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On the Formation of Perseus OB1 at High Galactic Latitudes
The Per OB1 association, which contains the remarkable double cluster hand χ Per, is unusual in not having a giant molecular cloud in itsvicinity. We show from Hipparcos data that the luminous members of thisassociation exhibit a bulk motion away from the Galactic plane, suchthat their average velocity increases with height above the Galacticplane. We find HAeBe and T Tauri stars toward probable remnant molecularclouds associated with Per OB1. These star-forming regions lie wellbeyond the location of the luminous member stars at heights of 280-400pc above the Galactic plane, far higher than that previously found forembedded clusters. We argue that the observed motion of the luminousmember stars is most naturally explained if many formed from moleculargas pushed and accelerated outward by an expanding superbubble, drivenpresumably by stellar winds and perhaps also by supernova explosions. Alarge shell of atomic hydrogen gas and dust that lies just beyond theremnant molecular clouds, believed to be driven by just such asuperbubble, may comprise the swept-up remains of the parental giantmolecular cloud from which this association formed. In support of thispicture, we find a weak trend for the younger O star members to lie athigher Galactic latitudes than the older supergiant members. Thestar-forming regions located at even larger heights above the Galacticplane presumably correspond to more recent episodes of star formation ator near the periphery of this superbubble.
| HD 183143: A Hypergiant
We present spectroscopic evidence that the luminosity of HD 183143 ishigher by one magnitude than thought previously. The star is yet anotherB6-8 Ia-0 white hypergiant of the Galaxy. Its absolute visual magnitudeis close to -8 mag, and its distance is close to 2 kpc. We describespectroscopic manifestations of the nonstationary behavior of itsatmosphere and wind.
| 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.
| An analysis of the optical spectra of the post-asymptotic giant branch stars LSIV -12 111 and HD 341617
High spectral resolution and signal-to-noise observations of theabsorption and emission line spectra in two post-asymptotic-giant-branch(PAGB) stellar candidates, LSIV -12 111 and HD 314617 are discussed. Theabsorption line spectra have been analysed using non-LTE modelatmosphere techniques to determine stellar atmospheric parameters andchemical compositions, both in absolute terms and relative to a standardstar, HD 13841. The atmospheric parameters differ from previousestimates based on LTE model atmospheres, probably due to non-LTEeffects. In turn these imply stellar masses that are generally largerthan have been previously estimated. Both PAGB candidates have relativeuniform underabundances of metals with mean values of -0.35 dex for LSIV-12 111 and -0.50 dex for HD 314617.Furthermore, their abundance patterns are remarkably similar to thatobserved for optically bright, F-type PAGBs. From the emission spectra,the plasma parameters and angular size of the circumstellar material areconstrained, and these are consistent with previous estimates and with aPAGB evolutionary stage.
| 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.
| High-resolution Keck I spectroscopy of Galactic halo post-asymptotic giant branch stars
Absolute and differential abundance analyses have been performed fromhigh-resolution, high signal-to-noise ratio optical (Keck I) spectra forthree evolved Galactic halo stars, namely PG 1704 + 222, HD 341617 andLS IV -04 01. Their derived atmospheric parameters indicate that allthree objects are undergoing a post-asymptotic giant branch (post-AGB)phase of evolution. A differential abundance analysis reveals HD 341617as having a mild carbon deficiency of 0.74 dex, possibly due to the starhaving evolved off the AGB before the onset of the third dredge-up.Although such carbon underabundances are typical of hot post-AGBobjects, the same trend is not observed in PG 1704 + 222, where thecarbon abundance is found to be consistent with those derived fornitrogen and oxygen. Hence, a dredge-up scenario need not be invoked toexplain the chemical composition of PG 1704 + 222. For LS IV -04 01 noiron deficiency is apparent relative to magnesium and silicon, and hencea gas-dust separation event in the AGB progenitor need not be invokedfor this star.
