TZ Cassiopeiae
Star in the constellation Cassiopeia
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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.
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| 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: −3.215±0.026[2] mas/yr Dec.: −2.145±0.028[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]