W Ursae Majoris
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 43m 45.46861s |
| Declination | +55h 57m 09.0758s |
| Apparent magnitude (V) | 7.90 (7.75–8.48) |
| Characteristics | |
| Spectral type | F8Vp + F8Vp |
| U−B color index | +0.08 |
| B−V color index | +0.66 |
| Variable type | W UMa |
| Astrometry | |
| Radial velocity (Rv) | -46 km/s |
| Proper motion (μ) |
RA: +15.47 mas/yr Dec.: –27.30 mas/yr |
| Parallax (π) | 18.72 ± 1.47mas |
| Distance | 170 ± 10 ly (53 ± 4 pc) |
| Orbit | |
| Period (P) | 0.3336 days |
| Semi-major axis (a) | 2.443 R☉ |
| Inclination (i) | 86.0° |
| Details | |
| Mass | 1.190 / 0.570 M☉ |
| Radius | 1.084 / 0.775 R☉ |
| Rotational velocity (v sin i) | 144.40 ± 6.52 km/s |
| Other designations | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
W Ursae Majoris (W UMa) is the variable star designation for a binary star system in the northern constellation of Ursa Major. It has an apparent visual magnitude of about 7.9, which is too faint to be seen with the naked eye. However, it can be viewed with a small telescope.Parallax measurements place it at a distance of roughly 170 light years (53 parsecs) from Earth.
In 1903, the luminosity of this system was found to vary by the German astronomers Gustav Müller and Paul Kempf. It has since become the prototype and for a class of variable stars called W Ursae Majoris variables. This system consists of a pair of stars in a tight, circular orbit with a period of 0.3336 days, or eight hours and 23 seconds. During every orbital cycle, each star eclipses the other, resulting in a decrease in magnitude. The maximum magnitude of the pair is 7.75. During the eclipse of the primary, the net magnitude drops by 0.73, while the eclipse of the secondary causes a magnitude decrease of 0.68.
The two stars in W Ursae Majoris are so close together that their outer envelopes are in direct contact, making them a contact binary system. As a result, they have the same stellar classification of F8Vp, which matches the spectrum of a main-sequence star that is generating energy through the nuclear fusion of hydrogen. However, the primary component has a larger mass and radius than the secondary, with 1.19 times the Sun's mass and 1.08 times the Sun's radius. The secondary has 0.57 solar masses and 0.78 solar radii.
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