Eta Horologii

Eta Horologii (η Horologii, η Hor) is a binary star system^[3] in the southern constellation of Horologium. It is visible to the naked eye with a combined apparent visual magnitude of 5.31.^[2] Based upon an annual parallax shift of 21.95 mas as seen from Earth,^[1] it is located around 149 light years from the Sun.

Eta Horologii

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Horologium
Right ascension	02h 37m 24.37297s[1]
Declination	−52° 32′ 35.0855″[1]
Apparent magnitude (V)	5.31[2]
Characteristics
Spectral type	A6 V + F0 V[3]
B−V color index	+0.27[2]
Astrometry
Radial velocity (Rv)	−3.0±7.4[4] km/s
Proper motion (μ)	RA: +112.70[1] mas/yr Dec.: +3.73[1] mas/yr
Parallax (π)	21.95±1.10 mas[1]
Distance	149 ± 7 ly (46 ± 2 pc)
Absolute magnitude (MV)	2.13[5]
Orbit[6]
Period (P)	3.01±0.18 yr
Semi-major axis (a)	0.0231±0.0014″
Eccentricity (e)	0.16±0.14
Details
η Hor A
Mass	1.75[7] M☉
Luminosity	12.6[8] L☉
Surface gravity (log g)	4.21[9] cgs
Temperature	7,552±257[9] K
Rotational velocity (v sin i)	6.6±2.2[5] km/s
Age	474[9] Myr
η Hor B
Mass	1.65[7] M☉
Other designations
η Hor, CPD−53°457, FK5 2182, HD 16555, HIP 12225, HR 778, SAO 232835[10]
Database references
SIMBAD	data

The orbit for this pair is not yet well constrained. They appear to have an orbital period of three years and an eccentricity of roughly 0.16.^[6] As of 2012, the pair have an angular separation of 78.7 mas, which corresponds to a projected separation of 3.6 AU.^[3] The primary member, component A, is an A-type main sequence star with a stellar classification of A6 V. The secondary, component B, has an inferred class of F0 V, which would indicate it is an F-type main sequence star.^[3]