21 Persei

21 Persei is a single,^[10] variable star in the northern constellation of Perseus, located about 331 light years away from the Sun. It is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of 5.10 km/s.^[2] The object is moving further from the Earth with a heliocentric radial velocity of +8.5 km/s.^[6] It has the variable star designation LT Persei; 21 Persei is the Flamsteed designation.

21 Persei

Location of 21 Persei (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Perseus
Right ascension	02h 57m 17.28228s[1]
Declination	31° 56′ 03.1976″[1]
Apparent magnitude (V)	5.10[2]
Characteristics
Spectral type	A2VspSiEu[3]
U−B color index	−0.24[4]
B−V color index	−0.01[4]
Variable type	α² CVn[5]
Astrometry
Radial velocity (Rv)	+8.50[6] km/s
Proper motion (μ)	RA: +1.319[1] mas/yr Dec.: -30.384[1] mas/yr
Parallax (π)	9.8477±0.2575 mas[1]
Distance	331 ± 9 ly (102 ± 3 pc)
Absolute magnitude (MV)	0.14[2]
Details
Mass	3.57[7] M☉
Luminosity	88.65[2] L☉
Surface gravity (log g)	4.05[7] cgs
Temperature	12,585[7] K
Metallicity [Fe/H]	+0.90[8] dex
Rotational velocity (v sin i)	20[7] km/s
Other designations
21 Per, LT Per, BD+31°509, FK5 2205, GC 3544, HD 18296, HIP 13775, HR 873, SAO 56031[9]
Database references
SIMBAD	data

A light curve for LT Persei, plotted from Hipparcos data^[11]

This is an Ap star with a stellar classification of A2VspSiEu,^[3] where the A2V indicates it is an A-type main-sequence star, 's' means narrow "sharp" absorption, and SiEu shows abundance anomalies of the elements silicon and europium. The star is an Alpha² Canum Venaticorum variable, meaning that the star has a strong magnetic field chromium, silicon, and strontium spectral lines. 21 Persei's period of variability is approximately 2.88 days.^[12]