  Results are discussed of an X-ray and optical observation campaign of the
low-mass X-ray binary A1246-58 performed with instruments on Satellite per
Astronomia X ('BeppoSAX'), the Rossi X-ray Timing Explorer (RXTE), the X-ray
Multi-mirror Mission ('XMM-Newton'), the Swift mission, and the Very Large
Telescope. Spectra and flux time histories are studied. The most important
results are the lack of hydrogen spectral features in the optical spectrum,
supporting the proposition that this is an ultracompact X-ray binary (UCXB),
the determination of a 4.3 kpc distance from time-resolved spectroscopy of
thermonuclear X-ray bursts, and the detection of intermediately long
thermonuclear bursts as seen in a number of other UCXBs. There is evidence for
a Ne/O abundance ratio in the line of sight that is higher than solar and
variable. This may be due to different changes in the ionization degrees of Ne
and O, which may be related to the variable irradiating flux. We discuss the
spectral variability and the peculiarities of the long-term light curve.
