1 Persei

1 Persei (1 Per) is an eclipsing binary^[3] star in the constellation Perseus. Its uneclipsed apparent magnitude is 5.49. The binary star consists of two B2 type main-sequence stars in a 25.9 day eccentric orbit.^[5] The stars are surrounded by a faint cloud of gas visible in mid-infrared, although whether they are the origin of the gas or simply passing through it is unclear.

1 Persei

Location of 1 Persei (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Perseus
Right ascension	01h 51m 59.32008s[1]
Declination	+55° 08′ 50.5837″[1]
Apparent magnitude (V)	5.49 - 5.74 - 5.85[2]
Characteristics
Spectral type	B1.5V[2]
Variable type	eclipsing binary[3]
Astrometry
Proper motion (μ)	RA: 12.716(74)[1] mas/yr Dec.: −8.410(79)[1] mas/yr
Parallax (π)	2.6944±0.0888 mas[1]
Distance	1,210 ± 40 ly (370 ± 10 pc)
Absolute magnitude (MV)	−1.37/−1.77[4]
Orbit[4]
Primary	1 Persei A
Companion	1 Persei B
Period (P)	25.935951±0.000003 d
Eccentricity (e)	0.3768±0.0014
Inclination (i)	88.048±0.002°
Periastron epoch (T)	2443563.466±0.005 HJD
Argument of periastron (ω) (secondary)	109.83±0.10°
Semi-amplitude (K1) (primary)	97.4±0.1 km/s
Semi-amplitude (K2) (secondary)	91.2±0.1 km/s
Details[4]
Primary
Mass	6.95 M☉
Radius	3.29 R☉
Luminosity	2,188 L☉
Surface gravity (log g)	4.25 cgs
Temperature	21,500 K
Rotation	1.45 days
Rotational velocity (v sin i)	115 km/s
Secondary
Mass	7.42 M☉
Radius	3.86 R☉
Luminosity	3,311 L☉
Surface gravity (log g)	4.14 cgs
Temperature	22,000 K
Rotation	1.40 days
Rotational velocity (v sin i)	140 km/s
Other designations
V436 Persei, BD+54 396, HD 11241, HIP 8704, HR 533, SAO 22690
Database references
SIMBAD	data

Observational history

A visual band light curve for V436 Persei, adapted from Janik et al. (2003)^[4]

The possible eclipsing binary nature of 1 Persei was first noticed by Donald Kurtz in 1977 when it was used as a comparison star to test for photometric variability of HD 11408.^[6] In 1979 French amateur observers succeeded in determining an orbital period of 25.9 days.^[7] During the primary eclipse, the brightness drops to magnitude 5.85. In the secondary eclipses, the brightness drops to magnitude 5.74. The eclipses each last for approximately 25 hours.^[2]