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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.
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| Photometry of stars in the uvgr system
Photoelectric photometry is presented for over 400 stars using the uvgrsystem of Thuan and Gunn. Stars were selected to cover a wide range ofspectral type, luminosity class, and metallicity. A mean main sequenceis derived along with reddening curves and approximate transformationsto the UBVR system. The calibration of the standard-star sequence issignificantly improved.
| H I, galaxy counts, and reddening - Variation in the gas-to-dust ratio, the extinction at high galactic latitudes, and a new method for determining galactic reddening
The interrelationships among Shane-Wirtanen (1967) galaxy counts, H Icolumn densities, and reddenings are reanalyzed, and many of theproblems raised by Heiles (1976) are resolved. These problems werecaused by two factors: subtle biases in the reddening data and avariable gas-to-dust ratio in the galaxy. A compilation of reddeningsfor RR Lyrae stars and globular clusters which are on the same systemand which are believed to be relatively free of biases is presented. Theextinction at the galactic poles, as determined by galaxy counts, isreexamined by using a new method to analyze galaxy counts. This methodpartially accounts for the nonrandom clustering of galaxies and permitsa reasonable estimate of the error in log N(gal) as a function oflatitude. The analysis shows that galaxy counts (or galaxy clustercounts) are too noisy to allow direct determination of the extinction orthe variation in extinction near the galactic poles. From all availabledata it is concluded that the reddening at the poles is small andirregularly distributed. It is found that there are zero offsets in therelations between E(B-V) and H I, and between galaxy counts and H I,which are at least partly the result of an instrumental effect in theradio data.
| Interstellar Absorption in the North Equatorial Polar Region.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962ApJ...136..363A&db_key=AST
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| Takýmyýldýz: | Kral-Sefe |
| Sað Açýklýk: | 01h15m30.81s |
| Yükselim: | +81°28'47.0" |
| Görünürdeki Parlaklýk: | 9.935 |
| özdevim Sað Açýklýk: | 1.7 |
| özdevim Yükselim: | -0.7 |
| B-T magnitude: | 9.866 |
| V-T magnitude: | 9.93 |
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