Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
| Parameters of galactic early B supergiants. The influence of the wind on the interstellar extinction determination
Context: The interstellar extinction, E(B-V), of OB supergiants isusually derived from the observed color index, (B-V), in comparison withthe intrinsic one. This method works properly only if the stellar winddoes not influence the optical continuum emission. Over the past years,many OB supergiants have been found to have wind-velocity distributionswith rather high ? values; i.e., their winds are only slowlyaccelerating, resulting in relative density enhancements within thewind-continuum forming region. It has been found that these kinds ofwinds might indeed influence the total continuum emission even atoptical wavelengths. Aims: We investigate the influence of thewind on the observed color indices of OB supergiants, in order todistinguish between interstellar and circumstellar extinctioncontributions. Methods: We first tested the influence of the windon the UBV band fluxes of a model O supergiant star with artificialwinds of different ? values and a fixed interstellar extinctionvalue. From the UBV magnitudes of these systems, the apparentinterstellar extinction was then derived by calculating the values ofE(B-V), from the (B-V) as well as from the (U-B) color index. Then weturned to a sample of galactic early-type B supergiants for which thestellar and wind parameters are known. All except one of these starshave ? values higher than 1.0, which makes this set the mostsuitable one for our investigation. We calculated each star's windcontribution to the BV band fluxes. The observed magnitudes werecorrected for the wind contributions, and the interstellar extinctionswere derived and compared with those derived purely from the (B-V) colorindex. Results: From our model supergiant, we find that withincreasing ? the wind starts to influence the observable colorindices. The wavelength dependence of the wind contribution is therebydifferent from that of the interstellar extinction contribution. Thus,the interstellar extinction values derived from the two color indices ofour reddened star plus wind systems disagree. This effect is strongerfor higher ?. In addition, E(B-V) derived from the (B-V) colorindex always overestimates the real interstellar extinction. This trendis also found for the investigated B supergiant sample. Consequently,the luminosities of these stars are systematically overestimated. Ourwind model always computes lower limits to the real wind contributions.This means that the real interstellar extinction values, hence thestellar luminosities of the studied B supergiant sample, might well belower.
| 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.
| Iron abundances from optical FeIII absorption lines in B-type stellar spectra
The role of optical FeIII absorption lines in B-type stars as ironabundance diagnostics is considered. To date, ultraviolet Fe lines havebeen widely used in B-type stars, although line blending can severelyhinder their diagnostic power. Using optical spectra, covering awavelength range ~3560-9200Å, a sample of Galactic B-typemain-sequence and supergiant stars of spectral types B0.5 to B7 areinvestigated. A comparison of the observed FeIII spectra of supergiants,and those predicted from the model atmosphere codes TLUSTY[plane-parallel, non-local thermodynamic equilibrium (LTE)], withspectra generated using SYNSPEC (LTE), and CMFGEN (spherical, non-LTE),reveal that non-LTE effects appear small. In addition, a sample ofmain-sequence and supergiant objects, observed with the Fiber-fedExtended Range Optical Spectrograph (FEROS), reveal LTE abundanceestimates consistent with the Galactic environment and previous opticalstudies. Based on the present study, we list a number of FeIIItransitions which we recommend for estimating the iron abundance fromearly B-type stellar spectra.
