LQ Hydrae
Star in the constellation Hydra
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LQ Hydrae is a single[13] variable star in the equatorial constellation of Hydra. It is sometimes identified as Gl 355 from the Gliese Catalogue; LQ Hydrae is the variable star designation, which is abbreviated LQ Hya.[14] The brightness of the star ranges from an apparent visual magnitude of 7.79 down to 7.86,[5] which is too faint to be readily visible to the naked eye. Based on parallax measurements, this star is located at a distance of 59.6 light years from the Sun. It is drifting further away with a radial velocity of 7.6 km/s.[7]
A visual band light curve for LQ Hydrae. The main plot (adapted from Berdyugina et al.[1]) shows the long-term variation, and the inset plot (adapted from Kiraga[2]) shows the periodic variation. | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 32m 25.568s[3] |
| Declination | −11° 11′ 04.69″[3] |
| Apparent magnitude (V) | 7.82[4] (7.79 to 7.86)[5] |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | K1Vp[6] |
| B−V color index | 0.933±0.021[4] |
| Variable type | BY Dra[5] |
| Astrometry | |
| Radial velocity (Rv) | 7.58±0.27[7] km/s |
| Proper motion (μ) | RA: −248.040 mas/yr[3] Dec.: 34.277 mas/yr[3] |
| Parallax (π) | 54.7362±0.0244 mas[3] |
| Distance | 59.59 ± 0.03 ly (18.269 ± 0.008 pc) |
| Absolute magnitude (MV) | 6.47[6] |
| Details | |
| Mass | 0.81[8] M☉ |
| Radius | 1.0[9] R☉ |
| Luminosity | 0.282±0.001[3] L☉ |
| Surface gravity (log g) | 4.57[8] cgs |
| Temperature | 4,812±39[8] K |
| Metallicity [Fe/H] | 0.32[8] dex |
| Rotation | 1.601[9] d |
| Rotational velocity (v sin i) | 25±2[10] km/s |
| Age | Under 75[11] Myr |
| Other designations | |
| LQ Hya, BD−10 2857, GC 13168, GJ 355, HD 82558, HIP 46816, SAO 155272, LTT 3510[12] | |
| Database references | |
| SIMBAD | data |
During a 1981 survey of southern stars, W. P. Bidelman found the H and K lines of ionized calcium for LQ Hya were filled in with emission. (W. D. Heintz independently made the same observation.) In 1986, F. C. Fekel and associates determined this is a young, rapidly rotating BY Draconis-type variable.[13][15] A decade of photometry was used to determine a rotation period of 1.601136±0.000013 days (1 day, 14 hours, and 24 minutes) The star spots on the surface showed significant evolution over time scales of a few months. Variations in rotational modulation of surface activity suggested the star is undergoing differential rotation.[10]
The high lithium abundance and rapid rotation of this star indicate it is a zero age main sequence star, or possibly even a pre-main sequence star.[14] A strong flare event was observed on December 22, 1993, with an estimated energy release of ~5.7×1033 erg.[11] Additional flares were detected thereafter, with ROSAT X-ray data from 1992 showing a strong flare during that time period.[14] Observations from December 2000 and 2001 showed that the magnetic field of the star is dramatically changing its topology on a time frame of a year or less.[16]
The stellar classification of LQ Hya is K1Vp,[6] indicating it is a K-type main-sequence star with some peculiar features in the spectrum. In some respects it is considered an analog of a young Sun around the age of 60 million years.[1] It shows strong emission of ultraviolet and has been detected in the X-ray band, showing an X-ray emission of 8.8×1029 erg/s and indicating high chromospheric activity levels.[14] The star shows dual magnetic activity cycles with period of 6.8 and 11.4 years,[14] which are somewhat comparable to the solar cycle in the Sun.