TU Ursae Majoris
Variable star
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TU Ursae Majoris is a variable star in the northern circumpolar constellation of Ursa Major. It is classified as a Bailey-type 'ab' RR Lyrae variable with a period of 0.557648 days[14] that ranges in brightness from apparent visual magnitude of 9.26 down to 10.24.[4] The distance to this star is approximately 2,090 light years based on parallax measurements.[10] It is located near the north galactic pole at a distance that indicates this is a member of the galactic halo.[15]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 29m 48.489s[2] |
| Declination | +30° 04′ 02.38″[2] |
| Apparent magnitude (V) | 10.03[3] (9.26 to 10.24)[4] |
| Characteristics | |
| Evolutionary stage | horizontal branch[5] |
| Spectral type | kA2hA9.5 (phase 0.03) kF0hF7.5 (phase 0.56)[6] |
| B−V color index | 0.355±0.034[3] |
| Variable type | RRab[4] |
| Astrometry | |
| Radial velocity (Rv) | 98.50±2.1[7] km/s |
| Proper motion (μ) | RA: −69.141 mas/yr[2] Dec.: −53.426 mas/yr[2] |
| Parallax (π) | 1.5641±0.0252 mas[2] |
| Distance | 2,090 ± 30 ly (640 ± 10 pc) |
| Absolute magnitude (MV) | 0.66[8] |
| Details | |
| Mass | 0.55[9] M☉ |
| Radius | 4.93[10] R☉ |
| Luminosity | 44.7[8] L☉ |
| Surface gravity (log g) | 2.10±0.15[11] cgs |
| Temperature | 6,200±65[11] K |
| Metallicity [Fe/H] | −1.31[11] dex |
| Rotational velocity (v sin i) | 12.76[12] km/s |
| Other designations | |
| TU Uma, BD+30 2162, HIP 56088, SAO 62578, PPM 75904[13] | |
| Database references | |
| SIMBAD | data |
The periodic variability of this star was discovered by P. Guthnick and R. Prager in 1929.[16][9] Its relative brightness has made this star the subject of regular observation since its discovery,[17] both photographically and then photoelectrically starting in 1957.[18] It was initially classed as a Bailey-type "a" RR Lyrae variable. The variations were found to be somewhat similar to RR Lyrae, with the periodicity of TU UMa differing by less than 1% of a day.[17] However, no evidence of a long-period modulation, known as the Blazhko effect, was found in this star.[18]
In 1990, A. Saha and R. E. White found variations in radial velocity over time that suggested this is a binary system.[15] However, confirmation of this proved difficult because of the distance and the pulsational behavior of the variable.[9] The system shows significant evidence of proper motion acceleration from a binary interaction.[19] Analysis of long-term oscillatory variations suggests an orbital period of 23.3 years and an eccentricity of 0.79,[20] with the secondary having at least 33% of the mass of the Sun.[9]