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The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500
We present the first installment of a massive spectroscopic survey ofGalactic O stars, based on new, high signal-to-noise ratio, R ~ 2500digital observations from both hemispheres selected from the GalacticO-Star Catalog of Maíz Apellániz et al. and Sota et al.The spectral classification system is rediscussed and a new atlas ispresented, which supersedes previous versions. Extensive sequences ofexceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p,Oe, and double-lined spectroscopic binaries. The remaining normalspectra bring this first sample to 184 stars, which is close to completeto B = 8 and north of ? = -20° and includes all of thenorthern objects in Maíz Apellániz et al. that are stillclassified as O stars. The systematic and random accuracies of theseclassifications are substantially higher than previously attainable,because of the quality, quantity, and homogeneity of the data andanalysis procedures. These results will enhance subsequentinvestigations in Galactic astronomy and stellar astrophysics. In thefuture, we will publish the rest of the survey, beginning with a secondpaper that will include most of the southern stars in MaízApellániz et al.The spectroscopic data in this article were gathered with threefacilities: the 1.5 m telescope at the Observatorio de Sierra Nevada(OSN), the 3.5 m telescope at Calar Alto Observatory (CAHA), and the duPont 2.5 m telescope at Las Campanas Observatory (LCO). Some of thesupporting imaging data were obtained with the 2.2 m telescope at CAHAand the NASA/ESA Hubble Space Telescope (HST). The rest were retrievedfrom the DSS2 and Two Micron All Sky Survey (2MASS) surveys. The HSTdata were obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| The Evolution of Circumstellar Disks Surrounding Intermediate-mass Stars: IC 1805
We report the results of a study of the intermediate- and high-massstars in the young, rich star-forming complex IC 1805, based on acombination of optical, near-infrared, and mid-infrared photometry, andclassification spectra. These data provide the basis for characterizingthe masses and ages for stars more massive than ~2 M sun andenable a study of the frequency and character of circumstellar disksassociated with intermediate- and high-mass stars. Optically thickaccretion disks among stars with masses 2 < M/M sun < 4are rare (~2% of members) and absent among more massive stars. A largerfraction (~10%) of stars with masses 2 < M/M sun < 4appear to be surrounded by disks that have evolved from the initialoptically thick accretion phase. We identify four classes of such disks.These classes are based on spectral energy distributions (SEDs) ofexcess emission above photospheric levels: disks that are (1) opticallythin based on the magnitude of the observed excess emission from 2 to 24μm, (2) optically thin in their inner regions (r < 20 AU) andoptically thick in their outer regions, (3) exhibit empty inner regions(r < 10 AU) and optically thin emission in their outer regions, and(4) exhibit empty inner regions and optically thick outer regions. Wediscuss, and assess the merits and liabilities of, proposed explanationsfor disks exhibiting these SED types and suggest additional observationsthat would test these proposals.
| High-resolution imaging of Galactic massive stars with AstraLux. I. 138 fields with ? > - 25°
Context. Massive stars have high-multiplicity fractions, and many ofthem have still undetected components, thus hampering the study of theirproperties. Aims: I study a sample of massive stars with highangular resolution to better characterize their multiplicity. Methods: I observed 138 fields that include at least one massive starwith AstraLux, a lucky imaging camera at the 2.2 m Calar Alto telescope.I also used observations of 3 of those fields with ACS/HRC on HST toobtain complementary information and to calibrate the AstraLux data. Theresults were compared with existing information from the WashingtonDouble Star Catalog, Tycho-2, 2MASS, and other literature results. Results: I discover 16 new optical companions of massive stars, themajority of which are likely to be physically bound to their primaries.I also improve the accuracy for the separation and magnitude differenceof many previously known systems. In a few cases the orbital motion isdetected when comparing the new data with existing ones and constraintson the orbits are provided. Conclusions: The analysis indicatethat the majority of the AstraLux detections are bound pairs. For arange of separations of 0.1 arcsec-14'' and magnitude differences lowerthan 8, I find that the multiplicity fraction for massive stars is closeto 50%. When objects outside those ranges are included, the multiplicityfraction should be considerably higher.Table 3 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/518/A1
| The High Angular Resolution Multiplicity of Massive Stars
