HR 4458
Binary star system in the constellation Hydra
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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, since Flamsteed numbered the stars of Crater and the central portion of Hydra as a separate constellation from the other parts of Hydra.[19] 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]
 | |
| 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 | |
| A | |
| Evolutionary stage | main sequence[2] |
| Spectral type | K0 V[6] |
| U−B color index | +0.325[3] |
| B−V color index | +0.80[3] |
| B | |
| Evolutionary stage | white dwarf[5] |
| Spectral type | DC8[7] |
| 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 | |
| 20 Crt, 289 G. Hya, CD−32°8179, GJ 432, HD 100623, HIP 56452, HR 4458, SAO 202583, LHS 308, LTT 4280, PLX 2678.00[18] | |
| B: VB 4, WD 1132−325 | |
| 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 called VB4 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]