Delta Andromedae

Delta Andromedae is a triple star^[12] system in the northern constellation of Andromeda. Its identifier is a Bayer designation that is Latinized from δ Andromedae, and abbreviated Delta And or δ And, respectively. The system is visible to the naked eye as a point of light with a combined apparent visual magnitude of 3.28.^[2] Based upon parallax measurements, it is located at a distance of approximately 105.5 light-years (32.3 parsecs) from the Sun.^[1] The system is drifting closer with a radial velocity of −10 km/s.^[6]

δ Andromedae

Location of δ Andromedae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Andromeda
Right ascension	00h 39m 19.67518s[1]
Declination	+30° 51′ 39.6783″[1]
Apparent magnitude (V)	3.28[2]
Characteristics
Spectral type	K3 III[3] + K4 ± 2[4]
U−B color index	+1.48[2]
B−V color index	+1.28[2]
R−I color index	+0.66[5]
Astrometry
Radial velocity (Rv)	−9.88±0.15[6] km/s
Proper motion (μ)	RA: +114.45[1] mas/yr Dec.: −84.02[1] mas/yr
Parallax (π)	30.91±0.15 mas[1]
Distance	105.5 ± 0.5 ly (32.4 ± 0.2 pc)
Absolute magnitude (MV)	+0.8[7]
Orbit[8]
Period (P)	15,000 d
Eccentricity (e)	0.34±0.14
Periastron epoch (T)	2415568 JD
Argument of periastron (ω) (primary)	356.1±5.2°
Semi-amplitude (K1) (primary)	4.0±2.7 km/s
Details[4]
δ And Aa
Mass	~1.3[9] M☉
Radius	13.6±0.3 R☉
Luminosity	68±4 L☉
Surface gravity (log g)	2.0±0.3[3] cgs
Temperature	4,315±9 K
Metallicity [Fe/H]	0.04 dex
Rotational velocity (v sin i)	6.5[6] km/s
Age	3.2 Gyr
δ And Ab
Mass	0.6–0.8 M☉
Other designations
δ And, Delta Andromedae, Delta And, 31 Andromedae, 31 And, NSV 15142, BD+30 91, FK5 20, HD 3627, HIP 3092, HR 165, SAO 54058, PPM 65514, WDS 00393+3052A[10][11]
Database references
SIMBAD	data

In Chinese, 奎宿 (Kuí Sù), meaning Legs (asterism), refers to an asterism consisting of δ Andromedae, η Andromedae, 65 Piscium, ζ Andromedae, ι Piscium, ε Andromedae, π Andromedae, ν Andromedae, μ Andromedae, β Andromedae, σ Piscium, τ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ¹ Piscium. Consequently, the Chinese name for δ Andromedae itself is 奎宿五 (Kuí Sù wǔ, English: the Fifth Star of Legs.)^[13] Apart from its Bayer designation, it was also given the title Delta by Elijah H. Burritt in his star atlas.^[14]

This is a long-period spectroscopic binary with an orbital period of approximately 15,000 days (41 years). The primary of the spectroscopic binary, component Aa, has a stellar classification of K3 III, indicating that it is an aging giant star.^[3][8] It most likely evolved from a F-type main sequence star after consuming the hydrogen at its core.^[15] The secondary, component Ab, is a relatively faint K-type dwarf, which has been imaged using a stellar coronagraph. The pair have a physical separation of 11.55±0.13 AU.^[4] The system has two companions, the closest of which is most likely an orbiting red dwarf of class M3 with a separation of at least 900 astronomical units.^[16]

An excess of infrared emission from δ Andromedae suggested that it may be surrounded by a shell of dust.^[3][17] In 2003 it was determined that this is more likely a circumstellar debris disk.^[15]