AB Andromedae
Binary star in the Andromeda constellation
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AB Andromedae (AB And) is a binary star in the constellation Andromeda. Paul Guthnick and Richard Prager discovered that the star is an eclipsing binary in 1927.[12][13] Its maximum apparent visual magnitude is 9.49 but shows a variation in brightness down to a magnitude of 10.46 in a periodic cycle of roughly 8 hours. The observed variability is typical of W Ursae Majoris variable stars,[3] so the two stars in this system form a contact binary.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 23h 11m 32.08593s[2] |
| Declination | +36° 53′ 35.1090″[2] |
| Apparent magnitude (V) | 9.49 ( – 10.32) – 10.46[3] |
| Characteristics | |
| Spectral type | G5+G5V[3] |
| Apparent magnitude (B) | 10.62[4] |
| Apparent magnitude (V) | 9.675[4] |
| Apparent magnitude (G) | 9.713[2] |
| Apparent magnitude (J) | 8.172[5] |
| Apparent magnitude (H) | 7.805[5] |
| Apparent magnitude (K) | 7.665[5] |
| B−V color index | 0.9163[4] |
| Variable type | EW |
| Astrometry | |
| Radial velocity (Rv) | −27.53±0.67[6] km/s |
| Proper motion (μ) | RA: 108.034±0.021 [2] mas/yr Dec.: −53.476±0.017[2] mas/yr |
| Parallax (π) | 11.7164±0.0200 mas[2] |
| Distance | 278.4 ± 0.5 ly (85.4 ± 0.1 pc) |
| Orbit[7] | |
| Period (P) | 0.3319 days |
| Semi-major axis (a) | 2.308 R☉[8] |
| Eccentricity (e) | 0.002±0.001 |
| Argument of periastron (ω) (secondary) | 40±5° |
| Argument of periastron (ω) (primary) | 220±5° |
| Semi-amplitude (K1) (primary) | 233±1 km/s |
| Semi-amplitude (K2) (secondary) | 133±1 km/s |
| Details | |
| Primary | |
| Mass | 1.03[9] M☉ |
| Radius | 1.15[9] R☉ |
| Luminosity | 0.77[9] L☉ |
| Surface gravity (log g) | 4.392[10] cgs |
| Temperature | 5,798[11] K |
| Age | 5.53±2.00[8] Gyr |
| Secondary | |
| Mass | 0.58[9] M☉ |
| Radius | 0.82[9] R☉ |
| Luminosity | 0.53[9] L☉ |
| Surface gravity (log g) | 4.347[10] cgs |
| Temperature | 5,450[11] K |
| Age | 5.53±2.00[8] Gyr |
| Other designations | |
| 2MASS J23113209+3653351, BD+36 5017, HIP 114508, SAO 73069, TYC 2763-904-1 | |
| Database references | |
| SIMBAD | data |
System
The observed spectral type of both stars in this system is G5, and one of them is a main sequence star very similar to the sun.[3] They are orbiting so close that their envelopes touch each other. This is a dynamically stable phase that should last until one of the two stars leaves the main sequence.
The system could also host a third body with an orbital period of 19,046 days, a minimum mass of 0.007 M☉ and an eccentricity of 0.22, but not all data collected in time are consistent with this hypothesis.[7]
Variability
The two stars eclipse each other during their orbit, but they have an elongated shape so they show a constant variation instead of discrete eclipses. Anyway, a periodicity can be seen clearly, but it changes with time; the period shows a long-term trend and a periodic modulation of 7,000 days. The effects responsible for this behaviour could be a third body in the system, magnetic interaction between two stars,[11] mass transfer from one star to the other, mass loss of the system, and recently even an internal mechanism in the touching envelopes have been proposed.[10]