 Visual bandlight curves for BY Draconis from six different years, adapted from Pettersenet al. (1992)[1] | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 18h 33m 55.7728s[2] |
| Declination | +51° 43′ 08.905″[2] |
| Apparent magnitude (V) | 8.07[2] |
| Characteristics | |
| Spectral type | K6Ve[2] |
| U−Bcolor index | +0.99[3] |
| B−Vcolor index | +1.19[3] |
| Variable type | BY Dra +UV Cet[4] |
| Astrometry | |
| Radial velocity (Rv) | −25.484±0.046[5] km/s |
| Proper motion (μ) | RA: 185.759[2]mas/yr Dec.: −325.590[2]mas/yr |
| Parallax (π) | 60.59±0.28 mas[2] |
| Distance | 53.8 ± 0.2 ly (16.50 ± 0.08 pc) |
| Absolute magnitude (MV) | 7.48 / 8.63[6] |
| Orbit[5] | |
| Primary | BY Dra A |
| Companion | BY Dra B |
| Period (P) | 5.9751139 ± 0.0000046 d |
| Semi-major axis (a) | 4.4472 ± 0.0091 mas |
| Eccentricity (e) | 0.30014 ± 0.00062 |
| Inclination (i) | 154.41± 0.29° |
| Longitude of the node (Ω) | 152.3 ± 0.1° |
| Periastronepoch (T) | JD 2453999.2144 ± 0.0021 |
| Argument of periastron (ω) (secondary) | 230.33 ± 0.17° |
| Semi-amplitude (K1) (primary) | 28.394 ± 0.060 km/s |
| Semi-amplitude (K2) (secondary) | 32.284 ± 0.061 km/s |
| Details[5] | |
| BY Dra A | |
| Mass | 0.792 ± 0.026 M☉ |
| BY Dra B | |
| Mass | 0.697 ± 0.023 M☉ |
| Other designations | |
| BY Dra,GJ 719,BD+51 2402,HD 234677,LTT 15477,SAO 31048,HIP 91009. | |
| Database references | |
| SIMBAD | BY Dra AB |
| BY Dra C | |
| ARICNS | data |
BY Draconis is amultiple star system in theconstellationDraco, consisting of at least three components. Components A and B aremain sequence stars,[5] and form a closebinary star system with a shortorbital period of only 5.98 days. Their individualspectroscopic classifications are dK5e and dK7e.[1] They form the prototype of a class ofvariable stars known asBY Draconis variables.[6]
The third component (C) is, by comparison, widely separated from the A-B pair by anangular distance of 17arcseconds, which corresponds to 260AU at the estimated distance of this star system—where an AU is the average distance from theEarth to the Sun. Component C is anM5 classred dwarf star. There may be a fourth component to the system, orbiting with a ≤1000‑day period, responsible for the eccentricity of the 5.98-day orbit, but this has not been visually confirmed.[5]
The variability of BY Draconis is caused by activity in the stellarphotosphere calledstarspots, which are comparable tosunspots on theSun, in combination withrapid rotation that changes the viewing angle of the activity relative to the observer. This variation has an average periodicity of 3.8285 days, but the brightness also changes over the course of several years—depending on the level of surface activity. Most observers believe that the primary star (A) is responsible for the variability as the secondary produces only a third of the total luminosity from the system. However, the spots may occur on both stars. Unlike the Sun, these spots may occur in the polar regions of the stars.[1]
