FG Virginis
Variable star in the constellation Virgo
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FG Virginis is a well-studied variable star in the equatorial constellation of Virgo. It is a dim star, near the lower limit of visibility to the naked eye, with an apparent visual magnitude that ranges from 6.53 down to 6.58.[3] The star is located at a distance of 273.5 light years from the Sun based on parallax measurements,[2] and is drifting further away with a radial velocity of +14 km/s.[2] Because of its position near the ecliptic, it is subject to lunar occultations.[12]
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Virgo |
| Right ascension | 12h 14m 15.457s[2] |
| Declination | −05° 42′ 59.75″[2] |
| Apparent magnitude (V) | 6.53 to 6.58[3] |
| Characteristics | |
| Evolutionary stage | Main sequence[2] |
| Spectral type | A8/9V[4] |
| U−B color index | 0.05[5] |
| B−V color index | 0.277±0.007[6] |
| Variable type | δ Sct[3] |
| Astrometry | |
| Radial velocity (Rv) | 14.2±0.5[2] km/s |
| Proper motion (μ) | RA: −85.128 mas/yr[2] Dec.: 114.628 mas/yr[2] |
| Parallax (π) | 11.9261±0.0308 mas[2] |
| Distance | 273.5 ± 0.7 ly (83.8 ± 0.2 pc) |
| Absolute magnitude (MV) | 2.10[6] |
| Details | |
| Mass | 1.80[7] M☉ |
| Radius | 2.27[8] R☉ |
| Luminosity | 11.95[6] L☉ |
| Surface gravity (log g) | 3.9[9] cgs |
| Temperature | 7,425[9] K |
| Rotation | 1.74±0.43 d[9] |
| Rotational velocity (v sin i) | 21.3±1.0[10] km/s |
| Other designations | |
| FG Vir, BD−04°3235, HD 106384, HIP 59676, SAO 138664, PPM 195288, WDS J12143-0543A[11] | |
| Database references | |
| SIMBAD | data |
The variability of this star was first reported by O. J. Eggen in 1971, who classified it as an ultra-short period cepheid – a proposed category of pulsating stars in the instability strip.[13] It was subsequently grouped in the class of Delta Scuti variables, which show a pulsation period of less than a day.[14] Observations in 1984 by P. Lopez de Coca showed at least one pulsation period with a cycle of 1.9 hours.[15] L. Mantegazza and associates in 1994 were able to detect seven or more pulsation modes, with the previously detected dominant mode being a radial pulsation with a frequency of 12.72 cycles per day.[16]
The star became of interest to astroseismology study because of its relatively slow rotation rate and the numerous modes of pulsation. A multi-site campaign involving the Whole Earth Telescope network was conducted in 1993 to observe this star, which detected ten modes.[1] This was increased to 24 frequencies in 1998,[17] then 67 independent frequencies with 79 total by 2005. Evidence suggests there are many more such modes.[18]
This is an A-type main-sequence star with a stellar classification of A8/9V,[4] but is near the end of its main sequence lifetime.[10] It is classified as a Delta Scuti variable that varies in brightness with an amplitude of 0.040 in visual magnitude and a period of 1.89 hours.[5] Element abundances are similar to the Sun, although there is a slight overabundance of barium and underabundances of sulfur and carbon.[19] It has a projected rotational velocity of 21 km/s, but the actual rotational velocity is likely much higher at around 80 km/s.[10]