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The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
We present interstellar elemental abundance measurements derived fromSpace Telescope Imaging Spectrograph echelle observations of 47 sightlines extending up to 6.5 kpc through the Galactic disk. These pathsprobe a variety of interstellar environments, covering ranges of nearly4 orders of magnitude in molecular hydrogen fraction f(H2)and more than 2 in mean hydrogen sight-line density. Coupling the current data with Goddard HighResolution Spectrograph data from 17 additional sight lines and thecorresponding Far Ultraviolet Spectroscopic Explorer and Copernicusobservations of H2 absorption features, we explore magnesium,phosphorus, manganese, nickel, copper, and germanium gas-phase abundancevariations as a function of : density-dependentdepletion is noted for each element, consistent with a smooth transitionbetween two abundance plateaus identified with warm and cold neutralinterstellar medium depletion levels. The observed scatter with respectto an analytic description of these transitions implies that totalelemental abundances are homogeneous on length scales of hundreds ofparsecs, to the limits of abundance measurement uncertainty. Theprobable upper limit we determine for intrinsic variability at any is 0.04 dex, aside from an apparent 0.10 dexdeficit in copper (and oxygen) abundances within 800 pc of the Sun.Magnesium dust abundances are shown to scale with the amount of siliconin dust, and in combination with a similar relationship between iron andsilicon, these data appear to favor the young F and G star values ofSofia & Meyer as an elemental abundance standard for the Galaxy.Based on observations with the NASA/ESA.
| Effects of Metallicity on the Rotational Velocities of Massive Stars
Recent theoretical predictions for low-metallicity massive stars predictthat these stars should have drastically reduced equatorial winds (massloss) while on the main sequence, and so should retain most of theirangular momentum. Observations of both the Be/(B+Be) ratio and theblue-to-red supergiant ratio appear to have a metallicity dependencethat may be caused by high rotational velocities. We have analyzed 39archival Hubble Space Telescope Imaging Spectrograph (STIS),high-resolution, ultraviolet spectra of O-type stars in the MagellanicClouds to determine their projected rotational velocities Vsini. Ourmethodology is based on a previous study of the projected rotationalvelocities of Galactic O-type stars using International UltravioletExplorer (IUE) short-wavelength prime (SWP) camera high-dispersionspectra, which resulted in a catalog of Vsini values for 177 O-typestars. Here we present complementary Vsini values for 21 LargeMagellanic Cloud and 22 Small Magellanic Cloud O-type stars based onSTIS and IUE UV spectroscopy. The distribution of Vsini values forO-type stars in the Magellanic Clouds is compared to that of GalacticO-type stars. Despite the theoretical predictions and indirectobservational evidence for high rotation, the O-type stars in theMagellanic Clouds do not appear to rotate faster than their Galacticcounterparts.
| Line profile variability in the spectra of Oef stars. II. HD 192281, HD 14442 and HD 14434
We present the very first analysis of the spectroscopic variability ofthe three rapidly rotating Oef stars HD 192281 (O5(ef)), HD 14442(O5.5ef) and HD 14434 (O6.5(ef)). Radial velocities of the He IIλ 4541 line reveal no evidence of binarity on time scales of afew days, or from one year to the next, for any of the targets. The HeII λ 4686 double-peaked emission and, to some extent, the Hβabsorption line display significant profile variability in the spectraof all three stars. Data gathered during different observing runs spreadover six years reveal a rather stable time scale for HD 192281 and HD14442, whereas the variability pattern changes significantly from oneyear to the other. The case of HD 14434 is less clear as no obvious timescale emerges from our analysis. In a tentative way to interpret thisvariability, stellar rotation remains a possible clock for HD 192281 andHD 14442. However, currently available models addressing stellarrotation fail to explain some crucial aspects of the observedvariability behaviour, which appear to be even more complex in the caseof HD 14434.Based on observations collected at the Observatoire de Haute-Provence,France.
