Rho2 Arietis

Rho² Arietis is an M-type red giant star in the northern constellation of Aries. Its name is a Bayer designation that is Latinized from ρ² Arietis, and abbreviated Rho² Ari or ρ² Ari. The brightness of this star varies from magnitude 5.45 to 6.01,^[12] making it faintly visible to the naked eye under good observing conditions. With an annual parallax shift of 9.28 mas,^[2] it is approximately 350 light-years (110 parsecs) distant from the Earth. It is drifting further away from the Sun with a radial velocity of +46 km/s.^[9]

A visual band light curve for Rho² Arietis, plotted from data presented in Tabur et al. (2009)^[13]

For other stars with this Bayer designation, see ρ Arietis.

ρ² Arietis

Location of ρ2 Arietis (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Aries[1]
Right ascension	02h 55m 48.49800s[2]
Declination	+18° 19′ 53.9029″[2]
Apparent magnitude (V)	5.93[3] (5.45–6.01)[4]
Characteristics
Evolutionary stage	AGB[5][6]
Spectral type	M6 III[7]
U−B color index	+1.12[3]
B−V color index	+1.51[3]
R−I color index	+2.17[8]
Variable type	SRb[4]
Astrometry
Radial velocity (Rv)	+46.0[9] km/s
Proper motion (μ)	RA: −7.78[2] mas/yr Dec.: −14.98[2] mas/yr
Parallax (π)	9.28±0.30 mas[2]
Distance	350 ± 10 ly (108 ± 3 pc)
Absolute magnitude (MV)	+0.60[1]
Details
Mass	1.21[6] M☉
Radius	107.9±6.2[6] R☉
Luminosity	1,390[6] L☉
Surface gravity (log g)	0.5[10] cgs
Temperature	3,400[10] K
Metallicity [Fe/H]	–0.25[6] dex
Rotation	<909[6] days
Rotational velocity (v sin i)	6.0±0.5[10] km/s
Other designations
ρ2 Ari, 45 Arietis, RZ Arietis, BD+17 457, GC 3517, HD 18191, HIP 13654, HR 867, SAO 93189, PPM 118672[11]
Database references
SIMBAD	data

Rho² Arietis is classified as a semiregular variable star with periods of 49.9 and 54.8 days.^[13] It has the variable star designation, RZ Arietis.^[4]

This is a red giant star with a stellar classification of M6 III;^[7] it is probably on the asymptotic giant branch, having exhausted its core helium.^[5][6] It is predicted to have started its life with 1.5 times the mass of the Sun, and is now down to 1.2 times the Sun's mass. At its current evolutionary stage Rho² Arietis has expanded to 108 times the Sun's radius. It is radiating 1,390 times the Sun's luminosity from its photosphere at an effective temperature of 3,400 K.^[6]

This star possesses a strong magnetic field, one of the strongest for M-type giants. It also possesses a high lithium abundance, higher than expected from evolutionary models. The strong magnetic field, rapid rotation and unusual lithium abundance suggest this star may have engulfed a planet when it was on the red-giant branch.^[6]