Omicron Andromedae (ο And, ο Andromedae) is a star system in the constellation Andromeda. It is approximately 692 light years from Earth. The system as a whole is classified as a blue-white B-type giant, with a mean combined apparent magnitude of +3.62.

Omicron Andromedae

Location of ο Andromedae (far right)
Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda
Right ascension	23h 01m 55.265s[1]
Declination	+42° 19′ 33.53″[1]
Apparent magnitude (V)	3.62[2] (3.55 - 3.78[3])
Characteristics
Spectral type	B6III[4] (B6IIIpe + A2p)[5]
U−B color index	−0.53[2]
B−V color index	−0.09[2]
Variable type	γ Cas[6][3]
Astrometry
Radial velocity (Rv)	-14.0[7] km/s
Proper motion (μ)	RA: +22.99[1] mas/yr Dec.: +0.88[1] mas/yr
Parallax (π)	4.75 ± 0.53 mas[1]
Distance	approx. 690 ly (approx. 210 pc)
Absolute magnitude (MV)	−2.6[8]
Orbit[9]
Primary	A
Companion	B
Period (P)	118.0 yr
Semi-major axis (a)	0.304″
Eccentricity (e)	0.340
Inclination (i)	107.4°
Orbit[10][11]
Primary	Aa
Companion	Ab
Period (P)	5.6 yr
Semi-major axis (a)	0.061″
Eccentricity (e)	0.22
Inclination (i)	152.0°
Orbit[12][11]
Primary	Ba
Companion	Bb
Period (P)	33.01 days
Eccentricity (e)	0.24
Semi-amplitude (K1) (primary)	54.8±0.8 km/s
Semi-amplitude (K2) (secondary)	71.6±0.8 km/s
Details
ο And Aa
Mass	9.85[11] M☉
Radius	6.6[8] R☉
Luminosity	1,380[13] L☉
Temperature	13,800[13] K
Rotational velocity (v sin i)	240[13] km/s
ο And Ab
Mass	4.51[11] M☉
ο And Ba
Mass	3.74[11] M☉
ο And Bb
Mass	2.86[11] M☉
Age	50.1 ± 6.8[14] Myr
Other designations
FK5 869, 1 And, BD+41°4664, CDS 1436, HIP 113726, HR 8762, SAO 52609[15]
ο And A: HD 217675
ο And B: HD 217676
Database references
SIMBAD	data

System

Omicron Andromedae is a multiple star containing at least three components. It may consist of two close pairs in a wider orbit, making a four-star system,[14] although the binarity of the primary star is in doubt.[11] This star system has a peculiar velocity of 34.5 ± 5.9 km/s.[14]

The components A and B were first resolved in 1949, when they were reported to be separated by less than 0.1".[16] In 1975 they were separated by 0.375"[12] and by 2014 by only 0.21".[17] An orbit has been derived with a period of 118 years.[9] The companion is 2.3 magnitudes fainter than the primary star.[5]

In 1975, a companion was discovered by speckle interferometry only 0.05" from component A.[5] Components Aa and Ab orbit every 5.6 years,[10] although the existence of this companion is now doubted.[11]

A spectroscopic binary in the system was suspected and in 1988 it was confirmed. Although a clear 33.01 day period was seen, it was unclear which component was the pair seen in the spectrum.[12] Eventually, it was settled that component B was a close spectroscopic binary.[10]

Properties

Omicron Andromedae is a Gamma Cassiopeiae type variable star and the system's brightness varies from magnitude +3.58 to +3.78. The variable component is the brightest and most massive star in the system, Aa.[3] Omicron Andromedae also shows variations with a period of about a day, similar to a β Lyrae-type eclipsing variable, but these are thought to be intrinsic to one of the components and not due to eclipses.[6]

The spectrum is predominantly that of a B6 giant star, from the brightest component in the system. It is a shell star and the spectrum contains emission lines with variable profiles.[5]

Spectral lines similar to an A2 star are also detectable in the spectrum and these are thought to originate in the B component.[5]

References

External links

• Image ο Andromedae

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[ru] Омикрон Андромеды