View source for V4998 Sagittarii

{{short description|Luminous blue variable star in the constellation Sagittarius}}
{{Starbox begin
| name        = V4998 Sagittarii
}}
{{Starbox image
| image       = [[File:LBV G0.120-0.048.jpg|280px]]
| caption     = V4998 Sagittarii and its surrounding shell nebula. The nebula appears as a transparent bubble-like body encircling the star.
| credit       = HST\NIMCOS
}}
{{Starbox observe
| constell    = [[Sagittarius (constellation)|Sagittarius]]
| epoch       = J2000
| equinox    = J2000
| ra         = {{nowrap|{{RA|17|46|05.625}}<ref name=2mass>{{cite journal |bibcode=2003yCat.2246....0C |title=VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) |journal=CDS/ADC Collection of Electronic Catalogues |pages=II/246 |volume=2246 |last1=Cutri |first1=Roc M. |last2=Skrutskie |first2=Michael F. |last3=Van Dyk |first3=Schuyler D. |last4=Beichman |first4=Charles A. |last5=Carpenter |first5=John M. |last6=Chester |first6=Thomas |last7=Cambresy |first7=Laurent |last8=Evans |first8=Tracey E. |last9=Fowler |first9=John W. |last10=Gizis |first10=John E. |last11=Howard |first11=Elizabeth V. |last12=Huchra |first12=John P. |last13=Jarrett |first13=Thomas H. |last14=Kopan |first14=Eugene L. |last15=Kirkpatrick |first15=J. Davy |last16=Light |first16=Robert M. |last17=Marsh |first17=Kenneth A. |last18=McCallon |first18=Howard L. |last19=Schneider |first19=Stephen E. |last20=Stiening |first20=Rae |last21=Sykes |first21=Matthew J. |last22=Weinberg |first22=Martin D. |last23=Wheaton |first23=William A. |last24=Wheelock |first24=Sherry L. |last25=Zacarias |first25=N. |year=2003 |url=http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246 }}</ref>}}
| dec       = {{nowrap|{{DEC|-28|51|31.92}}<ref name=2mass/>}}
| appmag_v  =
}}
{{Starbox character
| class=
| type=LBV<ref name=mauerhan>{{cite journal |title=Discovery of a Luminous Blue Variable with an Ejection Nebula Near the Quintuplet Cluster |journal=The Astrophysical Journal |last1=Mauerhan |first1=J. C. |last2=Morris |first2=M. R. |last3=Cotera |first3=A. |last4=Dong |first4=H. |last5=Wang |first5=Q. D. |last6=Stolovy |first6=S. R. |last7=Lang |first7=C. |last8=Glass |first8=I. S. |display-authors=5 |volume=713 |issue=1 |pages=L33–L36 |date=April 2010 |arxiv=1002.3379 |bibcode=2010ApJ...713L..33M |doi=10.1088/2041-8205/713/1/L33|s2cid=42696538 }}</ref><ref name=clark2018>{{cite journal |bibcode=2018A&A...618A...2C |title=An updated stellar census of the Quintuplet cluster |last1=Clark |first1=J. S. |last2=Lohr |first2=M. E. |last3=Patrick |first3=L. R. |last4=Najarro |first4=F. |last5=Dong |first5=H. |last6=Figer |first6=D. F. |journal=Astronomy and Astrophysics |year=2018 |volume=618 |pages=A2 |doi=10.1051/0004-6361/201833041 |arxiv=1805.10139 |s2cid=53501337 }}</ref>
| appmag_1_passband=B
| appmag_1=19.5<ref name=2mass/>
| appmag_2_passband=R
| appmag_2=17.2<ref name=2mass/>
| appmag_3_passband=J
| appmag_3=12.534<ref name=2mass/>
| appmag_4_passband=H
| appmag_4=9.239<ref name=2mass/>
| appmag_5_passband=K
| appmag_5=7.462<ref name=2mass/>
| variable=[[Luminous blue variable|LBV]]<ref name=mauerhan/>
}}
{{Starbox astrometry
 | radial_v =
 | prop_mo_ra =
 | prop_mo_dec =
 | parallax =
 | p_error =
 | parallax_footnote =
 | dist_ly =
 | dist_pc =8,000<ref name=mauerhan/>
 | absmag_v =
 | absmag_bol =
 }}
{{Starbox detail
| radius=463{{efn|name=radius}}
| luminosity  = 4,000,000<ref name=mauerhan/>
| temperature = 12,000<ref name=survey>{{cite journal|doi=10.1088/0004-637X/785/2/120|bibcode=2014ApJ...785..120L|arxiv = 1403.5298|title = Nature Versus Nurture: Luminous Blue Variable Nebulae in and Near Massive Stellar Clusters at the Galactic Center|journal=The Astrophysical Journal|volume=785|issue=2|pages=120|year = 2014|last1 = Lau|first1 = R. M.|last2=Herter|first2=T. L.|last3=Morris|first3=M. R.|last4=Adams|first4=J. D.|s2cid=118447462}}</ref>
| age=
}}
{{Starbox catalog
| names = [[Variable star designation|V]]4998&nbsp;Sagittarii, LBV&nbsp;G0.120-0.048, LBV3, [[2MASS]]&nbsp;J17460562-2851319, [[Spitzer Space Telescope|SSTGC]]&nbsp;595621
}}
{{Starbox reference
| Simbad      = 2MASS+J17460562-2851319
}}
{{Starbox end}}