| The Homogeneity of Interstellar Oxygen in the Galactic Disk
We present an analysis of high-resolution Hubble Space Telescope (HST)Space Telescope Imaging Spectrograph (STIS) observations of O Iλ1356 and H I Lyα absorption in 36 sight lines that probe avariety of Galactic disk environments and include paths that range overnearly 4 orders of magnitude in f(H2), over 2 orders ofmagnitude in , and that extend up to 6.5 kpc inlength. Since the majority of these sight lines have also been observedby the Far Ultraviolet Spectroscopic Explorer (FUSE), we have undertakenthe study of gas-phase O/H abundance ratio homogeneity using the currentsample and previously published Goddard High Resolution Spectrograph(GHRS) results. Two distinct trends are identified in the 56 sight linesample: an apparent decrease in gas-phase oxygen abundance withincreasing mean sight-line density () and a gapbetween the mean O/H ratio for sight lines shorter and longer than about800 pc. The first effect is a smooth transition between two depletionlevels associated with large mean density intervals; it is centered near=1.5cm-3 and is similar to trendsevident in gas-phase abundances of other elements. Paths less dense thanthe central value exhibit a mean O/H ratio of log10(O/H)=-3.41+/-0.01 (or 390+/-10ppm), which is consistent with averages determined for several longlow-density paths observed by STIS (André et al. 2003) and shortlow-density paths observed by FUSE (Moos et al. 2002). Sight lines ofhigher mean density exhibit an average O/H value of log10(O/H)=-3.55+/-0.02 (284+/-12ppm). The data points for low- paths are scatteredmore widely than those for denser sight lines, because O/H ratios forsuch paths shorter than 800 pc are generally about 0.10 dex lower thanthe values for longer ones. Scenarios that would be consistent withthese results include a recent infall of metal-poor gas onto the localGalactic disk and an interstellar environment toward Orion that isconducive to reducing the apparent gas-phase oxygen abundance.Based on observations with the NASA/ESA Hubble Space Telescope (HST) andthe NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE). HSTspectra were obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS5-26555 FUSE is operated for NASA by theJohns Hopkins University under NASA contract NAS5-32985.
| 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 Origin of the High-Ionization Intermediate-Velocity Gas toward HD 14434
We present Far-Ultraviolet Spectroscopic Explorer and Space TelescopeImaging Spectrograph observations of high-ionization interstellarabsorption toward HD 14434 (l=135.1d, b=-3.8d d~2.3 kpc), an O5.5 V starin the Perseus OB1 association. Intermediate-velocity interstellar Si IVand C IV absorption is present at VLSR=-67 km s-1,while low-ionization gas associated with the Perseus arm is detected atabout -50 km s-1. Neither N V nor O VI is detected atVLSR=-67 km s-1, although Al III and Fe III,tracers of warm ionized gas, are seen. The high-ion column densities inthe -67 km s-1 component are log[N(CIV)]=13.92+/-0.02cm-2, log[N(SiIV)]=13.34+/-0.02 cm-2,log[N(NV)]<=12.65 cm-2, and log[N(OVI)]<=13.73cm-2 (3 σ limits). The observed C IV/Si IV ratio of3.8+/-0.3 in this intermediate-velocity cloud (IVC) is similar to theGalactic average (4.3+/-1.9). Our analysis of the Si IV and C IV linewidths yields a temperature of T~10,450+/-3400 K for this component. Atthis low temperature, neither Si IV nor C IV can be produced viacollisions. We investigate several photoionization models to explain theintermediate-velocity Si IV and C IV absorption toward HD 14434.Photoionization models employing cooling of a hot (T~106 K)diffuse plasma as the source of ionizing radiation reproduce theobserved properties of the IVC toward HD 14434 quite well. The hotplasma responsible for the ionizing radiation in these models may beattributed to hot gas contained in a supershell in or near the Perseusarm or from a more generally distributed hot ionized medium.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the data archive at the Space Telescope Science Institute.STScI is operated by the Association of Universities for Research inAstronomy, Inc., under the NASA contract NAS 5-26555.
| A Method for Simultaneous Determination of AV and R and Applications
A method for the simultaneous determination of the interstellarextinction (AV) and of the ratio of total to selectiveextinction (R), derived from the 1989 Cardelli, Clayton, & Mathisfitting of the interstellar extinction law, is presented and applied toa set of 1900 color excesses derived from observations of stars inUBVRIJHKL. The method is used to study the stability of AVand R within selected regions in Perseus, Scorpius, Monoceros, Orion,Sagittarius, Ophiuchus, Carina, and Serpens. Analysis shows that R isapproximately constant and peculiar to each sector, with mean valuesthat vary from 3.2 in Perseus to 5.6 in Ophiuchus. These results aresimilar to published values by Aiello et al., He et al., Vrba &Rydgren, O'Donnell, and Cardelli, Clayton, & Mathis.
| Line profile variability in the spectra of Oef stars. I. BD + 60deg 2522
We report the analysis of a long term observing campaign designed tomonitor the spectroscopic variability of the Oef star BD+60deg 2522. We find that the double-peaked He {II} lambda4686 emission line undergoes strong profile variability on time scalesof 2-3 day. However, the time scale as well as the pattern of thesevariations turn out to be epoch dependent and the phenomenon is thusmost likely not ruled by a single stable clock. On the other hand, theabsorption lines in the spectrum of BD +60deg 2522 displayline profile variability on time scales of a few hours that might berelated to non-radial pulsations. We tentatively propose that thebeating of several non-radial pulsation modes triggers transientlarge-scale density perturbations in a confined stellar wind thatproduce the 2-3 day time scale variability.Based on observations collected at the Observatoire de Haute Provence,France.
