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On the nature of the galactic early-B hypergiants
Aims: Despite their importance to a number of astrophysicalfields, the lifecycles of very massive stars are still poorly defined.In order to address this shortcoming, we present a detailed quantitativestudy of the physical properties of four early-B hypergiants (BHGs) ofspectral type B1-4 Ia+; Cyg OB2 #12, ?1 Sco,HD 190603 and BP Cru. These are combined with an analysis of theirlong-term spectroscopic and photometric behaviour in order to determinetheir evolutionary status. Methods: Quantitative analysis ofUV-radio photometric and spectroscopic datasets was undertaken with anon-LTE model atmosphere code in order to derive physical parameters forcomparison with apparently closely related objects, such as Bsupergiants (BSGs) and luminous blue variables (LBVs), and theoreticalevolutionary predictions. Results: The long-term photospheric andspectroscopic datasets compiled for the early-B HGs revealed that theyare remarkably stable over long periods ( ? 40 yrs), with thepossible exception of ?1 Sco prior to the 20th century;in contrast to the typical excursions that characterise LBVs.Quantitative analysis of ?1 Sco, HD 190603 and BP Cruyielded physical properties intermediate between BSGs and LBVs; wetherefore suggest that BHGs are the immediate descendants andprogenitors (respectively) of such stars, for initial masses in therange ~30-60 M&sun;. Comparison of the properties of?1 Sco with the stellar population of its hostcluster/association NGC 6231/Sco OB1 provides further support for suchan evolutionary scenario. In contrast, while the wind properties of CygOB2 #12 are consistent with this hypothesis, the combination of extremeluminosity and spectroscopic mass (~110 M&sun;) andcomparatively low temperature means it cannot be accommodated in such ascheme. Likewise, despite its co-location with several LBVs above theHumphreys-Davidson (HD) limit, the lack of long term variability and itsunevolved chemistry apparently excludes such an identification. Sincesuch massive stars are not expected to evolve to such cool temperatures,instead traversing an O4-6Ia ? O4-6Ia+ ? WN7-9hapathway, the properties of Cyg OB2 #12 are therefore difficult tounderstand under current evolutionary paradigms. Finally, we note thatas with AG Car in its cool phase, despite exceeding the HD limit, theproperties of Cyg OB2 #12 imply that it lies below the Eddington limit -thus we conclude that the HD limit does not define a region of the HRdiagram inherently inimical to the presence of massive stars.Appendices are available in electronic form at http://www.aanda.org
| The first X-ray survey of Galactic luminous blue variables
Aims: The X-ray emission of massive stars has been studied whenthese objects are in their main-sequence phase, as well as when they arein their Wolf-Rayet phase. However, the X-ray properties of thetransitional luminous blue variable (LBV) phase remain unknown. Methods: Using a dedicated but limited XMM-Newton survey and archivalXMM-Newton and Chandra observations, we performed the first X-ray surveyof LBVs: about half of the known LBVs or candidate LBVs were studied. Results: Apart from the well known X-ray sources eta Car and CygOB2 #12, four additional LBVs are detected in this survey, though somedoubt remains on the association with the X-ray source for two of these.For the other LBVs, upper limits on the flux were derived, down to log[LX/LBOL] - 9.4 for P Cyg. This variety in thestrength of the X-ray emission is discussed, with particular emphasis onthe potential influence of binarity.Based on observations collected with XMM-Newton, an ESA Science Missionwith instruments and contributions directly funded by ESA Member Statesand the USA (NASA), and with Chandra.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| MWC 930 - a new luminous blue variable candidate
We present the results of optical high-resolution and near-infraredlow-resolution spectroscopy and multicolour optical and near-infraredphotometry of the emission-line star MWC 930. The spectrum is rich withFeII emissions, most of which have P Cyg-type profiles. The emissionlines are strong and narrow, indicating a powerful stellar wind with alow terminal velocity (v&infy;~ 140kms-1). Thephotospheric absorption lines are broad and show splitting, which mightbe due to the object's binarity. MWC 930 is most probably located in theNorma spiral arm at a distance of D= 3-4kpc. This strong and slow windas well as the star's luminosity (logL/Lsolar~ 5.5) and theinfrared excess shape suggest that MWC 930 is an unusual B-typesupergiant, most likely undergoing the luminous blue variableevolutionary phase.
