Alpha Columbae or α Columbae, officially named Phact (/ˈfækt/),[12][13] is a third magnitude star in the southern constellation of Columba. It has an apparent visual magnitude of 2.6,[2] making it the brightest member of Columba. Based upon parallax measurements made during the Hipparcos mission, Alpha Columbae is located at a distance of around 261 light-years (80 parsecs).[1]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Columba |
| Right ascension | 05h 39m 38.94103s[1] |
| Declination | −34° 04′ 26.7950″[1] |
| Apparent magnitude (V) | 2.645[2] |
| Characteristics | |
| Spectral type | B9Ve[3] or B7 IV[4] |
| U−B color index | −0.44[2] |
| B−V color index | −0.125[2] |
| R−I color index | −0.09[5] |
| Astrometry | |
| Radial velocity (Rv) | +35.0[6] km/s |
| Proper motion (μ) | RA: −1.58[1] mas/yr Dec.: −24.82[1] mas/yr |
| Parallax (π) | 12.48 ± 0.36 mas[1] |
| Distance | 261 ± 8 ly (80 ± 2 pc) |
| Absolute magnitude (MV) | −1.87[7] |
| Details | |
| Mass | 4.5[8] M☉ |
| Radius | 7±0.14[9] R☉ |
| Luminosity (bolometric) | 1,000[8] L☉ |
| Surface gravity (log g) | 3.5±0.04[9] cgs |
| Temperature | 12,200±122[9] K |
| Rotational velocity (v sin i) | 176[10] km/s |
| Age | 93[3] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Nomenclature
α Columbae, Latinized to Alpha Columbae, is the star's Bayer designation.
The traditional name of Phact (also rendered Phad, Phaet, Phakt)[14] derives from the Arabic فاختة fākhitah 'ring dove'. It was originally applied to the constellation Cygnus and later transferred to this star.[15][16][17][18] The etymology of its name hadāri (unknown meaning)[19] has also been suggested. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[20] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[21] included a table of the first two batches of names approved by the WGSN; which included Phact for this star.
In Chinese, 丈人 (Zhàng Rén), meaning Grandfather, refers to an asterism consisting of α Columbae and ε Columbae.[22] Consequently, α Columbae itself is known as 丈人一 (Zhàng Rén yī, English: the First Star of Grandfather.).[23] From this Chinese name, the name Chang Jin has appeared[24]
Properties
This is believed to be a solitary star,[10][25] although it has a faint optical companion at an angular separation of 13.5 arcseconds, making it a double star.[26] The stellar classification of Alpha Columbae is B9Ve,[3] matching a B-type main-sequence star. The spectrum shows it to be a Be star surrounded by a hot gaseous disk, which is generating emission lines because of hydrogen recombination.[14] Like most if not all such stars, it is rotating rapidly with a projected rotational velocity of 176 km s−1. The azimuthal equatorial velocity may be 457 km s−1.[10] It is a suspected Gamma Cassiopeiae type (GCAS) variable star, with its apparent magnitude varying from 2.62m to 2.66m.
References
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