ER Ursae Majoris
Prototype for a subclass of SU Ursae Majoris dwarf novae.
ER Ursae Majoris (ER UMa) is a variable star located in the northern circumpolar constellation Ursa Major. It serves as the prototype for a subclass of SU Ursae Majoris dwarf novae. The star's brightness varies from a peak apparent visual magnitude of 12.4 down to 15.2, making it too faint for naked-eye observation. Based on parallax measurements, its distance is roughly 1,163 light-years.
The system was first identified as an ultraviolet excess object in the Palomar-Green (PG) survey by R. F. Green and colleagues in 1986, receiving the catalog designation PG 0943+521, and was confirmed as a cataclysmic variable. In 1992, it was classified as a dwarf nova with a magnitude range of 12.3 to 15.2. The following year, F. A. Ringwald proposed an orbital period of 0.1997 days from radial velocity variations, though with some uncertainty.
In 1995, T. Kato and C. Kunjaya confirmed it as an SU Ursae Majoris-type dwarf nova and noted its unusual behavior: a long superoutburst lasting about 20 days and an exceptionally short supercycle of roughly 43 days. Large-amplitude superhumps appear near the start of a superoutburst, increasing brightness by about 0.35 magnitude. The system's properties suggest a high mass transfer rate, and its white dwarf component is hotter than in typical dwarf novae. During quiescence, the accretion rate is 7.3×10⁻¹¹ solar masses per year.
- Constellation
- Ursa Major
- Apparent visual magnitude (peak)
- 12.4
- Apparent visual magnitude (minimum)
- 15.2
- Distance
- approximately 1,163 light years
- Orbital period (candidate)
- 0.1997 days
- Superoutburst duration
- about 20 days
- Supercycle
- around 43 days
Lore & Background
ER Ursae Majoris was identified as an ultraviolet excess object as part of the Palomar-Green (PG) survey by R. F. Green and associate in 1986, receiving the catalog identifier PG 0943+521, and was confirmed to be a 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.
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. Large amplitude superhumps were found to occur near the start of a superoutburst, with a brightness increase of around 0.35 magnitude. 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.
Reader's Guide
ER Ursae Majoris holds significance as the prototype system for a subclass of SU Ursae Majoris dwarf novae, distinguished by its remarkably short supercycle of around 43 days and long superoutbursts lasting about 20 days. This unusual behavior, identified by T. Kato and C. Kunjaya in 1995, sets it apart from typical dwarf novae. The system's properties, including a high mass transfer rate and a hotter white dwarf component, provide a valuable laboratory for studying accretion processes in cataclysmic variables. Its large amplitude superhumps, which increase brightness by about 0.35 magnitude near the start of a superoutburst, offer insights into the dynamics of the accretion disk. The candidate orbital period of 0.1997 days, though uncertain, adds to the understanding of the binary system's architecture. As a faint object not visible to the naked eye, its study relies on photometric and spectroscopic observations, contributing to the broader knowledge of dwarf nova behavior and evolution.
Did You Know?
- Its supercycle is very short at around 43 days, with superoutbursts lasting about 20 days.
- The system has a candidate orbital period of 0.1997 days, found with some uncertainty.
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