'''V4998 Sagittarii''' is a [[luminous blue variable star]] (LBV) in the constellation of [[Sagittarius (constellation)|Sagittarius]]. Located some [[100 exametres|25,000 light-years]] away, the star is positioned about 7 [[parsec|pc]] (23 [[light-year|ly]]) 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 around 4 million times the [[Sun]] ({{Solar luminosity|link=y}}).  This places the star as one of the [[list of most massive stars|most massive]] and [[list of most luminous stars|luminous stars known]].

==Observational history==
[[File:Quintuplet cluster region (1002.3379).jpg|thumb|upright=1.4|left|Quintuplet cluster region centred on the [[Pistol Star]], with V4998 Sgr at top right]]
The star was first discovered in a 1993 survey that searched for bright [[near-infrared]] sources within 0.55°<sup>2</sup> of the [[Galactic Center]]. 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 (astronomer)|Shuji Sato]], and Kimiaki Kawara. The survey named the star NHS93&nbsp;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.<ref name=NHS>{{cite journal|bibcode=1993ApJ...406..501N|title=Bright near-infrared sources within 1 deg of the Galactic center. I - Survey and 1-20 micron photometry|journal=Astrophysical Journal|volume=406|pages=501|last1=Nagata|first1=Tetsuya|last2=Hyland|first2=A. R.|last3=Straw|first3=S. M.|last4=Sato|first4=Shuji|last5=Kawara|first5=Kimiaki|year=1993|doi=10.1086/172462|doi-access=free}}</ref>

The next observation was made by the [[2MASS]] survey, which took place in 1997-2001. The star was designated 2MASS&nbsp;J17460562-2851319 and its position, luminosity, and ''JHKs'' magnitudes were catalogued.<ref name=2mass/> 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&nbsp;10-1, GMC standing for Glass, Matsumoto, and Carter.<ref name=GMC>{{cite journal|bibcode = 2001MNRAS.321...77G|title = Large-amplitude variables near the Galactic Centre|journal = Monthly Notices of the Royal Astronomical Society|volume = 321|pages = 77–95|last1 = Glass|first1 = I. S.|last2 = Matsumoto|first2 = S.|last3 = Carter|first3 = B. S.|last4 = Sekiguchi|first4 = K.|year = 2001|issue = 1|doi = 10.1046/j.1365-8711.2001.03971.x|doi-access = free}}</ref>  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&nbsp;595621.<ref name=SPITZER>{{cite journal|bibcode = 2008ApJS..175..147R|arxiv = 0709.3113|last2 = Arendt|pages = 147–164|volume = 175|issue = 1|first2 = Richard G.|last3 = Sellgren|first3 = Kris|last4 = Stolovy|first4 = Susan R.|last5 = Cotera|first5 = Angela|last6 = Smith|first6 = Howard A.|last7 = Zadeh|first7 = Farhad Yusef|title = Point Sources from a Spitzer IRAC Survey of the Galactic Center|journal = The Astrophysical Journal Supplement Series|last1 = Ramírez|first1 = Solange V.|year = 2008|doi = 10.1086/524015|s2cid = 17768615}}</ref> It was also observed by a 2009 near-infrared survey that targeted the Galactic Center. 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.<ref name=MKN>{{cite journal|title = A near-infrared survey of Miras and the distance to the Galactic Centre|last1 = Matsunaga|first1 = Noriyuki|date = 2009|journal = Monthly Notices of the Royal Astronomical Society|doi = 10.1111/j.1365-2966.2009.15393.x|bibcode = 2009MNRAS.399.1709M|last2 = Kawadu|first2 = Takahiro|last3 = Nishiyama|first3 = Shogo|volume = 399|issue = 4|pages = 1709–1729|last4 = Nagayama|first4 = Takahiro|last5 = Hatano|first5 = Hirofumi|last6 = Tamura|first6 = Motohide|last7 = Glass|first7 = I. S.|last8 = Nagata|first8 = Tetsuya| doi-access=free |arxiv = 0907.2761 |s2cid = 13447758}}</ref>

