9 Persei

This article is about i Persei and is not to be confused with ι (iota) Persei or l Persei.

9 Persei is a single^[11] variable star in the northern constellation Perseus, located around 4,300 light years away from the Sun. It has the Bayer designation i Persei; 9 Persei is the Flamsteed designation. This body is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of about 5.2. It is moving closer to the Sun with a heliocentric radial velocity of −15.2 km/s.^[5] The star is a member of the Perseus OB1 association of co-moving stars.^[12]

A light curve for V474 Persei. The main plot shows the variation over a year, and the inset plot shows the same data folded over the best-fit period. The data was published by Burggraaff et al. (2018)^[13]

9 Persei

Location of 9 Persei (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Perseus
Right ascension	02h 22m 21.43482s[1]
Declination	+55° 50′ 44.3518″[1]
Apparent magnitude (V)	5.15 - 5.25[2]
Characteristics
Spectral type	A2 Ia[3]
U−B color index	−0.11[4]
B−V color index	+0.37[4]
Variable type	α Cyg[2]
Astrometry
Radial velocity (Rv)	−15.20[5] km/s
Proper motion (μ)	RA: +0.374[1] mas/yr Dec.: −1.798[1] mas/yr
Parallax (π)	0.7603±0.1139 mas[1]
Distance	approx. 4,300 ly (approx. 1,300 pc)
Absolute magnitude (MV)	−4.73[6]
Details
Mass	10.5[7] M☉
Radius	88.9+3.8 −2.8[1] R☉
Luminosity	12,331±2,189[1] L☉
Surface gravity (log g)	1.74[8] cgs
Temperature	9,840[9] K
Metallicity [Fe/H]	+0.26[8] dex
Rotational velocity (v sin i)	25[3] km/s
Other designations
i Persei, 9 Per, V474 Per, BD+55°598, FK5 2159, GC 2836, HD 14489, HIP 11060, HR 685, SAO 23256, CCDM J02224+5551A, WDS J02224+5551A[10]
Database references
SIMBAD	data

The Double Cluster. 9 Persei is the brightest star on right side of the image. North is to the left.

This is a blue supergiant with a stellar classification of A2 Ia,^[3] a massive star that has used up its core hydrogen and is now fusing heavier elements. It is an Alpha Cygni variable (designated V474 Persei), a type of non-radial pulsating variable. It ranges in magnitude from 5.15 down to 5.25.^[14] The star has 10.5^[7] times the mass of the Sun and has expanded to 89^[1] times the Sun's radius. It is radiating over 12,000^[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 9,840 K.^[9]

9 Persei has one visual companion, designated component B, at an angular separation of 12.3″ and magnitude 12.0.^[15]