NOAO >   Observing Info >   Approved Programs >   2002B-0076

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Proposal Information for 2002B-0076


PI: Thomas E. Harrison, New Mexico State University, tharriso@nmsu.edu
Address: Box 30001/MSC 4500, Las Cruces, NM 88003, USA

CoI: Steve Howell, Planetary Science Institute
CoI: Heather Osborne, New Mexico State University
CoI: Joni Johnson, New Mexico State University
CoI: Dawn Gelino, University of California, San Diego

Title: The Unusual Infrared Light Curves of Cataclysmic Variables with Brown Dwarf Secondaries

Abstract: The shortest period cataclysmic variables, those with periods of 90 minutes or less, almost certainly harbor secondary stars with masses near 0.06 M_\sun. Thus, they have the masses of brown dwarfs. The history of these ``brown dwarfs'', however, is quite different: They were created through extensive mass loss from a star of significantly larger mass. The short period (81 min.) system EF Eri has been stuck in a prolonged minimum of seven years during which mass transfer has nearly ceased allowing an opportunity to investigate the nature its secondary star. Using SQIID on the 2.1 m in 2001B, we obtained \it JHK photometry of EF Eri over two orbital cycles. The light curves were remarkable, with 0.8 mag peak-to-peak variations in the K-band. We have modeled these variations and find that the only viable explanation is heating of one face of the brown dwarf secondary by the white dwarf primary. In this scenario, the heated face has a temperature near 1600 K (L4V), and the unheated side is at 1125 K (T1V)! Our sparse \it JHK data set for LL And (P_\rm orb=78 min) shows similar variations. We request one night with SQIID on the KPNO 4 m to obtain high S/N light curves for LL And, EF Eri, and AK Cnc. \it Such observations provide insight into the response of brown dwarf atmospheres to irradiation that cannot be obtained for isolated objects.


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