We have undertaken a detailed near-infrared spectroscopic analysis of eight notable white dwarfs, predominantly of southern declination. In each case the spectrum failed to reveal compelling evidence for the presence of a spatially unresolved, cool, late-type companion. Therefore, we have placed an approximate limit on the spectral type of a putative companion to each degenerate. From these limits we conclude that if GD659, GD50, GD71 or WD2359−434 possesses an unresolved companion then most probably it is substellar in nature (M < 0.072 M⊙). Furthermore, any spatially unresolved late-type companion to RE J0457−280, RE J0623−374, RE J0723−274 or RE J2214−491 most likely has M < 0.082 M⊙. These results imply that if weak accretion from a nearby late-type companion is the cause of the unusual photospheric composition observed in a number of these degenerates then the companions are of very low mass, beyond the detection thresholds of this study. Furthermore, these results do not contradict a previously noted deficit of very-low-mass stellar and brown dwarf companions to main sequence F, G, K and early-M type primaries (a ≲ 1000 au).

Item Type:	Refereed Article
Keywords:	stars: abundances; binaries: spectroscopic; stars: low-mass, brown dwarfs; white dwarfs
Research Division:	Physical Sciences
Research Group:	Astronomical sciences
Research Field:	Stellar astronomy and planetary systems
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the physical sciences
UTAS Author:	Dobbie, PD (Dr Paul Dobbie)
ID Code:	81107
Year Published:	2005
Deposited By:	Mathematics and Physics
Deposited On:	2012-11-22
Last Modified:	2013-06-26
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