ER Ursae Majoris
Variable binary star system in the constellation Ursa Major
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ER Ursae Majoris is a variable star in the northern circumpolar constellation of Ursa Major, abbreviated ER UMa. It is a prototype system for a subclass of SU Ursae Majoris dwarf novae.[5] The system ranges in brightness from a peak apparent visual magnitude of 12.4 down to 15.2,[3] which is too faint to be visible to the naked eye. The distance to this system, based on parallax measurements, is approximately 1,163 light years.[2]
A visual band light curve for ER Ursae Majoris. The main plot shows a normal outburst in 2004, with the estimated value for the unobserved maximum plotted in red. The inset plot shows superhump oscillations. Adapted from Zhao et al. (2006).[1] | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 47m 11.941s[2] |
| Declination | +51° 54′ 08.95″[2] |
| Apparent magnitude (V) | 12.4 to 15.2[3] |
| Characteristics | |
| Variable type | Dwarf nova(?)[3] |
| Astrometry | |
| Proper motion (μ) | RA: 33.659 mas/yr[2] Dec.: −6.209 mas/yr[2] |
| Parallax (π) | 2.8039±0.0205 mas[2] |
| Distance | 1,163 ± 9 ly (357 ± 3 pc) |
| Orbit[4] | |
| Period (P) | 0.06366±0.00003 d |
| Eccentricity (e) | 0.00 (assumed) |
| Inclination (i) | 18–50[5]° |
| Periastron epoch (T) | 2,449,740.0637±0.0008 HJD |
| Argument of periastron (ω) (secondary) | 0.00 (assumed)° |
| Semi-amplitude (K1) (primary) | 48±4 km/s |
| Details | |
| White dwarf | |
| Mass | 1.0±0.2[5] M☉ |
| Temperature | 32,000[5] K |
| Donor star | |
| Mass | 0.10[5] M☉ |
| Other designations | |
| PG 0943+521, ER UMa, AAVSO 0939+52, GSC 03439-00550, 2MASS J09471193+5154089[6] | |
| Database references | |
| SIMBAD | data |
This system was identified as an ultraviolet excess object as part of the Palomar-Green (PG) survey by R. F. Green and associate in 1986. It was given the catalog identifier PG 0943+521, and was confirmed to be cataclysmic variable. In 1992, it was determined this is a dwarf nova that ranges in brightness from magnitude 12.3 down to 15.2. F. A. Ringwald in 1993 found a candidate orbital period of 0.1997 days based on radial velocity variation, but with some uncertainty.[7]
In 1995, T. Kato and C. Kunjaya confirmed this is a SU Ursae Majoris-type dwarf nova, and noted the unusual nature of this system, finding it has a long superoutburst lasting about 20 days and the supercycle (the time between superoutbursts) is very short at around 43 days.[8] Large amplitude superhumps were found to occur near the start of a superoutburst, with a brightness increase of around 0.35 magnitude.[9] The properties of the system suggest a high mass transfer rate and the white dwarf component is hotter than in other typical dwarf novae. During periods of quiescence, the accretion rate is 7.3×10−11 M☉·yr−1.[5]