| CCD uvbybeta photometry of young open clusters. I. The double cluster h and chi Persei
We present CCD uvbybeta photometry for stars in the nuclei of the youngdouble cluster h and chi Persei. We find that the reddening is highlyvariable through the h Per nucleus, increasing from west to east, withvalues ranging from E(b-y) = 0.328+/-0.022 in the western part to E(b-y)= 0.465+/-0.024 in the south-east. Towards chi Per the reddening isfairly constant, with E(b-y) = 0.398+/-0.025. Both clusters share acommon distance modulus of 11.7+/-0.1 mag, and an age of log t =7.10+/-0.05 years. Tables 6 and 7 are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/394/479
| Photometric study of the double cluster h & chi Persei
We present uvbybeta CCD photometry of the central region of the doublecluster h & chi Persei. We identify ~350 stars, of which 214 werenot included in Oosterhof's catalogue. Our magnitude limit V=16.5 allowsus to reach early F spectral type and obtain very accurate fits to theZAMS. We derive reddening values of E(b-y) = 0.44+/-0.02 for h Perseiand E(b-y) = 0.39+/-0.05 for chi Persei. From the ZAMS fitting, wederive distance moduli V0-MV = 11.66+/-0.20 andV0-MV = 11.56+/-0.20 for h and chi Perseirespectively. These values are perfectly compatible with both clustersbeing placed at the same distance and having identical reddenings. Theshift in the main-sequence turnoff and isochrone fitting, however, showthat there is a significant age difference between both clusters, withthe bulk of stars in h Persei being older than chi Persei. There is,however, a significant population of stars in h Persei which are youngerthan chi Persei. All this argues for at least three different epochs ofstar formation, corresponding approximately to log t = 7.0, 7.15 and 7.3Tables 2, 8 and 9 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/372/477. Based onobservations obtained with the Jacobus Kapteyn Telescope operated on theisland of La Palma by the Isaac Newton Group, in the SpanishObservatorio Roque de los Muchachos of the Instituto deAstrofísica de Canarias.
| Differential O and Si Abundances in M33 Early B Supergiants
We present non-LTE analyses of four M33 early B supergiant stars andfive Galactic counterparts. This is the first time that B supergiantsbeyond the Magellanic Clouds are analyzed by means of detailed non-LTEtechniques. Among the M33 stars, new spectroscopic observations of B38(ob21-108) are presented and the object is classified as B1 Ia. Theclassification of another M33 star, B133, is changed with respect to aformer study. Equivalent widths of O and Si lines are measured for theM33 objects. Stellar temperatures, gravities, microturbulences, and Siabundances are derived for all objects using the Si ionizationequilibrium and the Balmer line wings. O abundances are then alsoderived. Important approximations made during the calculations aredescribed, and their influence on the results is analyzed (namely, weset the Lyman resonance lines in detailed balance during the calculationof the atmospheric structure for stars cooler than 20,000 K, and we setthe Si III resonance lines in detailed balance during the line formationcalculations for all models). It is found that these approximations haveno significant effect on the results at any microturbulence. We found adifference in the derived temperatures of the earlier Galactic stars ascompared to those obtained by other authors, which we attribute to thedifferent lines used for their derivation. A difference can also bepresent in the results when using the Si II/Si III and the Si III/Si IVionization equilibria. We conclude that a strict differential analysisis needed to detect abundance differences. Thus, we compare results lineby line in M33 and Galactic stars of stellar parameters as similar aspossible. Three of the four M33 stars turned out to be O deficient ascompared to their Galactic counterparts, and only one, close to thecenter of M33 (M33 1054), is found to be moderately O enriched. Fromthese differential analyses we find that our data are compatible with aradial O gradient in M33 as that derived from H II region data: weobtain -0.19+/-0.13 or -0.20+/-0.07 dex kpc-1, depending onwhether B133 is included or not. Our data are also consistent with otherpossibilities such as a steep increase of the O abundance in the innerregion (at projected distances less than 9' from the center of M33),followed by a flat O abundance profile toward the outer parts of M33. Sishows the same pattern, and it is shown that Si and O correlate well, asexpected for α-elements, supporting then the high value of the Oabundance gradient in M33 as compared to the Milky Way and other nearbyspiral galaxies. The results are compared with those of a moreapproximate technique, and it is concluded that this last can be used,attention being drawn to certain problems that are indicated. As animportant additional point, it is shown that M33 1054 is most probably asingle object, in spite of the bright absolute magnitude found in theliterature.
