Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Sagittarius |
Right ascension | 18h 08m 04.04831s [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 (Rv) | +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] , 110,000–190,000 [7] L☉ |
Temperature | 2,900 [8] (near min), 3,200-3,400 (near max) [6] , 2,400–3,300 [7] K |
Other designations | |
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]
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]
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. [14] This would make it one of the very rare red hypergiant stars.
More recent[ when? ] papers state 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]
Red supergiants (RSGs) are stars with a supergiant luminosity class of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares A are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.
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.
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, located approximately 1,900 parsecs away from the Sun in the direction of the constellation Sagittarius. It is one of the largest-known stars. If placed at the center of the Solar System, the star's surface would engulf Mars.
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.
VY Canis Majoris is an extreme oxygen-rich (O-rich) red hypergiant (RHG) or red supergiant (RSG) and pulsating variable star 1.2 kiloparsecs from the Solar System in the slightly southern constellation of Canis Major. It is one of the largest known stars, one of the most luminous and massive red supergiants, and one of the most luminous stars in the Milky Way.
A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae.
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.
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.
IRC+10420, also known as V1302 Aql, is a yellow hypergiant star located in the constellation of Aquila at a distance of 4-6 kiloparsecs of the Sun.
HD 168607 is a blue hypergiant and luminous blue variable (LBV) star located in the constellation of Sagittarius, easy to see with amateur telescopes. It forms a pair with HD 168625, also a blue hypergiant and possible luminous blue variable, that can be seen at the south-east of M17, the Omega Nebula.
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 by radius, 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.
PZ Cassiopeiae is a red supergiant star located in the constellation of Cassiopeia, and a semi-regular variable star.
HD 179821 or V1427 Aquilae is either a post-red supergiant yellow hypergiant or a post-AGB yellow supergiant star in the constellation of Aquila, surrounded by a detached dust shell. It is a semi-regular variable nearing the end of its life.
UY Scuti (BD-12°5055) is a red supergiant star in the constellation Scutum. It is possibly considered one of the largest known stars by radius and is also a pulsating variable star, with a maximum brightness of magnitude 8.29 and a minimum of magnitude 10.56. Its radius has been given various estimates with high uncertainty, including 1,708 ± 192 solar radii (1.188×109 ± 134,000,000 kilometres; 7.94 ± 0.89 astronomical units), thus a volume nearly 5 billion times that of the Sun, as based on the modelling spectrum by the Very Large Telescope (VLT), and 755 solar radii (525,000,000 kilometres; 3.51 astronomical units), thus a volume over 2 billion times that of the Sun, as based on parallax measurements by the GAIA DR2 database. It is approximately 1.8 kiloparsecs (5,900 light-years) from Earth as measured by the GAIA EDR3 database. Nonetheless, based on these estimates, if placed at the center of the Solar System, its photosphere in general would possibly approach the orbit of Jupiter.
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.
XX Persei is a semiregular variable red supergiant star in the constellation Perseus, between the Double Cluster and the border with Andromeda.
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.
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.
{{citation}}
: CS1 maint: numeric names: authors list (link)