We present the results of a speckle interferometric survey of Galacticmassive stars that complements and expands upon a similar survey madeover a decade ago. The speckle observations were made with the Kitt PeakNational Observatory and Cerro Tololo Inter-American Observatory 4 mtelescopes and USNO speckle camera, and they are sensitive to thedetection of binaries in the angular separation regime between 0farcs03and 5'' with relatively bright companions (ΔV < 3). We reporton the discovery of companions to 14 OB stars. In total we resolvedcompanions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%),and 89 of 139 B-stars (64%; an enriched visual binary sample that weselected for future orbital determinations). We made a statisticalanalysis of the binary frequency among the subsample that are listed inthe Galactic O Star Catalog by compiling published data on other visualcompanions detected through adaptive optics studies and/or noted in theWashington Double Star Catalog and by collecting published informationon radial velocities and spectroscopic binaries. We find that the binaryfrequency is much higher among O-stars in clusters and associationscompared to the numbers for field and runaway O-stars, consistent withpredictions for the ejection processes for runaway stars. We present afirst orbit for the O-star δ Orionis; a linear solution of theclose, apparently optical, companion of the O-star ι Orionis; andan improved orbit of the Be star δ Scorpii. Finally, we listastrometric data for another 249 resolved and 221 unresolved targetsthat are lower mass stars that we observed for various other scienceprograms.
| Broad-band optical polarimetric study of IC 1805
We present the BVR broad-band polarimetric observations of 51 starsbelonging to the young open cluster IC 1805. Along with the photometricdata from the literature, we have modelled and subtracted the foregrounddust contribution from the maximum polarization (Pmax) andcolour excess [E (B - V)]. The mean value of the Pmax forintracluster medium and the foreground are found to be 5.008 +/- 0.005and 4.865 +/- 0.022 per cent, respectively. Moreover, the mean value ofthe wavelength of maximum polarization (λmax) forintracluster medium is 0.541 +/- 0.003μ m, which is quite similar asthe general interstellar medium (ISM). The resulting intracluster dustcomponent is found to have negligible polarization efficiency ascompared to interstellar dust. Some of the observed stars in IC 1805have shown the indication of intrinsic polarization in theirmeasurements.
| Stellar Rotation in Young Clusters. II. Evolution of Stellar Rotation and Surface Helium Abundance
We derive the effective temperatures and gravities of 461 OB stars in 19young clusters by fitting the Hγ profile in their spectra. We usesynthetic model profiles for rotating stars to develop a method toestimate the polar gravity for these stars, which we argue is a usefulindicator of their evolutionary status. We combine these results withprojected rotational velocity measurements obtained in a previous paperon these same open clusters. We find that the more massive B starsexperience a spin-down as predicted by the theories for the evolution ofrotating stars. Furthermore, we find that the members of binary starsalso experience a marked spin-down with advanced evolutionary state dueto tidal interactions. We also derive non-LTE-corrected heliumabundances for most of the sample by fitting the He Iλλ4026, 4387, 4471 lines. A large number of heliumpeculiar stars are found among cooler stars withTeff<23,000 K. The analysis of the high-mass stars (8.5Msolar
| Stellar Rotation in Young Clusters. I. Evolution of Projected Rotational Velocity Distributions
Open clusters offer us the means to study stellar properties in sampleswith well-defined ages and initial chemical composition. Here we presenta survey of projected rotational velocities for a large sample of mainlyB-type stars in young clusters to study the time evolution of therotational properties of massive stars. The survey is based onmoderate-resolution spectra made with the WIYN 3.5 m and CTIO 4 mtelescopes and Hydra multi-object spectrographs, and the target starsare members of 19 young open clusters with an age range of approximately6-73 Myr. We made fits of the observed lines He I λλ4026,4387, 4471, and Mg II λ4481, using model theoretical profiles tofind projected rotational velocities for a total of 496 OB stars. Wefind that there are fewer slow rotators among the cluster B-type starsrelative to nearby B stars in the field. We present evidence consistentwith the idea that the more massive B stars (M>9 Msolar)spin down during their main-sequence phase. However, we also find thatthe rotational velocity distribution appears to show an increase in thenumbers of rapid rotators among clusters with ages of 10 Myr and higher.These rapid rotators appear to be distributed between the zero age andterminal age main-sequence locations in the Hertzsprung-Russell diagram,and thus only a minority of them can be explained as the result of aspin-up at the terminal age main sequence due to core contraction. Wesuggest instead that some of these rapid rotators may have been spun upthrough mass transfer in close binary systems.
