VX Sagittarii

Asymptotic giant branch star in the constellation Sagittarius

VX Sagittarii
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Sagittarius
Right ascension	18^h 08^m 04.04831^s^[1]
Declination	−22° 13′ 26.6327″^[1]
Apparent magnitude (V)	6.5 - 14.0^[2]
Characteristics
Evolutionary stage	AGB, (possibly TŻO)^[3]
Spectral type	M4eIa - M10eIa^[4]
Apparent magnitude (U)	11.72
Apparent magnitude (B)	9.41
Apparent magnitude (V)	6.52
Apparent magnitude (I)	2.11
Apparent magnitude (J)	1.23
Apparent magnitude (H)	0.13
Apparent magnitude (K)	−0.50
Apparent magnitude (L)	−1.61
Variable type	SRc^[2]
Astrometry

Radial velocity (R_v)	+6.47±3.37^[5] km/s
Proper motion (μ)	RA: +0.36±0.76^[5] mas/yr Dec.: −2.92±0.78^[5] mas/yr
Parallax (π)	0.64 ± 0.04 mas^[5]
Distance	5,100 ± 300 ly (1,560 ± 100 pc)

Details

Mass	12^[6] `M`_☉
Radius	1,356,^[3] between 1,120 and 1,550^[5], 1,350–1,940 (pulsation)^[7] `R`_☉
Luminosity	195000±62000^[5] `L`_☉
Temperature	2,900^[8] (near min), 3,200-3,400 (near max)^[6], 2,400–3,300^[7] K

Other designations
VX Sgr, HIP 88838, BD−22°4575, CD−22°12589, HD 165674, 2MASS J18080404-2213266, AAVSO 1802-22
Database references
SIMBAD	data

VX Sagittarii is an asymptotic giant branch star located more than 1.5 kiloparsec away from the Sun in the constellation of Sagittarius. It is a pulsating variable star with an unusually large magnitude range. It is one of the largest stars discovered, with a radius varying between 1,350 and 1,940 solar radii (940,000,000 and 1.35×10⁹ km; 6.3 and 9.0 au). It is the most luminous known AGB star, at bolometric magnitude –8.6, which is brighter than the theoretical limit at –8.0.^[3]

Observations

A visual band light curve for VX Sagittarii, plotted from AAVSO data^[9]

The star is classed as a cool semiregular variable of type SRc with a pulsational period of 732 days. The variations sometimes have an amplitude comparable to a long period variable, at other times they are much smaller. The spectral type varies between M4e around visual maximum and M9.8e at minimum light, and the luminosity class is Ia indicating a bright supergiant. The spectrum shows emission lines indicating that the star is losing mass through a strong stellar wind.^[7]

The annual parallax of VX Sagittarii has been measured as 0.64±0.06 mas, indicating a distance of about 5,100 light years. This is compatible with the distance to Sagittarius OB1, the stellar association that VX Sagittarii is thought to belong to. Its radial velocity and proper motions are also consistent with other members of the association.^[5]

Stellar characteristics

The effective temperature of VX Sagittarii is variable from around 2,400 K at visual minimum to around 3,300 K near maximum. Such low temperatures are comparable to the very coolest AGB stars and unprecedented for a massive supergiant.^[6]^[7] Its atmosphere is extended, irregular, and variable during the pulsations of the star, but the bolometric luminosity varies less than the visual brightness and is calculated to be about 195,000 L_☉. At an effective temperature of 3,300 K, the radius is expected to be somewhere between 1,120 R_☉ and 1,550 R_☉.^[5] Older studies frequently calculated higher luminosities.^[10]^[11]

The atmosphere of VX Sgr shows molecular water layers and SiO masers in the atmosphere, typical of an OH/IR star.^[12] The masers have been used to derive a distance of 1,590 parsecs.^[13] The spectrum also indicates strong VO and CN. In many respects the atmosphere is similar to low mass AGB stars such as Mira variables, but with a supergiant's luminosity and size.^[6]

Another paper from May 2018 suggests that VX Sagitarii may be a hypergiant.^[5] This would make it one of the very rare red hypergiant stars. However, a 2021 paper concludes that VX Sagittarii is a massive AGB star, rather than a red supergiant or hypergiant. Because it displays rubidium in its spectrum and has a high mass loss and luminosity, it is possible that it is a type of AGB star known as a super-AGB star, a type of star with masses in between low-mass stars and high-mass stars.^[3]

