Beta Caeli

Beta Caeli is a star with an orbiting companion in the southern constellation of Caelum. Its name is a Bayer designation that is Latinized from β Caeli, and abbreviated Beta Cae or β Cae. This star is dimly visible to the naked eye, having an apparent visual magnitude of 5.04.^[2] Based upon an annual parallax shift of 34.6 mas as seen from Earth,^[1] it is located at a distance of 94 light-years (29 pc). The star is moving away from the Sun with a radial velocity of +27.5 km/s.^[1]

Beta Caeli

Location of β Caeli (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Caelum
Right ascension	04h 42m 03.482s[1]
Declination	−37° 08′ 39.59″[1]
Apparent magnitude (V)	5.04[2]
Characteristics
Spectral type	F3 V[3] or F3 IV[4]
U−B color index	+0.01[2]
B−V color index	+0.38[2]
Astrometry
Radial velocity (Rv)	27.47±0.24[1] km/s
Proper motion (μ)	RA: +42.561 mas/yr[1] Dec.: +212.705 mas/yr[1]
Parallax (π)	34.6088±0.0531 mas[1]
Distance	94.2 ± 0.1 ly (28.89 ± 0.04 pc)
Absolute magnitude (MV)	+2.64[5]
Orbit[6]
Primary	A
Companion	B
Period (P)	7.5 yr
Semi-major axis (a)	4.6 AU
Eccentricity (e)	0.6
Inclination (i)	27 or 153°
Longitude of the node (Ω)	151°
Argument of periastron (ω) (secondary)	38°
Details
β Cae A
Mass	1.482±0.040[1] M☉
Radius	1.902+0.001 −0.004[1] R☉
Luminosity	6.615+0.020 −0.019[1] L☉
Surface gravity (log g)	3.981+0.003 −0.002[1] cgs
Temperature	6,665.7+1.6 −1.4[1] K
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {M}}/{\ce {H}}\right]\end{smallmatrix}}}$ = −0.12[3]
Rotation	0.8669±0.0013[6] days
Rotational velocity (v sin i)	97.5±4.9[5] km/s
Age	0.2 or 1.17[6] Gyr 1.941±0.307[1] Gyr
β Cae B
Mass	0.08 or 0.2[6] M☉
Temperature	3,593±160[6] K
Other designations
β Cae, CD−37°1867, FK5 1130, GJ 176.1, GJ 9165, HD 29992, HIP 21861, HR 1503, SAO 195239[7]
Database references
SIMBAD	data

Characteristics

Beta Caeli is a probable single-lined spectroscopic binary system, meaning only the spectral lines of the visible component can be seen.^[8] This primary component has a stellar classification of F3 V^[3] or F3 IV,^[4] indicating it is either an F-type main-sequence star or a somewhat more evolved subgiant star, respectively. It has an estimated 1.5 times the mass of the Sun and about 1.9 times the Sun's radius.^[1] The star is 200 million^[6] to two billion years old^[1] and has a high rate of spin with a projected rotational velocity of around 97.5 km/s.^[5] It is radiating 6.6 times the luminosity of the Sun from its photosphere^[1] at an effective temperature of 6,666 K.^[1] Based on the amount of iron detected, the abundance of elements with mass greater than helium is lower than in the Sun.^[3]

The low-mass companion is orbiting about 5 AU from the primary, with an orbital period of around seven years. Its exact mass is uncertain; an orbital solution suggest it is close to the brown dwarf regime at around 0.08 M_☉, but models of stellar atmospheres suggest a higher mass of 0.2 M_☉.^[6] It was first detected in 2017 and was believed to be either a brown dwarf or a star with minimum mass around 40 Jupiter masses.^[8] In 2022, Beta Caeli was imaged with the Gemini Planet Imager, with a point source that very likely is β Caeli B being detected.^[6] This object may be the source of the X-ray emission coming from the same location, which suggests the companion could be a late-type star.^[8]

The existence of additional companions beyond 55 astronomical units is ruled out.^[8]

See also

• Alpha Trianguli, similar configuration