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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.
| HD 121190: A cool multiperiodic slowly pulsating B star with moderate rotation
We have gathered and analysed multicolour Geneva photometry andhigh-resolution spectroscopy of the stars HD 121190 (B9V) and HD 106419(B9III) whose short-term periodic variability had become evident fromtheir HIPPARCOS data. We find three significant frequencies for HD121190 in the Geneva data: 2.6831, 2.6199 and 2.4713 c d-1and classify the star as a slowly pulsating B star, the coolest singlestar of that class known to date. Its amplitude ratios are compatiblewith low-degree gravity modes. The spectra reveal low-amplitudevariability and v sin i=118 km s-1 which implies that thestar rotates at 26% of its critical velocity. For HD 106419 we areunable to confirm the period found from the HIPPARCOS photometry in ourground-based data; rather we find a marginally significant frequency of0.8986 c d-1. This star is probably an evolved slowlypulsating B star with complex variations. HD 106409 is also a moderaterotator as the spectra reveal v sin i=78 km s-1, which isalso 26% of its critical velocity.Based on data gathered with the Swiss 0.7 m telescope equipped with thephotometer P7 of the Geneva Observatory and with the FEROS spectrographattached to the ESO 2.2 m telescope, both situated at La Silla in Chile.
| 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 MAIA candidate star HD 208727
HD 208727 is a suspected member of the enigmatic MAIA variables andshows the largest yet observed amplitude in light variation for any ofthe potential members. Proven beyond doubt pulsation would pose aserious problem for stellar modelling and opacities, because eitheropacity source for driving pulsation has to be a different or newidentified, yet unkown, pulsation mechanism. We conclude from ourinvestigation that rotation is a more likely explanation for the lightvariability of HD 208727.
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Osservazione e dati astrometrici
| Costellazione: | Mosca |
| Ascensione retta: | 12h14m49.31s |
| Declinazione: | -71°32'03.4" |
| Magnitudine apparente: | 8.303 |
| Distanza: | 301.205 parsec |
| Moto proprio RA: | -9.6 |
| Moto proprio Dec: | -3.6 |
| B-T magnitude: | 8.478 |
| V-T magnitude: | 8.318 |
Cataloghi e designazioni:
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