F Eridani

f Eridani is a binary,^[11] or possibly a triple, star system in the equatorial constellation of Eridanus, consisting of stars HD 24071 and HD 24072. They share a single Hipparcos catalogue entry, HIP 17797, but have separate Bright Star Catalogue listings, HR 1189 and 1190. f Eridani is the Bayer designation of the pair.

HD 24071 and HD 24072

Location of HD 24160 (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Eridanus
HD 24072
Right ascension	03h 48m 35.87402s[1]
Declination	−37° 37′ 12.5158″[1]
Apparent magnitude (V)	4.721±0.009[2]
HD 24071
Right ascension	03h 48m 35.47769s[3]
Declination	−37° 37′ 19.2124″[3]
Apparent magnitude (V)	5.246±0.009[2]
Characteristics
HD 24072
Spectral type	B9.5 Van[4]
HD 24071
Spectral type	A1 Va[4]
Variable type	suspected[5]
Astrometry
HD 24072
Proper motion (μ)	RA: +81.136[1] mas/yr Dec.: −6.795[1] mas/yr
Parallax (π)	18.8093±0.2220 mas[1]
Distance	173 ± 2 ly (53.2 ± 0.6 pc)
Absolute magnitude (MV)	1.194±0.190[2]
HD 24071
Proper motion (μ)	RA: +63.372[3] mas/yr Dec.: −8.121[3] mas/yr
Parallax (π)	18.7976 ± 0.0582 mas[3]
Distance	173.5 ± 0.5 ly (53.2 ± 0.2 pc)
Absolute magnitude (MV)	1.719±0.190[2]
Details
HD 24072
Mass	2.6[6] M☉
Radius	2.0[6] R☉
Luminosity	35[6] L☉
Surface gravity (log g)	4.26[6] cgs
Temperature	10,046[6] K
Metallicity [Fe/H]	−0.49[7] dex
Rotational velocity (v sin i)	225[8] km/s
Age	45±4[2] Myr
HD 24071
Mass	2.1[3] M☉
Radius	1.7[3] R☉
Luminosity	20[3] L☉
Surface gravity (log g)	4.16[3] cgs
Temperature	9,503[3] K
Metallicity [Fe/H]	−0.54[7] dex
Rotational velocity (v sin i)	39[8] km/s
Age	45±4[2] Myr
Other designations
f Eridani, CD−38 1297, HIP 17797, WDS J03486-3737
HD 24072: HR 1190, SAO 194551[9]
HD 24071: HR 1189, SAO 194550[10]
Database references
SIMBAD	data
	HD 24072
	HD 24071

f Eridani is visible to the naked eye as a single star with a magnitude of 4.25.^[12] HD 24071 has an apparent visual magnitude of 5.25 and HD 24072 a magnitude of 4.72.^[2] As of 2009, the pair had an angular separation of 8.40″ along a position angle of 216°.^[13] Both stars have an annual parallax shift 18.8 mas, which provides a distance estimate to the system of 173 light years. The pair are members of the Tucana-Horologium moving group, a 45 million year old set of stars that share a common motion through space.^[2]

The brighter component, HD 24072, is a B-type main-sequence star with a classification of B9.5 Van.^[4] The n suffix indicates "nebulous" absorption lines which are caused by its rapid rotation. It has a projected rotational velocity of 225 km/s.^[8]

HD 24071 may itself be a spectroscopic binary. The visible component is an A-type main-sequence star with a stellar classification of A1 Va.^[4] It is a suspected variable star of unknown type showing an amplitude of 0.05 magnitude,^[5] and is a source of X-ray emission, which may originate from a companion of class G2-5V.^[14]