SU Persei

SU Persei is a red supergiant star located in the constellation of Perseus. It is located within the Double Cluster, 7,250⁺⁴⁷⁰
₋₄₂₀ light-years away.^[10] It is a semiregular variable star^[3] that ranges in brightness from magnitude 7.2 to 8.7,^[3] which makes it too faint to be seen with the naked eye, but can be seen with binoculars or a telescope.

SU Persei

Location of SU Persei (circled) near the Double Cluster (north is towards bottom right)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Perseus[1]
Right ascension	02h 22m 06.89s[2]
Declination	+56° 36′ 14.9″[2]
Apparent magnitude (V)	7.2 - 8.7[3]
Characteristics
Evolutionary stage	red supergiant[4]
Spectral type	M3.5Iab[3]
Variable type	SRc[3]
Astrometry
Radial velocity (Rv)	−44.8±0.3[4] km/s
Proper motion (μ)	RA: −0.765[2] mas/yr Dec.: −1.204[2] mas/yr
Parallax (π)	0.4168±0.0279 mas[2]
Distance	7,800 ± 500 ly (2,400 ± 200 pc)
Absolute magnitude (MV)	−5.78[5]
Details
Mass	13±4[6] M☉
Radius	1,044+31 −21 – 1,139+34 −23[6] R☉
Luminosity	91,201[5] L☉
Surface gravity (log g)	−0.1[7] cgs
Temperature	3,650±50[6] K
Other designations
SU Persei, BD+55°597, HD 14469,[8] ASASSN-V J022206.86+563614.8[3]
Database references
SIMBAD	data

A light curve for SU Persei, plotted from ASAS-SN data^[9]

SU Persei was imaged by the CHARA array in 2015, 2016, 2019, 2020, and 2021.^[11] Observations during 2015 and 2016 with CHARA show that the star has an angular diameter between 3.51 and 3.68 milliarcseconds. Considering its large distance from Earth, this results in a radius between 1,044 and 1,139 times that of the Sun, making it one of the largest stars known.^[6]

SU Persei is losing mass at a rate of 1.62+0.72
−0.63×10⁻⁶ M_☉ per year, via a stellar wind.^[12]

In 1907, Henrietta Swan Leavitt discovered that the star's brightness varies by examining photographic plates.^[13] It was given its variable star designation, SU Persei, in 1908.^[14]

See also

• List of stars in Perseus
• List of stars with resolved images
• AZ Cygni