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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.
| Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
| On the apparent normality of O and B stars far from the galactic plane
Results of a search for subluminosity or other peculiarities in thespectra of apparently normal OB stars located at large distances fromthe galactic plane are presented. Photographic spectrograms werecompared for stars of type B5 and earlier located within 0.5 kpc of andfurther than 1.5 kpc from the galactic plane, and for three subdwarfstars. Values of the projected axial rotation, surface gravity, absolutemagnitude and the strengths of certain He I and Balmer lines determinedfor both groups of OB stars are found to be similar, and distinct fromthe spectral characteristics of the subdwarfs. The results suggest that,unless the normality of the distant OB stars is illusory, either OBstars can be formed outside the galactic plane, or a mechanism mustexist to eject them from the plane with large velocities, unless theirmain sequence lifetimes are substantially longer than currentlybelieved.
| Four-colour and H beta photometry of southern B stars at high galactic latitudes
Four-color and H beta photometry has been obtained for 105 early-type HDstars with galactic latitudes less than -45 deg. They are mostly late Bstars of luminosity class V to III. Two new Am stars and several Ap orBp stars are detected photometrically. Absolute magnitudes aredetermined from the photometry and from MK types where available. Theinterstellar reddening of many of the more distant stars is very small,suggesting either the existence of undetected peculiar stars in thesample or that there are areas of effectively zero reddening at highsouthern galactic latitudes.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דלי |
| התרוממות ימנית: | 22h15m39.23s |
| סירוב: | -24°35'00.6" |
| גודל גלוי: | 9.358 |
| תנועה נכונה: | -2 |
| תנועה נכונה: | -13.6 |
| B-T magnitude: | 9.248 |
| V-T magnitude: | 9.349 |
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