Omicron Andromedae

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"1 Andromedae" and "1 And" redirect here. For the galaxy, see Andromeda I. For ι Andromedae, see Iota Andromedae. For other uses, see And 1.
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′ 33.66″[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[8] mas/yr
Dec.: +0.88[8] mas/yr
Parallax (π)4.75±0.53 mas[8][9]
Distanceapprox. 690 ly
(approx. 210 pc)
Absolute magnitude (MV)−2.6[10]
Orbit[9]
PrimaryA
CompanionB
Period (P)118.0 yr
Semi-major axis (a)0.304″
Eccentricity (e)0.340
Inclination (i)107.4°
Orbit[11][12]
PrimaryAa
CompanionAb
Period (P)5.6 yr
Semi-major axis (a)0.061″
Eccentricity (e)0.22
Inclination (i)152.0°
Orbit[13][12]
PrimaryBa
CompanionBb
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
Mass6.5±0.5[14] M☉
Radius11.5±1.3[14] R☉
Luminosity5,300±900[14] L☉
Temperature14,540±170[14] K
Rotational velocity (v sin i)240[15] km/s
Age52±9[14] Myr
ο And Ab
Mass4.51[12] M☉
ο And Ba
Mass3.74[12] M☉
ο And Bb
Mass2.86[12] M☉
Age50.1 ± 6.8[16] Myr
Other designations
Alfarasalkamil, 1 And, AAVSO 2257+41, BD+41°4664, FK5 869, HIP 113726, HR 8762, SAO 52609, PPM 63726[17]
ο And A: HD 217675
ο And B: HD 217676
Database references
SIMBADdata

Omicron Andromedae, also named Alfarasalkamil,[18] is a star system in the northern constellation Andromeda. Its Bayer designation is Latinized from ο Andromedae, and is abbreviated Omi And or ο And, respectively. Based on parallax measurements, it is located at a distance of approximately 690 light years from Earth.[8] The system as a whole is classified as a blue-white B-type giant,[4] with a typical combined apparent magnitude of +3.62.[2] This is sufficiently bright that the star can be viewed with the naked eye on a dark night.

Nomenclature

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This star was in the head of the traditional Arabic constellation Al Faras al Kamil, the Complete Horse, as opposed to Pegasus which is the front half of a horse.[19] The IAU Working Group on Star Names approved the name Alfarasalkamil for Omicron Andromedae Aa on 8 May 2025 and it is now so entered in the IAU Catalog of Star Names.[18]

It was also the brightest star of the obsolete constellation Honores Friderici.[20]

System

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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,[16] although the binarity of the primary star is in doubt.[12] This star system has a peculiar velocity of 34.5 ± 5.9 km/s, which qualifies it as a runaway star.[16]

The components A and B were first resolved in 1949, when they were reported to be separated by less than 0.1".[21] In 1975 they were separated by 0.375"[13] and by 2014 by only 0.21".[22] 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,[11] although the existence of this companion is now doubted.[12]

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.[13] Eventually, it was settled that component B was a close spectroscopic binary.[11]

Properties

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A light curve for Omicron Andromedae, plotted from TESS data[23]

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] Rapid variations in its spectrum have been reported.[24]

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

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  1. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value). (Erratum: Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).). Gaia EDR3 record for this source at VizieR.
  2. ^ a b c d Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  3. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  4. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  5. ^ a b c d e Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  6. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  7. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  8. ^ a b c d Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  9. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  10. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  11. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  12. ^ a b c d e f g Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  13. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  14. ^ a b c d e Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  15. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  16. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  17. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  18. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  19. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  20. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  21. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  22. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  23. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  24. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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