References

^ ^a ^b Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
^ ^a ^b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
^ ^a ^b ^c ^d Tabernero, H. M.; Dorda, R.; Negueruela, I.; Marfil, E. (2021). "The nature of VX Sagitarii". Astronomy & Astrophysics. 646: A98. arXiv:2011.09184. doi:10.1051/0004-6361/202039236. S2CID 227013580.
^ Kiss, L. L.; Szabó, G. M.; Bedding, T. R. (2006). "Variability in red supergiant stars: Pulsations, long secondary periods and convection noise". Monthly Notices of the Royal Astronomical Society. 372 (4): 1721–1734. arXiv:astro-ph/0608438. Bibcode:2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x. S2CID 5203133.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Xu, Shuangjing; Zhang, Bo; Reid, Mark J; Menten, Karl M; Zheng, Xingwu; Wang, Guangli (2018). "The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration". The Astrophysical Journal. 859 (1): 14. arXiv:1804.00894. Bibcode:2018ApJ...859...14X. doi:10.3847/1538-4357/aabba6. S2CID 55572194.
^ ^a ^b ^c ^d Chiavassa, A.; Lacour, S.; Millour, F.; Driebe, T.; Wittkowski, M.; Plez, B.; Thiébaut, E.; Josselin, E.; Freytag, B.; Scholz, M.; Haubois, X. (2009). "VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere". Astronomy and Astrophysics. 511: A51. arXiv:0911.4422. Bibcode:2010A&A...511A..51C. doi:10.1051/0004-6361/200913288. S2CID 55877127.
^ ^a ^b ^c ^d Lockwood, G.W.; Wing, R. F. (1982). "The light and spectrum variations of VX Sagittarii, an extremely cool supergiant". Monthly Notices of the Royal Astronomical Society. 198 (2): 385–404. Bibcode:1982MNRAS.198..385L. doi:10.1093/mnras/198.2.385.
^ García-Hernández, D. A; García-Lario, P; Plez, B; Manchado, A; d'Antona, F; Lub, J; Habing, H (2007). "Lithium and zirconium abundances in massive Galactic O-rich AGB stars". Astronomy and Astrophysics. 462 (2): 711. arXiv:astro-ph/0609106. Bibcode:2007A&A...462..711G. doi:10.1051/0004-6361:20065785. S2CID 16016698.
^ "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
^ De Jager, C.; Nieuwenhuijzen, H.; Van Der Hucht, K. A. (1988). "Mass loss rates in the Hertzsprung-Russell diagram". Astronomy and Astrophysics Supplement Series. 72: 259. Bibcode:1988A&AS...72..259D.
^ Nicolas Mauron; Eric Josselin (2010). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy & Astrophysics. 526: A156. arXiv:1010.5369v1. Bibcode:2011A&A...526A.156M. doi:10.1051/0004-6361/201013993. S2CID 119276502.
^ Greenhill; et al. (1995). "The SiO Masers and Dust Shell of VX SGR". Astrophysics and Space Science. 224 (1–2): 1–9. Bibcode:1995Ap&SS.224..469G. doi:10.1007/BF00667909. S2CID 189849486.
^ Chen, X.; Shen, Z. Q.; Xu, Y. (2007). "Measuring the Distance of VX Sagittarii with SiO Maser Proper Motions". Chinese Journal of Astronomy and Astrophysics. 7 (4): 531. Bibcode:2007ChJAA...7..531C. doi:10.1088/1009-9271/7/4/09.

