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Paper: Finding the Cool Companions of the PG DA White Dwarfs
Volume: 334, 14th European Workshop on White Dwarfs
Page: 419
Authors: Holberg, J.B.; Magargal, K.
Abstract: We have used the Two Micron All-Sky Survey to identify those DA white dwarfs in the Palomar-Green (PG) Survey, which exhibit J, H, Ks band near infrared excesses. From these excesses we have further estimated the approximate spectral type of the companion, assuming they can be attributed to a single main sequence or brown dwarf companion. The technique employed the use of observed V band magnitudes along with accurate spectroscopically determined effective temperatures and gravities to predict the J, H, Ks band white dwarf fluxes and compared them with those found from the 2MASS Point Source Catalog. In all, we recovered J band fluxes for 296 our of 347 PG DA stars, however only 254 of these presently have reliable V band fluxes. Among these 254, we find 25 new stars with clear NIR excesses and an additional 15 stars with probable excesses. Combined with previously known binaries and NIR IR excess PG DA stars, the binary fraction could be as high as 31%. Three previously classified DAO stars were discovered to have NIR excesses.
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