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Star formation history of Canis Major R1. I. Wide-Field X-ray study of the young stellar population
Aims: The CMa R1 star-forming region contains several compact clustersas well as many young early-B stars. It is associated with a well-knownbright rimmed nebula, the nature of which is unclear (fossil HII regionor supernova remnant). To help elucidate the nature of the nebula, ourgoal was to reconstruct the star-formation history of the CMa R1 region,including the previously unknown older, fainter low-mass stellarpopulation, using X-rays. Methods: We analyzed images obtainedwith the ROSAT satellite, covering 5 sq. deg. Complementary VRIphotometry was performed with the Gemini South telescope.Colour-magnitude and colour-colour diagrams were used in conjunctionwith pre-main sequence evolutionary tracks to derive the masses and agesof the X-ray sources. Results: The ROSAT images show two distinctclusters. One is associated with the known optical clusters near Z CMa,to which 40 members are added. The other, which we name the “GUCMa” cluster, is new, and contains 60 members. The ROSAT sourcesare young stars with masses down to M_star 0.5 M_?, and ages upto 10 Myr. The mass functions of the two clusters are similar, but theGU CMa cluster is older than the cluster around Z CMa by at least a fewMyr. Also, the GU CMa cluster is away from any molecular cloud, implyingthat star formation must have ceased; on the contrary (as alreadyknown), star formation is very active in the Z CMa region.Based in part on observations obtained at the Gemini Observatory, whichis operated by the Association of Universities for Research inAstronomy, Inc., under a cooperative agreement with the NSF on behalf ofthe Gemini partnership: the National Science Foundation (United States),the Science and Technology Facilities Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), Ministério da Ciência eTecnologia (Brazil) and Ministerio de Ciencia, Tecnología eInnovación Productiva (Argentina).
| 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.
| Stellar associations in the region of CMa
Forty-three early-type stars brighter than 9 mag at 1640 A were observedin the region of CMa with the Glazar Space Telescope. The observed starsare shown to compose three groups situated at distances of 320, 570, and1100 pc. The first two groups are B-associations, and the third is anO-association. It is concluded that the dust matter situated atdistances up to 1000 pc yields an interstellar extinction parameter of0.7 mag at 1640 A.
| 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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