| Tycho-2 stars with infrared excess in the MSX Point Source Catalogue
Stars of all evolutionary phases have been found to have excess infraredemission due to the presence of circumstellar material. To identify suchstars, we have positionally correlated the infrared Mid-Course SpaceExperiment (MSX) Point Source Catalogue and the Tycho-2 opticalcatalogue. Near-mid-infrared colour criteria have been developed toselect infrared excess stars. The search yielded 1938 excess stars; overhalf (979) have never previously been detected by IRAS. The excess starswere found to be young objects such as Herbig Ae/Be and Be stars, andevolved objects such as OH/IR (infrared) and carbon stars. A number ofB-type excess stars were also discovered whose infrared colours couldnot be readily explained by known catalogued objects.
| 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.
| On the population of galactic Luminous Blue Variables
We report the first results of a long term infrared monitoring campaignof known and candidate galactic Luminous Blue Variables (LBVs). Inparticular, we are able to confirm the LBV nature ofG24.73+0.69, a luminous mid-B supergiant associatedwith a dusty ejection nebula. We find that prior to 2003 SeptemberG24.73+0.69 exhibited low amplitude (Δ JHK 0.4 mag) variability, but in the ~200 day period between 2003September-2004 April it abruptly brightened by ~0.7 mag in the broadbandJ filter. Subsequently, a further ~0.4 mag increase was observed between2004 April-October, resulting in an overall difference of ~1.1 magbetween (current) photometric mimimum and maximum; similar variabilityalso being observed in the H and K bands. In light of the numerousrecent IR studies of the galactic hot star population we also compile anupdated census of confirmed and candidate galactic LBVs, reporting 12and 23 members respectively for each class. Finally, we utilise this newcensus to construct an H-R diagram for the galactic LBV population,resulting in a striking confirmation of the LBV-minimum light strip.
| 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.
| An atlas of spectra of B6-A2 hypergiants and supergiants from 4800 to 6700 Å
We present an atlas of spectra of 5 emission-line stars: thelow-luminosity luminous blue variables (LBVs) HD 168625 and HD 160529,the white hypergiants (and LBV candidates) HD 168607 and AS 314, and thesupergiant HD 183143. The spectra were obtained with 2 echellespectrometers at the 6-m telescope of the Russian Academy of Sciences inthe spectral range 4800 to 6700 Å, with a resolution of 0.4Å. We have identified 380 spectral lines and diffuse interstellarbands within the spectra. Specific spectral features of the objects aredescribed.The complete atlas and Table 2 are only available in electronic form atthe CDS via anonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/1035
| S Doradus variables in the Galaxy and the Magellanic Clouds
The goal in writing this paper is five fold: (1) to summarize thescientific achievements in the 20th century on S Dor variables (orLBVs); (2) to present an inventory of these variables in the Galaxy andthe Magellanic Clouds with a description of their physical state andinstability properties; (3) to emphasize the photometric achievements ofthe various types of instabilities. Generally this seems to be aneglected item resulting in a number of misunderstandings continuouslywandering through literature; (4) to investigate the structure of the SDor-area on the HR-diagram; (5) to estimate the total numbers of S Dorvariables in the three stellar systems. The position of the strongactive S Dor variables in minimum brightness obey the following linearrelation on the HR-diagram:log L/Lsun = 1.37 log T_eff -0.03. The relatively small dispersion of less active and supposed ex-and dormant S Dor variables with respect to this relation is twice aslarge at the blue side than at the red side. This might be caused byevolution to the WR stage and/or to high rotation. S Dor variables canbe subject to five types of instabilities: the very rare genuineeruptive episodes (the ``SD-eruptions''), two different brighteningphases caused by slow pulsations (the ``SD-phases''): one on a timescale of years, the other on a time scale of decades at a more or lessconstant luminosity and two types of microvariations: one on a timescale of weeks, the other on a time scale of about 100 d. So far, noperiodicities of light curve characteristics of any of theseinstabilities have ever been found. The durations of active andnon-active stages are estimated for about half of the sample based onscattered magnitude estimations such as from historical records, and onmodern monitoring campaigns. It would be a misunderstanding to believethat all S Dor variables should be always spectacular. It is estimatedthat most of them will not be spectacular at all for at least 70% oftheir lifetime as an S Dor variable. Tables 1 to 6 and 8 to 17 are onlyavailable in electronic form at http://www.edpsciences.org, Table 7 isonly available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/366/508. Figures 2--10,12, 14, 15, 17--19 are only available in electronic form athttp://www.edpsciences.org, see Note added in proof
