AH Scorpii
Red supergiant star in the constellation Scorpius
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AH Scorpii (abbreviated to AH Sco) is a red supergiant or hypergiant 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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scorpius |
| Right ascension | 17h 11m 17.01945s[1] |
| Declination | −32° 19′ 30.7140″[1] |
| Apparent magnitude (V) | 6.5 - 9.6[2] |
| Characteristics | |
| Evolutionary stage | OH/IR RSG[3] / RHG[4] |
| Spectral type | M4-5 Ia-Iab[5] |
| B−V color index | +2.57[6] |
| Variable type | SRc[5] |
| Astrometry | |
| Radial velocity (Rv) | −13.40±2.4[7] km/s |
| Proper motion (μ) | RA: −2.322±0.115[1] mas/yr Dec.: −2.610±0.068[1] mas/yr |
| Parallax (π) | 0.5632±0.0799 mas[1] |
| Distance | 7,400±620 ly (2,260±190[8] pc) |
| Absolute magnitude (MV) | −5.8[9] |
| Details | |
| Mass | 20[10] M☉ |
| Radius | 1,411±124[6] R☉ |
| Luminosity | 329,000±86,000[6] L☉ |
| Surface gravity (log g) | –0.5[6] cgs |
| Temperature | 3,682±190[6] K |
| Other designations | |
| AN 223.1907, IRC−30282, RAFGL 1927, AH Sco, AAVSO 1704-32, CD32°12429, HD 155161, HIP 84071, GSC 07365-00527, IRAS 17080-3215, 2MASS J17111702-3219308 | |
| Database references | |
| SIMBAD | data |
Observational history
In 1907, Henrietta Swan Leavitt and Edward Charles Pickering announced the discovery of this variable star.[12] It was given its variable star designation, AH Scorpii, in 1912.[13] The total visual magnitude range is 6.5 - 9.6.[2]
Distance
Prior to the 21st century, the distance of AH Scorpii was considered to be uncertain, between about 1.5 and 4.6 kpc. VLBI measurements of the masers have provided an accurate distance of 2,260 parsecs based on observation of SiO, H2O, and OH masers in its oxygen-rich circumstellar material. The masers were observed to be approaching the star at 13 km/s, indicating overall contraction at around phase 0.55 of the visual variations.[8] Gaia Data Release 3 includes a parallax of 0.5632±0.0799 mas, corresponding to a distance of about 1.9 kpc.[1]
Characteristics
The star is a dust-enshrouded red supergiant[14] and is classified as a semiregular variable star with a main period of 714 days.[2] No long secondary periods have been detected.[15]
Modelling of AH Scorpii near maximum light has determined an effective temperature of 3,682±190 K and a luminosity of 330,000±86,000 L☉. A radius of 1,411±124 R☉ was determined from an angular diameter of 5.81±0.15 mas and the given distance of 2.26±0.19 kpc.[6] Its angular diameter was re-measured at 5.05±0.5 mas in 2023.[16]