NIRI Spectra of EF Eri: An Object that Transitions from an L-dwarf, to a T-dwarf, and Back Again

Details NIRI Spectra of EF Eri: An Object that Transitions from an L-dwarf, to a T-dwarf, and Back Again NIRI Spectra of EF Eri: An Object that Transitions from an L-dwarf, to a T-dwarf, and Back Again

Aug 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002noao.prop...68h&link_type=abstract

NOAO Proposal ID #2002B-0068

Physics

Scientific paper

The shortest period cataclysmic variables, those with periods of 90 minutes or less, are believed to 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 (P_orb=81 min) system EF Eri has been stuck in a prolonged minimum of seven years during which mass transfer has nearly ceased. This affords us an opportunity to investigate the nature of the secondary star. Using SQIID on the 2.1 m in 2001B, we obtained 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)! We request NIRI time on Gemini north to obtain phase-resolved data to observe the spectroscopic transitions of the secondary star in EF Eri. Such observations provide insight into the chemistry of brown dwarf atmospheres that cannot be obtained for isolated objects.

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