Alpheratz
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 08m 23.25988s |
| Declination | +29° 05′ 25.5520″ |
| Apparent magnitude (V) | 2.06 (2.22 + 4.21) |
| Characteristics | |
| U−B color index | −0.46 |
| B−V color index | −0.11 |
| R−I color index | −0.10 |
| Primary | |
| Spectral type | B8IV-VHgMn |
| B−V color index | −0.06 |
| Secondary | |
| Spectral type | A7V |
| B−V color index | 0.22 |
| Astrometry | |
| Primary | |
| Radial velocity (Rv) | −10.6 ± 0.3 km/s |
| Proper motion (μ) | RA: 135.68 mas/yr Dec.: −162.95 mas/yr |
| Parallax (π) | 33.62±0.35 mas |
| Distance | 97 ± 1 ly (29.7 ± 0.3 pc) |
| Absolute magnitude (MV) | −0.193 |
| Secondary | |
| Absolute magnitude (MV) | 1.797 |
| Orbit | |
| Period (P) | 96.69 days |
| Semi-major axis (a) | 23.917±0.127 mas (0.7146±0.0327 AU) |
| Eccentricity (e) | 0.526±0.013 |
| Inclination (i) | 105.8±0.17° |
| Longitude of the node (Ω) | 104.46±0.48° |
| Periastron epoch (T) | MJD 47374.563 ± 0.095 |
| Argument of periastron (ω) (secondary) | 257.4 ± 0.31° |
| Details | |
| Primary | |
| Mass | 3.63±0.201 M☉ |
| Radius | 2.94 ± 0.34 R☉ |
| Luminosity (bolometric) | 158+41 −33 L☉ |
| Surface gravity (log g) | 3.75 cgs |
| Temperature | 11,950 K |
| Rotation | 2.38 d |
| Rotational velocity (v sin i) | 53 km/s |
| Age | 60; 200+117 −74 Myr |
| Secondary | |
| Mass | 1.875±0.096 M☉ |
| Radius | 2.03 ± 0.23 R☉ |
| Luminosity (bolometric) | 14.79+3.83 −3.04 L☉ |
| Surface gravity (log g) | 4.0 cgs |
| Temperature | 7,935 K |
| Age | 70; 447+184 −130 Myr |
| Other designations | |
| Alpheratz, Sirrah, Sirah, H 5 32A, α And, Alpha Andromedae, Alpha And, δ Pegasi, δ Peg, Delta Pegasi, Delta Peg, 21 Andromedae, 21 And, BD+28°4, FK5 1, GC 127, HD 358, HIP 677, HR 15, SAO 73765, PPM 89441, ADS 94 A, CCDM J00083+2905A, WDS 00084+2905A/Aa, LTT 10039, NLTT 346 | |
| Database references | |
| SIMBAD | data |
Alpheratz is a prominent star system in the constellation of Andromeda. Pronounced /ælˈfɪəræts/, it has the Bayer designation Alpha Andromedae, Latinised from α Andromedae, and abbreviated Alpha And or α And, respectively. Alpheratz is the brightest star in the constellation when Mirach (β Andromedae) undergoes its periodical dimming. Immediately northeast of the constellation of Pegasus, it is the upper left star of the Great Square of Pegasus. It is located at a distance of 97 light-years from Earth.
Although it appears to the naked eye as a single star with overall apparent visual magnitude +2.06, it is actually a binary system composed of two stars in close orbit. The chemical composition of the brighter of the two stars is unusual as it is a mercury-manganese star whose atmosphere contains abnormally high abundances of mercury, manganese, and other elements, including gallium and xenon. It is the brightest mercury-manganese star known.