HD 2638
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cetus |
| Right ascension | 00h 29m 59.8721s |
| Declination | −05° 45′ 50.399″ |
| Apparent magnitude (V) | 9.44 |
| Characteristics | |
| Spectral type | K1V (G8V + M1V) |
| B−V color index | +0.886±0.003 |
| Astrometry | |
| Radial velocity (Rv) | +9.576±0.0010 km/s |
| Proper motion (μ) | RA: −107.019±0.094 mas/yr Dec.: −223.039±0.062 mas/yr |
| Parallax (π) | 18.1656±0.0510 mas |
| Distance | 179.5 ± 0.5 ly (55.0 ± 0.2 pc) |
| Absolute magnitude (MV) | 5.96 |
| Orbit | |
| Primary | HD 2638 A |
| Companion | HD 2638 BC |
| Period (P) | 130 yr |
| Semi-major axis (a) | 25.5±1.9 AU |
| Details | |
| 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 dex |
| Age | 1.9±2.6 Gyr |
| BC | |
| Mass | 0.425±0.067 M☉ |
| Radius | 0.46±0.02 R☉ |
| Luminosity | 0.030±0.005 L☉ |
| Surface gravity (log g) | 4.80±0.02 cgs |
| Temperature | 3571±48 K |
| Other designations | |
| BD−06°82, Gaia DR2 2526925389919277056, HD 2638, HIP 2350, WDS J00293-0555BC, NLTT 1594, 2MASS J00295988-0545502 | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
HD 2638 is a ternary star system system in the equatorial constellation of Cetus. The pair have an angular separation of 0.53″ along a position angle of 166.7°, as of 2015. This is system too faint to be visible to the naked eye, having a combined apparent visual magnitude of 9.44; 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. The magnitude 7.76 star HD 2567 forms a common proper motion companion to this pair at projected separation 839″.
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. They have a combined stellar classification of K1V. The primary component is a G-type main-sequence star with a class of G8V. It is smaller and less massive than the Sun, and has a lower luminosity. The secondary is a binary consisting of two red dwarf stars on close orbit with combined mass less than half the mass of the primary, and a composite spectral class of M1V.