Eta Cassiopeiae
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 00h 49m 06.295s |
| Declination | +57° 48′ 54.64″ |
| Apparent magnitude (V) | 3.44/7.51 |
| Characteristics | |
| Spectral type | G0 V + K7 V |
| U−B color index | +0.02/1.03 |
| B−V color index | +0.58/1.39 |
| Variable type | RS CVn? |
| Astrometry | |
| A | |
| Radial velocity (Rv) | +10.0±0.1 km/s |
| Proper motion (μ) | RA: +1078.609 mas/yr Dec.: −551.133 mas/yr |
| Parallax (π) | 168.8322±0.1663 mas |
| Distance | 19.32 ± 0.02 ly (5.923 ± 0.006 pc) |
| Absolute magnitude (MV) | 4.57 |
| B | |
| Proper motion (μ) | RA: +1,144.693 mas/yr Dec.: −469.668 mas/yr |
| Parallax (π) | 168.7186±0.0216 mas |
| Distance | 19.331 ± 0.002 ly (5.9270 ± 0.0008 pc) |
| Orbit | |
| Primary | η Cas A |
| Name | η Cas B |
| Period (P) | 472.2±1.1 yr |
| Semi-major axis (a) | 70.55±0.15 AU |
| Eccentricity (e) | 0.49416±0.00070 |
| Inclination (i) | 34.938±0.078° |
| Longitude of the node (Ω) | 98.31±0.15° |
| Periastron epoch (T) | 1889.6 |
| Argument of periastron (ω) (secondary) | 88.34±0.25° |
| Details | |
| η Cas A | |
| Mass | 1.0258+0.0070 −0.0069 M☉ |
| Radius | 1.0336±0.0027 R☉ |
| Luminosity | 1.2321±0.0074 L☉ |
| Surface gravity (log g) | 4.40+0.04 −0.03 cgs |
| Temperature | 6,012+25 −22 K |
| Metallicity [Fe/H] | −0.26±0.03 dex |
| Rotational velocity (v sin i) | 3.15 km/s |
| Age | 5.4±0.9 Gyr |
| η Cas B | |
| Mass | 0.5487±0.0056 M☉ |
| Radius | 0.57+0.02 −0.03 R☉ |
| Luminosity | 0.082±0.000 L☉ |
| Surface gravity (log g) | 4.750±0.005 cgs |
| Temperature | 4,011±38 K |
| Other designations | |
| Achird, η Cas, 24 Cassiopeiae, BD+57°150, GC 962, GJ 34, HD 4614, HIP 3821, HR 219, SAO 21732, ADS 671, CCDM J00491+5749, LFT 74, LHS 123/122, LTT 10287, Wolf 24 | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
Eta Cassiopeiae is a binary star system in the northern constellation of Cassiopeia. Its name is a Bayer designation that is Latinized from η Cassiopeiae and abbreviated Eta Cas or η Cas. The binary nature of this system was first discovered by William Herschel in August 1779. Based upon parallax measurements, the distance to this system is 19.32 light-years (5.92 parsecs). The two components are designated Eta Cassiopeiae A (officially named Achird /ˈeɪtʃərd/) and B.