Theta Cassiopeiae

Theta Cassiopeiae or θ Cassiopeiae is a solitary^[5] star in the northern constellation of Cassiopeia. It shares the traditional name Marfak /ˈmɑːrfæk/ with μ Cassiopeiae, positioned less than half a degree to the WSW,^[13] which is derived from the Arabic term Al Marfik or Al Mirfaq (المرفق), meaning "the elbow".^[14] At an apparent visual magnitude of 4.3,^[3] Theta Cassiopeiae is visible to the naked eye. Based upon an annual parallax shift of 24.42 mas,^[2] it is located about 134 light years from the Sun. It has a total annual proper motion of 0.227 arcseconds per year,^[15] and is slowly drifting further away from the Sun with a radial velocity of 2.5 km/s.^[7]

Theta Cassiopeiae

Location of θ Cassiopeiae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cassiopeia[1]
Right ascension	01h 11m 06.16225s[2]
Declination	+55° 08′ 59.6472″[2]
Apparent magnitude (V)	4.334[3]
Characteristics
Evolutionary stage	main sequence[4]
Spectral type	A7 V[5]
U−B color index	+0.130[3]
B−V color index	+0.170[3]
Variable type	Suspected δ Sct[6]
Astrometry
Radial velocity (Rv)	2.5±0.6[7] km/s
Proper motion (μ)	RA: +226.77[2] mas/yr Dec.: −18.75[2] mas/yr
Parallax (π)	24.42±0.24 mas[2]
Distance	134 ± 1 ly (41.0 ± 0.4 pc)
Absolute magnitude (MV)	+1.28[8]
Details
Mass	1.9[9] M☉
Radius	2.5[9] R☉
Luminosity	23[9] L☉
Surface gravity (log g)	3.91[9] cgs
Temperature	7,954[9] K
Metallicity [Fe/H]	+0.07[10] dex
Rotational velocity (v sin i)	103[4] km/s
Age	650[11] Myr
Other designations
Marfak, θ Cas, 33 Cassiopeiae, BD+54°236, HD 6961, HIP 5542, HR 343, SAO 22070[12]
Database references
SIMBAD	data

In Chinese, 閣道 (Gé Dào), meaning Flying Corridor, refers to an asterism consisting of θ Cassiopeiae, ι Cassiopeiae, ε Cassiopeiae, δ Cassiopeiae, ν Cassiopeiae and ο Cassiopeiae.^[16] Consequently, θ Cassiopeiae itself is known as 閣道四 (Gé Dào sì, English: the Fourth Star of Flying Corridor.)^[17]

This is an A-type main sequence star with a stellar classification of A7 V.^[5] The star has 1.9 times the Sun's mass and 2.5 times the Sun's radius.^[9] It is about 650 million years in age^[11] and is spinning with a projected rotational velocity of 103 km/s.^[4] This is a candidate Vega-type system, which means it displays an infrared excess suggesting it has an orbiting debris disk.^[18] It is a suspected Delta Scuti variable.^[6]

The star appears to be a member of a leading tidal tail of the Hyades cluster.^[19]