Chiavassa, A.; et al. (February 2022), "The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE", Astronomy & Astrophysics, 658: A185, arXiv:2112.10695, Bibcode:2022A&A...658A.185C, doi:10.1051/0004-6361/202142514, S2CID 245335318, A185.
Su, Jiang-Bo; et al. (December 2020), "Observational characteristics of SiO masers around VX Sgr", Research in Astronomy and Astrophysics, 20 (12): 192, Bibcode:2020RAA....20..192S, doi:10.1088/1674-4527/20/12/192, S2CID 221408165, 192.
Su, J. B.; et al. (January 2018), "Dynamics of SiO Masers around VX Sgr", The Astrophysical Journal, 853 (1): 42, Bibcode:2018ApJ...853...42S, doi:10.3847/1538-4357/aaa12b, S2CID 125500678, 42.
Su, J. B.; et al. (September 2014), "Outward Motions of SiO Masers around VX Sgr", Journal of Astrophysics and Astronomy, 35 (3): 539–540, Bibcode:2014JApA...35..539S, doi:10.1007/s12036-014-9280-2, S2CID 255487708.
Su, J. B.; et al. (July 2012), "High-resolution VLBA Observations of Three 7 mm SiO Masers toward VX Sgr at Five Epochs", The Astrophysical Journal, 754 (1): 47, Bibcode:2012ApJ...754...47S, doi:10.1088/0004-637X/754/1/47, S2CID 120825137, 47.
Su, J. B.; et al. (June 2011), "Pumping Mechanisms for SiO Masers around VX Sgr", Journal of Astrophysics and Astronomy, 32 (1–2): 261–264, Bibcode:2011JApA...32..261S, doi:10.1007/s12036-011-9002-y, S2CID 121796389.
Lu, R. -S.; et al. (2010), "High-frequency VLBI Imaging of Sgr A* and VX Sgr", Proceedings of the 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radio arrays. September 20-24, 2010. Manchester, UK, vol. 10, p. 087, Bibcode:2010evn..confE..87L, doi:10.22323/1.125.0087, 87.
Chen, Xi; et al. (April 2006), "Inward Motions of the Compact SiO Masers around VX Sagittarii", The Astrophysical Journal, 640 (2): 982–994, arXiv:astro-ph/0512011, Bibcode:2006ApJ...640..982C, doi:10.1086/500168, S2CID 14240593.
Kamohara, Ryuichi; et al. (April 2005), "Time Variation of SiO Masers in VX Sagittarii over an Optically Quiescent Phase", Publications of the Astronomical Society of Japan, 57 (2): 341–345, Bibcode:2005PASJ...57..341K, doi:10.1093/pasj/57.2.341.
Murakawa, K.; et al. (September 2003), "The radially expanding molecular outflow of VX Sagittarii", Monthly Notices of the Royal Astronomical Society, 344 (1): 112, Bibcode:2003MNRAS.344....1M, doi:10.1046/j.1365-8711.2003.06626.x.
Yates, J. A.; et al. (2002), Mineese, Victor; Reid, Mark (eds.), "The H2O maser proper motions of RT Vir and VX Sgr", Cosmic Masers: From Proto-Stars to Black Holes, IAU Symposium #206, held 5-10 March 2001 in Angra dos Reis, Rio de Janeiro, Brazil, vol. 206, San Francisco: Astronomical Society of the Pacific, p. 298, Bibcode:2002IAUS..206..298Y.
Szymczak, M.; et al. (June 2001), "Magnetic field structure in the outer OH maser envelope of VX Sagittarii", Astronomy and Astrophysics, 371 (3): 1012–1017, Bibcode:2001A&A...371.1012S, doi:10.1051/0004-6361:20010451, S2CID 123021236.
Pashchenko, M. I.; Rudnitskii, G. M. (May 1999), "Observations of late-type variable stars in the water-vapor radio line. The supergiant VX Sagittarii", Astronomy Reports, 43 (5): 311–324, Bibcode:1999ARep...43..311P.
Berulis, I. I.; et al. (1999), "H2O maser emission of the M-type supergiant VX Sgr", Astronomical and Astrophysical Transactions, 18 (1): 77–82, Bibcode:1999A&AT...18...77B, doi:10.1080/10556799908203038.
