AAS 202nd Meeting, May 2003
Session 7 Cataclysmic Variables
Poster, Monday, May 26, 2003, 9:20am-6:30pm, West Exhibit Hall

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[7.01] Phase-Resolved K-Band Spectroscopy of EF Eridanus using NIRI on Gemini North: Detection of its Carbon-Deficient Brown Dwarf-like Secondary Star

T. E. Harrison (NMSU), S. B. Howell (UCR), H. L. Osborne, J. J. Johnson (NMSU)

We have used NIRI on Gemini to obtain phase-resolved K-band spectra of the ultra-short period magnetic cataclysmic variable EF Eri. By modeling multi-wavelength photometry, Harrison et al. (2003) have found that the secondary star in EF Eri is very cool, but is being heavily irradiated by the white dwarf primary. The light curve modeling suggests that the un-irradiated hemisphere of the secondary star in EF Eri has an effective temperature near 1,000 K, while the irradiated hemisphere has an effective temperature near 1,600 K. If this model is correct, the spectrum of EF Eri should change dramatically over the 1.35 hr orbital period. We have obtained K-band spectra covering a complete orbital cycle. The resulting spectra are consistent with a very cool object, but are peculiar in that they show that the secondary star is extremely deficient in carbon. Given that CO and Methane (CH4) are strong opacity sources for the expected temperature range of this secondary star means that the strong absorption line features that shape the K-band spectra of normal L and T dwarfs are not present in EF Eri. We present comparisons of the K-band spectra of EF Eri to those of actual brown dwarfs, and to model spectra. This research has been funded under NSF program AST-9986823.

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