| 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
| The wind momentum-luminosity relationship of galactic A- and B-supergiants
The Balmer lines of four A Ia-supergiants (spectral type A0 to A3) andfourteen B Ia and Ib-supergiants (spectral type B0 to B3) in the solarneighbourhood are analyzed by means of NLTE unified model atmospheres todetermine the properties of their stellar winds, in particular theirwind momenta. As in previous work for O-stars (Puls et al. \cite{pul96})a tight relationship between stellar wind momentum and luminosity(``WLR'') is found. However, the WLR varies as function of spectraltype. Wind momenta are strongest for O-supergiants, then decrease fromearly B (B0 and B1) to mid B (B1.5 to B3) spectral types and becomestronger again for A-supergiants. The slope of the WLR appears to besteeper for A- and mid B-supergiants than for O-supergiants. Thespectral type dependence is interpreted as an effect of ionizationchanging the effective number and the line strength distributionfunction of spectral lines absorbing photon momentum around the stellarflux maximum. This interpretation needs to be confirmed by theoreticalcalculations for radiation driven winds. The ``Pistol-Star'' in theGalactic Centre, an extreme mid B-hypergiant recently identified as oneof the most luminous stars (Figer et al. \cite{fig99}) is found tocoincide with the extrapolation of the mid B-supergiant WLR towardshigher luminosities. However, the wind momentum of the Luminous BlueVariable P Cygni, a mid B-supergiant with extremely strong mass-loss, is1.2 dex higher than the WLR of the ``normal'' supergiants. Thissignificant difference is explained in terms of the well-known stellarwind bi-stability of supergiants very close to the Eddinton-limit inthis particular range of effective temperatures. A-supergiants in M31observed with HIRES at the Keck telescope have wind momenta compatiblewith their galactic counterparts. The potential of the WLR as a new,independent extragalactic distance indicator is discussed. It isconcluded that with ten to twenty objects, photometry with HST andmedium resolution spectroscopy with 8m-telescopes from the grounddistance moduli can be obtained with an accuracy of about 0fm1 out tothe Virgo and Fornax clusters of galaxies.
| Galactic B-supergiants: A non-LTE model atmosphere analysis to estimate atmospheric parameters and chemical compositions
A non-LTE model atmosphere analysis of moderate resolution (R ~ 5 000)spectra of 46 Galactic B-type supergiants is presented. Standardtechniques are adopted, viz. plane-parallel geometry and radiative andhydrostatic equilibrium. Spectroscopic atmospheric parameters (T_eff,log g & v_turb) and chemical abundances (He, C, N, O, Mg & Si)are estimated, both as a test of the validity of such an approach and inan attempt to provide consistent results for supergiants covering asignificant range of spectral types. The values of the estimatedatmospheric parameters and their dependence on the physics adopted inthe model atmospheres calculations are discussed. The absolute metalabundances are compared to those of main sequence B-type stars and, ingeneral, their chemical compositions appear to be similar. Theabundances for He, C, N & O are considered in some detail and arediscussed in the context of possible evolutionary histories for thisstellar sample. Specifically, it is found that the supergiant sample canbe subdivided into a number of evolutionarily distinct groups. The lowermass objects are predominantly chemically near-normal i.e. theirphotospheres show little or no evidence for chemical processing, whereasthe higher mass supergiants have CNO ratios which are indicative of CNand possibly NO-cycle burning. An attempt is made to quantify thedifference in nitrogen and carbon abundances between the high and lowmass targets but this is hampered by theoretical uncertainties. Thepossibilities that the most highly processed supergiants may have eitherlarger rotational velocities or have undergone mass transfer within abinary system are discussed.
| 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.
| 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.
| Spectroscopic observations of AB supergiants in M 33.
We have observed 10 luminous blue stars in M 33 at intermediatedispersion and have determined spectral types and luminosity classesfrom the blue and red spectrograms by comparing with galactic and SMCstars. Halpha_ profiles have proved to be very useful indisentangling luminosity and metallicity effects, and constitute avaluable diagnostic when comparing spectral classifications in galaxieswith different metallicities. We derive qualitative estimates of thestellar metallicities which range from solar to SMC-like and are broadlyconsistent with abundance gradient results obtained for M 33 from Hiiregion studies. Comparison of the new data for B 324 with previous workshows that there is evidence for significant spectral variabilitystrongly suggesting an LBV nature for this star.
| 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.
| Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
| Galactic B-supergiants. II - Line strengths in the visible: Evidence for evolutionary effects?
