Alpha Columbae

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]

Alpha Columbae

Location of α Columbae (circled)
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
Alpha Col, α Col, NSV 2549, CD−34 2375, CPD−34 703, FK5 215, GC 7078, HD 37795, HIP 26634, HR 1956, SAO 196059, PPM 281732, CCDM  J05396−3404 A[11]
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 2.62^m to 2.66^m.