YZ Cassiopeiae

YZ Cassiopeiae (21 Cas) is a star system 103.8 parsecs (339 ly) away from Earth, in the constellation Cassiopeia. It comprises three stars: an eclipsing Algol-type binary and a visually fainter star about 3000 AU distant.^[11] It is faintly visible to the naked eye under good observing conditions.

ConstellationCassiopeia^[1]

Right ascension00^h 45^m 39.0777^s[2]

Declination+74° 59′ 17.063″^[2]

Apparentmagnitude(V)5.653^[3]

Quick facts Constellation, Right ascension ...

YZ Cas

Location of YZ Cassiopeiae (circled)
Observation data Epoch J2000      Equinox ICRS
Constellation	Cassiopeia[1]
A
Right ascension	00h 45m 39.0777s[2]
Declination	+74° 59′ 17.063″[2]
Apparent magnitude (V)	5.653[3]
B
Right ascension	00h 45m 42,1503s[4]
Declination	+74° 58′ 43.242″[4]
Apparent magnitude (V)	11.23[5]
Characteristics
A
Spectral type	A2IV[6] (A1Vm + F2V[7])
U−B color index	+0.07[5]
B−V color index	+0.05[5]
Variable type	Algol[8]
B
Spectral type	F2V[9]
U−B color index	+0.64[5]
B−V color index	+0.94[5]
Astrometry
Radial velocity (Rv)	+8.90±0.4[10] km/s
Proper motion (μ)	RA: −15.07[2] mas/yr Dec.: −22.17[2] mas/yr
Parallax (π)	11.24±0.55 mas[2]
Distance	103.8[9] pc
Absolute magnitude (MV)	+0.251[7]
Orbit[11]
Name	TYC 4307-2168-1
Period (P)	86 580 yr
Orbit[9]
Primary	Aa
Name	Ab
Period (P)	4.467 days
Semi-major axis (a)	17.47 R☉[12]
Eccentricity (e)	0.0
Inclination (i)	88.332°
Details
Aa
Mass	2.308[12] M☉
Radius	2.547[12] R☉
Luminosity	41.69[12] L☉
Surface gravity (log g)	3.988[9] cgs
Temperature	9,200[12] K
Rotational velocity (v sin i)	29.2[9] km/s
Ab
Mass	1.325[13] M☉
Radius	1.359[12] R☉
Luminosity	3.34[12] L☉
Surface gravity (log g)	4.311[9] cgs
Temperature	6,890[13] K
Metallicity [Fe/H]	+0.10[13] dex
Rotational velocity (v sin i)	15.0[9] km/s
Age	490 - 550[9] Myr
Other designations
21 Cassiopeiae, HR 192, BD+74 27, HD 4161, SAO 4216, HIP 3572, GC 891, ADS 624 A, CCDM J00457+7459[14]
Database references
SIMBAD	data

Close

The primary star in the YZ Cassiopeiae system is a white subgiant (main sequence) star of spectral type A1Vm and 2.31 solar masses^[11] (M_☉) with a less massive main sequence dwarf star of type F2V^[3] and 1.35 M_☉.^[11]

In 1924, Joel Stebbins announced his discovery that the star, then known as 21 Cassiopeiae, is an eclipsing binary.^[16] It was given its variable star designation, YZ Cassiopeiae, in 1925.^[17] The apparent magnitude of the eclipsing binary varies from 5.65 to 6.05^[3] with a period of 4.4672 days.^[11] Combined, they appear to have a spectral type of A2IV.^[11]

The binary has a dimmer (magnitude 9.7 according to Norton,^[18] or 10.5 by SIMBAD) companion of 0.8 M_☉^[11] orbiting with a period of about 86 580 years.^[11]