Following the discovery by Lennon et al. (1992) of anomalously weakcarbon lines in the Galactic B-supergiants, a search was conducted forthe signatures of CNO processed material in the atmospheres of thesestars. It was found that the NII line strengths around spectral type B2correlate with luminosity, but exhibit a clear anticorrelation with theCII lines. It is suggested that this trend may be evidence for CNOprocessed material contaminating the atmospheres of the most luminousstars. The CNO processing signature was found to be most pronounced inthe more luminous supergiants, in qualitative agreement with stellarevolution calculations (provided that such stars have passed through aprevious red-supergiant phase of evolution).
| Galactic B-supergiants. I - an atlas of O9-B9 supergiant spectra from 3950 A to 4950 A
CCD spectra are presented for supergiants of spectral types O9-B9 andluminosity subclasses Ia and Ib. They cover the wavelength region fromapproximately 3950 A to 4950 A at a resolution of 0.8 A, and normallyhave a signal-to-noise in excess of 150 at 4600 A. The spectra arediscussed in respect to their classification. A number of stars showclear evidence of the 'filling in' of hydrogen lines by emission fromthe stellar wind, while HD 190603, a B1.5 Ia(+) hypergiant, exhibits anH-beta P-Cygni type line-profile. Also reported is the finding of a newnitrogen weak star, HD 13866, in the Per OB1 association which isclassified here as BC2 Ib.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
| Groups of stars with common motion in the Galaxy. Groups of O and B stars
Not Available
| Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature
A new determination of the visual absolute magnitude of Be stars iscarried out. For this, a new calibration of visual absolute magnitudesof B stars of luminosity classes, V, IV, and III is first obtained froma sample of 215 stars. The absolute luminosity excess in the visual isdetermined for a sample of 49 Be stars. It is found that this excess iscorrelated with the effective temperature of the underlying stars. Awell defined correlation between this excess and the emission in thefirst two Balmer lines is established. From these results, using asimple model of circumstellar envelope, it is inferred that the zones ofthe circumstellar envelope contributing to the emission in the continuumand in the lines have to be rather small. It is also deduced that theemission measure of the envelope is correlated with the temperature ofthe central star and that the irregular photometric variations of Bestars are an envelope-opacity phenomenon.
| Carbon and nitrogen abundances in the BN supergiant HD 93840, and their implications for normal Galactic supergiants
It is demonstrated how carbon and nitrogen abundances of luminous Bstars can be determined by a combined analysis of their UV photosphericand wind lines. It is shown that HD 93840 has nearly the sametemperature and surface gravity as the normal B1 Ib star Zeta Per. Thesetwo stars are compared on the basis of their UV photospheric siliconspectra and the differences in their photospheric CNO and metallic linesare discussed. A quantitative comparison between the wind profiles ofthe two stars is made. A simple model for the compositions of bothatmospheres is used to derive the fraction of material in eachatmosphere which has undergone CNO processing. It is argued that theenriched material must have resided in a nuclear burning core for only avery short time. Best estimates of 0.09 + or - 0.07 and 0.90 + or - 0.1are made for the carbon abundances relative to cosmic ones for HD 93840and Zeta Per, respectively.
| Catalogue of Hydrogen Line Spectral Profiles of 236 B-Stars A-Stars and F-Stars
Not Available
| Distribution and motions of OB stars in the direction of H and KHI Perseus.
Not Available
| Early-type stars in the stellar associations Per OB1, SCO OB1, and CYG OB1 by observations with space telescope 'Glazar'
This paper presents results of observations at 1640 A carried out inSeptember 1988 with the Soviet space telescope Glazar on the regions ofstellar associations Per OB1, Sco OB1, and Cyg OB1. Thirty twophotographs were obtained, on which 94 images of stars were identifiedand measured. In stellar associations Per OB1, Sco OB1, and Cyg OB1, 42,22, and 30 hot stars brighter than 10 mag at 1640 A were detected,respectively. A comparison of Glazar measurements of stellar magnitudeswith those available from TD-1 telescope measurements and from ANSmeasurements showed reasonably good agreement.
| Geneva photometry of stars in the double cluster H and Chi Persei
Results are presented of a campaign of photometric observations of starsin the double cluster h and Chi Persei that spanned eight years. Thelong-time scale of the data has made it possible to discover that atleast half of the brighter stars in h and Chi Persei are variable stars.It appears that most of these variables are Be stars or related objects.Accurate color-magnitude diagrams for the brightest stars of the doublecluster show that the reddening is not as uniform as was assumed so far;that the observed parameters of many stars are very much affected by thehigh rotational velocities, and thus cannot be easily interpreted interms of physical quantities; and that the reported age and distancedifferences of both clusters are probably spurious. It is noted that thelarge intrinsic scatter of the colors and magnitudes of the h and ChiPersei stars casts doubt on the validity of photometric calibrationsthat rely heavily on observations of the double cluster.
| The Distribution of Early Type Stars in the Direction of Stellar Associations PERSEUS-OB1 SCORPIUS-OB1 and CYGNUS-OB1
Not Available
| A list of MK standard stars
Not Available
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