AH Scorpii

AH Scorpii (abbreviated to AH Sco) 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.

AH Scorpii

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	Red supergiant
Spectral type	M4-5 Ia-Iab[3]
B−V color index	+2.57[4]
Variable type	SRc[3]
Astrometry
Radial velocity (Rv)	−13.40±2.4[5] 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[6] pc)
Absolute magnitude (MV)	−5.8[7]
Details
Mass	20[8] M☉
Radius	1,411±124[4] R☉
Luminosity	329,000±86,000[4] L☉
Surface gravity (log g)	−0.5[4] cgs
Temperature	3,682[4] K
Other designations
AH Sco, AN 223.1907, GSC 07365-00527, HD 155161, HIP 84071, CD−32°12429, 2MASS J17111702-3219308, IRC−30282, IRAS 17080-3215, RAFGL 1927, AAVSO 1704-32
Database references
SIMBAD	data

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.^[6] Gaia Data Release 3 includes a parallax of 0.5632±0.0799 mas, corresponding to a distance of about 1.9 kpc.^[1]

Characteristics

A visual band light curve for AH Scorpii, plotted from AAVSO data^[9]

AH Scorpii is a dust-enshrouded red supergiant^[10] and is classified as a semiregular variable star with a main period of 714 days. The total visual magnitude range is 6.5 - 9.6.^[2] No long secondary periods have been detected.^[11] 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.^[4] Its angular diameter was re-measured at 5.05±0.5 mas in 2023.^[12]

See also

• VY Canis Majoris
• NML Cygni
• KW Sagittarii
• UY Scuti