| Fourier method of determining the rotational velocities in OB stars
Aims.We present a comprehensive study that applies the Fourier transformto a sample of O and early B-type stars (either dwarfs, giants, orsupergiants) to determine their projected rotational velocities. We thencompare them with previous values obtained with other methods and seekevidence of extra broadening in the spectral lines Methods: The Fouriertechnique, extensively used in the study of cooler stars, has only beenmarginally applied to early-type stars. The comparison of v sin i valuesobtained through the ft and FWHM methods shows that the FWHM techniquemust be used with care in the analysis of OB giants and supergiants andwhen it is applied to He I lines. In contrast, the ft method appears tobe a powerful tool for deriving reliable projected rotational velocitiesand separating the effect of rotation from other broadening mechanismspresent in these stars. Results: The analysis of the sample of OB starsshows that while dwarfs and giants display a broad range of projectedrotational velocities, from less than 30 up to 450 km s-1,supergiants have in general values close to or below 100 kms-1. The analysis has also definitely shown that, while theeffect of extra broadening is negligible in OB dwarfs, it is clearlypresent in supergiants. When examining the behavior of the projectedrotational velocities with the stellar parameters and across the HRdiagram, we conclude, in agreement with previous researchers, that therotational velocity should decrease when the stars evolve. On thecontrary, macroturbulence may be constant, therefore resulting in anincreasing importance as compared to rotation when the stars evolve.The int and wht telescops are operated on the island of La Palma by theRGO in the Spanish Observatorium of El Roque de los Muchachos of theInstituto de Astrofísica de Canarias. Tables 2-10 are onlyavailable in electronic form at http://www.aanda.org
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Physical parameters and wind properties of galactic early B supergiants
We present optical studies of the physical and wind properties, plus CNOchemical abundances, of 25 O9.5-B3 Galactic supergiants. We employnon-LTE, line blanketed, extended model atmospheres, which provide amodest downward revision in the effective temperature scale of early Bsupergiants of up to 1-2 kK relative to previous non-blanketed results.The so-called "bistability jump" at B1 (Teff 21 kK)from Lamers et al. is rather a more gradual trend (with large scatter)from v&infy;/vesc3.4 for B0-0.5 supergiantsabove 24 kK to v&infy;/vesc 2.5 for B0.7-1supergiants with 20 kK ≤ Teff ≤ 24 kK, andv&infy;/vesc 1.9 for B1.5-3 supergiants below20 kK. This, in part, explains the break in observed UV spectralcharacteristics between B0.5 and B0.7 subtypes as discussed by Walbornet al. We compare derived (homogeneous) wind densities with recentresults for Magellanic Cloud B supergiants and generally confirmtheoretical expectations for stronger winds amongst Galacticsupergiants. However, winds are substantially weaker than predictionsfrom current radiatively driven wind theory, especially at mid-Bsubtypes, a problem which is exacerbated if winds are already clumped inthe Hα line forming region. In general, CNO elemental abundancesreveal strongly processed material at the surface of Galactic Bsupergiants, with mean N/C and N/O abundances 10 and 5 times higher thanthe Solar value, respectively, with HD 2905 (BC0.7 Ia) indicating thelowest degree of processing in our sample, and HD 152236 (B1.5Ia+) the highest.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Total to Selective Extinction Ratios and Visual Extinctions from Ultraviolet Data
We present determinations of the total to selective extinction ratio R_Vand visual extinction A_V values for Milky Way stars using ultravioletcolor excesses. We extend the analysis of Gnacinski and Sikorski (1999)by using non-equal weights derived from observational errors. We presenta detailed discussion of various statistical errors. In addition, weestimate the level of systematic errors by considering differentnormalization of the extinction curve adopted by Wegner (2002). Ourcatalog of 782 R_V and A_V values and their errors is available in theelectronic form on the World Wide Web.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Quantitative Spectral Analysis of Early B-Type Supergiants in the Sculptor Galaxy NGC 300
The spectra of two early B-type supergiant stars in the Sculptor spiralgalaxy NGC 300 are analyzed by means of non-LTE line-blanketed unifiedmodel atmospheres, aimed at determining their chemical composition andthe fundamental stellar and wind parameters. For the first time, adetailed chemical abundance pattern (He, C, N, O, Mg, and Si) isobtained for a B-type supergiant beyond the Local Group. The derivedstellar properties are consistent with those of other Local Group B-typesupergiants of similar types and metallicities. One of the stars shows anear solar metallicity, while the other one resembles more a SMC Bsupergiant. The effects of the lower metallicity can be detected in thederived wind momentum.Based on observations obtained at the ESO Very Large Telescope.
| Massive star abundances in the Galaxy and the Magellanic Clouds
The use of photospheric abundances in OB-type main-sequence stars and Aand B-type supergiants as probes of rotation and evolutionary status isreviewed. The abundances of CNO and boron can be comparedquantitatively with stellar evolutionary calculations. In particularthe abundance ratios of N/O and N/C can be derived in blue supergiantsto determine if they are consistent with the stars having gone through ared supergiant phase and dredge-up of core material to the surface. Theresults from several different studies are reviewed and compared. Forblue supergiant stars in the mass-range 5 - 80 Msun thesituation appears consistent -- there is no evidence for stars of anymass having undergone blue-loops in the HR diagram. The stellar samplesshow significant signs of having N enriched atmospheres, and thequantitative values are consistent with stellar evolutionarycalculations which invoke turbulent diffusive mixing while massive starsare on the main-sequence. Results on the interesting blue supergiantSher 25 are presented, and linked to sk; the B3Ia progenitor of SN1987A. A spectacular ejection nebula surrounds Sher 25, much like thatwhich was ejected by sk during its final stages of evolution. Both ofthese were thought to have been formed during a mass-loss event when thestars were in the red supergiant phase. The CNO abundances derived inSher 25 suggest the nebula was ejected during the blue supergiant phase,and that rotation can explain the N-enrichment found in the stellarphotosphere.
