  We report the discovery of the carbon-rich ultra metal-poor unevolved star
J0815+4729. This dwarf star was selected from SDSS/BOSS as a metal-poor
candidate and follow-up spectroscopic observations at medium-resolution were
obtained with ISIS at William Herschel Telescope and OSIRIS at Gran Telescopio
de Canarias. We use the FERRE code to derive the main stellar parameters,
Teff=6215+-82 K, and logg=4.7+-0.5, an upper limit to the metallicity of
[Fe/H]<~-5.8, and a carbon abundance of [C/Fe]>~+5.0, while [alpha/Fe]=0.4 is
assumed. The metallicity upper limit is based on the Ca II K line, that at the
resolving power of the OSIRIS spectrograph cannot be resolved from possible
interstellar calcium. The star could be the most iron-poor unevolved star
known, and is also amongst the ones with the largest overabundances of carbon.
High-resolution spectroscopy of J0815+4729 will certainly help to derive other
important element abundances, possibly providing new fundamental constraints on
the early stages of the Universe, the formation of the first stars and the
properties of the first supernovae.