[[File:V4998SgrLightCurve.png|thumb|left|A near-infrared ([[Photometric system#Photometric letters|K band]]) [[light curve]] for V4998 Sagittarii, adapted from Mauerhan ''et al.'' (2010)<ref name=mauerhan/>]]
A narrowband imaging survey of the Galactic Center region conducted by the [[Hubble Space Telescope]] (HST) Near Infrared Camera and Multi Object Spectrometer ([[NICMOS]]) revealed LBV G0.120-0.048 as a strong source of [[Paschen-alpha]] (Paschen-α) emission which exceeded that of the [[Pistol star]].<ref name="mauerhan"/> Therefore the star was selected for [[spectroscopy]]. The survey, which was conducted in 2010, confirmed that the star was a [[luminous blue variable]] and the star was designated LBV&nbsp;G0.120-0.048, LBV meaning luminous blue variable and G0.120-0.048 standing for its Galactic coordinates.<ref name="mauerhan"/> 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.<ref name="mauerhan"/> The star's [[stellar spectrum|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 assumed.<ref name="mauerhan"/> The extinction rates were measured and a luminosity of about {{Solar luminosity|4,000,000}} was obtained.<ref name="mauerhan"/> It also has the designation MMC2010 from a 2010 survey, MMC standing for the three leading scientists of the survey, Mauerhan, Morris, and Cotera.  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&nbsp;92.<ref name=DWC>{{cite journal|title = A multiwavelength study of evolved massive stars in the Galactic Centre|last1 = Dong|first1 = H.|date = 2011|journal = Monthly Notices of the Royal Astronomical Society|doi = 10.1111/j.1365-2966.2012.21200.x|bibcode = 2012MNRAS.425..884D|arxiv = 1204.6298|last2 = Wang|first2 = Q. D.|last3 = Morris|first3 = M. R.|issue = 2|volume = 425|pages = 884–906| doi-access=free |s2cid = 119217006}}</ref>

In 2014 a group decided to study the LBVs in the Quintuplet cluster. The mass of the star's nebula was measured at {{solar mass|6.2}}. Also measured was the star's [[effective temperature]] and it was found to be 12,000 [[kelvin|K]].<ref name=survey/> The star was designated LBV3 in that survey because it was the third LBV in the Quintuplet cluster.<ref name=survey/>

== Characteristics ==
V4998 Sgr's high mass compresses its core and accelerates fusion primarily by the [[CNO cycle]] which leads to a luminosity of about {{Solar luminosity|4,000,000}} and a temperature of 12000 [[kelvin|K]]. It boasts a large ejection [[nebula]] with a diameter of about 0.8 parsec (2.5 ly) and a mass of {{solar mass|6.2}}.<ref name=survey/> 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.<ref name=survey/>

The star is a projected 7 pc (23 ly) away from the Quintuplet starburst cluster, which lies in the direction of the [[Galactic Center]]. The cluster contains around 100 O-type stars and several Wolf–Rayet stars. There are also two other luminous blue variables beside V4998 Sagittarii: the [[Pistol star]] and qF362.<ref name="mauerhan"/>

== 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 star|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 and Ic supernovae|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 stars such as this one.<ref name="groh0114">{{Cite book|chapter=Evolution of very massive stars|title=Wolf–Rayet stars in the framework of stellar evolution |location=Liège |publisher=Université de Liège|volume=33|pages=81|last1=Ødegaard|first1=K. J. R.|series=Liège International Astrophysical Colloquia |date=1996|bibcode=1996LIACo..33...81O}}</ref>

==References==
{{reflist}}

==Notes==
{{notelist|refs=

{{efn | name=radius | Applying the [[Stefan-Boltzmann Law]] with a nominal [[sun|solar]] [[effective temperature]] of 5,772&nbsp;[[Kelvin|K]]: <math>\sqrt{(5772/12000)^4 * 4,000,000} = 462.72 </math>}}

}}

{{Stars of Sagittarius}}

{{DEFAULTSORT:LBV G0.120-0.048}}
[[Category:Luminous blue variables]]
[[Category:Sagittarius (constellation)]]
[[Category:Objects with variable star designations|Sagittarii, V4647]]
[[Category:2MASS objects|J17460562-2851319]]