectra of 70 normal OB stars in the near-IR I(1-μm) band. The strongest features are those due to lines of thehydrogen Paschen series and neutral and ionized helium, which are, forthe most part, in absorption. The information content in this spectralrange is sufficient for only a rough classification of hot stars into`early O', `late O' and `B' types. Curiously, the leading He i tripletline, He i λ1.0830 μm, is usually not detectable, although ina few stars it is in emission; its behaviour generally correlates withthe leading helium singlet line, He i λ 2.058 μ m. These twofeatures appear to be present in emission only in stars with extremes ofmass loss or wind extension.
| Near-Infrared H-Band Features in Late O and B Stars
We examine the spectral characteristics of normal OB stars withhigh-signal-to-noise ratio (>120) H-band (1.6 μm) spectra at aresolution of 2000. We find that several atomic lines vary smoothly withstellar temperature, as first shown by Blum et al. However, we find apreviously unreported, significant variation in the strength of some ofthese lines with stellar luminosity. B supergiant stars show stronger Hei and weaker Br 11 as compared with low-luminosity B dwarf stars of thesame spectral class. It is for this reason that luminosity class mustalso be determined to obtain an accurate spectral type for a given starusing H-band spectra. We suggest a method for estimating the spectraltype and luminosity of an OB star over the wavelength range from 1.66 to1.72 μm using hydrogen Br 11 at 1.681 mum, He i at 1.700 mum, and Heii at 1.693 mum. The use of the near-infrared spectral range forclassification has obvious advantages over optical classification whenapplied to heavily reddened stars, such as in star-forming regions ordeeply embedded lines of sight within the plane of the Galaxy, such asthe Galactic center. Furthermore, the H band is less likely to becontaminated by infrared excess emission, which is frequently seenaround massive young stellar objects beyond 2 mum.
| Line profile variability in the spectrum of the O(f) supergiant HD 192639
We report the results of a medium-resolution spectroscopic investigationof the O(f) supergiant HD 192639. Particular attention is paid to the He{ii}\ lambda 4686 line. This line displays strong profile variability ontime scales of a few days, changing from a P-Cygni profile with adouble-peaked emission component to a pure blue-shifted emission line.It appears that the variability of most of the absorption lines presentin our spectra is correlated to the deformation of the He {ii}\ lambda4686 line and arises probably from a large scale structure in thelow-velocity part of the stellar wind rather than from a photosphericphenomenon. We find that the time scale of the variability could beconsistent with the estimated rotational period of HD 192639. Based onobservations collected at the Observatoire de Haute Provence, France.
| 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.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Dust shells around certain early-type stars with emission lines.
Not Available
| On the wind momentum problem of O-type stars in the galaxy
We have examined the wind momentum problem of O-type stars in theGalaxy. It is shown that the discrepancy between theoretical andempirical mass loss rates and terminal velocities can be reversed byusing recently updated values of force multiplier parameters. With thesenew values, the momentum problem found by former investigators isreversed so that there now appears to be more than enough radiationforce in order to accelerate the stellar winds of a sample of GalacticO-type stars.
| A Survey for H alpha Emission in Massive Binaries: The Search for Colliding Wind Candidates
I report the results of the first all-sky survey of H alpha emission inthe spectra of O-type binaries. The survey includes 26 systems, of which10 have emission that extends clearly above the continuum. This is thefirst report of emission for four of these. An additional three systemsshow small distortions in the H alpha profile that may result from weakemission. I compare the distribution of emission systems in H-R diagramsfor both binary and single stars, using a survey of single O-type starsdone by Conti (1974). Emission in main-sequence systems is extremelyrare and is completely absent in my sample of binary stars. Among binarystars, 78% of the systems containing giants show some emission, while nosingle giants in Conti's sample do. In the case of supergiants, 78% ofsingle stars show emission, while all supergiant binaries show strongemission. H alpha emission may come from a variety sources, but the factthat binaries have a higher incidence and strength of emission inpost--main-sequence stages may indicate that wind interactions are acommon source of emission in massive binaries. To ascertain whether ornot colliding winds have been observed, it will be necessary to studythe H alpha line profile throughout several orbits of each candidatecolliding wind system and look for recurring orbital-phase--relatedvariations. Such a study is underway.
| 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.
