Abstract
We present a near-infrared photometric search for unresolved substellar companions and debris disks around white dwarfs in the UKIRT Infrared Deep Sky Survey Large Area Survey. We cross-correlate the SDSS DR4 and McCook & Sion catalogues of white dwarfs with the UKIDSS DR8 producing 3109 and 163 unique matches respectively. Cooling models are fitted to the optical photometry of a subsample of DA white dwarfs and extended to the near-infrared. A comparison is then made with the observed photometry to identify those stars with a near-infrared excess consistent with the presence of a cool companion or debris disk. Where present, we have estimated the approximate spectral type of any putative companion, or an upper limit on the temperature of a debris disk. In total we identify 14-16 new candidate white dwarf + very low mass stellar systems, 9-11 candidate white dwarf + brown dwarf systems, and 3 candidate white dwarf + debris disks. We place lower limits on the unresolved (<2") companions to all DA white dwarfs and thus assess the sensitivity of UKIDSS to such objects. We use this result to estimate unresolved binary fractions of f(WD+dL)>0.4+/-0.3%, f(WD+dT)>0.2% and f(WD+BD)>0.5+/-0.3%.
Highlights
Near-infrared (NIR) surveys of white dwarfs enable the detection and study of late stellar and substellar companions, and circumstellar dust disks
Consideration of stellar evolution suggests the possible existence of two distinct populations: close systems in which the secondary has survived a phase of common envelope evolution and which may eventually lead to the formation of a cataclysmic variable (CV), and wide pairs where the secondary has migrated outwards in response to mass-loss from the white dwarf’s progenitor (Farihi et al 2006)
In this paper we present the first results from studying white dwarfs detected in the eigth data release (DR8) of the UKIRT Infrared Deep Sky Survey, the largest and deepest survey of the nearinfrared sky yet undertaken
Summary
Near-infrared (NIR) surveys of white dwarfs enable the detection and study of late stellar and substellar companions, and circumstellar dust disks. The brown dwarf is expected to be irradiated by the white dwarf’s high UV flux, possibly leading to substantial temperature differences between the “day” and “night” hemispheres. Such systems can provide laboratories for testing models of irradiated ”hot Jupiter” atmospheres (e.g. HD 189733b; Knutson et al 2007). These disks have been found around relatively cool white dwarfs whose atmospheres are polluted with heavy elements These metals should sink from the photospheres on a timescale of days, so the presence of close, orbiting dust disks provides a reservoir for on-going low level accretion. In this paper we present the first results from studying white dwarfs detected in the eigth data release (DR8) of the UKIRT Infrared Deep Sky Survey, the largest and deepest survey of the nearinfrared sky yet undertaken
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