| The Star Formation History and Mass Function of the Double Cluster h and χ Persei
The h and χ Per ``double cluster'' is examined using wide-field(0.98d×0.98d) CCD UBV imaging supplemented by optical spectra ofseveral hundred of the brightest stars. Restricting our analysis to nearthe cluster nuclei, we find identical reddenings [E(B-V)=0.56+/-0.01],distance moduli (11.85+/-0.05), and ages (12.8+/-1.0 Myr) for the twoclusters. In addition, we find an initial mass function slope for eachof the cluster nuclei that is quite normal for high-mass stars,Γ=-1.3+/-0.2, indistinguishable from a Salpeter value. We derivemasses of 3700 Msolar (h) and 2800 Msolar (χ)integrating the present-day mass function from 1 to 120Msolar. There is evidence of mild mass segregation within thecluster cores. Our data are consistent with the stars having formed at asingle epoch; claims to the contrary are very likely due to theinclusion of the substantial population of early-type stars located atsimilar distances in the Perseus spiral arm, in addition tocontamination by G and K giants at various distances. We discuss theuniqueness of the double cluster, citing other examples of suchstructures in the literature but concluding that the nearly identicalnature of the two cluster cores is unusual. We fail to settle thelong-standing controversy regarding whether or not the double cluster isthe core of the Per OB1 association and argue that this may beunanswerable with current techniques. We also emphasize the need forfurther work on the pre-main-sequence population of this nearby andhighly interesting region.
| On the Absolute Magnitudes of the O Stars
The conclusion published in 1992 by Garmany & Stencel from a studyof northern OB associations, that the absolute magnitudes of the O starsshow ``a large scatter ... intrinsic to the classification system,'' iscritically examined. It is found that the differences between theirderived absolute magnitudes of O stars and this author's 1973calibration exhibit large systematic effects in several associations,ranging from -0.74 to +1.02 mag with substantially smaller dispersions.Of course, when these results are combined, the scatter equals the fullrange of the systematic effects. To investigate the possibility ofdistance errors, the Garmany & Stencel B0-B2.5 stars in the sameassociations are subjected to the same analysis. The results for the Bstars show no significant systematic differences, eliminating errors inthe association distances derived by Garmany & Stencel from the Bstars as the source of the differences found for the O stars. It isnoteworthy that the dispersions in the absolute magnitudes of the Bstars within a given association are similar to or larger than those ofthe O stars. An examination of the distribution on the sky of the starsshows that the O and B stars in the discrepant associations aregenerally not colocated; such was already known to be the case for theimportant Perseus OB1 association. It is suggested that despite theirefforts to improve them, significant problems remain with theassociation memberships adopted by Garmany & Stencel; the relativelysmall dispersions of the O star absolute magnitudes even in thediscrepant cases indicate that they belong to different, usually moredistant associations near the lines of sight to the B associations withwhich they have been mistakenly connected. Several individual cases ofunrecognized multiple systems and classification errors are also foundin the Garmany & Stencel sample. It is concluded that the scatter inthe absolute magnitudes of the O stars is not as large as found byGarmany & Stencel, and not larger than that of the B stars.
| Cometary molecular clouds around RNO 6. On-going star formation near the double cluster h and chi Persei
We present molecular line observations of the star-forming cloud aroundRNO 6 along with a newly discovered nearby molecular cloud that we nameRNO 6 NW. Both clouds display striking similarities in their cometarystructures and overall kinematics. By using 13CO lineobservations, we estimate that these clouds have similar sizes ( ~ 4.5pc) and masses ( ~ 200 Msun). Both molecular clouds RNO 6 andRNO 6 NW are active in star formation. From new high resolution near-IRnarrowband images, we confirm that RNO 6 hosts an embedded IR clusterthat includes a Herbig Be star. A conspicuous H_2 filament is found todelineate the dense cometary head of the globule. RNO 6 NW hosts atleast two IR sources and a bipolar molecular outflow of ~ 0.9 pc oflength and ~ 0.5 Msun of mass. We show that the cometarystructure of both clouds has been created by the UV radiation fromnumerous OB stars lying ~ 1.5{o} to the north. Such OB starsare associated with the double cluster h and chi Persei, and areprobably members of the Per OB1 association. Thus star formation insidethese clouds has been very likely triggered by the Radiation DrivenImplosion (RDI) mechanism. From comparison to RDI theoretical models, wefind that the similar kinematics and morphology of both clouds is wellexplained if they are at a re-expansion phase. Triggered sequential starformation also explains the observed spatial distribution of the membersof the near-IR cluster inside the RNO 6 cloud, and the morphology of theH_2 filament. We conclude that the RNO 6 and RNO 6 NW clouds arehigh-mass counterparts to the cometary globules of smaller masses whichhave been studied up to now. Thus our observations demonstrate that theRDI mechanism can produce, not only low mass stars in small globules,but also intermediate mass stars and clusters in massive clouds.
