TW Horologii
Star in the constellation Horologium / From Wikipedia, the free encyclopedia
TW Horologii is a carbon star and semiregular variable in the southern constellation of Horologium,[11] near the eastern constellation border with Reticulum. It has a ruddy hue and, with an apparent visual magnitude that ranges from 5.52 down to 5.95,[4] is visible to the naked eye and one of the brightest carbon stars.[11] Based on parallax measurements, it is located at a distance of approximately 1,370 light years from the Sun.[2] It is drifting further away with a radial velocity of +14 km/s.[3] In the past this star has been considered a member of the open cluster NGC 1252, but this now seems unlikely.[12]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Horologium |
Right ascension | 03h 12m 33.16062s[2] |
Declination | −57° 19′ 17.5710″[2] |
Apparent magnitude (V) | 5.71[3] (5.52 to 5.95)[4] |
Characteristics | |
Spectral type | C-N4IIIb: (C23.5)[5] |
U−B color index | +2.93[6] |
B−V color index | +2.419±0.014[3] |
Variable type | SRb[4] |
Astrometry | |
Radial velocity (Rv) | +14.3±2.9[3] km/s |
Proper motion (μ) | RA: +18.492[2] mas/yr Dec.: +13.298[2] mas/yr |
Parallax (π) | 2.3755 ± 0.1295 mas[2] |
Distance | 1,370 ± 70 ly (420 ± 20 pc) |
Absolute magnitude (MV) | −1.79[3] |
Absolute bolometric magnitude (Mbol) | −4.62[7] |
Details | |
Mass | 3.29±0.65[8] M☉ |
Radius | 163.6+18.7 −27.9[2] R☉ |
Luminosity | 4,390±281[2] L☉ |
Surface gravity (log g) | 0.049[9] cgs |
Temperature | 3,674+360 −194[2] K |
Other designations | |
Database references | |
SIMBAD | data |
This is an aging red giant star on the asymptotic giant branch[7] with a stellar classification of C-N4IIIb: and a C2 index of C23.5. It has been listed as a standard star for that MK spectral class.[5] The star is classified as a semiregular variable of type SRb and has a periodicity of 158 days.[4] It has expanded to 164[2] times the radius of the Sun and, on average, is radiating 4,390 times the Sun's luminosity from its swollen photosphere at an effective temperature of 3,674 K.[2] The short-lived element technetium has been observed in the spectrum, an indicator of thermal pulses during helium shell burning.[13]
Based on the detection of excess ultraviolet excess, it is most likely a binary star system.[14] An analysis of the motion of TW Horologii suggests a low-mass companion, although the UV excess suggests it is hot.[8]
In 2013 the luminosity of Mira variables, based on Hipparcos parallaxes, was used to calibrate a Period-luminosity relationship for carbon stars. The absolute magnitude of TW Horologii was calculated to be −1.79.[3]