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Post Info TOPIC: B supergiant Sher 25


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Sher 25
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It is speculated that Sher 25 is near the point of going supernova, as it has recently thrown off matter in a pattern similar to that of supernova 1987A in the Large Magellanic Cloud, with a circumstellar ring and bipolar outflow filaments.
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Position (J2000): R.A. 11 15 07.8 | Dec. -61 15' 17''

Google earth file: Sher 25.kmz (1kb, kmz)



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RE: B supergiant Sher 25
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Title: The blue supergiant Sher 25 and its intriguing hourglass nebula
Authors: M. A. Hendry, S. J. Smartt, E. D. Skillman, C. J. Evans, C. Trundle, D. J. Lennon, P. A. Crowther, I. Hunter

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log[O/H] = 8.61 0.13 dex) is similar to that in the background nebula (8.56 0.07), suggesting the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 0.15, compared to the background value of 7.47 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M_sun, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

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Sher 25 is an old blue supergiant star located approximately 20,000 ly from the sun. Its Apparent magnitude is 12.2 and it is a B spectral type. It is part of the constellation Carina. This star as commonly thought to be nearing the point of exploding as a supernova and is located in H II region NGC 3603.

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-- Edited by Blobrana at 08:53, 2008-02-25

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