V4998 Sagittarii

V4998 Sagittarii

V4998 Sagittarii and its surrounding shell nebula. The nebula appears as a transparent bubble-like body encircling the star.
Credit: HST\NIMCOS
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 26h 65m 23.4s[1]
Declination −28° 85′ 88.66″[1]
Apparent magnitude (V) 12.53[2]
Characteristics
Evolutionary stage Luminous Blue Variable[2]
Spectral type B9
Variable type SRC[3]
Details
Radius300 R☉
Luminosity~4,000,000[2] L☉
Temperature12,000[3] K
Age~4,000,000 years
Other designations
2MASS J17460562-2851319, V4998 Sagittarii, SSTGC 595621, GMC2001 10-1, MMC2010, DWC2011 92, MKN2009 1066, NHS93 22, LBV3, LBV G0.120-0.048
Database references
SIMBADdata

V4998 Sagittarii is a luminous blue variable star (LBV) in the constellation of Sagittarius. Located some 25,000 light years away, the star is positioned ~7 pc (~23 ly) away from a starburst cluster known as the Quintuplet cluster.[2] It has an ejection nebula measuring over 0.8 pc in diameter, formed 5000-10,000 years ago through large eruptions.[3] The star has a large mass comparable to the Pistol star and a luminosity of ~4,000,000 solar luminosities (L☉).[3] This places the star as one of the most massive and luminous stars known. Despite the star's extreme luminosity, it glows dimly at magnitude 12.53 due to distance and extinction.[2]

Observational History

The star was first discovered in a 1993 survey that searched for bright near-infrared sources within 0.55²° of the Galactic Centre.[4] The survey used 1-20 micron photometry and used a two channel InSb detector on the 1 meter ANU telescope in Australia.[4] 50 objects were targeted and most of them had bolometric magnitudes below -5.[4] The star itself was observed in May 1987.[4] Its Position, JHKLNMQ Magnitudes, Right ascension, Declination, and Silicate absorption were noted.[4] The survey was conducted by Tetsuya Nagata, A. R. Hyland, S. M. Straw, Shuji Sato, and Kimiaki Kawara.[4] The survey named the star NHS93 22, NHS standing for the three leading scientists in the survey (Nagata, Hyland, and Straw); 93 signifying the date of discovery; and 22 indicating that it was the 22nd star observed.[4] The next observation was made by the 2MASS survey, which took place in 1997-2001. The star was designated 2MASS J17460562-2851319 and its position, luminosity, and JHKs magnitudes were catalogued.[5] After that, the star was observed in a 2001 survey called the "Study of Long Period Variables stars near the Galactic Centre." The survey named the star GMC2001 10-1, GMC standing for Glass, Matsumoto, and Carter.[6] V4998 Sagittarii was observed in 2003 by the General Catalog of Variable Stars (GCVS) and was designated V4889 Sagittarii, ‘’V’’ indicating that it was a variable star and 4889 denoting its serial number.[7] It was observed by the Infrared Array Camera on board the Spitzer Space Telescope in a 2008 survey covering 2.0 by 1.4 degrees (280 by 210 pc) and was given the name SSTGC 595621.[8] It was also observed by a 2009 near-infrared survey that targeted the Galactic Centre. The star was designated MKN2009 in that survey, MKN standing for the three leading scientists (Matsunaga, Kawadu, and Nishiyama) and 2009 specifying the date of the survey.[9] A narrowband imaging survey of the Galactic centre region conducted by the Hubble Space Telescope, (HST), Near Infrared Camera, (NIC), and Multi Object Spectrometer (NIMCOS) revealed LBV G0. 120-0.048 as a strong source of Paschen-alpha (Paschen-α) which exceeded that of the Pistol star.[2] The star was selected for spectroscopy by a group of astronomers owing to that cause. The survey, which was conducted in 2010, confirmed that the star was a luminous blue variable and the star was named LBV G0.120-0.048, LBV meaning luminous blue variable and G0.120-0.048 standing for its Galactic coordinates.[2] It was also found through the use of Pα imaging that the star had a large ejection nebula with a diameter over 0.8 pc which was ejected by it 5000-10,000 years ago through large eruptions.[2] The star's spectrum was studied and it was found that the spectrum was similar to the Pistol star so a mass similar to the Pistol star was derived.[2] The extinction rates were measured and a luminosity of ~4,000,000 L☉ was obtained.[2] It also has another name of MNC2010, the name MMC standing for the three leading scientists of the survey, Mauerhan, Morris, and Cotera. The survey took place in 2010, hence the name MMC2010. In 2011, a survey led by Dong, Wang, and Cotera reached for stars in the Galactic centre that emitted Paschen-α. The stars targeted were the ones detected from the HST/NICMOS Paschen-α survey of the Galactic Centre. V4998 Sagittarii was one of the stars observed and it was given another designation of DWC2011 22.[10] The most recent survey was in 2014, when a group decided to study the LBVs in the Quintuplet cluster. The star's nebula's mass was measured and it was found that it had a mass of 6.2 M☉. Also measured was the star's temperature and it was found that it was 12,000 K.[3] The star was designated LBV3 in that survey because it was the third LBV in the Quintuplet cluster.[3]