| 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.
| Chemical composition of B-type supergiants in the OB 8, OB 10, OB 48, OB 78 associations of M 31
Absolute and differential chemical abundances are presented for thelargest group of massive stars in M 31 studied to date. These resultswere derived from intermediate resolution spectra of seven B-typesupergiants, lying within four OB associations covering a galactocentricdistance of 5-12 kpc. The results are mainly based on an LTE analysis,and we additionally present a full non-LTE, unified model atmosphereanalysis of one star (OB 78-277) to demonstrate the reliability of thedifferential LTE technique. A comparison of the stellar oxygen abundancewith that of previous nebular results shows that there is an offset ofbetween ~ 0.15-0.4 dex between the two methods which is criticallydependent on the empirical calibration adopted for the R_23 parameterwith [O/H]. However within the typical errors of the stellar and nebularanalyses (and given the strength of dependence of the nebular results onthe calibration used) the oxygen abundances determined in each methodare fairly consistent. We determine the radial oxygen abundance gradientfrom these stars, and do not detect any systematic gradient across thisgalactocentric range. We find that the inner regions of M 31 are not, aspreviously thought, very ``metal rich''. Our abundances of C, N, O, Mg,Si, Al, S and Fe in the M 31 supergiants are very similar to those ofmassive stars in the solar neighbourhood.
| The evolutionary status of Sher 25 - implications for blue supergiants and the progenitor of SN 1987A
The blue supergiant Sher 25 in the massive Galactic cluster NGC 3603 issurrounded by a striking emission line nebula. The nebula contains anequatorial ring and probable bi-polar outflows, and is similar inmorphology, mass and kinematics to the shell now visible around SN1987A. It has been suggested that both nebulae were ejected while Sher25 and the progenitor of SN 1987A were in previous red supergiantphases. In the case of Sher 25 this is based on the qualitativestrengths of nebular [N II] emission which is indicative of nitrogenenriched gas. This gas may have been dredged up to the stellar surfaceby convective mixing during a previous red supergiant phase. We presentoptical high-resolution spectra of Sher 25 and a model photosphere andunified stellar wind analysis which determines the atmosphericparameters, mass-loss rate and photospheric abundances for C, N, O, Mg,and Si. We compare these results, in particular CNO, to other GalacticB-type supergiants and find that Sher 25 does not appear extreme orabnormal in terms of its photospheric nitrogen abundance. The C/N andN/O ratios are compared to surface abundances predicted by stellarevolutionary calculations which assume the star has gone through a redsupergiant phase and convective dredge-up. In particular we find thatthe N/O abundance is incompatible with the star having a previous redsupergiant phase, and that the nebulae is likely to have been ejectedwhile the star was a blue supergiant. The results are compatible withsome degree of rotationally induced mixing having occurred while thestar was on or near the main-sequence. This is similar to what hasrecently been found for nebulae surrounding LBVs. In addition our windanalysis suggests the star currently has a relatively normal mass-lossrate in comparison with other Galactic B-type supergiants and sitscomfortably within the wind momentum-luminosity relationship. In lightof the evidence regarding massive evolved early-type stars in the Galaxywe suggest there is no object which shows any evidence of having had aprevious red supergiant phase and hence of undergoing blue loops in theHR diagram.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Atlas of Interstellar Extinction Curves of OB Stars Covering the Whole Available Wavelength Range
The paper presents a collection of 436 extinction curves covering thewhole available range of wavelengths from satellite UV to near-IR. Thedata were taken from the ANS photometric catalogue and from thecompilations of IR photometric measurements. The data curves have beenobtained with the aid of ``artificial standards": Papaj et al. (1993)and Wegner (1994, 1995). The visual magnitudes and spectralclassifications of O and B type stars with EB-V>= 0.05were taken from the SIMBAD database. The curves are given in the form ofplots and tables E{lambda - V} / EB-V versus1/λ. The observed variety of extinction laws among slightlyreddened stars is apparently due to the various physical parameters ofinterstellar clouds.
