W Orionis
Star in the constellation Orion
From Wikipedia, the free encyclopedia
W Orionis is a carbon star in the constellation Orion, approximately 400 parsecs (1,300 ly) away. It varies regularly in brightness between extremes of magnitude 4.4 and 6.9 roughly every 7 months. When it is near its maximum brightness, it is faintly visible to the naked eye of an observer with good observing conditions.
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 05m 23.72142s[1] |
| Declination | +01° 10′ 39.4512″[1] |
| Apparent magnitude (V) | 4.4 - 6.9[2] |
| Characteristics | |
| Evolutionary stage | AGB |
| Spectral type | C-N5 C25.5[3] (C5,4(N5)[4]) |
| U−B color index | +6.84[5] |
| B−V color index | +3.42[5] |
| Variable type | SRb[4] |
| Astrometry | |
| Radial velocity (Rv) | +16.50[6] km/s |
| Proper motion (μ) | RA: +7.5[1] mas/yr Dec.: -1.4[1] mas/yr |
| Parallax (π) | 2.65±0.95 mas[1] |
| Distance | approx. 1,200 ly (approx. 400 pc) |
| Absolute magnitude (MV) | −5.76[7] |
| Details | |
| Mass | 1-2[8] M☉ |
| Radius | 406[8] R☉ |
| Luminosity | 6,761[8] L☉ |
| Surface gravity (log g) | −0.60[8] cgs |
| Temperature | 2,600[8] K |
| Metallicity [Fe/H] | 0.0[8] dex |
| Other designations | |
| W Ori, BD+00°939, HD 32736, HIP 23680 | |
| Database references | |
| SIMBAD | data |
Variability
Evelyn Leland discovered that the star is a variable star based on observations done in the last decades of the 19th century, when it was known as BD +00°939. The discovery was announced in 1895.[10] It was listed with its variable star designation, W Orionis, in Annie Jump Cannon's 1907 work Second Catalog of Variable Stars.[11] W Orionis is a semiregular variable with an approximately 212‑day cycle.[4] A long secondary period of 2,450 days has also been reported.[12]
Properties
The angular diameter of W Orionis has been measured using interferometry and a value of 9.7 mas is found. Although it is known to be a pulsating variable star, no changes in the diameter were seen.[8]
Technetium has not been detected in W Orionis, an unexpected result since this s-process element should be dredged up in all thermally-pulsating AGB stars and especially in carbon stars.[8]