Alpheratz
Alpheratz /ælˈfɪəræts/, or Alpha Andromedae (α Andromedae, abbreviated Alpha And or α And), is a bright star 97 light-years from the Sun and is the brightest star in the constellation of Andromeda when Beta Andromedae undergoes its periodical dimming. Immediately northeast of the constellation of Pegasus, it is the upper left star of the Great Square of Pegasus.
| 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 |
| Secondary | |
| Spectral type | A3V |
| 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) | −0.19 ± 0.30 |
| Secondary | |
| Absolute magnitude (MV) | 2.00 ± 0.30 |
| Orbit | |
| Period (P) | 96.7015 ± 0.0044 days |
| Semi-major axis (a) | 24.0 ± 0.13 mas |
| Eccentricity (e) | 0.535 ± 0.0046 |
| Inclination (i) | 105.6 ± 0.23° |
| Longitude of the node (Ω) | 284.4 ± 0.21° |
| Periastron epoch (T) | MJD 47374.563 ± 0.095 |
| Argument of periastron (ω) (secondary) | 257.4 ± 0.31° |
| Details | |
| Primary | |
| Mass | 3.8 ± 0.2 M☉ |
| Radius | 2.7 ± 0.4 R☉ |
| Luminosity (bolometric) | 240 L☉ |
| Surface gravity (log g) | 3.75 cgs |
| Temperature | 13,800 K |
| Metallicity | [M/H] = 0.2 |
| Rotation | 2.38195 d |
| Rotational velocity (v sin i) | 52 km/s |
| Age | 60 Myr |
| Secondary | |
| Mass | 1.85 ± 0.13 M☉ |
| Radius | 1.65 ± 0.3 R☉ |
| Luminosity (bolometric) | 13 L☉ |
| Surface gravity (log g) | 4.0 cgs |
| Temperature | 8,500 K |
| Metallicity | [M/H] = 0.2 |
| Rotational velocity (v sin i) | 110 ± 5 km/s |
| Age | 70 Myr |
| Other designations | |
Alpheratz, Sirrah, Sirah, α And, Alpha Andromedae, Alpha And, δ Pegasi, δ Peg, Delta Pegasi, Delta Peg, 21 Andromedae, 21 And, H 5 32A, MKT 11, ADS 94 A, BD+28°4, CCDM J00083+2905A, FK5 1, GC 127, HD 358, HIP 677, HR 15, IDS 00032+2832 A, LTT 10039, NLTT 346, PPM 89441, SAO 73765, WDS 00084+2905A/Aa | |
| Database references | |
| SIMBAD | data |
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 levels of mercury, manganese, and other elements, including gallium and xenon. It is the brightest mercury-manganese star known.