| AS 314: A dusty A-type hypergiant
We present the results of our observations of the poorly-studiedemission-line star AS 314 which include high-resolution spectroscopy,obtained at the 6 -meter telescope of the Russian Academy of Sciences,multicolor optical and near-infrared photometry. The strong Hαline, Hβ and Hγ of moderate strength and a number of weak Feii lines were detected in emission. The Balmer lines and most of the Feii lines show narrow P Cyg-type profiles which implies a very lowterminal velocity of the stellar wind. Very weak signs of emission arefound in Hdelta . Photospheric lines detected for the first time allowedus to determine the object's spectral type, A0. The luminosity, M_bol ~-8.0 mag was estimated using several methods and implies that AS 314 isa hypergiant, which is located at about 10 kpc from the Sun and has aninitial mass of ~ 20; Msun . Modeling of the Balmer lineprofiles resulted in the following parameters of the stellar wind: dot{M} = 2\ 10-5;Msun yr-1, v_infty =75;km s-1. The star is located within the LBV strip in theHRD. Its noticeable far-IR excess is due to the circumstellar dustemission and is likely evidence of an LBV-type outburst in the past.Table 5 is only available in electronic form in the online edition ofthe present issue.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| A new catalogue of members and candidate members of the Herbig Ae/Be (HAEBE) stellar group
A new up-to-date catalogue of Herbig Ae/Be (HAEBE) stars and relatedobjects is certainly needed, for both well-seasoned researchers and, inparticular, for new investigators starting to study the many interestingastrophysical properties of these very young objects. We present a briefdiscussion of the current observational characteristics that distinguishthis class from their main sequence counterparts. The HAEBE and relatedstars are listed in five tables, containing 287 objects. Table 1contains all Ae and Be stars which historically are recognized as trueHAEBE stars or potential candidate members. Table 2 gives the stars ofspectral type Fe, and emission line stars with very uncertain or unknownspectral type. In Table 3 are given all known Extreme Emission LineObjects (EELOs), of which most have not been identified to belong to anyspecific group. Table 4a and b list other Bep or B[e] stars with strongIR-excess and unknown spectral type. Table 5 contains the non-emissionline possible young objects. Furthermore, Table 6 contains 35 starsrejected from former published lists of HAEBE stars. In these tables weare including coordinates, spectral types, visual magnitudes, ranges inphotometric variability and references of several key publicationsrelated to each object. Relevant remarks, such as the presence of anebula in the vicinity of an object, are also given.
| Early-type emission-line stars with large infrared excesses
A catalog is presented of early-type emission-line stars obtained bycross-identification between Wackerling's catalog and the IRAS catalogof point sources. A study of the distribution in space of the starsshows that these stars belong to the extreme Population I; thus thepresent compilation provides a rather complete sample for further studyof the evolution of pre- and post-main sequence stars of medium and highmasses.
| Distances, reddenings and distribution of emission B-stars in the galactic centre region /l/ not greater than 45 deg
The distribution of Be stars in the region surrounding the Galacticcenter and their correlation to the spiral structure of the Galaxy hasbeen studied. The results are discussed in terms of reddenings anddistances of these stars. Data are presented on the Galacticcoordinates, colors, interstellar color excesses, reddening-freemagnitudes and colors, adopted absolute magnitudes, distances in kpc,distances from the Galactic plane, and MK spectral type.
| Photometric observations of emission B-stars in the southern Milky Way
In order to study the distribution of Be stars and their correlation tothe local spiral structure of the Galaxy photoelectric UBV photometrywas carried out for a total of 488 Be stars located in the southernMilky Way between galactic longitudes 315 and 45 deg. UBV magnitudes arepresented for these stars.
| The space distribution and kinematics of supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..602H&db_key=AST
| A survey of O and B stars in a region of Scutum
Not Available
| Photometric and Spectroscopic Studies of Early-Type Stars Between Galactic Longitude L = 338° and L = 33°.
Not Available
| Additional Stars whose Spectra have a Bright H α Line.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...112...72M&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Щит |
| Прямое восхождение: | 18h39m26.10s |
| Склонение: | -13°50'47.2" |
| Видимая звёздная величина: | 9.943 |
| Собственное движение RA: | -3.8 |
| Собственное движение Dec: | -7.2 |
| B-T magnitude: | 10.89 |
| V-T magnitude: | 10.022 |
Каталоги и обозначения:
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