| UBVI and Hα Photometry of the h and χ Persei Cluster
UBVI and Hα photometry is presented for 17319 stars in vicinity ofthe young double cluster h and χ Persei. Our photometry extends overa 37'×1deg field centered on theassociation. We construct reddening contours within the imaged field. Wefind that the two clusters share a common distance modulus of11.75+/-0.05 and ages of logage(yr)=7.1+/-0.1. From the V-Hαcolor, a measure of the Hα emission strength, we conduct a surveyfor emission line objects within the association. We detect a sample of33 Be stars, eight of which are new detections. We present a scenario ofevolutionary enhancement of the Be phenomenon to account for the peak inBe fraction toward the top of the main sequence in the population of hand χ Persei and similar young clusters.
| 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
| A Search for Interstellar Bubbles surrounding Massive Stars in Perseus OB1
We have examined the interstellar medium in the vicinity of massivestars belonging to the Per OB1 association based on neutral hydrogen 21cm observations obtained with the 100 m radio telescope at Effelsberg(HPBW=8.4′) and complementary data from the Leiden-Dwingeloo H ISurvey (HPBW=36'). The higher angular resolution H I observationsallowed us to discover probable wind-blown bubbles related to fourmassive stars in the association, namely, HD 14442 [O5n(f)p], HD 14947[O5If+], HD 13022 [O9.5II-III((n))], and HD 13338 [O9.5V], while thedetection of a wind-blown bubble associated with HD 16691 [O5If+] isless conclusive. A clear H I shell coincident in position with two B1IIIstars (HD 15233 and Hilt 311) was also detected. Some of these featuresalso have infrared and/or molecular counterparts. The energetics of thestructures related to each massive star is analyzed. The new H Iinterstellar bubbles appear to be similar to the ones found surroundingWolf-Rayet stars and other Of stars. The large-scale maps obtained usingthe lower angular resolution H I data show that most of the early-typestars belonging to Per OB1 are placed in a region of low H I emission.The association could have blown a H I shell of about 350×550 pcin size. This large H I shell has an infrared counterpart.
| 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
| On the Correlation between CO Absorption and Far-Ultraviolet Nonlinear Extinction toward Galactic OB Stars
A sample of 59 sight lines to reddened Galactic OB stars was examinedfor correlations of the strength of the CO Fourth Positive(A1Π-X1Σ+) absorption bandsystem with the ultraviolet interstellar extinction curve parameters. Weused archival high-dispersion NEWSIPS IUE spectra to measure the COabsorption for comparison with parametric fits of the extinction curvesfrom the literature. A strong correlation with the nonlinear far-UVcurvature term was found with greater absorption, normalized to E(B-V),being associated with more curvature. A weaker trend with the linearextinction term was also found. Mechanisms for enhancing CO in dustenvironments exhibiting high nonlinear curvature are discussed.
| Settling onto the Main Sequence: ROSAT Observations of H and χ Persei
We have studied X-rays from the double cluster h and χ Per with an11 ks ROSAT position-sensitive proportional counter (PSPC) observation.Emission is concentrated toward the two cluster centers. Whether theemission is diffuse emission or from a population of unresolved faintsources is uncertain because the resolution is poor at the distance ofthe clusters (2.4 kpc). Twenty-three sources were found with an X-rayluminosity of logL=31.5 ergs s-1 or greater. These sourceswere found in the cluster nuclei, between the clusters, and in a haloaround the cluster pair. The ROSAT PSPC error circle is too large forthe identification of X-ray sources with individual optical objects.However, because of a lack of correlation between X-ray sources and Bstars, we conclude that the X-rays are produced by late spectral typepre-main-sequence stars. The X-ray sources are brighter than all but thevery brightest sources in the younger Orion Nebula cluster, which makesthem important in tracing the final stages approaching the mainsequence. Based on observations made with the ROSAT satellite.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| 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.
