HD 166
Star in the constellation Andromeda
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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.[3] It appears within one degree of the star Alpha Andromedae[10] and is a member of the Hercules-Lyra association moving group.[4] It also happens to be less than 2 degrees from right ascension 00h 00m.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Andromeda[1] |
| Right ascension | 00h 06m 36.78401s[2] |
| Declination | +29° 01′ 17.4127″[2] |
| Apparent magnitude (V) | 6.13 – 6.17[3] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | K0Ve[3][4] |
| U−B color index | +0.30[5] |
| B−V color index | +0.755[5] |
| Variable type | BY Dra[3] |
| Astrometry | |
| Radial velocity (Rv) | −6.75±0.12[2] km/s |
| Proper motion (μ) | RA: 380.159 mas/yr[2] Dec.: −177.730 mas/yr[2] |
| Parallax (π) | 72.6419±0.0292 mas[2] |
| Distance | 44.90 ± 0.02 ly (13.766 ± 0.006 pc) |
| Absolute magnitude (MV) | 5.41[6] |
| Details | |
| Mass | 0.889[7] M☉ |
| Radius | 0.9172±0.0090[7] R☉ |
| Luminosity | 0.6078±0.0099[7] L☉ |
| Surface gravity (log g) | 4.49±0.09[8] cgs |
| Temperature | 5509±34[8] K |
| Metallicity [Fe/H] | 0.00±0.03[8] dex |
| Rotation | 6.23±0.01 days[9] |
| Rotational velocity (v sin i) | 4.1 [9] km/s |
| Age | 78±28[8] Myr |
| Other designations | |
| V439 And, NSV 33, BD+28°4704, GC 95, GJ 5, HD 166, HIP 544, HR 8, SAO 73743, PPM 89410, ADS 69 A, GSC 01735-00927, GSC 01735-02532 | |
| 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[3] 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,[7] and is emitting like a blackbody with an effective temperature of 5,327K.[8] It has a diameter that is about 90% the size of the Sun[7] and a radial velocity of −6.9 km/s.[4] Age estimates range from as low as 78 million years old based on its chromospheric activity,[8] up to 9.6 billion years based on a comparison with theoretical evolutionary tracks.[7] X-ray emission has been detected from this star, with an estimated luminosity of 8.5×1028 erg s−1.[12]
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.[13]
Variability
Eric J. Gaidos et al. first detected variability in HD 166 in the year 2000.[9] It was given its variable star designation, V439 Andromedae, in 2006.[14] It has been found that the periodicity in the photometric variability of HD 166 is coincident with the rotation period.[9] 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.