Trigilio 7, C.; et al. (June 1998), "The circumstellar magnetic field of VX Sagittarii", Monthly Notices of the Royal Astronomical Society, 297 (2): 497–501, Bibcode:1998MNRAS.297..497T, doi:10.1046/j.1365-8711.1998.01538.x.{{citation}}: CS1 maint: numeric names: authors list (link)
Doeleman, S. S.; et al. (1998), Zensus, J. A.; Taylor, G. B.; Wrobel, J. M. (eds.), "86 GHz VLBI Imaging of the SiO Masers in VX SGR", Radio Emission from Galactic and Extragalactic Compact Sources, IAU Colloquium 164, ASP Conference Series, vol. 144, p. 363, Bibcode:1998ASPC..144..363D.
Zell, Philip J.; Fix, John D. (July 1996), "The Spatial Distribution of Circularly Polarized 1612 MHz OH Maser Emission From VX SGR", Astronomical Journal, 112: 252, Bibcode:1996AJ....112..252Z, doi:10.1086/118007.
Trigilio, C.; et al. (1996), Pallavicini, Roberto; Dupree, Andrea K. (eds.), "Magnetic field measurements in the circumstellar envelope of VX SGR", Cool stars, stellar systems, and the sun: Proceedings of the 9th Cambridge workshop; held 3-6 October 1995 in Florence, Italy, Astronomical Society of the Pacific Conference Series, vol. 109, San Francisco: Astronomical Society of the Pacific, p. 549, Bibcode:1996ASPC..109..549T.
Greenhill, Lincoln J.; et al. (June 1994), Breckinridge, James B. (ed.), "Circumstellar envelope of VX SGR resolved with long-baseline interferometry at millimeter and midinfrared wavelengths", Conference Proceedings of SPIE: Amplitude and Intensity Spatial Interferometry II, Amplitude and Intensity Spatial Interferometry II, vol. 2200, pp. 304–315, Bibcode:1994SPIE.2200..304G, doi:10.1117/12.177248, S2CID 120318207.
Greenhill, L. J.; et al. (May 1993), "The Circumstellar Envelope of VX SGR", Bulletin of the American Astronomical Society, 25: 824, Bibcode:1993AAS...182.2203G.
Yu, Zhiyao (June 1992), "The Circumstellar Envelope of VX-Sagittarii", Astrophysics and Space Science, 192 (1): 53–62, Bibcode:1992Ap&SS.192...53Y, doi:10.1007/BF00653259, S2CID 119015723.
Pijpers, F. P. (November 1990), "A model for the wind of the M supergiant VX Sagittarii", Astronomy and Astrophysics, 238: 256, Bibcode:1990A&A...238..256P.
Netzer, Nathan (July 1989), "Interaction of Dust and Radiation in Circumstellar Envelopes. I. The Expansion Velocity Gradient in the Envelope of VX Sagittarii", Astrophysical Journal, 342: 1068, Bibcode:1989ApJ...342.1068N, doi:10.1086/167663.
Chapman, J. M.; Cohen, R. J. (May 1986), "MERLIN observations of the circumstellar envelope of VX Sagittarius", Monthly Notices of the Royal Astronomical Society, 220 (3): 513–528, Bibcode:1986MNRAS.220..513C, doi:10.1093/mnras/220.3.513.
Smith, Horace A. (February 1978), "Beat Phenomena in the Light Curve of VX Sgr", The Journal of the American Association of Variable Star Observers, 6 (2): 63, Bibcode:1978JAVSO...6...63S.
Dinerstein, Harriet (1973), "VX Sagittarii: A Variable at Many Wavelengths", Journal of the American Association of Variable Star Observers, 2 (2): 52–59, Bibcode:1973JAVSO...2...52D.
Humphreys, Roberta M.; Lockwood, G. W. (March 1972), "Spectroscopic and Photometric Changes in the Peculiar Infrared Star VX Sagittarius", Astrophysical Journal, 172: L59, Bibcode:1972ApJ...172L..59H, doi:10.1086/180891.
Robinson, B. J.; et al. (March 1971), "Similarity of the OH Emissions from VX Sagittarii and VY Canis Majoris", Astrophysical Letters, 8: 171, Bibcode:1971ApL.....8..171R.

