42 Capricorni
| Observation data Epoch J2000 Equinox | |
|---|---|
| Constellation | Capricornus |
| Right ascension | 21h 41m 32.85882s |
| Declination | −14° 02′ 51.3964″ |
| Apparent magnitude (V) | 5.18 |
| Characteristics | |
| Spectral type | G1 IV (G1 IV + G2 V) |
| U−B color index | +0.20 |
| B−V color index | +0.65 |
| Variable type | RS CVn |
| Astrometry | |
| Radial velocity (Rv) | −1.20±0.05 km/s |
| Proper motion (μ) | RA: −123.05 mas/yr Dec.: −308.50 mas/yr |
| Parallax (π) | 30.09±0.32 mas |
| Distance | 108 ± 1 ly (33.2 ± 0.4 pc) |
| Absolute magnitude (MV) | +2.73 (2.79 + 4.73) |
| Orbit | |
| Period (P) | 13.174 d |
| Eccentricity (e) | 0.1763±0.0025 |
| Periastron epoch (T) | 2447863.626 ± 0.027 JD |
| Argument of periastron (ω) (secondary) | 166.45±0.83° |
| Semi-amplitude (K1) (primary) | 25.57±0.06 km/s |
| Semi-amplitude (K2) (secondary) | 35.16±0.25 km/s |
| Details | |
| 42 Cap A | |
| Mass | 1.09 M☉ |
| Radius | 2.6 R☉ |
| Surface gravity (log g) | 3.76 cgs |
| Temperature | 5,634 K |
| Metallicity [Fe/H] | −0.10 dex |
| Rotational velocity (v sin i) | 5.2 km/s |
| Age | 6.7 Gyr |
| 42 Cap B | |
| Rotational velocity (v sin i) | 4.4 km/s |
| Other designations | |
| BY Cap, 42 Cap, BD−14° 6102, FK5 1150, HD 206301, HIP 107095, HR 8283, SAO 164580 | |
| Database references | |
| SIMBAD | data |
42 Capricorni is a binary star system in the zodiac constellation of Capricornus. It has a combined apparent visual magnitude of 5.18, so it is faintly visible to the naked eye. Its annual parallax shift of 30.09 mas yields a distance estimate of about 108 light years; the system is moving closer to the Sun with a radial velocity of −1.2 km/s. 42 Capricorni is 0.2 degree south of the ecliptic and so is subject to lunar occultations.
In 1995 Gregory W. Henry et al. announced that 42 Capricorni is a variable star, a discovery that was made during a survey of chromospherically active late-type stars using an automated telescope. It was given its variable star designation, BY Capricorni, in the year 2000. The star is an RS Canum Venaticorum variable, indicating the presence of an active chromosphere with star spots.
This is a double-lined close spectroscopic binary with an orbital period of 13.174 days and an eccentricity of 0.18. The binary nature of this system was discovered in 1918 by the English astronomer Joseph Lunt. It has a combined spectrum that matches a stellar classification of G1 IV, with the individual components having estimated classes of G1 V and G2 V. The system is a source of X-ray emission.