HD 166 or V439 Andromedae (ADS 69 A) is a 6th magnitude star in the constellation Andromeda, approximately 45 light years away from Earth. It is a variable star of the BY Draconis type, varying between magnitudes 6.13 and 6.18 with a 6.23 days periodicity.[2] It appears within one degree of the star Alpha Andromedae[9] and is a member of the Hercules-Lyra association moving group.[3] It also happens to be less than 2 degrees from right ascension 00h 00m.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 06m 36.7841s[1] |
| Declination | +29° 01′ 17.4103″[1] |
| Apparent magnitude (V) | 6.13 – 6.17[2] |
| Characteristics | |
| Spectral type | K0Ve[2][3] |
| U−B color index | +0.30[4] |
| B−V color index | +0.755[4] |
| Variable type | BY Dra[2] |
| Astrometry | |
| Radial velocity (Rv) | −6.9±0.2[3] km/s |
| Proper motion (μ) | RA: 380.092±0.060[1] mas/yr Dec.: −177.573±0.037[1] mas/yr |
| Parallax (π) | 72.5764 ± 0.0498 mas[1] |
| Distance | 44.94 ± 0.03 ly (13.779 ± 0.009 pc) |
| Absolute magnitude (MV) | 5.41[5] |
| Details | |
| Mass | 0.889[6] M☉ |
| Radius | 0.9172±0.0090[6] R☉ |
| Luminosity | 0.6078±0.0099[6] L☉ |
| Surface gravity (log g) | 4.49±0.09[7] cgs |
| Temperature | 5509±34[7] K |
| Metallicity [Fe/H] | 0.00±0.03[7] dex |
| Rotation | 6.23±0.01 days[8] |
| Rotational velocity (v sin i) | 4.1 [8] km/s |
| Age | 78±28[7] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Star characteristics
HD 166 is a K-type main sequence star, cooler and dimmer than the Sun, and has a stellar classification of K0Ve[2] where the e suffix indicates the presence of emission lines in the spectrum. The star has a proper motion of 0.422 arcseconds per year in a direction 114.1° from north. It has an estimated visual luminosity of 61% of the Sun,[6] and is emitting like a blackbody with an effective temperature of 5,327K.[7] It has a diameter that is about 90% the size of the Sun[6] and a radial velocity of −6.9 km/s.[3] Age estimates range from as low as 78 million years old based on its chromospheric activity,[7] up to 9.6 billion years based on a comparison with theoretical evolutionary tracks.[6] X-ray emission has been detected from this star, with an estimated luminosity of 8.5×1028 erg s−1.[10]
An infrared excess has been detected around HD 166, most likely indicating the presence of a circumstellar disk at a radius of 7.5 AU. The temperature of this dust is 90 K.[11]
Variability
It has been found that the periodicity in the photometric variability of HD 166 is coincident with the rotation period.[8] This leads to its classification as a BY Draconis variable, where brightness variations are caused by the presence of large starspots on the surface and by chromospheric activity.