| A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
| Projected Rotational Velocities of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..737P&db_key=AST
| The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...460..914V&db_key=AST
| Two-dimensional Ultraviolet Spectral Typing of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...460..906P&db_key=AST
| A New Puzzle Regarding the Diffuse Interstellar Bands
In the case of 5 O stars out of 14, the average difference between theline-of-sight velocity component shown by the diffuse interstellar bands(DIBs) and that shown by the interstellar Na I lines exceeds the range+- 10 km s ^-1. For 9 O stars this difference lies in the range +- 6 kms^-1. What does this mean? Because the typical standard deviation ofv_DIB from three DIBs is 3.8 +- 1.2 km s^-1 while that of v_NaI from twointerstellar lines is 1.8 +- 1.3 km s^-1, the larger values of v_DIB -v_NaI are meaningful. They imply that the grains or molecules carryingthe DIBs move with the interstellar Na atoms along the lines of sight toonly some O stars. (SECTION: Interstellar Medium and Nebulae)
| O-star mass-loss and wind momentum rates in the Galaxy and the Magellanic Clouds Observations and theoretical predictions.
A new, very fast approximate method is presented to determine mass-lossrates of O-stars from Halpha_ line profiles. The method usesH and HeII departure coefficients from unified model atmospheresparametrized in a simple way as function of wind velocity together withphotospheric NLTE line profiles as the inner boundary condition for anumerically exact radiative transfer solution to derive a windcontaminated Halpha_-profile. The method is also applied toHgamma_ to determine stellar gravities corrected for windemission. A detailed analytical discussion of Halpha_ lineformation in O-star winds is given and it is demonstrated that formervery simple approaches considering only optically thin wind emissionlead to significant systematic errors. Scaling relations and generalizedcurves of growth are presented that connect mass-loss rate, terminalvelocity, stellar parameters and Halpha_ equivalent width.The method is applied to samples of O-stars in the Galaxy, LMC and SMCand mass-loss rates are derived from Halpha_ in combinationwith terminal velocities measured from IUE and HST spectra. The resultsreveal that a tight empirical relation exists between the radiusmodified stellar wind momentum rate˙(M)vinfinity_R_*_^0.5^ and the stellar luminosity. Thevariations of this relationship between the Galaxy, LMC and SMC areexplained in terms of different abundances. Furthermore, for almost allobjects with dense winds (mostly supergiants), the commonly usedvelocity field exponent β could be derived, indicating a typicalvalue of β=~1. A comparison with the improved theory of radiationdriven winds (as presented recently by Pauldrach et al. 1994) shows thatthe observed wind momentum-luminosity relationship can be understoodqualitatively in terms of the theory. However, there exist significantsystematic discrepancies as a function of effective temperature,luminosity class and wind performance numberη=˙(M)vinfinity_c/L. We stress that thesediscrepancies would not have been detected with previous simplifiedHalpha_ -approaches. The deficiencies of the theory arediscussed and suggestions for future improvements are made.
| 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.
| A Study of the Spectra of Seven Of Stars. II. Line Profiles and Equivalent Widths
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..461U&db_key=AST
| A Study of the Spectra of Seven Of Stars. I. Radial Velocities
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..433U&db_key=AST
| Evaluation of a 512X512-Element Platinum Silicide Schottky-Barrier Infrared Image Sensor and Pilot Observations of Cygnus X Region
We present evaluation of the performance of Mitsubishi's 512X512 elementplatinum silicide (PtSi) Schottky-Barrier infrared image sensor forapplication to astronomical observation. An infrared camera system,incorporating the PtSi array, was built and its performance wasevaluated both in the laboratory and in observations. Dark current, DCstability, noise, quantum efficiency (QE), linearity, and uniformitywere measured. Results of a series of measurements show that the arrayhas potential capability for astronomical use. Several problems such aslow QE and "splashes" are discussed. To demonstrate the effectiveness ofthe array by using this infrared camera, we have mapped an area of 8X9square degrees of the Cygnus X region with a small telescope consistingof a silicon singlet lens. More than 1000 stars brighter than 6.5 mag inH-band were detected in the region. (SECTION: AstronomicalInstrumentation)
| The supershell around CYG OB1 and OB3 : the velocity field in the vicinity of the star BD +37 3927 (Of).
Not Available
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הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 20h19m08.50s |
| סירוב: | +39°16'24.2" |
| גודל גלוי: | 7.431 |
| מרחק: | 2439.024 פארסק |
| תנועה נכונה: | -4.1 |
| תנועה נכונה: | -5.6 |
| B-T magnitude: | 7.888 |
| V-T magnitude: | 7.469 |
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