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A ``Missing'' Supernova Remnant Revealed by the 21 cm Line of Atomic Hydrogen
Although some 20,000-30,000 supernova remnants (SNRs) are expected toexist in the Milky Way, only about 230 are currently known. This impliesthat most SNRs are ``missing.'' Recently, we proposed that small(<~1°), faint, high-velocity features seen in large-scale 21 cmline surveys of atomic hydrogen (H I) in the Galactic plane could beexamples of such missing old SNRs. Here we report on high-resolution H Iobservations of one such candidate, FVW 190.2+1.1, which is revealed tobe a rapidly expanding (~80 km s-1) shell. The parameters ofthis shell seem only consistent with FVW 190.2+1.1 being the remnant ofa SN explosion that occurred in the outermost fringes of the Galaxy some~3×105 yr ago. This shell is not seen in any other waveband, suggesting that it represents the oldest type of SNR, that whichis essentially invisible except via its H I line emission. FVW 190.2+1.1is one of a hundred ``forbidden-velocity wings'' (FVWs) recentlyidentified in the Galactic plane, and our discovery suggests that manyof these are likely to be among the oldest SNRs. We discuss the possiblelink between FVWs and fast-moving atomic clouds in the Galaxy.
| 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.
| Distribution of early type stars and dusty matter in the direction of the star cluster NGC 2175
The distribution of 120 O-B9-A2 stars and of the interstellar dust inthe direction of the star clusters NGC 2175 and NGC 2175s (the complexS252) is studied in terms of V, (B-V), and (U-B) data. Ten star groups(associations) are found at distances of 410, 720, 1000, 1500, 2200,3100, 4000, 5200, 7000, and 8100 pc. Three of these, at distances of410, 720, and 1000 pc, are type B associations. The remaining seven areOB associations. They are designated as Gem B 0.41, Gem B 0.72, Gem B1.0, Gem OB 1.5, Gem OB 2.2, Gem OB 3.1, Gem OB 4.0, Gem OB 5.2, Gem OB7.0, and Gem OB 8.1. The V absorption (AV) for stars No.2, 18, 20, 23,24, 26, 40, 41, 47, 69, 87, 88, 90, 95, 100 and 109 is estimated to be2m.78,4m.72, 2m.69, 3m.33, 2m.61, 2m.86, 4m.67, 6m.21, 3m.14, 3m.92,2m.69, 3m.04, 5m.95, 5m.95, 3m.20 and 5m.66, respectively. For most ofthese stars the absorption lies between 0m.5 and 2m.5. This largeabsorption may be caused by circumstellar absorption. The dust in theassociations Gem B 0.41 and Gem B 0.72 is distributed nonuniformly.There is no dust in the space between the associations. Essentiallythere is no dust inside those groups (associations) which lie atdistances greater than 1 kpc.
| O stars with weak winds: the Galactic case
We study the stellar and wind properties of a sample of Galactic Odwarfs to track the conditions under which weak winds (i.e. mass lossrates lower than 10-8 Mȯ yr-1)appear. The sample is composed of low and high luminosity dwarfsincluding Vz stars and stars known to display qualitatively weak winds.Atmosphere models including non-LTE treatment, spherical expansion andline blanketing are computed with the code CMFGEN (Hillier & Miller1998, ApJ, 496, 407). Both UV and Hα lines are used to derive windproperties while optical H and He lines give the stellar parameters. Wefind that the stars of our sample are usually 1 to 4 Myr old. Mass lossrates of all stars are found to be lower than expected from thehydrodynamical predictions of Vink et al. (2001, A&A, 369, 574). Forstars with log {L}/{Lȯ} 5.2, the reduction is byless than a factor 5 and is mainly due to the inclusion of clumping inthe models. For stars with log {L}/{Lȯ} 5.2 thereduction can be as high as a factor 100. The inclusion of X-rayemission (possibly due to magnetic mechanisms) in models with lowdensity is crucial to derive accurate mass loss rates from UV lines,while it is found to be unimportant for high density winds. The modifiedwind momentum - luminosity relation shows a significant change of slopearound this transition luminosity. Terminal velocities of low luminositystars are also found to be low. Both mass loss rates and terminalvelocities of low L stars are consistent with a reduced line forceparameter α. However, the physical reason for such a reduction isstill not clear although the finding of weak winds in Galactic starsexcludes the role of a reduced metallicity. There may be a link betweenan early evolutionary state and a weak wind, but this has to beconfirmed by further studies of Vz stars. X-rays, through the change inthe ionisation structure they imply, may be at the origin of a reductionof the radiative acceleration, leading to lower mass loss rates. Abetter understanding of the origin of X-rays is of crucial importancefor the study of the physics of weak winds.
| 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.
| 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.
| 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.
| 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.
