DW Ursae Majoris

Lore & Background

In 1982, R. F. Green and associates identified this star as a cataclysmic variable candidate with the Palomar–Green survey designation PG 1030+590. A. W. Shafter and F. V. Hessman in 1984 found it to be a close eclipsing binary system with a period of 3.27 hours. This is a nova-like binary where mass is being transferred from a late-type star to a white dwarf companion, first accumulating in an accretion disk orbiting the white dwarf. Typically, the light curve for an eclipsing binary of this type should display a hump-like feature from where the stream of material interacts with the disk, but during early observations, no such feature was observed before the eclipse.

The behavior of the emission lines in the spectrum of this star were found to resemble those of other SW Sextantis variables. In 2000, the system was observed with the Hubble Space Telescope and was found to be in a low state about three magnitudes fainter, unlike previous observations where it had been in a high state. Comparison of the ultraviolet spectrum in the two states suggested that the accretion disk is self-eclipsing and can obscure the view of the white dwarf. The light output of the system undergoes a 13.6 year cycle of variation, probably because of precession of the accretion disk. Both positive and negative superhumps are observed that vary over time in a complex fashion.

Reader's Guide

DW Ursae Majoris is significant as a cataclysmic variable of the SX Sextantis type, a subclass of nova-like binaries. Its importance lies in the discovery that its accretion disk can self-eclipse, obscuring the white dwarf, a behavior inferred from Hubble Space Telescope observations in 2000. The system exhibits a 13.6-year cycle of variation, likely due to precession of the accretion disk, and displays both positive and negative superhumps that vary in a complex manner. The absence of the expected hump feature in early light curves before eclipse was notable, and the emission-line spectrum resembles that of other SW Sextantis variables. The mass transfer rate from the donor star is about 10−8 M☉·yr−1. These characteristics make DW UMa a key object for studying accretion disk dynamics and long-term variability in interacting binary systems.

Did You Know?

• DW Ursae Majoris was identified as a cataclysmic variable candidate in 1982 by R. F. Green and associates with the Palomar–Green survey designation PG 1030+590.
• The system has an orbital period of 3.27 hours, determined by A. W. Shafter and F. V. Hessman in 1984.
• In 2000, Hubble Space Telescope observations showed the system in a low state about three magnitudes fainter than previous high states.