X-Shooting EF Eridani: further evidence for a massive white dwarf and a sub-stellar secondary^*

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: aschwope@aip.de
² European Southern Observatory, Casilla 19001, Santiago 19, Chile
³ Excellence Cluster Universe, Technische Universität München, Boltzmannstrasse 2, 85748 Garching, Germany

Received: 23 September 2009
Accepted: 3 March 2010

Abstract

High resolution spectral observations of the polar EF Eridani obtained in a low state with X-Shooter revealed narrow emission lines from the irradiated secondary. The lines were most prominent in the near-IR Caii-triplet, the more intensive Hα line had additional emission likely originating from an accretion stream. The lines with a radial velocity amplitude, K₂’ = 385 ± 4 km s^-1, serve as tracer of the otherwise unseen companion. The mass function implies a massive white dwarf with M_wd >0.65  at 3σ confidence, and a short distance to the binary, d ~ 111 pc (<145 pc at 3σ confidence). The spectral energy distribution from the UV to the IR together with the high mass ratio gives further strong evidence of EF Eri being a post period-minimum object with M₂ < 0.06 .