Mu Cassiopeiae

μ Cassiopeiae
Location of μ Cassiopeiae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 01h 08m 16.30295s[1]
Declination +54° 55′ 12.5612″[1]
Apparent magnitude (V) 5.159[2]
(5.14/11.45[3])
Characteristics
Spectral type G5Vb[4] + M4V[5]
U−B color index +0.10[6]
B−V color index 0.695±0.006[5]
Variable type Suspected[7]
Astrometry
Radial velocity (Rv)−98.3[2] km/s
Proper motion (μ) RA: +3,468.251[1] mas/yr
Dec.: −1,564.844[1] mas/yr
Parallax (π)130.2881 ± 0.4348 mas[1]
Distance25.03 ± 0.08 ly
(7.68 ± 0.03 pc)
Absolute magnitude (MV)5.78/11.6[8]
Orbit[5]
Companionμ 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[5]
Aa
Mass0.7440±0.0122 M☉
Radius0.789±0.008 R☉
Luminosity0.445±0.005 L☉
Surface gravity (log g)4.515±0.011 cgs
Temperature5,306±31 K
Metallicity [Fe/H]−0.81±0.03 dex
Rotational velocity (v sin i)2.4 km/s
Age12.7±2.7[5]
3.1[2]
5.9[9] Gyr
Ab
Mass0.1728±0.0035[5] M☉
Radius0.29[3] R☉
Luminosity0.0062[3] L☉
Temperature3,025[3] 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
SIMBADdata

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".[10] It is dimly visible to the naked eye as a point of light with an apparent visual magnitude of 5.16.[2] 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 −98 km/s.[2] This star will move into the constellation Perseus around 5200 AD.[11]

Mu Cassiopeiae is given as a standard star for the spectral class G5Vb,[4] although it is frequently described as a subdwarf, meaning it has a luminosity below that expected for a G5 main sequence star.[12] The metallicity, or abundance of heavy elements, is about one-sixth that in the Sun.[5] It is slightly smaller than the Sun with less mass and a lower luminosity.[5]

This is one of the first high-velocity stars to be identified.[5] 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.[5] They are low metal, Population II stars that are thought to have formed before the galactic disk first appeared.

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