AO Cassiopeiae

AO Cassiopeiae, also known as Pearce's Star, is a binary system composed of an O8 main sequence star and an O9.2 bright giant that respectively weigh anywhere between 20.30 and 57.75 times and 14.8 and 31.73 times the mass of the Sun.^[11]

A light curve for AO Cassiopeiae, plotted from Hipparcos data

AO Cas

Location of AO Cas (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Cassiopeia[1]
Right ascension	00h 17m 43.063s[2]
Declination	+51° 25′ 59.12″[2]
Apparent magnitude (V)	6.07-6.24[3]
Characteristics
Spectral type	O8V((f)) + O9.2II[4]
U−B color index	−0.97[5]
B−V color index	−0.13[5]
Variable type	Eclipsing Variable star[3]
Astrometry
Radial velocity (Rv)	−31.10[6] km/s
Proper motion (μ)	RA: −2.988[2] mas/yr Dec.: −2.374[2] mas/yr
Parallax (π)	0.7546±0.0579 mas[2]
Distance	4,300 ± 300 ly (1,300 ± 100 pc)
Absolute magnitude (MV)	−[7]
Orbit[8]
Period (P)	3.52348 days
Semi-major axis (a)	28.57 R☉
Eccentricity (e)	0
Inclination (i)	65.7°
Longitude of the node (Ω)	3.10°
Semi-amplitude (K1) (primary)	143.7 km/s
Semi-amplitude (K2) (secondary)	230.6 km/s
Details[8]
II
Mass	9.65 M☉
Radius	9.43 R☉
Luminosity	115,000[9] L☉
Surface gravity (log g)	3.45 cgs
Temperature	29,239 K
Rotational velocity (v sin i)	120[9] km/s
V
Mass	15.59 M☉
Radius	4.61 R☉
Luminosity	66,000[9] L☉
Surface gravity (log g)	4.30 cgs
Temperature	33,675 K
Rotational velocity (v sin i)	130[9] km/s
Other designations
Pearce's Star,[10] AO Cas, HR 65, BD+50°46, HD 1337, SAO 21273, HIP 1415
Database references
SIMBAD	data

The AO Cas system is an eclipsing binary with a period of roughly 3.5 days, with the apparent magnitude ranging between 6.07 and 6.24.^[12] Stars of this brightness are generally just visible to the unaided eye in dark skies in semirural locations.^[13] The component stars are so close to each other they are ellipsoidal (egg-shaped).^[14] AO Cas is considered a contact binary, with both stars at or near their Roche lobes.^[3]