| 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
| Measurements of [O I] λ6300/Hα Line Intensity Ratios for Four O Star H II Regions
We have used the Wisconsin Hα Mapper facility to measure the [O I]λ6300/Hα line intensity ratios for four O star H IIregions: S27 (observation coordinates l=6.3d,b=+23.6d), S252(l=190.1d,b=+0.6d), S261 (l=194.1d,b=-1.9d), and S264(l=195.1d,b=-12.0d). We find that the ratios range from 0.0015 to0.0053. These results are roughly a factor of 10 lower than measured [OI]/Hα ratios in directions that sample the warm ionized componentof the interstellar medium. This difference implies a significantlylower hydrogen ionization ratio n(H+)/n(H0) orhigher electron temperature in the diffuse ionized gas compared withthat in the bright discrete O star H II regions.
| NICS-TNG infrared spectroscopy of NGC 1068: The first extragalactic measurement of [P II] and a new tool to constrain the origin of [Fe II] line emission in galaxies
We report 0.9-1.4 mu m spectroscopic observations of NGC 1068 collectedduring the commissioning phase of the near infrared camera spectrometer(NICS) of the Telescopio Nazionale Galileo (TNG). These yielded thefirst extragalactic measurement of [P II] (1.188 mu m) line emission. Inthe central 0.75arcsecx2 arcsec the [Fe II]/[P II] line-intensity ratiois close to unity, similar to that measured in the Orion bar and afactor of la 20 smaller than in supernova remnants. This indicates thatmost of iron is locked into grains and, therefore, argues against shockexcitation being the primary origin of [Fe II] line emission in thecentral regions of NGC 1068. We propose the [Fe II]/[P II] ratio as asimple and effective tool to study and perhaps resolve the long debatedquestions related to the origin of [Fe II] line emission and, moregenerally, to constrain the role of shock excitation in active galaxies.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Observations of methanol masers in star-forming regions
We present VLBI observations of 6.7 and 12.2 GHz methanol masers inthree star-forming regions, NGC7538, W75N and S252. Our results reveallinear structures in the VLBI maps and monotonic velocity gradients inthe three sources. All these results are consistent with Keplerian disksof diameter of /~1000-2000 AU around young stars of mass /~(10-30)Msolar.
| 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.
| 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 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.
| Tomographic Separation of Composite Spectra. IV. The Physical Properties of the Massive Close Binary DH Cephei
We present the results of a Doppler tomographic reconstruction of the UVspectra of the double-lined, O binary DH Cephei based on observationsmade with the International Ultraviolet Explorer. We describecross-correlation methods we use to obtain precise radial velocities,and we present a radial velocity curve based on combined optical and UVmeasurements. We also show how we use fits of the cross-correlationfunctions to estimate the UV flux ratio and projected rotationalvelocities. The individual component spectra are classified as O6 V + O7V using UV criteria defined by Penny, Gies, & Bagnuolo. We place theindividual components in the theoretical Hertzsprung-Russell diagramusing the distance modulus and reddening estimated for its home cluster,NGC 7380, and we find that the stars are larger than estimates fromprior studies of the "ellipsoidal" light variations. We reconsider theellipsoidal light curve and show that there is a range in acceptablestellar radii (as a function of orbital inclination). We discuss theconstraints on inclination and system masses based on cluster distancemodulus, presumed synchronous rotation, and on consistency with massesderived from evolutionary tracks (which involves the issue of thetemperature calibration of O stars). We find that primary and secondarymasses of 39--50 Mȯ and 35--45 Mȯ, respectively, satisfy allthe constraints from spectroscopy, photometry, distance modulus, andsingle-star evolutionary tracks.
| 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
| 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
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| Metal line strengths of blue stragglers towards the young galactic association Perseus OB1.
We present equivalent width measurements of lines of HeI, CIII, NIII,OII, MgII and SiIV from high resolution optical spectra of eight bluestragglers towards the young galactic association Perseus OB1, togetherwith similar data from ultraviolet spectra. We have carried outintercomparisons of the observed line strengths between target stars ofsimilar effective temperatures, and comparisons between the target starsand data for other O-type stars, in order to search for possibleabundance anomalies in our target stars. We find firm evidence that twostars, HD 12323 and HD 13268, exhibit CNO bicycle processed material attheir surfaces, and we outline evolutionary scenarios to explain thisphenomenon. One further star, HD 12993, also shows marginal evidence forprocessed material at its surface. There is no evidence for abundanceanomalies in the five remaining stars, and we consider that they may notbe association members. Hence their identification as blue stragglers isin doubt.
