Archive for the ‘Wolf Rayet’ Category

Wolf-Rayet WR103 in Sagittarius

Posted by Paulo Cacella on 15th August 2010 in Spectroscopy, Stars, Wolf Rayet, Wolf-Rayet
WR103 is also know as HD164270 / V4072SGR / HIP 88287 / SAO 209609 is a Wolf-Rayet star in Sagittarius. / / / /Wolf–Rayet stars (often referred to as WR stars) are evolved, massive stars (over 20 solar masses), which are losing mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s. While our own Sun loses approximately 10?14 solar masses every year, Wolf–Rayet stars typically lose 10?5 solar masses a year. / / / /Wolf–Rayet stars are very hot, with surface temperatures in the range of 25,000 K to 50,000 K. / / / /Wolf–Rayet stars are a normal stage in the evolution of very massive stars, in which strong, broad emission lines of helium and nitrogen (“WN” sequence) or helium, carbon, and oxygen (“WC” sequence) are visible. Due to their strong emission lines they can be identified in nearby galaxies. About 300 Wolf–Rayets are catalogued in our own Milky Way Galaxy. This number has changed during the last years as the result of very deep photometric and spectroscopic surveys dedicated to discovering this kind of object in the Galactic plane. Additionally, about 100 are known in the Large Magellanic Cloud, while only 12 have been identified in the Small Magellanic Cloud, and a few more in galaxies in the Local Group, and nearby galaxies (M83NGC300, etc.). / / / /Several astronomers, among them Rublev (1965) and Conti (1976), originally proposed that the WR stars as a class are descended from massive O-stars in which the strong stellar winds characteristic of extremely luminous stars have ejected the unprocessed outer H-rich layers. The characteristic emission lines are formed in the extended and dense high-velocity wind region enveloping the very hot stellar photosphere, which produces a flood of UV radiation that causes fluorescence in the line-forming wind region. This ejection process uncovers in succession, first the nitrogen-rich products of CNO cycle burning of hydrogen (WN stars), and later the carbon-rich layer due to He burning (WC & WO stars). Most of these stars are believed finally to progress to become supernovae of Type Ib or Type Ic. A few (roughly 10%) of the central stars of planetary nebulae are, despite their much lower (typically ~0.6 solar) masses, also observationally of the WR-type; i.e., they show emission line spectra with broad lines from helium, carbon and oxygen. Denoted [WR], they are much older objects descended from evolved low-mass stars and are closely related to white dwarfs, rather than to the very young, very massive stars that comprise the bulk of the WR class. / /

Evolution models

/ /Evolution models of WR stars. / / / /For stars of ~75MS / /
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  • O ? WN(H-rich) ? LBV ? WN(H-poor) ? WC ? SN Ic
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/ /For stars of ~40-75MS / /
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  • O ? LBV ? WN(H-poor) ? WC ? SN Ic
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/ /For stars of 25-40MS / /
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  • O ? LBV ? WN(H-poor) ? SN Ib
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/ /OR / /
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  • O ? RSG ? WN(H-poor) ? SN Ib
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/ /It is possible for a Wolf–Rayet star to progress to a “collapsar” stage in its death throes: This is when the core of the star collapses to form a black hole, pulling in the surrounding material. This is thought to be the precursor of a long gamma-ray burst. / / / /The best known (and most visible) example of a Wolf–Rayet star is Gamma 2 Velorum (?² Vel), which is a bright star visible to those located south of 40 degrees northern latitude. One of the members of the star system (Gamma Velorum is actually at least six stars) is a Wolf–Rayet star. Due to the exotic nature of its spectrum (bright emission lines in lieu of dark absorption lines) it is dubbed the “Spectral Gem of the Southern Skies”. / / / /To understand better WR stars take a look here in this paper / / / /Our first WR target is WR103. A 8.8 magnitude star in Sagittarius. It is a WC9 star with surface temperature of around 50K Kelvin and absolute magnitude of -4.6. The distance is approx 6200 ly / / / /Then we get the synthetic CCD visual spectrum. This is awesome with pronounced lines. / / / / / / / /Then we have my spectrum showing all the main lines / / / / / / / /And a Reference Spectrum / / / /