BZ Ursae Majoris
Dwarf Nova in the constellation Ursa Major
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BZ Ursae Majoris is a dwarf nova star system in the northern circumpolar constellation of Ursa Major. It consists of a white dwarf primary in a close orbit with a red dwarf. The latter star is donating mass, which is accumulating in an accretion disk orbiting the white dwarf.[14] The system is located at a distance of approximately 505 light years from the Sun based on parallax measurements.[3]
10.2 to 15.9[5]
A visual band light curve for BZ Ursae Majoris. The main plot (from AAVSO data[1]) shows several outbursts, and the inset plot (adapted from Kato et al.[2]) shows a single superoutburst in detail. | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 08h 53m 44.174s[3] |
| Declination | +57° 48′ 40.59″[3] |
| Apparent magnitude (V) | 15.7 to 16.5[4] 10.2 to 15.9[5] |
| Characteristics | |
| Spectral type | M5.5:Ve[6] |
| Variable type | SU UMa[7] |
| Astrometry | |
| Proper motion (μ) | RA: 26.318 mas/yr[3] Dec.: −15.915 mas/yr[3] |
| Parallax (π) | 6.4561±0.0441 mas[3] |
| Distance | 505 ± 3 ly (155 ± 1 pc) |
| Orbit[6] | |
| Period (P) | 97.8±0.1 h |
| Inclination (i) | ~60[8]° |
| Periastron epoch (T) | 2,448,319.897±0.003 HJD |
| Details | |
| White dwarf | |
| Mass | 0.65[9][10] M☉ |
| Radius | 6,880[11] km |
| Surface gravity (log g) | 7.5[5][12] cgs |
| Temperature | 15,000[5][12] K |
| Rotational velocity (v sin i) | 200[5] km/s |
| Donor star | |
| Mass | 0.13[6] M☉ |
| Other designations | |
| BZ UMa, 2MASS J08534416+5748406, PG 0849+580[13] | |
| Database references | |
| SIMBAD | data |
This system was discovered to vary in brightness by B. E. Markaryan in 1968,[15] and it was given the variable star designation BZ UMa.[16] After four years of observation by the AAVSO, it was proposed to be a cataclysmic variable by M. Mayall.[14] In 1982, R. F. Green and associates identified it as a cataclysmic variable candidate of the U Gem-type, based on its spectrum.[17] The same year, W. Wenzel showed that this star had very long intervals between outbursts, placing it intermediate between the U Gem and WZ Sge classes.[18] P. Szkody and L. Feinswog examined the infrared light curve of the system, estimating an orbital inclination of 60° with no evidence of heating from the white dwarf.[8]
R. Claudi and associates in 1990 found a periodic modulation of hydrogen emission lines, indicating an orbital period of 1.62 h. They suggested it be classified as a SU UMa star.[19] Spectroscopic examination of the system using the Hubble Space Telescope during 2001 showed an anomalous abundance ratio of nitrogen to carbon that indicates CNO-processing.[20] This may be the result of an earlier evolutionary stage of the donor star that was stripped of its outer layers. A superoutburst was observed in 2007 that displayed superhumps. A lack of circular polarization indicates the white dwarf is not strongly magnetic, and thus this system is most likely not an intermediate polar.[14]