| Early-type stars in the young open cluster IC 1805. II. The probably single stars HD 15570 and HD 15629, and the massive binary/triple system HD 15558
Aims.We address the issue of the multiplicity of the three brightestearly-type stars of the young open cluster IC 1805, namely HD 15570, HD15629 and HD 15558. Methods: .For the three stars, we measured theradial velocity by fitting Gaussian curves to line profiles in theoptical domain. In the case of the massive binary HD 15558, we also useda spectral disentangling method to separate the spectra of the primaryand of the secondary in order to derive the radial velocities of the twocomponents. These measurements were used to compute orbital solutionsfor HD 15558. Results: .For HD 15570 and HD 15629, the radialvelocities do not present any significant trend attributable to a binarymotion on time scales of a few days, nor from one year to the next. Inthe case of HD 15558 we obtained an improved SB1 orbital solution with aperiod of about 442 days, and we report for the first time on thedetection of the spectral signature of its secondary star. We derivespectral types O5.5III(f) and O7V for the primary and the secondary ofHD 15558. We tentatively compute a first SB2 orbital solution althoughthe radial velocities from the secondary star should be considered withcaution. The mass ratio is rather high, i.e. about 3, and leads to veryextreme minimum masses, in particular for the primary object. Minimummasses of the order of 150 ± 50 and 50 ± 15 M_ȯ arefound respectively for the primary and the secondary. Conclusions:.We propose that HD 15558 could be a triple system. This scenario couldhelp to reconcile the very large minimum mass derived for the primaryobject with its spectral type. In addition, considering new andpreviously published results, we find that the binary frequency amongO-stars in IC 1805 has a lower limit of 20%, and that previouslypublished values (80%) are probably overestimated.
| Stellar Rotation: A Clue to the Origin of High-Mass Stars?
We present the results of a study aimed at assessing whether low- andhigh-mass stars form similarly. Our approach is (1) to examine theobserved projected rotational velocities among a large sample of newlyformed stars spanning a range in mass between 0.2 and 50Msolar and (2) to search for evidence of a discontinuity inrotational properties that might indicate a difference in the stellarformation process at some characteristic mass. Our database includesrecently published values of vsini for young intermediate- and low-massstars in Orion, as well as new observations of O stars located in youngclusters and OB associations. We find that the median of the quantityvobs/vc (observed rotational speed divided byequatorial breakup velocity) is typically about 0.15 and shows noevidence of a discontinuity over the full range of stellar masses, whilethe quantity Jsini/M (derived angular momentum per unit mass) exhibits aslow, monotonic rise (J/M~M0.3) with increasing mass with noevidence of a discontinuity. We suggest that these observations are mostsimply interpreted as indicative of a single stellar formation andangular momentum regulation mechanism, one that results in rotationrates well below breakup and angular momenta per unit mass that differsystematically by no more than a factor of 3-4 over a mass rangespanning a factor of 250.
| Modeling the Neutral Hydrogen Interstellar Medium: A Better Kinematic Distance Tool
An advanced approach to the kinematic distance method is developed. Themethod is applicable to second- and third-quadrant Galactic objects withknown velocities. It is based on fitting a model of the density andvelocity features in an isothermal H I disk to observed H I data. Thevelocity field of the gas is modeled with a power law for basic circularrotation, underlying noncircular motions from a two-armed density wavepattern. With a reasonable number of adjustable parameters andconstraints the model reproduces observations toward many Galacticobjects, and accurate distances are found from the modeled velocityfield. High-resolution H I spectral line data from the Canadian GalacticPlane Survey (CGPS; Taylor et al.) are used to discriminate clouds fromthe intercloud medium (the ``stratum'') for which the model is intended.The ability of the model to reproduce these data is demonstrated in one-[Tb(v)] and two- [Tb(l, v)] dimensional fits.Distances to 22 H II regions and SNRs calculated by the fitted velocityfield compare extremely well with other kinematically independentdistances.