Constellation of Sagittarius

Stars

Bayer	α (Rukbat) β¹ (Arkab Prior) β² (Arkab Posterior) γ¹ (W) γ² (Alnasl) δ (Kaus Media) ε (Kaus Australis) ζ (Ascella) η θ¹ θ² ι κ¹ κ² λ (Kaus Borealis) μ (Polis) ν¹ (Ainalrami) ν² ξ¹ ξ² ο π (Albaldah) ρ¹ ρ² σ (Nunki) τ υ φ χ¹ χ² χ³ ψ ω (Terebellum)
Flamsteed	1 4 5 6 7 9 12 14 15 16 17 18 21 23 24 25 26 28 29 30 31 33 43 (d) 50 51 (h¹) 52 (h²) 53 54 (e¹) 55 (e²) 56 (f) 57 59 (b) 60 (A) 61 (g) 62 (c) 63 65 63 Oph
Variable	T U X (3) Y RR RS RY RZ VX VY VZ WZ XX XZ YY YZ AQ AS AV BB FN GM GU KW MV V348 V350 V356 V440 V505 V523 V526 V617 V630 V725 V732 V774 V919 V1017 V1059 V1216 V1223 V1647 V1942 V3792 V3795 V3804 V3879 V3885 V3890 V3892 V3894 V3903 (11) V3961 V3984 V4021 V4024 V4028 V4029 V4030 V4046 V4050 V4064 V4072 V4089 V4091 V4138 V4140 V4160 V4169 V4190 V4198 V4199 V4200 V4332 V4333 V4334 V4371 V4375 V4381 V4387 V4405 V4407 V4434 V4444 V4580 V4633 V4641 V4647 (Pistol Star) V4650 V4728 V4743 V4745 V4998 V5112 V5115 V5116 V5125 V5157 V5555 V5558 V5652 V5668 V5856
HR	6617 6679 6680 6691 6692 6693 6704 6716 6739 6748 6762 6766 6769 6777 6780 6788 6798 6835 6836 6838 6842 6864 6874 6889 6907 6909 6914 6919 6933 6936 6944 6960 6972 6988 6990 6998 7026 7029 7035 7038 7072 7104 7126 7128 7151 7159 7164 7166 7168 7182 7186 7195 7203 7205 7211 7230 7239 7240 7246 7265 7276 7277 7282 7316 7317 7327 7330 7334 7350 7355 7360 7367 7378 7380 7392 7398 7410 7433 7443 7454 7473 7491 7496 7507 7532 7538 7585 7616 7627 7629 7630 7631 7639 7643 7652 7658 7659 7703 7706 7725 7765 7799 7801 7808
HD	163296 163758 164604 (Pincoya) 164816 165052 169142 170657 171238 175390 175754 180902 181342 181720 183577 187085 187150 190647 313846 316285
Other	2MASS 19281982-2640123 2MASS J18352154–3123385 2MASS J19513587-3510375 4U 1755-33 4U 1820-30 A1742-294 Ap 1-11 AS 295 BD -18 5550 Bursting Pulsar CWISEP J1935-1546 GCIRS 13E 745 GGD 27 GRO J1744−28 GRS 1758-258 GS 1826-24 GX 3-1 GX 5-1 GX 9-1 GX 13+1 HATS-36 Herschel 36 HETE J1900.1-2455 IRAS 17423-1755 IRAS 18162−2048 GCIRS 3 GCIRS 7 GCIRS 8* GCIRS 16SW Gomez's Hamburger G0.238-0.071 K2-2016-BLG-0005L LBV 1806-20 LS IV -12 111 MACHO 176.18833.411 MACHO-1997-BLG-41 MACHO-98-BLG-35 NGC 6822-WR 12 PSR B1744−24A PSR B1749−28 PSR B1757−24 PSR B1758−23 PSR B1800−21 PSR B1821−24 PSR B1857−26 PSR J1808−2024 PSR J1747−2958 PSR J1748−2446ad S2 S55 S62 S4716 SAX J1747.0−2853 SAX J1808.4−3658 SAX J1810.8−2609 SWEEPS J175853.92−291120.6 SWEEPS J175902.00-291323.7 SWEEPS J175902.67−291153.5 Swift J1745-26 SWIFT J1756.9−2508 Th 4-4 W33A WASP-67 WD 0032−317 WR 102 c ea ka WR 101-2 WR 104 WR 110 WR 111 WR 112 XTE J1748−288 XTE J1807−294 XTE J1810−197 XTE J1814−338

Exoplanets	HATS-36b HD 164604 b HD 181720 b K2-2016-BLG-0005Lb KMT-2022-BLG-0440L b MOA-2007-BLG-192Lb MOA-2007-BLG-400Lb MOA-2009-BLG-387Lb MOA-2010-BLG-477Lb OGLE-2003-BLG-235Lb OGLE-2005-BLG-169Lb OGLE-2018-BLG-1119Lb OGLE-TR-10b OGLE-TR-56b SWIFT J1756.9-2508 b

Star
clusters

NGC	NGC 6440 NGC 6520 NGC 6522 NGC 6528 NGC 6530 NGC 6540 NGC 6544 NGC 6553 NGC 6558 NGC 6569 NGC 6603 NGC 6624 NGC 6638 NGC 6642 NGC 6717 NGC 6723
Other	1806−20 cluster 2MASS-GC02 Arches Cluster CO-0.40-0.22 Messier 18 Messier 21 Messier 22 Messier 23 Messier 25 Messier 28 Messier 54 Messier 55 Messier 69 Messier 70 Messier 75 Quintuplet cluster Small Sagittarius Star Cloud

Nebulae

NGC	NGC 6822 (Bubble Nebula) NGC 6445 NGC 6559 NGC 6563 NGC 6565 NGC 6578 NGC 6589 NGC 6590 NGC 6818
Other	Barnard 92 G1.9+0.3 HCN-0.009-0.044 Lagoon Nebula Large Molecule Heimat M 1-42 M2-42 Omega Nebula Pistol Nebula Red Spider Nebula Ring Nebula Trifid Nebula

Galaxies

NGC	NGC 6822 NGC 6902
Other	PKS 2000-330 Sagittarius Dwarf Irregular Galaxy Sagittarius Dwarf Spheroidal Galaxy

Galaxy clusters	ESO 593-8

Astronomical events	GLEAM-X J162759.5−523504.3 MOA-2007-BLG-192L MOA-2007-BLG-400L MOA-2009-BLG-387L MOA-2010-BLG-477L MOA-2011-BLG-262L OGLE-2003-BLG-235L OGLE-2005-BLG-169L Nova Sagittarii 1982