Sher 25

Sher 25 is a blue supergiant star in the constellation Carina, located approximately 25,000 light years from the Sun in the H II region NGC 3603 of the Milky Way.[5] It is a spectral type B1Iab star with an apparent magnitude of 12.2.[6] Its initial main sequence mass is calculated at 60 times the mass of our Sun, but a star of this type will have already lost a substantial fraction of that mass. It is unclear whether Sher 25 has been through a red supergiant phase or has just evolved from the main sequence, so the current mass is very uncertain.[4]

Sher 25

HST image of NGC 3603. Sher 25 is the bright star at the 1 o'clock position relative to the center of the cluster, between two patches of nebula and with a faint ring surrounding it.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Carina
Right ascension  11h 15m 7.649s[1]
Declination −61° 15′ 17.59″[1]
Apparent magnitude (V) 12.23[1]
Characteristics
Spectral type B1Iab[1]
U−B color index 0.13[2]
B−V color index 1.42[2]
Variable type cLBV[3]
Astrometry
Distance25,000[1] ly
(7,600[1] pc)
Absolute magnitude (MV)-7.8[1]
Details
Mass40 ± 5[4] M☉
Radius54[1] R☉
Luminosity (bolometric)608,000[1] L☉
Surface gravity (log g)2.6[4] cgs
Temperature22,000[1][4] K
Rotational velocity (v sin i)65[3] km/s
Age4[1] Myr
Other designations
Sher 25, NGC 3603-25, NGC 3603 MTT 13, NGC 3603 MDS 5
Database references
SIMBADdata

The name derives from the original cataloguing of stars in NGC 3603 by David Sher. This catalogue entry is more properly referred to as NGC 3603 Sher 25 to distinguish it from stars numbered 25 by Sher in other clusters. The same star was numbered 13 by Melnick, Tapia, and Terlevich[2] (NGC 3603 MTT 13) and 5 in a Hubble Space Telescope survey by Moffat, Drissen, and Shara[7] (NGC 3603 MDS 5).

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.[3]

Regular variations in the doppler shift of the star's spectral lines with a period of a few days have suggested orbital motion about a companion star, but pulsations are a more likely explanation.[8]

References
  1. Melena, N. W.; Massey, P.; Morrell, N. I.; Zangari, A. M. (2008). "The Massive Star Content of Ngc 3603". The Astronomical Journal. 135 (3): 878. arXiv:0712.2621. Bibcode:2008AJ....135..878M. doi:10.1088/0004-6256/135/3/878.
  2. Melnick, J.; Tapia, M.; Terlevich, R. (1989). "The galactic giant H II region NGC 3603". Astronomy and Astrophysics. 213: 89. Bibcode:1989A&A...213...89M.CS1 maint: uses authors parameter (link)
  3. Smartt, S. J.; Lennon, D. J.; Kudritzki, R. P.; Rosales, F.; Ryans, R. S. I.; Wright, N. (2002). "The evolutionary status of Sher 25 - implications for blue supergiants and the progenitor of SN 1987A". Astronomy and Astrophysics. 391 (3): 979. arXiv:astro-ph/0205242. Bibcode:2002A&A...391..979S. doi:10.1051/0004-6361:20020829.
  4. Hendry, M. A.; Smartt, S. J.; Skillman, E. D.; Evans, C. J.; Trundle, C.; Lennon, D. J.; Crowther, P. A.; Hunter, I. (2008). "The blue supergiant Sher 25 and its intriguing hourglass nebula". Monthly Notices of the Royal Astronomical Society. 388 (3): 1127. arXiv:0803.4262. Bibcode:2008MNRAS.388.1127H. doi:10.1111/j.1365-2966.2008.13347.x.
  5. Sher, D. (1965). "Distances of Five Open Cluster Near Eta Carinae". Monthly Notices of the Royal Astronomical Society. 129 (3): 237–262. Bibcode:1965MNRAS.129..237S. doi:10.1093/mnras/129.3.237. ISSN 0035-8711.
  6. Brandner, Wolfgang; Grebel, Eva K.; Chu, You-Hua; Weis, Kerstin (January 1997). "Ring Nebula and Bipolar Outflows Associated with the B1.5 Supergiant Sher 25 in NGC 3603". Astrophysical Journal Letters. 475: L45. arXiv:astro-ph/9611046. Bibcode:1997ApJ...475L..45B. doi:10.1086/310460.
  7. Moffat, A. F. J.; Drissen, L.; Shara, M. M. (1994). "NGC 3603 and its Wolf-Rayet stars: Galactic clone of R136 at the core of 30 Doradus, but without the massive surrounding cluster halo". The Astrophysical Journal. 436: 183. Bibcode:1994ApJ...436..183M. doi:10.1086/174891.
  8. Taylor, W. D.; Evans, C. J.; Simon-Diaz, S.; Sana, H.; Langer, N.; Smith, N.; Smartt, S. J. (2014). "Sher 25: pulsating but apparently alone". Monthly Notices of the Royal Astronomical Society. 442 (2): 1483–1490. arXiv:1405.2101. Bibcode:2014MNRAS.442.1483T. doi:10.1093/mnras/stu925. ISSN 0035-8711.
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