| On the normal energy distribution in stellar spectra: O5-O8 stars
The spectral energy curves for a number of O4-O8 stars are analyzedusing measurements taken from six sources of spectrophotometric data.Based on the normal UBV color indices for O stars, these stars aredivided into three groups (O5, O6-O7, and O8), for each of which thenormal energy distribution is derived and presented. Comparison of thesedistributions indicates clear differences between the O5 and O8subclasses at UV wavelengths. A single normal distribution curve is,therefore, insufficient to characterize the O spectral class as a whole.
| A Lower Limit to the Distance of High-Velocity Cloud Complex H
We derive a lower limit for the distance of the high-velocity cloud(HVC) complex H, which is a structure covering 480 square degrees on thesky and is centered on l = 131 deg, b = 1 deg. Considering theuncertainties in the derivation of stellar distances, we find that thedistance to the HVC is certainly larger than 3.4 kpc, probably largerthan 5 kpc, and possibly larger than 6.5 kpc. This distance limit isbased on the result that we do not find absorption associated with theHVC in IUE spectra of 17 OB stars. The three most distant of these starswere observed by us; we used the IUE archives to analyze the spectra ofthe other 14 stars. We do not have conclusive evidence that heavyelements are present in this HVC. This would require a detection ofabsorption in the spectrum of an extragalactic background source.However, the nondetections can still be considered secure, as the columndensity detection limits for the Mg II lambda lambda 2796, 2802, C IIlambda 1334, and O I lambda 1302 lines are a factor of 30-4100 below thecolumn density values expected for normal interstellar medium gas phaseabundances. Our lower limit to the distance is used to discuss possibleorigins of HVC complex H. It seems unlikely that it is associated with asuperbubble at large Galactocentric radii, an infalling dwarf galaxy, orthe outer arm. It might be an unusual Galactic fountain cloud or anintergalactic cloud.
| Dust shells around certain early-type stars with emission lines.
Not Available
| UV Spectral Classification of O and B Stars in the Small Magellanic =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1951N&db_key=AST
| 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.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| Be stars in open clusters I. uvbyβ photometry.
We present uvbyβ photometry for Be stars in eight open clusters andtwo OB associations. It is shown that Be stars occupy anomalouspositions in the photometric diagrams, which can be explained in termsof the circumstellar continuum radiation contribution to the photometricindices. In the (b-y)_0_-M_V_ plane Be stars appear redder than the nonemission B stars, due to the additional reddening caused by the hydrogenfree-bound and free-free recombination in the circumstellar envelope. Inthe c_0_-M_V_ plane the earlier Be stars present lower c_0_ values thanabsorption-line B stars, which is caused by emission in the Balmerdiscontinuity, while the later Be stars deviate towards higher c_0_values, indicating absorption in the Balmer discontinuity ofcircumstellar origin.
| 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
| 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.
| 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.
| Blue stragglers in the young galactic association Perseus OB1.
Moderate spectral resolution, very high signal-to-noise optical spectrahave been obtained for eight blue stragglers towards the youngassociation Per OB1. These have been used to estimate projectedrotational and radial velocities. The line profiles of hydrogen andneutral and ionized helium have been analysed using non-LTE modelatmosphere calculations to deduce effective temperatures and logarithmicsurface gravities. Helium abundances have also been derived, althoughfor some targets this quantity was not well constrained. In addition,stellar radii, luminosities, and masses have been estimated both byspectroscopic methods and by comparison with evolutionary tracks. Thespectroscopic estimates were based on absolute magnitudes deduced fromeither assuming a unique distance modulus, or from a spectraltype-absolute magnitude calibration; the latter leads to a range ofdistance moduli of 1.4 magnitudes. Both sets of spectroscopic masseswere systematically smaller than the evolutionary masses, butluminosities deduced from spectral types gave a smaller and lessscattered set of mass discrepancies. None of these stars is definitelygenerically related to Per OB1 and they may therefore represent a moreheterogeneous group than has previously been thought, containingpossibly one helium and nitrogen enriched spectroscopic binary, twostars belonging to other associations/clusters, two runaway stars(nitrogen enhanced and possibly helium rich), and a group of O-typestars beyond Per OB1 containing two very fast rotators which may behelium enriched.
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Osservazione e dati astrometrici
| Costellazione: | Perseo |
| Ascensione retta: | 02h21m52.41s |
| Declinazione: | +56°54'18.0" |
| Magnitudine apparente: | 8.523 |
| Distanza: | 10000000 parsec |
| Moto proprio RA: | -0.1 |
| Moto proprio Dec: | -3 |
| B-T magnitude: | 8.658 |
| V-T magnitude: | 8.535 |
Cataloghi e designazioni:
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