Characteristics

V4998 Sgr’s high mass compresses its core and ignites fusion using the CNO cycle which leads to a luminosity of ~4,000,000 L☉ and a temperature of 12,000 K (11,700 °C; 21,100 °F). It boasts a large ejection nebula with a diameter of ~0.8 parsec (~2.5 ly) and a mass of 6.2 M☉.[3] Since comparable nebulae typically last no more than 10,000 years, V4998 Sagittarii is presumed to have undergone a massive eruption 5000-10,000 years ago.[3]

The star is a projected ~7 pc (~23 ly) away from the Quintuplet starburst cluster.[2] The cluster itself is close to the Galactic center. Most stars that are near to the Galactic center are extreme Population I stars and have very high metallicities which makes the massive stars relatively short-lived. The cluster contains around 100 O stars and a few Wolf-Rayet stars. There are also two other luminous blue variables beside V4998 Sagittarii: the Pistol star and qF362. Although V4998 Sagittarii is not in the Quintuplet cluster, its mass and velocity indicate that it once resided in the cluster, but then was then ejected, presumably by a stellar merger which would have given the star an extra boost to its velocity. Another possibility is that the star could have formed within the same molecular cloud as the Quintuplet cluster, but never became a bound member of the cluster.[2]

Evolution

The star's high mass loss rate combined with its eruptions will strip off its hydrogen layers and expose a hot helium core. It will proceed to the Wolf-Rayet sequence. It will eventually start fusing heavy elements in its core, and when it develops a large iron core the star will collapse in on itself and explode as a type Ib or Ic supernovae. Depending on the amount of mass lost before the supernova explosion, the remnant will be a neutron star or black hole. A black hole is predicted for the most massive starts such as this one.[11]

See also

References

  1. ↑ 1.0 1.1 Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C 2246: 0. Bibcode:2003yCat.2246....0C.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 Mauerhan, J. C.; Morris, M. R.; Cotera, A.; Dong, H.; Wang, Q. D. et al. (April 2010). "Discovery of a Luminous Blue Variable with an Ejection Nebula Near the Quintuplet Cluster". The Astrophysical Journal 713 (1): L33–L36. arXiv:1002.3379. Bibcode:2010ApJ...713L..33M. doi:10.1088/2041-8205/713/1/L33.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Lau, R. M.; Herter, T. L.; Morris, M. R.; Adams, J. D. (2014). "Nature versus Nurture: Luminous Blue Variable Nebulae in and near Massive Stellar Clusters at the Galactic Center". The Astrophysical Journal 785 (2): 120. arXiv:1403.5298. Bibcode:2014ApJ...785..120L. doi:10.1088/0004-637X/785/2/120. Retrieved 2014.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Nagata, Tetsuya; Hyland, A. R.; Straw, S. M.; Sato, Shuji; Kawara, Kimiaki (1993). "Bright near-infrared sources within 1 deg of the Galactic centre". The Astrophysical Journal 406: 501–511. Bibcode:1993ApJ...406..501N. doi:10.1086/172462. ISSN 0004-637X.
  5. ↑ "SIMBAD: 2MASS J17460562-2851319". SIMBAD. SIMBAD.
  6. ↑ Glass, I. S.; Matsumoto, S.; Carter, B. S.; Sekiguchi, K. (2001). "Large-amplitude variables near the Galactic Centre". Monthly Notices of the Royal Astronomical Society. Monthly Notices of the Royal Astronomical Society 321 (1): 77–95. Bibcode:2001MNRAS.321...77G. doi:10.1046/j.1365-8711.2001.03971.x.
  7. ↑ "GCVS Query result; V4998 Sagittarii".
  8. ↑ Ramírez, Solange V.; Arendt, Richard G.; Sellgren, Kris; Stolovy, Susan R.; Cotera, Angela; Smith, Howard A.; Zadeh, Farhad Yusef (2008). "Point Sources from a Spitzer IRAC Survey of the Galactic Center". The Astrophysical Journal 175 (1): 147–164. arXiv:0709.3113. Bibcode:2008ApJS..175..147R. doi:10.1086/524015.
  9. ↑ Matsunaga, Noriyuki; Kawadu, Takahiro; Nishiyama, Shogo; Nagayama, Takahiro; Hatano, Hirofumi; Tamura, Motohide; Glass, I. S.; Nagata, Tetsuya (2009). "A near-infrared survey of Miras and the distance to the Galactic Centre". Monthly Notices of the Royal Astronomical Society 399 (4): 1709–1729. Bibcode:2009MNRAS.399.1709M. doi:10.1111/j.1365-2966.2009.15393.x.
  10. ↑ Dong, H.; Wang, Q. D.; Morris, M. R. (2011). "A multiwavelength study of evolved massive stars in the Galactic Centre". Monthly Notices of the Royal Astronomical Society 425 (2): 884–906. arXiv:1204.6298. Bibcode:2012MNRAS.425..884D. doi:10.1111/j.1365-2966.2012.21200.x.
  11. ↑ Ødegaard, K. J. R. (1996). "Evolution of very massive stars". Wolf-Rayet stars in the framework of stellar evolution. Liege: Universite de Liege 33: 81. Bibcode:1996LIACo..33...81O.