HR 4458

HR 4458 (HD 100623) is a binary star system 31.18 light-years away in the equatorial constellation of Hydra. It has the Flamsteed designation 20 Crateris^[19] and the Gould designation 289 G. Hydrae;^[20] the former refers to the constellation Crater, but when the IAU formally defined constellation boundaries, it was placed in Hydra. This object is visible to the naked eye as a dim, orange-hued star with an apparent visual magnitude of 5.97.^[3] It is moving closer to the Earth with a heliocentric radial velocity of −22 km/s.^[21]

HR 4458

Observation data Epoch J2000      Equinox J2000
Constellation	Hydra[1]
A
Right ascension	11h 34m 29.48644s[2]
Declination	−32° 49′ 52.8228″[2]
Apparent magnitude (V)	5.97[3]
B
Right ascension	11h 34m 30.47776s[4]
Declination	−32° 50′ 02.4048″[4]
Apparent magnitude (V)	15[5]
Characteristics
Spectral type	K0 V[6] + DC8[7]
U−B color index	0.325[3]
B−V color index	0.80[3]
V−R color index	0.44[citation needed]
R−I color index	0.40[citation needed]
Astrometry
A
Radial velocity (Rv)	−22.09±0.12[2] km/s
Proper motion (μ)	RA: –670.230 mas/yr[2] Dec.: +822.399 mas/yr[2]
Parallax (π)	104.6133±0.0277 mas[2]
Distance	31.177 ± 0.008 ly (9.559 ± 0.003 pc)
Absolute magnitude (MV)	6.05[8]
B
Proper motion (μ)	RA: –701.802 mas/yr[4] Dec.: +828.928 mas/yr[4]
Parallax (π)	104.6570±0.0267 mas[4]
Distance	31.164 ± 0.008 ly (9.555 ± 0.002 pc)
Absolute magnitude (MV)	15[9]
Details
HR 4458 A
Mass	0.87[2] M☉
Radius	0.84[10] R☉
Luminosity (bolometric)	0.368[11] L☉
Surface gravity (log g)	4.59[12] cgs
Temperature	5,241[12] K
Metallicity [Fe/H]	−0.37[12] dex
Rotational velocity (v sin i)	6.79[13] km/s
Age	4.6–5.8[14] Gyr
HR 4458 B
Mass	0.58[15] M☉
Luminosity (bolometric)	0.000088[16] L☉
Surface gravity (log g)	8.12[17] cgs
Temperature	5,000[15] K
Age	5.69[15][a] Gyr
Other designations
289 G. Hya, 20 Crt, CD−32°8179, GJ 432, HD 100623, HIP 56452, HR 4458, SAO 202583, LHS 308, LTT 4280, PLX 2678.00[18]
B: WD 1132-325, VB 4
Database references
SIMBAD	A
	B
ARICNS	data

The primary component is a K-type main-sequence star with a stellar classification of K0 V.^[6] It is around five billion years old^[14] with 84% of the Sun's radius.^[10] The star is radiating 37% of the Sun's luminosity^[11] from its photosphere at an effective temperature of 5,241 K.^[12] It has been examined for the presence of an infrared excess, but none was detected.^[11]

There is a 15th-magnitude common proper motion companion at an angular separation of 16.2″,^[7] corresponding to a projected separation of 162.5 AU.^[22] This is a white dwarf star with a classification of DC8.^[7] The orbital period of the pair is estimated as 1,110 years.^[22]

Notes

1. Cooling age