The masses, radii and luminosities of the components of U Geminorum

Abstract

We present a phase-resolved spectroscopic study of the secondary star in the cataclysmic variable U Gem. We use our data to measure the radial velocity semi-amplitude, systemic velocity and rotational velocity of the secondary star. Combining this with literature data allows us to determine masses and radii for both the secondary star and white dwarf which are independent of any assumptions about their structure. We use these to compare their properties with those of field stars and find that both components follow field mass-radius relationships. The secondary star has the mass, radius, luminosity and photometric temperature of an M2 star, but a spectroscopic temperature of M4. The latter may well be due to a high metallicity. There is a troubling inconsistency between the radius of the white dwarf inferred from its gravitational redshift and inclination and that inferred from its temperature, flux, and astrometric distance. We find that there are two fundamental limits to the accuracy of the parameters we can derive. First the radial velocity curve of the secondary star deviates from a sinusoid, in part because of its asphericity (which can be modelled) and in part because the line flux is not evenly distributed over its surface. Second we cannot be certain which spectral type is the best match for the lines of the secondary star, and the derived rotational velocity is a function of the spectral type of the template star used.

arXiv comment12 pages, 10 figures. Accepted for MNRAS

References in corpus (9)

• The Palomar/MSU Nearby Star Spectroscopic Survey III: Chromospheric Activity, M-dwarf Ages and the Local Star Formation History
• The 0.4-Mo Eclipsing Binary CU Cancri: Absolute Dimensions, Comparison with Evolutionary Models and Possible Evidence for a Circumstellar Dust Disk
• A TiO study of the black-hole binary GRO J0422+32 in a very low state
• A new method of determining the inclination angle in interacting binaries
• Mass estimates in short-period compact binaries
• Spectroscopic Evidence for Starspots on the Secondary Star of SS Cygni
• A TiO study of the dwarf nova IP Pegasi
• Mirror eclipses in the cataclysmic variable IP Peg
• What We Learn from Quantitative Ultraviolet Spectroscopy of Naked White D warfs in Cataclysmic Variables

Cited by in corpus (16)

• Post-common-envelope binaries from SDSS. XI: The white dwarf mass distributions of CVs and pre-CVs
• Post Common Envelope Binaries from SDSS. I: 101 white dwarf main sequence binaries with multiple SDSS spectroscopy
• Adiabatic Mass Loss in Binary Stars. II. From Zero-Age Main Sequence to the Base of the Giant Branch
• Comprehensive simulations of superhumps
• U Geminorum: a test case for orbital parameters determination
• The pre-cataclysmic variable, LTT560
• The dwarf nova SS Cygni: what is wrong?
• Identification of twenty-three accreting binaries in the Galactic Bulge Survey
• Orbital periods of cataclysmic variables identified by the SDSS. VI. The 4.5-hr period eclipsing system SDSS J100658.40+233724.4
• FUSE Spectroscopy of the White Dwarf in U Geminorum
• Orbital periods of cataclysmic variables identified by the SDSS. V. VLT, NTT and Magellan observations of nine equatorial systems
• Optical spectroscopy of the dwarf nova U Geminorum
• Abundance Derivations for the Secondary Stars in Cataclysmic Variables from Near-Infrared Spectroscopy
• Tidal torques, disc radius variations, and instabilities in dwarf novae and soft X-ray transients
• L1 Stream Deflection and Ballistic Launching at the Disk Bow Shock: An Absorption-line Velocity Analysis in Semi-detached Binaries
• The statistical significance of the superhump signal in U Gem