B Persei

This article is about b Persei. For β Persei, see Algol.

b Persei (also known as HD 26961) is a spectroscopic triple star in the constellation Perseus. Its apparent magnitude is 4.60, making it visible to the naked eye.^[6] It is about 320 light years away.^[1]

b Persei

Location of b Persei (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Perseus
Right ascension	04h 18m 14.61690s[1]
Declination	+50° 17′ 43.8058″[1]
Apparent magnitude (V)	4.52 - 4.68[2]
Characteristics
Spectral type	A1III[3]
B−V color index	+0.04[4]
Variable type	Ellipsoidal[2]
Astrometry
Radial velocity (Rv)	19.8±0.9[5] km/s
Proper motion (μ)	RA: 45.42±0.40[1] mas/yr Dec.: −56.72±0.32[1] mas/yr
Parallax (π)	10.40±0.35 mas[1]
Distance	310 ± 10 ly (96 ± 3 pc)
Absolute magnitude (MV)	0.3[6]
Orbit[7]
Primary	A or Aa
Companion	B or Ab
Period (P)	1.52735997±0.00000036 days
Eccentricity (e)	0.0
Inclination (i)	22±3 or 55±3[6]°
Periastron epoch (T)	2450001.0931±0.003
Orbit[8]
Primary	AB
Companion	C or Ac
Period (P)	703.06±0.07 days
Semi-major axis (a)	26.22±0.06 mas
Eccentricity (e)	0.185±0.003
Inclination (i)	90.5±0.1°
Longitude of the node (Ω)	120.0±0.1°
Periastron epoch (T)	2440080±3
Argument of periastron (ω) (secondary)	212±1°
Details
A or Aa
Mass	2.25[6] M☉
Radius	3.2[9] R☉
Luminosity	59[6] L☉
Temperature	9,000[6] K
Rotational velocity (v sin i)	81[10] km/s
B or Ab
Mass	0.56[11] M☉
Radius	0.25[9] R☉
Luminosity	4.5 - 5.9[6] L☉
Temperature	6,700[6] K
C or Ac
Mass	1.24[11] M☉
Luminosity	2[12] L☉
Other designations
BD+49°1150, GC 5174, HD 26961, HR 1324, HIP 20070, SAO 24531
Database references
SIMBAD	data

Light curves for b Persei. The top panel, plotted from TESS data,^[13] shows the variability of the inner binary pair. The lower panels, plotted from AAVSO data,^[14] show two eclipses.

In addition to the primary, an A-type giant, there is a smaller and cooler companion in a 1.53 day orbit, probably an F-class star around absolute magnitude 3.0, and a more distant companion (star C or Ac) in an orbit calculated to be 702 days long.^[6] The close binary pair forms a rotating ellipsoidal variable with a 1.53 day period. Star C forms an Algol-type variable system with the close binary, showing both primary eclipses (when star C passes in front of the inner pair) and secondary eclipses (when the inner pair passes in front of star C).^[15] Timings of the eclipses show a 704.5-day period.^[12]