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|Title: ||Ultracool Companions to White Dwarfs|
|Authors: ||Steele, Paul Raymond|
|Supervisors: ||Burleigh, Matthew|
|Award Date: ||7-Jul-2010|
|Presented at: ||University of Leicester|
|Citation: ||Steele, P. R., Burleigh, M. R., Dobbie, P. D. and Barstow, M. A., “Near-Infrared spectroscopy of the very low mass companion to the hot DA white dwarf PG 1234+482”, MNRAS, 2007, 382, 1804-1808|
Steele, P. R., Burleigh, M. R., Barstow, M. A., Jameson, R. F. and Dobbie, P. D., “White dwarfs with unresolved substellar companions and debris disks in the UKIDSS Survey”, '16th European Workshop on White Dwarfs', Vol. 172, Journal of Physics Conference Series
Steele, P. R., Burleigh, M. R., Farihi, J., G¨ansicke, B. T., Jameson, R. F., Dobbie, P. D. and Barstow, M. A., “PHL 5038: A spatially resolved white dwarf + brown dwarf binary”, A&A, 2009, 500, 1207-1210
|Abstract: ||In this thesis I present a new near-infrared photometric search for unresolved ultracool companions and debris disks to white dwarfs in UKIDSS DR5. 24 DA white dwarfs were found with multiple excesses indicative of a low mass companion, with 7 of these having a predicted mass in the range associated with brown dwarfs. The results of this survey show that the unresolved brown dwarf companion fraction to DA white dwarfs is 0.5 ≤ fWD+BD ≤ 1.8 ± 0.7%. I also calculate the unresolved L-dwarf companion fraction to be 0.5 ≤ fWD+dL ≤ 1.5 ± 0.6%, which is much higher than the previous estimate of Farihi, Becklin & Zuckerman (2005). However, the results are consistent with previous estimates of the brown dwarf companion fraction to main sequence stars.
I analyse the near-infrared spectra of eleven known DA white dwarf + M-dwarf binaries, and compare the spectral types assigned using optical photometry against those assigned using near-infrared spectra. I search for evidence that the known short period systems once existed in a common envelope phase. No such evidence was found.
I also present the spectroscopic analysis of two particularly interesting binaries; PG 1234+ 482 and PHL 5038. PG 1234+482 is the hottest and youngest DA white dwarf with a cool companion on the stellar-substellar borderline. I discuss the possibility that the companion is a brown dwarf, and the possibility that the secondary is the source of contamination by heavy metals in the white dwarf's atmosphere. PHL 5038 was identified to have a near-infrared excess in UKIDSS, and the spectroscopic analysis in this thesis confirms that the secondary in this system can be resolved at a projected orbital separation of 55AU, and is a brown dwarf with spectral type L8-L9. This is only the second such pair found (over 20 years later) after GD165AB. The secondary in this system has the potential to be used as a benchmark brown dwarf for testing substellar atmospheric models.|
|Appears in Collections:||Theses, Dept. of Physics and Astronomy|
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