| 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.
| 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.
| 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.
| 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.
| 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
| Spectroscopic observations of young open clusters: IC 1805, NGC 654 and NGC 6823
Spectroscopic observations were made for a sample of 263 stars fromthree young open clusters IC 1805, NGC 654 and NGC 6823 with CCDdetectors in the blue and yellow-red spectral regions. MKK types wereproperly determined for these stars by carefully comparing spectra ofprogram stars with those of a complete grid of MKK standards, which wereobserved with the same instruments as the program stars. For most of theobserved stars precise MKK types were assigned for the first time. A fewof early-type emission-line stars were discovered or confirmed. Thepresence of Be stars in the studied clusters is discussed. Spectra ofthe observed MKK standards also reveal lots of features showingtemperature or luminosity effect in the yellow-red region, which helpedin our stellar spectral classification.
| 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.
| Cometary globules. III. Triggered star formation in IC 1848.
We present a multiwavelength study from molecular and continuumobservations of the cometary globule CG5 in the HII region IC1848. CG5is associated with the luminous IRAS point source 02252+6120(L=1100Lsun_) and shows evidence for an energetic outflow andongoing star formation (a cluster of low-mass stars has formed insidethe cloud). CG5 is presently undergoing a second episode ofphoto-ionisation from a cluster of O stars in the nebula, characterisedby a shock at the surface of the cloud; the shock was detected inseveral millimeter lines (CO, CS) and in the thermal continuum dustemission. Photo-ionisation conditions at the surface of the globule wereestimated from measurements of the VLA free-free continuum emission. Avirial analysis suggests that CG5 is probably permeated by a staticmagnetic field of strength =~125μG and is subject to an outerpressure 4 times as large as its inner pressure. It is in a globallymagnetically subcritical state whereas its core is close to virialequilibrium. Photo-ionisation is found to play a key role in theevolution of CG5 because a) it confines the molecular gas and containsthe gas dispersal favored by the energy injection from the outflow whileevaporating the superficial layers at the same time, b) the overpressureof the compressed gas ahead of the ionisation front is sufficient totrigger the collapse of initially (sub)critical condensations inside thecloud and initiate star formation. We find that the outflow containsenough momentum to have contributed to this star-formation process. Inaddition, the energy of the outflow is sufficient to sustain turbulencein the cloud and maintain it in a magnetically subcritical state, i.e.it tends to stabilize the cloud against collapse and regulate starformation.
| A galactic chimney in the Perseus arm of the Milky Way
GALAXIES are surrounded by large haloes of hot gas1 whichmust be replenished as the gas cools. This has led to theconcept2 of galactic 'chimneys'-cavities in the interstellarmedium, created by multiple supernova explosions, that can act asconduits for the efficient transport of hot gas from a galaxy's disk toits halo. Here we present a high-resolution map of atomic hydrogen inthe Perseus arm of our Galaxy, which shows clear evidence for theexistence of such a chimney. This chimney appears to have been formed bythe energetic winds from a cluster of young massive stars, and maycurrently have reached the stage of blowing out into the halo.
| The Initial Mass Function and Massive Star Evolution in the OB Associations of the Northern Milky Way
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...454..151M&db_key=AST
| 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.
| Near-infrared photometric study of open star cluster IC 1805
The JHK magnitudes of 29 stars in the region of open star cluster IC1805 were measured. These, and the existing infrared and opticalobservations, indicate a normal interstellar extinction law in thedirection of the cluster. Further, most of the early-type stars havenear-infrared fluxes as expected from their spectral types. Patchydistribution of ionized gas and dust appears to be the cause ofnonuniform extinction across the cluster face.
