TZ Cassiopeiae

TZ Cassiopeiae (TZ Cas, HIP 117763, SAO 20912) is a variable star in the constellation Cassiopeia with an apparent magnitude of around +9 to +10. It is approximately 8,400 light-years away from Earth. The star is a red supergiant star with a spectral type of M3 and a temperature around 3,600 K.

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

TZ Cassiopeiae

Observation data Epoch J2000      Equinox J2000
Constellation	Cassiopeia[1]
Right ascension	23h 52m 56.23689s[2]
Declination	61° 00′ 08.3915″[2]
Apparent magnitude (V)	9.18[3] (+8.86 - +10.5[4])
Characteristics
Evolutionary stage	red supergiant[5]
Spectral type	M3 Iab[6]
U−B color index	+2.43[3]
B−V color index	+2.57[3]
Variable type	Lc[4]
Astrometry
Radial velocity (Rv)	−54.28[7] km/s
Proper motion (μ)	RA: −3.865[2] mas/yr Dec.: −2.145[2] mas/yr
Parallax (π)	0.3888±0.0300 mas[2]
Distance	8,400 ± 600 ly (2,600 ± 200 pc)
Absolute magnitude (MV)	−5.98[8]
Details[5]
Mass	15 M☉
Radius	646 R☉
Luminosity	68,500 L☉
Surface gravity (log g)	−0.01 cgs
Temperature	3,670 K
Metallicity [Fe/H]	+0.15[9] dex
Other designations
BD+60°2634, HIP 117763, SAO 20192, 2MASS J23525623+6100083, AAVSO 2348+60
Database references
SIMBAD	data

TZ Cassiopeiae was reported as being variable by Williamina Fleming and published posthumously in 1911.^[11] It is a slow irregular variable star with a possible period of 3,100 days.^[12] It is irradiating over 68,500 times the luminosity of the Sun, and it is 640 times larger than the Sun.^[5] It is a member of the Cas OB5 stellar association, together with the nearby red supergiant PZ Cassiopeiae.^[13]

The initial mass of TZ Cassiopeiae has been estimated from its position relative to theoretical stellar evolutionary tracks to be around 15 M_☉.^[5]

TZ Cas is losing mass through a powerful stellar wind at two millionths of a solar mass each year.^[14] It is unclear whether this is sufficient to cause the star to lose its atmosphere and become a blue supergiant before the core exhausts its fuel and collapses as a supernova. Either as a red or blue supergiant, or a Wolf–Rayet star, it will inevitably end its life violently in a supernova explosion when the core collapse occurs.^[15]