BK Camelopardalis

BK Camelopardalis is a variable star in the northern circumpolar constellation of Camelopardalis, near the constellation border with Cassiopeia. It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude that fluctuates around 4.74.^[2] The star is located approximately 540 light years away from the Sun based on parallax.^[1] It is a proposed member of the Cassiopeia–Taurus group of co-moving stars.^[9]

BK Camelopardalis

Location of BK Camelopardalis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Camelopardalis
Right ascension	03h 19m 59.27222s[1]
Declination	+65° 39′ 08.2519″[1]
Apparent magnitude (V)	4.74[2] (4.76 - 4.90)[3]
Characteristics
Evolutionary stage	main sequence[4]
Spectral type	B2.5 Vne[5]
U−B color index	−0.77[6]
B−V color index	−0.108±0.002[2]
R−I color index	−0.13[6]
Variable type	Be star[3]
Astrometry
Radial velocity (Rv)	−3.4±3.5[2] km/s
Proper motion (μ)	RA: +10.506[1] mas/yr Dec.: −14.677[1] mas/yr
Parallax (π)	6.0704±0.3539 mas[1]
Distance	540 ± 30 ly (165 ± 10 pc)
Absolute magnitude (MV)	−2.07[2]
Details
Mass	7.5[5] M☉
Radius	4.0[7] R☉
Luminosity	1080.69[2] L☉
Surface gravity (log g)	4.20[4] cgs
Temperature	18,720[4] K
Rotational velocity (v sin i)	328[4] km/s
Age	31.6[5] Myr
Other designations
BK Cam, BD+65°340, HD 20336, HIP 15520, HR 985, SAO 12704[8]
Database references
SIMBAD	data

Description

This is a main sequence Be star^[4] with a stellar classification of B2.5 Vne,^[5] where the 'n' suffix indicates "nebulous" (broad) lines due to rapid rotation. The presence of emission lines in the spectrum has been known since at least 1895.^[10] Spectrograms of the star have been taken since 1905, providing a long history of its cycles of variation.^[11] It ranges in brightness from a peak of 4.76 down to 4.90.^[3]

BK Camelopardalis is 32^[5] million years old and is spinning with a projected rotational velocity of 328 km/s.^[4] It has 7.5^[5] times the mass of the Sun and four^[7] times the Sun's radius. The star is radiating 1,081^[2] times the luminosity of the Sun from its photosphere at an effective temperature of 18,720 K.^[4]

This star lies at the center of a circular, disk-like structure spanning 1.4°, which may be a "magnetic funnel-like structure" that is emitting in the radio band. Neutral hydrogen along the trajectory of this star has been found to be deficient, which may be the result of ionizing radiation from the star.^[12]

Two stars have been resolved close to BK Camelopardalis. The first, designated Ab, is separated by about 0.13 arcseconds. If it is physically associated with BK Camelopardalis, it would have an orbital period of several decades. The second star is designated as B but is likely an optical pair with the central BK Camelopardalis; that is, a chance alignment.^[13]

Chinese name

In Chinese, 紫微右垣 (Zǐ Wēi Yòu Yuán), meaning Right Wall of Purple Forbidden Enclosure, refers to an asterism consisting of BK Camelopardalis, α Draconis, κ Draconis, λ Draconis, 24 Ursae Majoris, 43 Camelopardalis and α Camelopardalis.^[14] Consequently, BK Camelopardalis itself is known as 紫微右垣七 (Zǐ Wēi Yòu Yuán qī, English: the Seventh Star of Right Wall of Purple Forbidden Enclosure.) representing 上丞 (Shǎngchéng), meaning First Prime Minister.^[15]