GY Andromedae
GY Andromedae (GY And) is an α2 Canum Venaticorum type variable star in the northern constellation Andromeda. Its brightness fluctuates in visual magnitude between 6.27m and 6.41m, making it a challenge to view with the naked eye even in good seeing conditions. The magnetic activity on this star shows an unusually long period of variability, cycling about once every 23 years. Based upon parallax measurements, this star is located at a distance of about 460 light-years (140 parsecs) from the Earth.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 01h 38m 31.82552s |
| Declination | +45° 23′ 58.9357″ |
| Apparent magnitude (V) | 6.36 |
| Characteristics | |
| Spectral type | B9 pe |
| U−B color index | -0.10 |
| B−V color index | +0.04 |
| Variable type | α2 CVn |
| Astrometry | |
| Radial velocity (Rv) | +3.0 km/s |
| Proper motion (μ) | RA: −17.292(211) mas/yr Dec.: −1.386(150) mas/yr |
| Parallax (π) | 7.1093 ± 0.1589 mas |
| Distance | 460 ± 10 ly (141 ± 3 pc) |
| Absolute magnitude (MV) | +0.68 |
| Details | |
| Mass | 2.47 ± 0.15 M☉ |
| Radius | 2.6 ± 0.4 R☉ |
| Luminosity | 52 L☉ |
| Surface gravity (log g) | 4.01 ± 0.14 cgs |
| Temperature | 10,723 K |
| Metallicity [Fe/H] | 0.86 dex |
| Rotational velocity (v sin i) | 31 km/s |
| Orbit | |
| Companion | GY And B |
| Period (P) | 272.99 days |
| Semi-major axis (a) | > 0.25 AU |
| Eccentricity (e) | 0.47 |
| Argument of periastron (ω) (secondary) | 17.7° |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is classified as an Ap/Bp star, with a peculiar spectrum showing lines of chromium and europium that change in intensity over a period matching the variability cycle, although opposite in phase. Its most striking characteristic is the presence of the unstable element promethium in its emission spectrum. All isotopes of this element are radioactive with half lives of 17.7 years or less. The promethium in the outer envelope may be generated by the spontaneous fission of higher mass transuranic elements.