Eta Cassiopeiae
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 00h 49m 06.29070s |
| Declination | +57° 48′ 54.6758″ |
| 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: +1,086.59 mas/yr Dec.: −559.43 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 |
| Companion | 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 | 0.66 R☉ |
| Luminosity | 0.0646+0.0131 −0.0109 L☉ |
| Temperature | 4,036±150 K |
| Other designations | |
| Achird, η Cas 24 Cassiopeiae, ADS 671, BD+57°150, GCTP 155, GJ 34, HD 4614, HIP 3821, HR 219, LHS 123/122, LFT 74, LTT 10287, SAO 21732, Wolf 24, Struve 60, GC 962, CCDM J00491+5749 | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
Eta Cassiopeiae (η Cassiopeiae, abbreviated Eta Cas, η Cas) is a binary star system in the northern constellation of Cassiopeia. Its binary nature was first discovered by William Herschel in August 1779. Based upon parallax measurements, the distance to this system is 19.42 light-years (5.95 parsecs). The two components are designated Eta Cassiopeiae A (officially named Achird /ˈeɪtʃərd/) and B.