Mu Cassiopeiae
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 01h 08m 16.30295s |
| Declination | +54° 55′ 12.5612″ |
| Apparent magnitude (V) | 5.159 (5.14/11.45) |
| Characteristics | |
| Spectral type | G5Vb + M4V |
| U−B color index | +0.10 |
| B−V color index | 0.695±0.006 |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | −97.09±0.25 km/s |
| Proper motion (μ) | RA: +3,468.251 mas/yr Dec.: −1,564.844 mas/yr |
| Parallax (π) | 130.2881±0.4348 mas |
| Distance | 25.03 ± 0.08 ly (7.68 ± 0.03 pc) |
| Absolute magnitude (MV) | 5.78/11.6 |
| Orbit | |
| Companion | μ Cas B |
| Period (P) | 21.568±0.015 yr |
| Semi-major axis (a) | 0.9985±0.0013″ |
| Eccentricity (e) | 0.5885±0.0011 |
| Inclination (i) | 110.671±0.064° |
| Longitude of the node (Ω) | 223.868±0.064° |
| Periastron epoch (T) | 1,997.2235±0.0067 |
| Argument of periastron (ω) (secondary) | 330.37±0.18° |
| Details | |
| Aa | |
| Mass | 0.7440±0.0122 M☉ |
| Radius | 0.789±0.008 R☉ |
| Luminosity | 0.445±0.005 L☉ |
| Surface gravity (log g) | 4.515±0.011 cgs |
| Temperature | 5,306±31 K |
| Metallicity [Fe/H] | −0.81±0.03 dex |
| Rotational velocity (v sin i) | 2.4 km/s |
| Age | 12.7±2.7 Gyr |
| Ab | |
| Mass | 0.1728±0.0035 M☉ |
| Radius | 0.29 R☉ |
| Luminosity | 0.0062 L☉ |
| Temperature | 3,025 K |
| Other designations | |
| Marfak, μ Cas, 30 Cassiopeiae, BD+54°223, FK5 1030, GC 1360, GJ 53, HD 6582, HIP 5336, HR 321, SAO 22024, CCDM J01080+5455, LFT 107, LHS 8, LTT 10460 | |
| Database references | |
| SIMBAD | data |
Mu Cassiopeiae, Latinized from μ Cassiopeiae, is a binary star system in the constellation Cassiopeia. This system shares the name Marfak /ˈmɑːrfæk/ with Theta Cassiopeiae, and the name was from Al Marfik or Al Mirfaq (المرفق), meaning "the elbow". It is dimly visible to the naked eye as a point of light with an apparent visual magnitude of 5.16. The system is located at a distance of 25 light-years from the Sun based on parallax, and is moving closer with a high radial velocity of −97 km/s. This star will move into the constellation Perseus around 5200 AD.
Mu Cassiopeiae is given as a standard star for the spectral class G5Vb, although it is frequently described as a subdwarf, meaning it has a luminosity below that expected for a G5 main sequence star. The metallicity, or abundance of heavy elements, is about one-sixth that in the Sun. It is slightly smaller than the Sun with less mass and a lower luminosity. It is among the oldest known stars, with an age of 12.7±2.7 billion years making it possibly the oldest star visible to the unaided eye.
This is one of the first high-velocity stars to be identified. Compared to other nearby stars including the Sun, this pair are moving at a relatively high velocity of 167 km/s through the Milky Way galaxy. They are low metal, Population II stars that are thought to have formed before the galactic disk first appeared.