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| 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.
| 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.
| 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.
| Near-Infrared H-Band Features in Late O and B Stars
We examine the spectral characteristics of normal OB stars withhigh-signal-to-noise ratio (>120) H-band (1.6 μm) spectra at aresolution of 2000. We find that several atomic lines vary smoothly withstellar temperature, as first shown by Blum et al. However, we find apreviously unreported, significant variation in the strength of some ofthese lines with stellar luminosity. B supergiant stars show stronger Hei and weaker Br 11 as compared with low-luminosity B dwarf stars of thesame spectral class. It is for this reason that luminosity class mustalso be determined to obtain an accurate spectral type for a given starusing H-band spectra. We suggest a method for estimating the spectraltype and luminosity of an OB star over the wavelength range from 1.66 to1.72 μm using hydrogen Br 11 at 1.681 mum, He i at 1.700 mum, and Heii at 1.693 mum. The use of the near-infrared spectral range forclassification has obvious advantages over optical classification whenapplied to heavily reddened stars, such as in star-forming regions ordeeply embedded lines of sight within the plane of the Galaxy, such asthe Galactic center. Furthermore, the H band is less likely to becontaminated by infrared excess emission, which is frequently seenaround massive young stellar objects beyond 2 mum.
| Stellar ? Elements Abundance Gradient in M33
In previous papers we have published preliminary results on the stellaroxygen-abundance gradient in M33 by using B-type supergiants. In thepresent study, we include one new B-supergiant and derive effectivetemperatures and gravities for these stars. The determination ofatmospheric parameters is based on analyses of silicon ionisationbalance.
| New identifications for blue objects towards the Galactic center: post-AGB stars, Be/disk stars and others
As part of a programme to investigate spatial variations in the Galacticchemical composition, we have been searching for normal B-type stars andA-type supergiants near the Galactic center. During this search we havefound eleven peculiar stars, and in some cases performed detailedabundance analyses of them which suggest that they may be at a post-AGBevolutionary stage. The A-type post-AGB candidates show [Fe/H]=-1.0 to-2.0, and [O/Fe] ~ +1.4, typical of the post-AGB abundance patternsdiscussed in the literature. One star, LS 3591 (=SAO 243756), has alsobeen examined recently by Oudmaijer (1996); its spectrum appears to bechanging very rapidly, which may indicate erratic mass loss or theincipient formation of a planetary nebula. A B-type post-AGB candidate,LS 4950, has a similar spectrum to a well studied post-AGB star, LSIV-12 111. However, an examination of the line strengths and elementalabundances of LS 4950 show that it is peculiar for both a Population II,post-AGB, B-type star and for a normal, Population I, B-type supergiant.Two other B-type stars, LS 4825 and LS 5112, are either post-AGB starsnear the Galactic center or normal B-type supergiants lying well beyondthe Galactic center. In addition, several Be-type stars have been newly(or more clearly) identified from our spectra. Tables 12, 13, 14, 15 andAppendices A,B are only available in electronic form at CDS viaanonymous ftp to: cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Revised spectral types for 64 B-supergiants in the Small Magellanic Cloud: metallicity effects.
The problem of the classification of metal poor stars, such as occur inthe Small Magellanic Cloud (SMC), is discussed with reference to theapplicability of the MK system in such an environment. An alternativemethod is presented here and applied to B-type supergiants in the SMC. Alocal reference system is first devised and then a transformation to MKspectral types is determined by comparing the trends of metal linestrengths in these two systems. For the determination of the luminosityclass, we emphasize the need to use the hydrogen Balmer line strengthsindependently of metal line-strength considerations. This method is usedto determine new spectral types for 64 supergiants in the SMC, 75% ofthe sample requiring classifications different from previous findings.These new types result in much improved line strength - spectral typecorrelations for He, C, N, O, Mg and Si. Corresponding changes in thedistribution of these stars in the Hertzsprung-Russell diagram of theSMC reveal more clearly than before the existence of a ridge which maybe the SMC analogue of a similar feature found for the LMC byFitzpatrick & Garmany (1990ApJ...363..119F). The group of veryluminous supergiants lying above this ridge includes the LBV AV415(R40), a property which this object has in common with LBVs in the LargeMagellanic Cloud. Also, for the first time, clear examples of BN/BCsupergiants are found in the SMC.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| 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.
| 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).
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Персей |
| Прямое восхождение: | 02h26m45.70s |
| Склонение: | +57°40'45.0" |
| Видимая звёздная величина: | 7.231 |
| Расстояние: | 1020.408 парсек |
| Собственное движение RA: | -0.8 |
| Собственное движение Dec: | -3.2 |
| B-T magnitude: | 7.978 |
| V-T magnitude: | 7.293 |
Каталоги и обозначения:
|
INHABITED SKY