| Terminal Velocities and the Bistability of Stellar Winds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..269L&db_key=AST
| Anatomy of the Gemini OB1 molecular cloud complex
We have investigated the large-scale morphology and properties of themolecular gas in the Gem OB1 cloud complex by mapping over 32 sq deg(177 pc x 221 pc) of the complex in (12)CO(J = 1-0) and (13)CO(J = 1-0)at 50 arcsec sampling with QUARRY on the FCRAO 14 m telescope. The moststriking characteristic of the molecular line images are the series ofarc- and ring-shaped structures found on spatial scales from a fewparsecs in diameter up to at least 35 pc. The morphology and in someinstances the kinematics suggest that these features represent swept-upmolecular material, most likely from expanding H II regions and windblown bubbles. The kinetic temperatures and column densities of themolecular gas were derived from the (12)CO and (13)CO data using theLocal Thermodynamic Equilibrium (LTE) analysis. Most of the moleculargas was found to have kinetic temperatures of less than or approximatelyequal to 10 K, and 50% of the mass of gas is contained in lines of sightwith H2 column densities less than or approximately equal to 2 x1021/sq cm. It was found that only 10% of the molecular massis contained in lines of sight with column densities in excess of1022/sq cm, and that these regions are found almostexclusively near the massive star forming regions within the arcs andrings of molecular gas. The average H2 densities in areas with (13)COemission are between 65-120/cu cm, consistent with previous studies ofcloud complexes, and is independent of whether the regions containsmassive star formation or not. For the Gem OB1 complex as a whole, theaverage H 2 density is 1.2/cu cm, which is only a few time the averageatomic hydrogen density in the interstellar medium. We suggest anoverall picture for the Gem OB1 complex in which most of the moleculargas is contained in relatively cold, low column density molecularmaterial. The high column density regions in the Gem OB1 complex formthrough the external compression of the molecular gas by the winds and HII regions from newly formed massive stars. Thus once massive starrformation is initiated, the structure and further evolution of the cloudcomplex is largely a result of the interactions of expanding H IIregions and stellar winds with the ambient molecular material.
| A search for the He I lambda 5876 recombination line from the diffuse interstellar medium
The He I lambda 5876/hydrogen alpha line intensity ratio in the warmionized component of the interstellar medium is significantly less thanthat observed in traditional H II regions surrounding O stars. Theobservations, carried out in two directions at low Galactic latitude,reveal that the helium is primarily neutral, n(HeII)/n(Hetotal approximately less than 0.27, within warm,low-density regions in which the hydrogen is primarily ionized. Thisimplies that the spectrum of the diffuse interstellar radiation fieldthat ionizes the hydrogen is softer than that from the Galactic O starpopulation in the solar neighborhood. Specifically, the ratio of heliumionizing to hydrogen ionizing photons Q(He0)/Q(H0)approximately less than 0.030, which corresponds to a spectral type ofO8 or later and, if representative of the interstellar background,challenges the O star ionization models.
| 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.
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| UBVRI photometry and polarimetry of the stars in S252 (NGC 2175). II. Interpretation.
Photoelectric UBVRI photometry and polarimetry and photographic UBVRphotometry have been used to study the stellar cluster NGC2175associated with the Hii region-molecular cloud complex Sharpless252. Thecolour excess E_B-V_ of stars in NGC2175 ranges from the foregroundcolour excess of 0.4mag up to 1.7mag. The distance modulus of S252obtained by fitting ZAMS to the colour-magnitude diagrams of NGC2175 is11.7+/-0.3mag (2.2+/-0.3kpc). The lower part of the colour-magnitudediagrams of the main cluster contains stars still contracting towardsZAMS indicating an age of the order of one million years for thecluster. The age of a small subcluster to the east of the Hii region isa few million years. High stellar polarizations up to 12% have beenobserved. The average wavelength of the maximum polarization in S252 is0.53+/-0.01μm and the polarization efficiency is near the empiricalmaximum value 3A_v_. The polarization field in S252 is regular butcannot be explained by a single magnetic field direction.
| An atlas of ultraviolet P Cygni profiles
We have selected spectra of 232 stars from the International UltravioletExplorer (IUE) archives for inclusion in an atlas intended for varioususes but tailored especially for the study of stellar winds. The atlascovers the range in spectral types from O3 to F8. The full atlas coversthe reduced and normalized high resolution spectra from the IUE long-and short-wavelength spectrographs. Here we discuss the selection of thestars and the data reduction, and we present in velocity units theprofiles of lines formed in the stellar winds. The selected lines covera wide range of ionizations, allowing a comparison of the profiles fromdifferent ions in the wind of each star and a comparison of thedifferent wind lines as a function spectral type and luminosity. We alsopresent the basic data on the program stars to facilitate study of thedependence of wind features on stellar parameters such as luminosity,temperature, escape velocity, and v sin i. We provide an overview of thecharacteristic behavior of the wind lines in the H-R diagram. Thecomplete spectra are available in digital form through the NASAAstrophysics Data System (ADS). We offer a description of the electronicdatabase that is available through the ADS and guidelines for obtainingaccess to that database.
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| קבוצת-כוכבים: | אוריון |
| התרוממות ימנית: | 06h09m39.57s |
| סירוב: | +20°29'15.5" |
| גודל גלוי: | 7.552 |
| מרחק: | 420.168 פארסק |
| תנועה נכונה: | 0.6 |
| תנועה נכונה: | -1.9 |
| B-T magnitude: | 7.581 |
| V-T magnitude: | 7.555 |
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