Pi Cassiopeiae

Pi Cassiopeiae is a close binary star^[8] system in the constellation Cassiopeia, near the southern border with Andromeda. Its name is a Bayer designation that is Latinized from π Cassiopeiae, and abbreviated Pi Cas or π Cas. This system is visible to the naked eye as a point of light with a combined apparent visual magnitude of +4.949.^[3] Based upon an annual parallax shift of 18.63 mas as seen from Earth,^[2] this system is located about 175 light-years (54 pc) 175 light years from the Sun. It is drifting further away with a radial velocity of +13 km/s.^[7]

A light curve for Pi Cassiopeiae, plotted from TESS data^[12]

Pi Cassiopeiae

Location of π Cassiopeiae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cassiopeia[1]
Right ascension	00h 43m 28.070s[2]
Declination	+47° 01′ 28.36″[2]
Apparent magnitude (V)	+4.949[3]
Characteristics
Evolutionary stage	Main sequence
Spectral type	A5V[4] + A5V[5]
B−V color index	+0.171[3]
Variable type	Ellipsoidal[6]
Astrometry
Radial velocity (Rv)	+12.9±0.8[7] km/s
Proper motion (μ)	RA: −24.570 mas/yr[2] Dec.: −36.886 mas/yr[2]
Parallax (π)	18.6293±0.1142 mas[2]
Distance	175 ± 1 ly (53.7 ± 0.3 pc)
Absolute magnitude (MV)	+1.30[1]
Orbit[8]
Period (P)	1.9642 d
Eccentricity (e)	0.00
Periastron epoch (T)	2427535.74 JD
Argument of periastron (ω) (secondary)	0.00°
Semi-amplitude (K1) (primary)	120.5 km/s
Semi-amplitude (K2) (secondary)	122.1 km/s
Details
A
Mass	1.82[2] M☉
Radius	1.9[5] R☉
Luminosity	22[9] L☉
Surface gravity (log g)	4.41[10] cgs
Temperature	8,392±285[10] K
Rotational velocity (v sin i)	60[5] km/s
Age	251[10] Myr
B
Mass	1.87[2] M☉
Radius	1.9[5] R☉
Rotational velocity (v sin i)	65[5] km/s
Other designations
π Cas, 20 Cas, BD+46°146, HD 4058, HIP 3414, HR 184, SAO 36602[11]
Database references
SIMBAD	data

This is a double-lined spectroscopic binary system with an orbital period of nearly two days in a circular orbit.^[8] It is classified as a rotating ellipsoidal variable star and its brightness varies by 0.02 magnitudes with a period of 23.57 hours,^[6] which equals half of its orbital period. The spectrum matches that of an A-type main-sequence star with a stellar classification of A5 V.^[4] The two stars have similar masses and spectra.^[5] A star at a projected separation of 1,700 AU has been identified as a possible white dwarf. It is at the same distance as Pi Cassiopeiae and shares a common proper motion. The age of the white dwarf is calculated to be about 500 million years.^[13]

Pi Cassiopeiae has been given the spectral class of kA3hF1mA5, indicating an Am star,^[14] but this is now considered doubtful.^[15]