tosi philippe 11 625 PostĂ©(e) 10 janvier 2019 Excellent đ Partager ce message Lien Ă poster Partager sur dâautres sites
litobrit 2 217 PostĂ©(e) 10 janvier 2019 Merci Philippe Partager ce message Lien Ă poster Partager sur dâautres sites
litobrit 2 217 PostĂ©(e) 12 janvier 2019 Une information transmise par Pascal Le Du. Cette Ă©toile particuliĂšre et son enveloppe a Ă©tĂ© Ă©tudiĂ©e en spectroscopie haute rĂ©solution avec le SALT. Peut-ĂȘtre les prĂ©mices d'une nĂ©buleuse planĂ©taire ?  2018MNRAS.474.1412G - Mon. Not. R. Astron. Soc., 474, 1412-1425 (2018)  Optical spectroscopy of the blue supergiant Sk-69° 279 and its circumstellar shell with SALT. GVARAMADZE V.V., KNIAZEV A.Y., MARYEVA O.V. and BERDNIKOV L.N. Abstract (from CDS): We report the results of optical spectroscopy of the blue supergiant Sk-69° 279 and its circular shell in the Large Magellanic Cloud (LMC) with the Southern African Large Telescope (SALT). We classify Sk-69° 279 as an O9.2 Iaf star and analyse its spectrum by using the stellar atmosphere code CMFGEN, obtaining a stellar temperature of â30 kK, a luminosity of log (L*/ Lâ) = 5.54, a mass-loss rate of log({dot}M/ Mâ yrâ1) = -5.26, and a wind velocity of 800km sâ1. We found also that Sk-69° 279 possesses an extended atmosphere with an effective temperature of â24 kK and that its surface helium and nitrogen abundances are enhanced, respectively, by factors of â2 and 20-30. This suggests that either Sk-69° 279 was initially a (single) fast-rotating ( >= 400 km s^- 1^) star, which only recently evolved off the main sequence, or that it is a product of close binary evolution. The long-slit spectroscopy of the shell around Sk-69° 279 revealed that its nitrogen abundance is enhanced by the same factor as the stellar atmosphere, which implies that the shell is composed mostly of the CNO processed material lost by the star. Our findings support previous propositions that some massive stars can produce compact circumstellar shells and, presumably, appear as luminous blue variables while they are still on the main sequence or have only recently left it.  1 Partager ce message Lien Ă poster Partager sur dâautres sites