The post-common-envelope binary central star of the planetary nebula
  ETHOS 1
  We present a detailed study of the binary central star of the planetary
nebula ETHOS 1 (PN G068.1+11.0). Simultaneous modelling of light and radial
velocity curves reveals the binary to comprise a hot and massive
pre-white-dwarf with an M-type main-sequence companion. A good fit to the
observations was found with a companion that follows expected
mass-temperature-radius relationships for low-mass stars, indicating that
despite being highly irradiated it is consistent with not being significantly
hotter or larger than a typical star of the same mass. Previous modelling
indicated that ETHOS 1 may comprise the first case where the orbital plane of
the central binary does not lie perpendicular to the nebular symmetry axis, at
odds with the expectation that the common envelope is ejected in the orbital
plane. We find no evidence for such a discrepancy, deriving a binary
inclination in agreement with that of the nebula as determined by
spatio-kinematic modelling. This makes ETHOS 1 the ninth post-common-envelope
planetary nebula in which the binary orbital and nebular symmetry axes have
been shown to be aligned, with as yet no known counter-examples. The
probability of finding such a correlation by chance is now less than 0.00002%.
