Doppler tomography of the black hole binary A0620-00 and the origin of
  chromospheric emission in quiescent X-ray binaries
  Doppler tomography of emission line profiles in low mass X-ray binaries
allows us to disentangle the different emission sites and study the structure
and variability of accretion disks. We present UVES high-resolution
spectroscopic observations of the black hole binary A0620-00 at
quiescence.These spectroscopic data constrain the orbital parameters
Porb=0.32301405(1) d and K2=437.1+-2.0 km/s. These values, together with the
mass ratio q=M2/M1=0.062+-0.010, imply a minimum mass for the compact object of
M1(sin i)^3=3.15+-0.10 Msun, consistent with previous works.The H$\alpha$
emission from the accretion disk is much weaker than in previous studies,
possibly due to a decrease in disk activity. Doppler imaging of the H$\alpha$
line shows for the first time a narrow component coming from the secondary
star, with an observed equivalent width of 1.4+-0.3 Angstroms, perhaps
associated to chromospheric activity. Subtracting a K-type template star and
correcting for the veiling of the accretion disk yields to an equivalent width
of 2.8+-0.3 Angstroms. A bright hot-spot is also detected at the position where
the gas stream trajectory intercepts with the accretion disk. The H$\alpha$
flux associated to the secondary star is too large to be powered by X-ray
irradiation. It is comparable to those observed in RS CVn binaries with similar
orbital periods and, therefore, is probably triggered by the rapid stellar
rotation.
