V762 Cassiopeiae

V762 Cassiopeiae is a cool evolved variable star located about 2,500 light-years away in the Cassiopeia constellation. Its apparent magnitude vary between 5.82 and 5.95, which makes it faintly visible to the naked eye under dark skies. It is a relatively cool star with an average surface temperature of 3,869 K.

V762 Cassiopeiae

The location of V762 Cassiopeiae
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cassiopeia[1]
Right ascension	01h 16m 11.902s[2]
Declination	+71° 44′ 37.83″[2]
Apparent magnitude (V)	5.82 – 5.95[3]
Characteristics
Evolutionary stage	RSG[4] or AGB[5]
Spectral type	K5I[4][3] or M3II[6]
Variable type	LC[3]
Astrometry
Radial velocity (Rv)	−21.37±0.91[2] km/s
Proper motion (μ)	RA: −1.658 mas/yr[2] Dec.: +1.791 mas/yr[2]
Parallax (π)	1.3148±0.0693 mas[2]
Distance	2,500 ± 100 ly (760 ± 40 pc)
Details
Mass	2.9[7] M☉
Radius	265.7[5] R☉
Luminosity	14,970[5] L☉
Surface gravity (log g)	0.90[7] cgs
Temperature	3,869±145[4][5] K
Metallicity [Fe/H]	−0.18[7] dex
Age	10.0±1.6[8] Myr
Other designations
V762 Cas, BD+70 90, HD 7389, HIP 5926, HR 365, SAO 4358, TYC 4305-2038-1[9]
Database references
SIMBAD	data

Characteristics

A light curve for V762 Cassiopeiae, plotted from Hipparcos data^[10]

V762 Cassiopeiae has a spectral classification of K5 I,^[4] suggesting that it is an evolved K-type red supergiant star. Other catalogues have published spectral types of K4,^[11] M,^[12] and M3II.^[6] The Bright Star Catalogue assigned a class of K1V,^[13] which originated from one of the earliest observations of this star^[14] and was adopted by the General Catalogue of Variable Stars.^[13] Recent estimates of the star's physical properties, considering its distance in excess of a thousand light-years,^[2] found that it is a red supergiant^[4] or asymptotic giant branch star.^[5]

At an estimated to be ten million years old,^[8] has around 2.9 times the Sun's mass and has expanded to 266 times the Sun's radius. It radiates 15,000 times the solar luminosity from its photosphere at an effective temperature of 3,869 K,^[5] which gives it an orange-red hue.^[15] Parallax measurements from the Gaia spacecraft show that V762 Cassiopeiae is located about 2,500 light-years away.^[2] At the estimated distance, V762 Cassiopeiae's apparent brightness is diminished by 1.04 magnitudes due to interstellar extinction.^[5]

Hipparcos satellite data showed that the star is variable, and because of that it was given the variable-star designation V762 Cassiopeiae, in 1999.^[16] The variability amplitude in visible light is only about 0.1 magnitudes. The International Variable Star Index lists it as a supergiant slow irregular variable,^[3] but the General Catalogue of Variable Stars (GCVS) classifies it as a possible BY Draconis star.^[17]

Distance and titleholding

Some websites claim V762 Cassiopeiae is the "farthest star visible to the naked eye", at a distance of 16,308 light-years.^[18][19] This distance is apparently based on the first Hipparcos published parallax of 0.22±0.59 mas, approximately 5,000 pc or 16,308 light years. However, given the statistical margin of error, the distance is meaningless. The Hipparcos new reduction gives a parallax of 1.18±0.45 mas, corresponding to a distance of about 2,800 light-years,^[20] and Gaia DR3 lists a parallax of 1.3148±0.0693 mas, corresponding to a distance of about 2,500 light-years.^[2]