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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.
| 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.
| The stellar composition of the star formation region CMa R1 - II. Spectroscopic and photometric observations of nine young stars
We present new high- and low-resolution spectroscopic and photometricdata of nine members of the young association CMa R1. All the stars havecircumstellar dust at some distance, as could be expected from theirassociation with reflection nebulosity. Four stars (HD52721, HD53367,LkHα220 and LkHα218) show Hα emission and we arguethat they are Herbig Be stars with discs. Our photometric andspectroscopic observations of these stars reveal new characteristics oftheir variability. We present first interpretations of the variabilityof HD52721, HD53367 and the two LkHα stars in terms of a partiallyeclipsing binary, a magnetic activity cycle and circumstellar dustvariations, respectively. The remaining five stars show no clearindications of Hα emission in their spectra, although theirspectral types and ages are comparable with those of HD52721 andHD53367. This indicates that the presence of a disc around a star in CMaR1 may depend on the environment of the star. In particular we find thatall Hα emission stars are located at or outside the arc-shapedborder of the Hii region, which suggests that the stars inside the archave lost their discs through evaporation by UV photons from nearby Ostars, or from the nearby (<25pc) supernova, about 1Myr ago.
| The stellar composition of the star formation region CMa R1 - I. Results from new photometric and spectroscopic classifications
A new photometric and spectroscopic survey of the star formation region(SFR) CMa R1 is described. In a sample of 165 stars brighter than 13thmag, 88 stars were found to be probable members of the SFR. They aredefined as early-type stars with E(B-V)>=0.16mag, which correspondsto a distance of about 1kpc. 74 of the probable members are B stars. 19stars are possibly associated with an IRAS point source. We derive amost probable distance of 1050+/-150pc to the association. It appearsthat about 80 candidate members are pre-main-sequence stars with ageslower than 6 million years, while the main sequence extends over6.0-7.6mag, which is consistent with star formation starting about 8million years ago and continuing until at least half a million yearsago. Two bright B stars in the association (GU CMa and FZ CMa) seem tobe much older and probably do not originate from the same star formationepisode. The star formation efficiency appears to increase roughlymonotonically with time up to half a million years ago. From our data,we conclude that only a minor fraction of the stars has been createdthrough the scenario suggested by Herbst & Assousa, in which themembers of CMa R1 form by compression of ambient material by a supernovashock wave. An extensive search for candidate members with Hαemission did not reveal new Herbig Ae/Be candidates, so that the numberof stars in this class seems to be limited to four: Z CMa, LkHα218, LkHα 220 and possibly HD 53367.
| 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.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| Observations of the polarization of the radiation of R-association stars
A Ritchey-Chretien 1-m telescope was used to perform observations of thepolarization parameters of the radiation of stars in the reflectionnebulae in the regions of Cas, Per R1, Ser, and CMa R1. The connectionbetween the polarization vector and the structure of the nebulae isconsidered, and it is shown that the occurrence of polarization is dueboth to the absorption of the light of the stars and to scattering byelongated dust grains. The orientation of the grains is due to themagnetic field.
| R associations. VI - The reddening law in dust clouds and the nature of early-type emission stars in nebulosity from a study of five associations
Positions, identification charts, UBVRIKLMN photometry and spectraltypes are given for stars, illuminating reflection nebulae that arevisible on the POSS prints, which have been identified in fiveassociations. With a ratio of total to selective extinction of 4.2, thereddening law applicable to the dust clouds in which the stars areembedded is steeper than normal. The five associations exhibit 18early-type stars with circumstellar shells, of which those with spectraltypes earlier than B5 characteristically have weak IR excesses, incontrast to the strong excesses indicative of circumstellar dust, oflater-type stars. Color-magnitude charts show a distribution lying abovethe ZAMS by up to about 2 mag for both the circumstellar shell stars andthose classified as rapid rotators. It is suggested that (1) rapidrotation accounts for the scatter in the color-magnitude diagram, and(2) many of the nebulous early-type emission-line stars are rapidrotators rather than pre-main sequence objects.
| Canis Major OB1, Canis Major R1, NGC 2353, and W Canis Majoris.
Abstract image available at:http://adsabs.harvard.edu/abs/1978PASP...90..436E
| Optical and infrared properties of the newly formed stars in Canis Major R1
Abstract image available at:http://adsabs.harvard.edu/abs/1978ApJ...223..471H
| A study of the stellar association Canis Major OB 1.
Abstract image available at:http://adsabs.harvard.edu/abs/1974A&A....37..229C
| Investigation of a Milky Way field in Canis Major
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79.1022C&db_key=AST
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| Takýmyýldýz: | Tekboynuz |
| Sað Açýklýk: | 07h05m37.62s |
| Yükselim: | -11°09'26.2" |
| Görünürdeki Parlaklýk: | 9.378 |
| özdevim Sað Açýklýk: | -6.8 |
| özdevim Yükselim: | 1.5 |
| B-T magnitude: | 9.31 |
| V-T magnitude: | 9.373 |
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