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.
  | |
| 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 | |
| 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]