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P.J. Green (SAO), B. Ali (U. Rochester)
We describe a near IR photometric search for cool red dwarf companions to hot white dwarfs (WDs). IR photometry offers a sensitive test for low mass main sequence (MS) companions, and our sample of EUV-detected WDs offers a threefold advantage over previous (largely proper motion-selected) samples: (1) the high WD temperatures insure excellent IR flux contrast with cool dwarfs (2) the range of evolutionary parameter space occupied by the WDs is considerably narrowed and (3) the random effects of the intervening ISM provides a complete but reasonably-sized sample.
We use detailed DA model atmosphere fits to optical spectra to predict WD K magnitudes and distances, against which we contrast our near IR observations. Our photometric survey reveals several DAs with a K excess, which is most likely caused by a cool, low mass dwarf companion. A few such composites have been found optically among WDs detected in recent EUV All-Sky Surveys. However, IR techniques can probe further down the MS, and to wider separations, where a significantly larger number of companions is expected.
Systems showing an IR excess will be followed up to determine the mass and spectral type of the cool companions, leading to better estimates of 1) the low mass MS luminosity function (2) the fraction of WDs with MS companions and (3) the mass ratio distribution in binaries. WD+MS systems are the progenitors of novae, CVs, symbiotics, Ba and CH giants, Feige~24-type systems, dwarf carbon stars, and other interacting binaries.
The author(s) of this abstract have provided an email address for comments about the abstract: pgreen@cfa.harvard.edu