HR 1099
Triple star system in the constellation Taurus
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HR 1099 is a triple star system in the equatorial constellation of Taurus, positioned 11′ to the north of the star 10 Tauri.[16] This system has the variable star designation V711 Tauri, while HR 1099 is the star's identifier from the Bright Star Catalogue. It ranges in brightness from a combined apparent visual magnitude of 5.71 down to 5.94,[7] which is bright enough to be dimly visible to the naked eye. The distance to this system is 96.6 light years based on parallax measurements,[2] but it is drifting closer with a radial velocity of about −15 km/s.
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Taurus[1] |
| A | |
| Right ascension | 03h 36m 47.291s[2] |
| Declination | 00° 35′ 15.94″[2] |
| Apparent magnitude (V) | 5.91[3] |
| B | |
| Right ascension | 03h 36m 46.844s[4] |
| Declination | 00° 35′ 15.93″[4] |
| Apparent magnitude (V) | 8.79[3] |
| Characteristics | |
| Spectral type | K2:Vnk[5] (K1 IV + G5 V + K3 V)[6] |
| Variable type | RS CVn[7] |
| Astrometry | |
| A | |
| Radial velocity (Rv) | −21.24±6.62[2] km/s |
| Proper motion (μ) | RA: −32.894 mas/yr[2] Dec.: −161.772 mas/yr[2] |
| Parallax (π) | 33.7528±0.0866 mas[2] |
| Distance | 96.6 ± 0.2 ly (29.63 ± 0.08 pc) |
| Absolute magnitude (MV) | 3.6[3] |
| B | |
| Radial velocity (Rv) | −15.34±0.18[4] km/s |
| Proper motion (μ) | RA: −34.359 mas/yr[4] Dec.: −138.137 mas/yr[4] |
| Parallax (π) | 33.8664±0.0226 mas[4] |
| Distance | 96.31 ± 0.06 ly (29.53 ± 0.02 pc) |
| Absolute magnitude (MV) | 6.5[3] |
| Orbit[8] | |
| Period (P) | 2.83774 d |
| Semi-major axis (a) | 10.3 R☉[9] |
| Eccentricity (e) | 0.00 (assumed) |
| Inclination (i) | 38[10]° |
| Periastron epoch (T) | 2,442,767.4 HJD |
| Argument of periastron (ω) (secondary) | 0.00 (assumed)° |
| Semi-amplitude (K1) (primary) | 52.6 km/s |
| Semi-amplitude (K2) (secondary) | 64.1 km/s |
| Details | |
| Component Aa | |
| Mass | 1.0[9] M☉ |
| Radius | 3.7[9] R☉ |
| Surface gravity (log g) | 3.30[6] cgs |
| Temperature | 4,750[6] K |
| Metallicity [Fe/H] | −0.16[11] dex |
| Rotational velocity (v sin i) | 39[10] km/s |
| Component Ab | |
| Mass | 0.8[9] M☉ |
| Radius | 1.1[9] R☉ |
| Surface gravity (log g) | 4.26[6] cgs |
| Temperature | 5,500[6] K |
| Component B | |
| Mass | 0.78[12] M☉ |
| Radius | 0.78[12] R☉ |
| Luminosity | 0.30[12] L☉ |
| Surface gravity (log g) | 4.55[12] cgs |
| Temperature | 4,829[12] K |
| Metallicity [Fe/H] | +0.10[11] dex |
| Rotational velocity (v sin i) | 4.1[13] km/s |
| Age | 2.2[4] Gyr |
| Other designations | |
| STF 422, V711 Tau, BD+00°616, GC 4311, HD 22468, HIP 16846, HR 1099, SAO 111291, PPM 146726, ADS 2644, WDS J03368+0035[14][15] | |
| Database references | |
| SIMBAD | data |
This system was discovered to be a double star by F. G. W. Struve in 1822, with the components A and B having an angular separation of 5.4″. (The separation was measured at 6.7″ in 2016.)[17] R. E. Wilson in 1953 determined that the brighter member of this pair, component A, has a variable radial velocity. In 1963, O. C. Wilson noted that the same component shows very high emission cores in the calcium H and K absorption lines.[18] Follow-up observations by O. C. Wilson in 1964 showed that the hydrogen–α line of component A is fully in emission and it displays moderate broadening due to rotation. He found a stellar classification of K3 V for component B, matching an ordinary K-type main-sequence star.[19]
Observations during 1974–1975 demonstrated that component A is a spectroscopic binary star system of the RS Canum Venaticorum variable class. Given its average magnitude of around 5.9, it is one of the brighter known variables of this type.[21] No eclipses were observed, but an orbital period of 2.838 days was determined. Most of the emission was found to be coming from the more massive member of this pair.[22] Radio emission from the binary was detected by F. N. Owen in 1976.[23] It was shown to be a soft X-ray source in 1978 using the HEAO 1 satellite.[24]
This double-lined spectroscopic binary system consists of an evolving K-type subgiant and an ordinary G-type main sequence star. The two stars are orbiting so close to each other that their tidal effects are giving them an elliptical shape. The subgiant is filling about 80% of its Roche lobe.[6] The chromosphere of the subgiant is one of the most active known, with a deep convective zone powering the magnetic dynamo.[25][5] The G-type companion has a shallow convection zone and is less active.[6]
In 1980, significant variations were found in some spectral features related to surface temperature, suggesting the presence of starspots.[26] Doppler imaging confirmed these starspots are associated with the K subgiant. (It was the first cool star to have its surface Doppler imaged.[27]) The evidence suggests that the spots first appear at low latitude then migrated toward the poles.[21] These spots are much larger than they are on the Sun.[6] About 70% of all spots have been observed at latitudes higher than 50°, particularly around the polar region.[10][25] A polar spot has persisted for at least twenty years.[6]
The baseline apparent magnitudes of the two stars, after subtracting the effects of starspots, is 5.80 and 7.20.[6] Long term monitoring indicates the subgiant has two activity cycles, similar to the 11-year solar cycle. A 5.3±0.1 year cycle is associated with symmetrical flip-flopping of the spotted area between hemispheres. The longer 15–16 year cycle is a periodic variation in the total spot area. The global magnetic field of the star may be precessing with respect to the axis of rotation.[27]