Upsilon1 Cassiopeiae

For other star systems with this Bayer designation, see υ Cassiopeiae.

Upsilon¹ Cassiopeiae (υ¹ Cassiopeiae) is an astrometric binary^[11] star system in the northern constellation of Cassiopeia. It is visible to the naked eye with an apparent visual magnitude of 4.82.^[3] Based upon an annual parallax shift of 9.93 mas as seen from Earth,^[2] this system is located about 330 light years from the Sun.

υ¹ Cassiopeiae

Location of υ1 Cassiopeiae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cassiopeia[1]
Right ascension	00h 55m 00.15523s[2]
Declination	+58° 58′ 21.7108″[2]
Apparent magnitude (V)	4.82[3]
Characteristics
Evolutionary stage	red clump[4]
Spectral type	K2 III[5]
U−B color index	+1.25[3]
B−V color index	+1.21[3]
Astrometry
Radial velocity (Rv)	−23.57[6] km/s
Proper motion (μ)	RA: −33.50±0.36[2] mas/yr Dec.: −40.82±0.33[2] mas/yr
Parallax (π)	9.93±0.49 mas[2]
Distance	330 ± 20 ly (101 ± 5 pc)
Absolute magnitude (MV)	−0.644[6]
Details
Mass	1.39[7] M☉
Radius	21[8] R☉
Luminosity	174[7] L☉
Surface gravity (log g)	1.76[6] cgs
Temperature	4,422±14[7] K
Metallicity [Fe/H]	−0.25[6] dex
Rotational velocity (v sin i)	1.1[9] km/s
Age	4.75[7] Gyr
Other designations
υ1 Cas, 26 Cas, BD+58°134, HD 5234, HIP 4292, HR 253, SAO 21832, ADS 748, CCDM J00551+5858, WDS J00550+5858A[10]
Database references
SIMBAD	data

υ¹ Cassiopeiae is the bright star in the lower right. The bright star in the upper left is υ² Cassiopeiae.

The visible component is an evolved K-type giant star with a stellar classification of K2 III.^[5] With an estimated age of 4.75 billion years,^[7] it is a red clump star that is generating energy through the fusion of helium at its core.^[4] The measured angular diameter, after correction for limb darkening, is 1.97±0.02 mas.^[12] At the estimated distance of the star, this yields a physical size of about 21 times the radius of the Sun.^[8] It has 1.39 times the mass of the Sun and is radiating 174 times the Sun's luminosity from its expanded photosphere at an effective temperature of 4,422 K.^[7]

There is a magnitude 12.50 visual companion at an angular separation of 17.80 arc seconds along a position angle of 61°, as of 2003. A more distant magnitude 12.89 companion lies at a separation of 93.30 arc seconds along a position angle of 125°, as measured in 2003. Neither star appears to be physically associated with υ¹ Cas.^[13]