Computer Science
Scientific paper
Apr 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009sptz.prop60056m&link_type=abstract
Spitzer Proposal ID #60056
Computer Science
Scientific paper
The mass-radius relation and cooling timescale for low-mass white dwarfs depends on their composition, particularly the amount of hydrogen remaining on their surface. There are currently no strong observational constraints on this parameter. This severely limits our ability to interpret observations of white dwarfs in close binary stars. RR Cae is a binary star in which an M-dwarf eclipses a low-mass white dwarf every 0.3037 days. This makes it possible, in principle, to measure a precise, model independent mass and radius for the white dwarf. In practice, this can only be done with lightcurves obtained at infrared wavelengths because i. flaring and star-spots from the M-dwarf distort the lightcurve at optical wavelengths and ii. the depth of the eclipse due to the transit of the white dwarf becomes undetectable at optical wavelengths. We will use Spitzer to obtain lightcurves at 3.6um of RR Cae. These lightcurves together with spectroscopic data already obained will be used to measure the mass and radius of the white dwarf to an accuracy of better than 1-percent. This will be the most precise reliable mass and radius measurement made for any white dwarf to-date. This level of precision is essential to make a useful estimate of the thickness of hydrogen layer on this white dwarf. RR Cae will also be a benchmark object for testing model atmospheres of cool white dwarfs because the surface gravity and effective temperature will then be known independently of the analysis of the spectrum. These observations are essential for the accurate interpretation of data for many types of white dwarf, including white dwarfs accreting metals from from the dust discs detected by Spitzer; cool white dwarfs used for measuring the age of globular clusters and the hundreds of white dwarf binaries identified in SDSS data. RR Cae is the only white dwarf known where data of this quality can be obtained.
Marsh Tom
Maxted Pierre
Wheatley Peter
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