VX Sagittarii

Last updated

VX Sagittarii
VXSgrLightCurve.png
A visual band light curve for VX Sagittarii, plotted from AAVSO data [1]
Observation data
Epoch J2000.0        Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 18h 08m 04.04831s [2]
Declination −22° 13 26.6327 [2]
Apparent magnitude  (V)6.5 - 14.0 [3]
Characteristics
Evolutionary stage AGB [4]
Spectral type M4eIa - M10eIa [5]
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 [3]
Astrometry
Radial velocity (Rv)+6.47±3.37 [6]  km/s
Proper motion (μ)RA: +0.36±0.76 [6]   mas/yr
Dec.: −2.92±0.78 [6]   mas/yr
Parallax (π)0.64 ± 0.04  mas [6]
Distance 5,100 ± 300  ly
(1,560 ± 100  pc)
Details
Mass 12 [7]   M
Radius 1,356, [4] between 1,120 and 1,550 [6] , 1,350–1,940 (pulsation) [8] , 1,480 [9] [lower-alpha 1]   R
Luminosity 195000±62000 [6]   L
Temperature 2,900 [10] (near min), 3,200-3,400 (near max) [7] , 2,400–3,300 [8]   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. [4]

Contents

Observations

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. [8]

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. [6]

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. [7] [8] 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. [6] Older studies frequently calculated higher luminosities. [11] [12]

The atmosphere of VX Sgr shows molecular water layers and SiO masers in the atmosphere, typical of an OH/IR star. [13] The masers have been used to derive a distance of 1,590 parsecs. [14] 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. [7]

Another paper from May 2018 suggests that VX Sagitarii may be a hypergiant. [6] 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. [4]

See also

Notes

  1. Calculated using angular diameter and distance in Table 1

Related Research Articles

<span class="mw-page-title-main">Asymptotic giant branch</span> Stars powered by fusion of hydrogen and helium in shell with an inactive core of carbon and oxygen

The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) late in their lives.

<span class="mw-page-title-main">Tau Sagittarii</span> Orange-hued giant star in the constellation Sagittarius

Tau Sagittarii is a star in the southern zodiac constellation of Sagittarius.

<span class="mw-page-title-main">X Sagittarii</span> Variable star and possible binary star system in the constellation Sagittarius

X Sagittarii is a variable star and candidate binary star system in the southern constellation of Sagittarius, near the western constellation boundary with Ophiuchus. It has a yellow-white hue and is visible to the naked eye with an apparent visual magnitude that fluctuates around 4.54. The star is located at a distance of approximately 950 light years from the Sun based on parallax, and is drifting closer with a radial velocity of −10 km/s. The star has an absolute magnitude of around −2.85.

KW Sagittarii is a red supergiant star, located approximately 2,420 parsecs away from the Sun in the direction of the constellation Sagittarius. It is one of the largest known stars, with a diameter about 1,000 times larger than the Sun. If placed at the center of the Solar System, the star's surface would engulf Mars, coming close to Jupiter's orbit.

<span class="mw-page-title-main">V725 Sagittarii</span> Star in the constellation Sagittarius

V725 Sagittarii is a variable star in the southern constellation of Sagittarius. As recently as a century ago, it was a Population II Cepheid; its transformation was documented by Henrietta Swope beginning in 1937, and is one of the most exciting and instructive events in variable-star astronomy. The star has varied between apparent visual magnitude 12.3 and 14.3.

<span class="mw-page-title-main">S Persei</span> Red supergiant or hypergiant variable star in the constellation Perseus

S Persei is a red supergiant or hypergiant located near the Double Cluster in Perseus, north of the cluster NGC 869. It is a member of the Perseus OB1 association and one of the largest known stars. If placed in the Solar System, its photosphere would engulf the orbit of Jupiter. It is also a semiregular variable, a star whose variations are less regular than those of Mira variables.

<span class="mw-page-title-main">TX Camelopardalis</span> Star in the constellation Camelopardalis

TX Camelopardalis is a Mira-type variable star in the constellation Camelopardalis. It is a classical long period variable star with pulsational period of 558.7 days. Water masers have been observed around the star.

<span class="mw-page-title-main">V4381 Sagittarii</span> Star in the constellation Sagittarius

V4381 Sagittarii is a variable star in the constellation Sagittarius. A white supergiant of spectral type A2/A3Iab, it is an Alpha Cygni variable that varies between apparent photographic magnitudes 6.57 and 6.62. Its visual apparent magnitude is about 6.54.

<span class="mw-page-title-main">OH/IR star</span>

An OH/IR star is an asymptotic giant branch (AGB) or a red supergiant or hypergiant star that shows strong OH maser emission and is unusually bright at near-infrared wavelengths.

<span class="mw-page-title-main">NML Cygni</span> Star in the constellation Cygnus

NML Cygni or V1489 Cygni is a red hypergiant or red supergiant (RSG) in the constellation Cygnus. It is possibly one of the largest known stars currently known, and is also possibly one of the most luminous and massive cool hypergiants, as well as one of the most luminous stars in the Milky Way.

