A visual band light curve for the April 1989 superoutburst of SU Ursae Majoris, adapted from Udalski et al. (1990) [1] | |
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Ursa Major |
Right ascension | 08h 12m 28.26946s [2] |
Declination | +62° 36′ 22.4280″ [2] |
Apparent magnitude (V) | 10.8–14.96 [3] |
Characteristics | |
Variable type | SU UMa [3] |
Astrometry | |
Radial velocity (Rv) | +27.0 [4] km/s |
Proper motion (μ) |
RA: +6.582
[2]
mas/
yr Dec.: −24.538 [2] mas/ yr |
Parallax (π) | 4.5347 ± 0.0286 mas [2] |
Distance | 719 ± 5
ly (221 ± 1 pc) |
Absolute magnitude (MV) | +5.1 [5] |
Orbit [6] | |
Period (P) | 0.076351±0.000043 d |
Inclination (i) | 42 [5]° |
Periastron epoch (T) | 2,446,143.6672±0.0015 HJD |
Semi-amplitude (K1) (primary) | 59±7 km s–1 km/s |
Details | |
White dwarf | |
Mass | 0.8 [7] M☉ |
Temperature | 28,000 [7] K |
Red dwarf | |
Mass | 0.105 [8] M☉ |
Radius | 0.167 [8] R☉ |
Other designations | |
Database references | |
SIMBAD | data |
SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96. [3] The distance to this system, as determined from its annual parallax shift of 4.53 mas, [2] is 719 light-years. It is moving further from the Earth with a heliocentric radial velocity of +27 km/s. [4]
The variable nature of this star was discovered at the Moscow Observatory by Lidiya Tseraskaya (L. Ceraski) in 1908. [10] It was classified as a U Geminorum-type variable, or dwarf nova. [11] Observation since 1926 showed that this variable undergoes two different types of eruptions: a short maxima lasting around two days that ranged in brightness between 11.6–12.9 magnitude, and a longer maxima extending for 13 days that ranged between 10.4–11.8 magnitude. The later event came to be referred to as 'supermaxima'. [12] Similar dwarf novae of this class have since been discovered, and SU UMa is now the prototype for this sub-category of variable stars. [13]
This is a single-lined spectroscopic binary with an orbital period of 1.83 hours. [6] It consists of a white dwarf star that is acquiring matter from its close companion via an accretion disk. This disk is unstable and undergoes periodic outbursts which increase the luminosity of the system. [14] For SU UMa, the accretion rate from the companion is 9.8×10−13 M☉·yr−1. [15] X-ray emission has been detected in the vicinity of the white dwarf, which drops by a factor of four during outbursts. This emission is theorized to come from the boundary layer between the white dwarf and its accretion disk. [14]