55 Ursae Majoris
Star in the constellation Ursa Major
From Wikipedia, the free encyclopedia
55 Ursae Majoris (55 UMa) is a triple star system in the constellation Ursa Major. Its apparent magnitude is 4.80. Two stars form a close spectroscopic binary with an orbital period of 2.55 days. The third star orbits the central pair every 1873 days.[4] All three stars are A-type main-sequence stars.[4]
Right ascension11h 19m 07.89965s[1]
Declination+38° 11′ 08.0285″[1]
Apparentmagnitude(V)4.80[2] (4.78 / 5.3)[3]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 19m 07.89965s[1] |
| Declination | +38° 11′ 08.0285″[1] |
| Apparent magnitude (V) | 4.80[2] (4.78 / 5.3)[3] |
| Characteristics | |
| Spectral type | A2V[2] (A1V + A2V + A1V)[4] |
| U−B color index | +0.04[5] |
| B−V color index | +0.09[5] |
| Astrometry | |
| Radial velocity (Rv) | -3.0 ± 2[6] km/s |
| Proper motion (μ) | RA: -58.80[1] mas/yr Dec.: -65.33[1] mas/yr |
| Parallax (π) | 17.00±0.34 mas[1] |
| Distance | 192 ± 4 ly (59 ± 1 pc) |
| Absolute magnitude (MV) | -0.09 ± 0.20[4] |
| Orbit[4] | |
| Primary | 55 UMa Aa |
| Name | 55 UMa Ab |
| Period (P) | 2.5537985 d |
| Eccentricity (e) | 0.323 |
| Periastron epoch (T) | 2449602.368 |
| Argument of periastron (ω) (secondary) | 116.8° |
| Semi-amplitude (K1) (primary) | 79.1 km/s |
| Semi-amplitude (K2) (secondary) | 89.1 km/s |
| Orbit[4] | |
| Primary | 55 UMa A |
| Name | 55 UMa B |
| Period (P) | 1872.7 ± 7.4 d |
| Semi-major axis (a) | 0.0913 ± 0.0009″ |
| Eccentricity (e) | 0.126 ± 0.008 |
| Inclination (i) | 64.8 ± 0.8° |
| Longitude of the node (Ω) | 130.0 ± 0.8° |
| Periastron epoch (T) | 2448805 ± 18 |
| Argument of periastron (ω) (secondary) | 223.9 ± 3.7° |
| Semi-amplitude (K1) (primary) | 8.4 ± 1.3 km/s |
| Semi-amplitude (K2) (secondary) | 20.2 ± 6.9 km/s |
| Details[4] | |
| 55 UMa Aa | |
| Mass | 2.0 M☉ |
| Surface gravity (log g) | 4.25 cgs |
| Temperature | 9230 ± 230 K |
| Rotational velocity (v sin i) | 30 ± 4 km/s |
| 55 UMa Ab | |
| Mass | 1.8 M☉ |
| Surface gravity (log g) | 4.25 cgs |
| Temperature | 8810 ± 250 K |
| Rotational velocity (v sin i) | 45 ± 5 km/s |
| 55 UMa B | |
| Mass | 2.1 M☉ |
| Surface gravity (log g) | 4.25 cgs |
| Temperature | 9290 ± 190 K |
| Rotational velocity (v sin i) | 55 ± 5 km/s |
| Other designations | |
| BD+38 2225, FK5 1293, HD 98353, HIP 55266, HR 4380, SAO 62491 | |
| Database references | |
| SIMBAD | data |
