00h29m59.87s, −05° 45′ 50.41″| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cetus |
| Right ascension | 00h29m 59.8721s[1] |
| Declination | –05° 45′ 50.3987″[1] |
| Apparent magnitude (V) | 9.44[2] |
| Characteristics | |
| Spectral type | K1V[3] (G8V + M1V)[4] |
| B−V color index | +0.886±0.003[2] |
| Astrometry | |
| Radial velocity (Rv) | +9.576±0.0010[1] km/s |
| Proper motion (μ) | RA: −107.019±0.094[1] mas/yr Dec.: −223.039±0.062[1] mas/yr |
| Parallax (π) | 18.1656 ± 0.0510 mas[1] |
| Distance | 179.5 ± 0.5 ly (55.0 ± 0.2 pc) |
| Absolute magnitude (MV) | 5.96[2] |
| Orbit[5] | |
| Primary | HD 2638 A |
| Companion | HD 2638 BC |
| Period (P) | 130 yr |
| Semi-major axis (a) | 25.5±1.9 AU |
| Details[6] | |
| A | |
| Mass | 0.89±0.02 M☉ |
| Radius | 0.8±0.01 R☉ |
| Luminosity | 0.407±0.004 L☉ |
| Surface gravity (log g) | 4.58±0.02 cgs |
| Temperature | 5,160±24 K |
| Metallicity [Fe/H] | 0.12±0.05[7] dex |
| Age | 1.9±2.6 Gyr |
| BC | |
| Mass | 0.425±0.067[4] M☉ |
| Radius | 0.46±0.02[4] R☉ |
| Luminosity | 0.030±0.005[4] L☉ |
| Surface gravity (log g) | 4.80±0.02[4] cgs |
| Temperature | 3571±48[4] K |
| Other designations | |
BD–06°82, Gaia DR2 2526925389919277056, HD 2638, HIP 2350, WDS J00293-0555BC, NLTT 1594, 2MASS J00295988-0545502[8] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
HD 2638 is a ternary star system[9] system in the equatorial constellationofCetus. The pair have an angular separationof0.53″ along a position angle of 166.7°, as of 2015.[9] This is system too faint to be visible to the naked eye, having a combined apparent visual magnitude of 9.44;[2] a small telescope is required. The distance to this system is 179.5 light years based on parallax, and it is drifting further away with a radial velocity of +9.6 km/s.[1] The magnitude 7.76 star HD 2567 forms a common proper motion companion to this pair[9] at projected separation 839″.[5]
The HD 2638 members A and BC have a projected separation of about 25.5±1.9 AU and thus an orbital period of around 130 years.[4] They have a combined stellar classification of K1V.[3] The primary component is a G-type main-sequence star with a class of G8V.[4] It is smaller and less massive than the Sun, and has a lower luminosity.[6] The secondary is a binary consisting of who red dwarf stars on close orbit with combined mass less than half the mass of the primary, and a composite spectral class of M1V.[4]
In 2005, the discovery of an extrasolar planet HD 2638 b orbiting the primary was announced by the Geneva Extrasolar Planet Search Team. The planet has a mass 0.48 times that of Jupiter and 152.6 times that of Earth.[10] The planet existence was placed under doubt in 2015 due to discovered additional stellar companions.[5]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | >0.48 MJ | 0.044 | 3.4442±0.0002 | 0.0407 | — | — |
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