66 Andromedae

66 Andromedae is a binary star^[3] system in the northern constellation of Andromeda, near the northern border with Perseus. The designation is from the star catalogue of English astronomer John Flamsteed, first published in 1712. It has a combined apparent magnitude of 6.16,^[2] which is near the lower limit of stars that are visible to the naked eye under good seeing conditions. An annual parallax shift of 18.3 mas^[6] provides a distance estimate of 178 light years. The net radial velocity of the system is poorly constrained, but the pair appear to be moving closer to the Earth with a heliocentric radial velocity of around −5 km/s.^[3]

66 Andromedae

Location of 66 Andromedae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda
Right ascension	02h 27m 51.77815s[1]
Declination	+50° 34′ 11.9081″[1]
Apparent magnitude (V)	6.16[2] (7.26/7.46)[3]
Characteristics
Spectral type	F4 V[3]
B−V color index	0.435 (4.2/4.5)[3]
Astrometry
Radial velocity (Rv)	−5.3±4.3[3] km/s
Proper motion (μ)	RA: +31.700[1] mas/yr Dec.: −90.312[1] mas/yr
Parallax (π)	18.2931±0.0416 mas[1]
Distance	178.3 ± 0.4 ly (54.7 ± 0.1 pc)
Absolute magnitude (MV)	3.1±0.1/3.4±0.1[3]
Orbit[3]
Period (P)	10.989861±0.000024 d
Semi-major axis (a)	≥ 6.9 Gm (9.9 R☉)
Eccentricity (e)	0.19236±0.00057
Periastron epoch (T)	2,454,007.675±0.006 JD
Argument of periastron (ω) (secondary)	250.55±0.18°
Semi-amplitude (K1) (primary)	46.719±0.034 km/s
Semi-amplitude (K2) (secondary)	48.083±0.038 km/s
Details[3]
66 And A
Mass	1.38 M☉
Radius	1.7±0.1 R☉
Luminosity	4.9±0.5 L☉
Surface gravity (log g)	4.21[4] cgs
Temperature	6,627±225[4] K
Metallicity [Fe/H]	−0.14±0.08[2] dex
Rotational velocity (v sin i)	4.2±1.0 km/s
Age	1.273[4] Gyr
66 And B
Radius	1.5±0.1 R☉
Luminosity	3.8±0.4 L☉
Rotational velocity (v sin i)	4.4±1.0 km/s
Other designations
66 And, BD+49°666, HD 15138, HIP 11465, HR 709, SAO 23353, PPM 27645[5]
Database references
SIMBAD	data

The variable velocity of this system was reported by Reynold K. Young from the David Dunlap Observatory in 1945. This is a double-lined spectroscopic binary system with an orbital period of 11 days and an eccentricity of 0.19.^[3] The two components are similar stars, each of 7th^[3] magnitude, with a combined stellar classification of F4 V,^[3] matching that of an F-type main sequence star. The system is around 1.3^[4] billion years old and both stars are spinning slowly with a projected rotational velocity of around 4–5 km/s.^[3]