2 Andromedae
Binary star system in the constellation Andromeda
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2 Andromedae, abbreviated 2 And, is a binary star[3] system in the northern constellation of Andromeda. 2 Andromedae is the Flamsteed designation. It is a faint star system but visible to the naked eye with a combined apparent visual magnitude of 5.09.[2] Based upon an annual parallax shift of 7.7 mas,[1] it is located 420 light years away. The binary nature of the star was discovered by American astronomer Sherburne Wesley Burnham at Lick Observatory in 1889.[12] The pair orbit each other over a period of 74 years with a high eccentricity of 0.8.[3]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 23h 02m 36.38176s[1] |
| Declination | +42° 45′ 28.0628″[1] |
| Apparent magnitude (V) | 5.09[2] (5.26 + 7.43)[3] |
| Characteristics | |
| 2 And A | |
| Spectral type | A1V[4] |
| U−B color index | +0.10[5] |
| B−V color index | +0.08[5] |
| 2 And B | |
| Spectral type | F1V/F4V[3] |
| Variable type | δ Sct?[3] |
| Astrometry | |
| 2 And A | |
| Radial velocity (Rv) | 2.1±2.4[6] km/s |
| Proper motion (μ) | RA: 56.38[1] mas/yr Dec.: −4.47[1] mas/yr |
| Parallax (π) | 7.74±0.51 mas[1] |
| Distance | 420 ± 30 ly (129 ± 9 pc) |
| Absolute magnitude (MV) | −0.39±0.16[7] |
| 2 And B | |
| Absolute magnitude (MV) | 1.88±0.16[7] |
| Orbit[3] | |
| Period (P) | 73.997±0.509 yr |
| Semi-major axis (a) | 0.225±0.011″ |
| Eccentricity (e) | 0.800±0.056 |
| Inclination (i) | 21.7±46.0° |
| Longitude of the node (Ω) | 159.5±2.0° |
| Periastron epoch (T) | 1870.280±0.595 |
| Argument of periastron (ω) (secondary) | 356.4±3.0° |
| Details | |
| 2 And A | |
| Mass | 2.7±0.1[7] M☉ |
| Luminosity | 130.50[2] L☉ |
| Surface gravity (log g) | 3.40±0.12[7] cgs |
| Temperature | 8,950±250[7] K |
| Rotational velocity (v sin i) | 212[8] km/s |
| Age | 100+309 −88[9] Myr |
| 2 And B | |
| Mass | 1.78±0.06[7] M☉ |
| Surface gravity (log g) | 3.90±0.16[7] cgs |
| Temperature | 7,720±250[7] K |
| Other designations | |
| 2 And, BD+41°4665, GJ 886.1, HD 217782, HIP 113788, HR 8766, SAO 52623, PPM 63742, WDS 23026+4245[10] | |
| Database references | |
| SIMBAD | 2 And |
| 2 And A | |
| 2 And B | |
The magnitude 5.26[3] primary, designated component A, is an A-type main-sequence star based on a stellar classification of A1V[4] or A2V,[3] although it may have already left the main sequence.[7] It was identified as a candidate Lambda Boötis star, but this was ruled out by Paunzen et al. (2003) as it doesn't match the typical characteristics of these objects.[13] Although 2 Andromedae does not display a significant infrared excess, it is a shell star that displays varying absorption features due to circumstellar dust grains. This may indicate it has an orbiting debris disk containing gas that is being viewed edge-on.[14] The star is about 100 million years old and is spinning rapidly with a projected rotational velocity of 212 km/s.[8]
The magnitude 7.43[3] secondary companion, component B, is a suspected variable star and may be a Delta Scuti variable.[3] Alternatively, it may be an ellipsoidal variable with a brown dwarf companion.[7] It is an F-type main-sequence star with a class of F1V/F4.[3]