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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.
| Diffuse interstellar bands of unprecedented strength in the line of sight towards high-mass X-ray binary 4U 1907+09
High-resolution VLT/UVES spectra of the strongly reddened O supergiantcompanion to the X-ray pulsar 4U 1907+09 provide aunique opportunity to study the nature of the diffuse interstellar bands(DIBs) at unprecedented strength. We detect about 180 known DIBs, ofwhich about 25 were listed as tentative and are now confirmed. A dozennew DIB candidates longwards of 6900 Å are identified. We showthat the observed 5797 Å DIB strength is in line with the Galacticcorrelation with reddening, whereas the 5780 Å DIB strength isrelatively weak. This indicates the contribution of denser regions,where the UV penetration is reduced. The presence of dense cloud coresis supported by the detection of C2 rotational transitions. Members ofone DIB family (5797, 6379 Å and 6196, 6613 Å) behavecoherently, although one can make a distinction between the twocorrelated pairs. The broadened profiles of narrow DIBs are shown to beconsistent with the premise that each of the main clouds in the line ofsight discerned in the interstellar K I profile is contributingproportionally to the DIB profile. We complement and extend the relationof DIB strength with reddening {E}(B-V), as well as withneutral hydrogen column density N(H I), respectively, using stronglyreddened sightlines towards another four distant HMXBs. The 5780 ÅDIB, and tentatively also the 5797 and 6613 Å DIBs, are bettercorrelated to the gas tracer H I than to the dust tracer{E}(B-V). The resulting relationship can be applied to anyline of sight to obtain an estimate of the H I column density. In thesearch for the nature of the DIB carrier, this strongly reddened line ofsight is a complementary addition to single cloud line of sight studies.
| VLT/UVES spectroscopy of the O supergiant companion to 4U 1907+09(7)
High-resolution optical spectra of the high-mass X-ray binary4U 1907+09 covering the wavelength range 4680-10 400Å indicate that the X-ray pulsar's massive companion is an O8/O9supergiant with a dense stellar wind. The interstellar atomic lines ofNa I and K I of this strongly reddened source ({E}(B-V) =3.45 mag) are used to set a lower limit to its distance: d ≈ 5 kpc,excluding the possibility that the massive companion is a Be star. Were-evaluate the system parameters; the new spectral classification of4U 1907+09's O supergiant companion is discussed inthe context of its similarity in X-ray and orbital properties toWray 15-977/GX 301-2. The Hαline shows variability similar to what is observed in other wind-fedsystems. A remarkable feature is the strong He ii 4686 Å emissionline, which possibly originates in the accretion flow towards the X-raypulsar.
| 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.
| Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..104..101S&db_key=AST
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| UBV photometry for southern OB stars
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
| MK spectral classifications for southern OB stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJS...35..111G&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | כתר דרומי |
| התרוממות ימנית: | 18h07m54.37s |
| סירוב: | -38°33'55.5" |
| גודל גלוי: | 7.334 |
| מרחק: | 288.184 פארסק |
| תנועה נכונה: | -1.5 |
| תנועה נכונה: | -5.2 |
| B-T magnitude: | 7.16 |
| V-T magnitude: | 7.32 |
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