<span class="mw-page-title-main">RY Sagittarii</span> Yellow supergiant star in the constellation Sagittarius

RY Sagittarii is a yellow supergiant and an R Coronae Borealis type variable star in the constellation Sagittarius. Although it ostensibly has the spectrum of a G-type star, it differs markedly from most in that it has almost no hydrogen and much carbon.

AH Scorpii is a red supergiant variable star located in the constellation Scorpius. It is one of the largest stars known by radius and is also one of the most luminous red supergiant stars in the Milky Way.

<span class="mw-page-title-main">XX Persei</span> Star in the constellation Perseus

XX Persei is a semiregular variable red supergiant star in the constellation Perseus, between the Double Cluster and the border with Andromeda.

<span class="mw-page-title-main">V4332 Sagittarii</span>

V4332 Sagittarii is a nova-like event in the constellation of Sagittarius. It was discovered February 24, 1994 at an apparent visual magnitude of 8.9 by Japanese amateur astronomer Minoru Yamamoto from Okazaki, Aichi, then confirmed by K. Hirosawa. Initially designated Nova Sagittarii 1994 #1, it was given the variable star designation V4332 Sgr. A spectra of the event taken March 4 lacked the characteristic features of a classical nova, with the only emission lines being of the Balmer series. Subsequent spectra showed a rapid decline in luminosity and a change of spectral type over a period of five days. By 2003, the object was ~1500 times less luminous than at peak magnitude and showed a spectrum of an M-type star.

<span class="mw-page-title-main">RT Virginis</span> Star in the constellation Virgo

RT Virginis is a variable star in the equatorial constellation of Virgo, abbreviated RT Vir. It ranges in brightness from an apparent visual magnitude of 7.7 down to 9.7, which is too faint to be visible to the naked eye. Based on parallax measurements made with the VLBI, the distance to this star is approximately 740 light years. It is receding from the Sun with a radial velocity of 17 km/s.

<span class="mw-page-title-main">U Sagittarii</span> Star in the constellation Sagittarius

U Sagittarii is a variable star in the southern constellation of Sagittarius, abbreviated U Sgr. It is a classical Cepheid variable that ranges in brightness from an apparent visual magnitude of 6.28 down to 7.15, with a pulsation period of 6.745226 days. At its brightest, this star is dimly visible to the naked eye. The distance to this star is approximately 2,080 light years based on parallax measurements, and it is drifting further away with a radial velocity of 2 km/s.

<span class="mw-page-title-main">R Crateris</span> Variable star in the constellation Crater

R Crateris is a star about 700 light years from the Earth in the constellation Crater. It is a semiregular variable star, ranging in brightness from magnitude 8.1 to 9.5 over a period of about 160 days. It is not visible to the naked-eye, but can be seen with a small telescope, or binoculars. R Crateris is a double star; the variable star and its magnitude 9.9 F8V companion are separated by 65.4 arcseconds.

<span class="mw-page-title-main">V356 Sagittarii</span> Star system in the constellation Sagittarius

V356 Sagittarii is an eclipsing binary star system in the southern constellation of Sagittarius, abbreviated V356 Sgr. It has a peak apparent visual magnitude of 6.84, which decreases to 7.66 during the primary eclipse and 7.24 with the secondary eclipse. Based on parallax measurements, this system is located at a distance of approximately 2,210 light years from the Sun.

<span class="mw-page-title-main">SW Virginis</span> Star in the constellation Virgo

SW Virginis is a star in the equatorial constellation of Virgo, abbreviated SW Vir. It is a variable star that ranges in brightness from an apparent visual magnitude of 6.65 down to 7.95, with a pulsation period of 153.8 days. The star is located at a distance of approximately 590 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −16 km/s. SW Vir is located near the ecliptic and is subject to lunar occultation, which has allowed its angular diameter to be directly measured.

References

  1. "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  2. 1 2 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.
  3. 1 2 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.
  4. 1 2 3 4 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.
  5. 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.
  6. 1 2 3 4 5 6 7 8 9 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.
  7. 1 2 3 4 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.
  8. 1 2 3 4 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 . ISSN   0035-8711.
  9. Wallstrom, S. H. J.; Danilovich, T.; Muller, H. S. P.; Gottlieb, C. A.; Maes, S.; Van de Sande, M.; Decin, L.; Richards, A. M. S.; Baudry, A.; Bolte, J.; Ceulemans, T.; De Ceuster, F.; de Koter, A.; Mellah, I. El; Esseldeurs, M. (7 December 2023). "ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA". Astronomy & Astrophysics. 681: A50. arXiv: 2312.03467 . doi:10.1051/0004-6361/202347632. ISSN   0004-6361.
  10. 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.
  11. 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.
  12. Mauron, N.; Josselin, E. (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. ISSN   0004-6361. S2CID   119276502.
  13. Greenhill, L. J.; et al. (1995). "The sio masers and dust shell of VX sgr". Astrophysics and Space Science. 224 (1–2): 469–470. Bibcode:1995Ap&SS.224..469G. doi:10.1007/BF00667909. ISSN   0004-640X. S2CID   189849486.
  14. 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 .

Further reading