Are Superhumps Good Measures of the Mass Ratio for AM CVn Systems?

Abstract

We extend recent work that included the effect of pressure forces to derive the precession rate of eccentric accretion discs in cataclysmic variables to the case of double degenerate systems. We find that the logical scaling of the pressure force in such systems results in predictions of unrealistically high primary masses. Using the prototype AM CVn as a calibrator for the magnitude of the effect, we find that there is no scaling that applies consistently to all the systems in the class. We discuss the reasons for the lack of a superhump period to mass ratio relationship analogous to that known for SU UMa systems and suggest that this is because these secondaries do not have a single valued mass-radius relationship. We highlight the unreliability of mass-ratios derived by applying the SU UMa expression to the AM CVn binaries.

7 pages, 2 tables, to appear in Monthly Notices of the Royal Astronomical Society

References in corpus (4)

• The dynamics of eccentric accretion discs in superhump systems
• Kinematics of the ultra-compact helium accretor AM Canum Venaticorum
• Superhumps: Confronting Theory with Observation
• Accretion disc dynamics in extreme mass ratio compact binaries

Cited by in corpus (9)

• HST/FGS Parallaxes of AM CVn Stars and Astrophysical Consequences
• Hunting For Eclipses: High Speed Observations of Cataclysmic Variables
• Spectroscopic and Photometric Periods of Six Ultracompact Accreting Binaries
• Superoutburst of SDSS J090221.35+381941.9: First Measurement of Mass Ratio in an AM CVn-Type Object using Growing Superhumps
• Phase-Resolved Spectroscopy of Gaia14aae: Line Emission From Near the White Dwarf Surface
• A Catalogue of Ultracompact Mass-Transferring White Dwarf Binaries
• NSV 1440: First WZ Sge-type Object in AM CVn stars and candidates
• Superoutburst of WZ Sge-type Dwarf Nova Below the Period Minimum: ASASSN-15po
• System parameters of three short period cataclysmic variable stars