| The upper main sequence of OB associations. II - The single-lined O stars: Spectral classification of northern stars and lines of C and N
The properties of the stars close to the upper main sequence of OBassociations are studied in order to provide constraints on the theoryof evolution of massive stars. The spectral classification of northernsingle-lined O stars, most of them belonging to the associations CygOB1, Per OB1 and Cas OB6, is presented. The classification is performedaccording to Conti's classification scheme for O stars, amended byMathys (1988). The behavior of the C and N lines of the stars isstudied, in order to determine whether CNO-processed material is visibleat their surface. Three new ON stars have been discovered: BD + 36 deg4063 (O9.71), HD 13268 (O8V), and HD 110360 (O7V).
| Reddening and polarimetric studies toward IC 1805
Near IR and (V-I) photometry is presented for probable members in thecluster IC 1805. From a color-difference analysis, the ratio of total toselective absorption R(v), is found to be uniform across the cluster andcalculated to be 3.1 + or - 0.1. Assuming a distance modulus to theHyades of 3.3 mag, a distance to IC 1805 of 2.4 + or - 0.1 kpc isobtained by employing several ZAMS fitting calibrations. The resultantC-M diagram contains both MS and ZAMS B type stars, implying thatmassive star formation in the cluster was a continuous process.Photometric and spectroscopic data for foreground stars toward thecluster indicate that at least two-thirds of the reddening of thecluster is due to the general interstellar material (IM). Multicolorpolarimetric measurements are also presented for 24 probable clustermembers and for 49 foreground objects. It is concluded that the visualpolarization across the local galactic spiral arm is 5 percent, and thatthe size distribution of grains within IC 1805 is similar to that in theforeground region. After correcting for foreground IM, the residualintracluster polarization indicates that the cluster may be located neara Parker (1966) magnetic well with field strength similar to that of theforeground IM.
| The Einstein X-ray Observatory Catalog of O-type stars
A catalog of X-ray count rates for all O-type stars surveyed by theEinstein Observatory is presented. The procedures by which the IPC andHigh Resolution Imager rates are converted to emitted X-ray luminositiesare discussed in detail. The catalog contains 289 stars with 89detections and 176 upper bounds for the observed count rates. Precisepositions for 43 O-type stars are given whose previously known locationswere unknown or erroneous. It is argued that most O-type stars are X-raypoint sources, but some are possibly embedded in extended nebulae and/orbubbles. The X-ray spectra of O-type stars are discussed briefly, and itis argued that their mean spectrum can reasonably be taken as an 0.5 keVthermal bremsstrahlung model. It is argued that at least 30 percent ofall O-type stars are variable in X-rays.
| Galactic cluster star radial velocities obtained with a focal reducer field spectrograph. I - The clusters IC 1805, NGC 2287, NGC 2548, IC 4665, NGC 6633, NGC 6940 and NGC 7092
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...62..301G&db_key=AST
| Catalog of BV magnitudes and spectral classes of 6000 stars
The present catalog, compiled at the Abastumani Observatory, contains BVmagnitudes and spectral classes of about 6000 stars up to V(lim) = 13.0min five circular areas of 18 sq deg located near the salactic-equatorplane. The catalog is intended for star-statistics studies ofstar-formation regions.
| Additional Variable Stars in the Northern Luminous Stars Catalogues
Not Available
| Study of the open cluster IC 1805
Photoelectric magnitudes and colours in the UBV system have beendetermined for 169 stars in IC 1805. The reddening is variable acrossthe cluster. The distance modulus to the cluster is estimated at 11.7 m.Star-formation activities are still in progress in the cluster region.
| The initial mass function for massive stars
A machine readable catalog of over 750 galactic O stars with publishedphotometry, spectral types, and luminosity classes has been compiled.The catalog is probably complete to a distance of about 2.5 kpc. Fromthis volume-limited data, the initial mass function (IMF) for stars moremassive than 20 solar masses has been derived. This IMF differs fromthat of Miller and Scalo (1979) and of Lequeux (1979), in havingproportionately more O type stars and not as steep a fall-off in numberof stars with increasing mass. Dividing the sample into stars inside andoutside the solar circle, a substantial difference in the IMF of themost massive stars is found. There are proportionally more toward thegalactic center. This gradient in the IMF may be related to the observedspace density of Wolf-Rayet stars, which are descendants of O typestars.
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