page_title: V4998 Sagittarii
section_title: Observational history
hierarchical_section_title: V4998 Sagittarii / Observational history
caption_attribution_description: English: Hubble Space Telescope image of the Quintuplet Cluster region. The Pistol Star is seen in the middle, surrounded by its ejection nebula. The luminous blue variable (LBV) star G0.120−0.048 is at the upper right, surrounded by a spherical nebula, believed to have been ejected by that star. LBV qF362 to the left of the Pistol Star also seems to be surrounded by a low-level nebular emission.
context_page_description: V4998 Sagittarii is an extremely luminous blue variable star in the constellation of Sagittarius. Located some 25,000 light years away, the star is positioned ~7 pc away from a starburst cluster known as the Quintuplet cluster. It has an ejection nebula measuring over 0.8 pc in diameter, formed 5000-10,000 years ago through large eruptions. The star has a large mass comparable to the Pistol star and a luminosity of ~4,000,000 times the Sun. This places the star as one of the most massive and luminous stars known.
context_section_description: The star was first discovered in a 1993 survey that searched for bright near-infrared sources within 0.55°² of the Galactic Centre. The survey used 1–20 micron photometry and used a two channel InSb detector on the 1 meter ANU telescope in Australia. 50 objects were targeted and most of them had bolometric magnitudes below -5. The star itself was observed in May 1987. Its Position, JHKLNMQ Magnitudes, Right ascension, Declination, and Silicate absorption were noted. The survey was conducted by Tetsuya Nagata, A. R. Hyland, S. M. Straw, Shuji Sato, and Kimiaki Kawara. 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.
  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. 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. 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. 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. 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.
  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. 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. 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. 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. The extinction rates were measured and a luminosity of ~4,000,000 L☉ was obtained. 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 92.
  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 at 6.2 M☉. Also measured was the star's temperature and it was found to be 12,000 K. The star was designated LBV3 in that survey because it was the third LBV in the Quintuplet cluster.
caption: Quintuplet cluster region centred on the Pistol Star, with V4998 Sgr at top right.
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