2 Andromedae

Not to be confused with Andromeda II.

2 Andromedae, abbreviated 2 And, is a binary star^[3] system in the northern constellation of Andromeda. 2 Andromedae is the Flamsteed designation. It is a faint star system but visible to the naked eye with a combined apparent visual magnitude of 5.09.^[2] Based upon an annual parallax shift of 7.7 mas,^[1] it is located 420 light years away. The binary nature of the star was discovered by American astronomer Sherburne Wesley Burnham at Lick Observatory in 1889.^[12] The pair orbit each other over a period of 74 years with a high eccentricity of 0.8.^[3]

2 Andromedae

Location of 2 Andromedae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda
Right ascension	23h 02m 36.38176s[1]
Declination	+42° 45′ 28.0628″[1]
Apparent magnitude (V)	5.09[2] (5.26 + 7.43)[3]
Characteristics
2 And A
Spectral type	A1V[4]
U−B color index	+0.10[5]
B−V color index	+0.08[5]
2 And B
Spectral type	F1V/F4V[3]
Variable type	δ Sct?[3]
Astrometry
2 And A
Radial velocity (Rv)	2.1±2.4[6] km/s
Proper motion (μ)	RA: 56.38[1] mas/yr Dec.: −4.47[1] mas/yr
Parallax (π)	7.74±0.51 mas[1]
Distance	420 ± 30 ly (129 ± 9 pc)
Absolute magnitude (MV)	−0.39±0.16[7]
2 And B
Absolute magnitude (MV)	1.88±0.16[7]
Orbit[3]
Period (P)	73.997±0.509 yr
Semi-major axis (a)	0.225±0.011″
Eccentricity (e)	0.800±0.056
Inclination (i)	21.7±46.0°
Longitude of the node (Ω)	159.5±2.0°
Periastron epoch (T)	1870.280±0.595
Argument of periastron (ω) (secondary)	356.4±3.0°
Details
2 And A
Mass	2.7±0.1[7] M☉
Luminosity	130.50[2] L☉
Surface gravity (log g)	3.40±0.12[7] cgs
Temperature	8,950±250[7] K
Rotational velocity (v sin i)	212[8] km/s
Age	100+309 −88[9] Myr
2 And B
Mass	1.78±0.06[7] M☉
Surface gravity (log g)	3.90±0.16[7] cgs
Temperature	7,720±250[7] K
Other designations
2 And, BD+41°4665, GJ 886.1, HD 217782, HIP 113788, HR 8766, SAO 52623, PPM 63742, WDS 23026+4245[10]
Database references
SIMBAD	2 And
	2 And A
	2 And B

A light curve for 2 Andromedae, plotted from TESS data^[11]

The magnitude 5.26^[3] primary, designated component A, is an A-type main-sequence star based on a stellar classification of A1V^[4] or A2V,^[3] although it may have already left the main sequence.^[7] It was identified as a candidate Lambda Boötis star, but this was ruled out by Paunzen et al. (2003) as it doesn't match the typical characteristics of these objects.^[13] Although 2 Andromedae does not display a significant infrared excess, it is a shell star that displays varying absorption features due to circumstellar dust grains. This may indicate it has an orbiting debris disk containing gas that is being viewed edge-on.^[14] The star is about 100 million years old and is spinning rapidly with a projected rotational velocity of 212 km/s.^[8]

The magnitude 7.43^[3] secondary companion, component B, is a suspected variable star and may be a Delta Scuti variable.^[3] Alternatively, it may be an ellipsoidal variable with a brown dwarf companion.^[7] It is an F-type main-sequence star with a class of F1V/F4.^[3]