  The spectroscopic data for the short-period (0.1984 d)eclipsing binary V38,
discovered by the OGLE micro-lensing team in Baade's Window field BW3, are
analyzed. Radial velocity curves are derived from mid-resolution spectra
obtained with EMMI-NTT at ESO - La Silla, and a simultaneous solution of the
existing light curve by OGLE and of the new radial velocity curves is obtained.
The system is formed by almost twin M3e dwarf components that are very close,
but not yet in contact. The spectra of both dwarfs show signatures of the
presence of strong chromospheres. Spectroscopy definitely confirms, therefore,
what was suggested on the basis of photometry: BW3 V38 is indeed a unique
system, as no other similar binary with M components and in such a tight orbit
is known. Within the limits posed by the relatively large errors, due to the
combined effect of system faintness and of the constraints on exposure time,
the derived physical parameters seem to agree with the relations obtained from
the other few known eclipsing binaries with late type components (which
indicate a discrepancy between the available evolutionary models and the data
at ~ 10% level). A possible explanation is the presence of strong magnetic
fields and fast rotation (that applies to the BW3 V38 case as well). A simple
computation of the system secular evolution by angular momentum loss and spin
orbit synchronization shows that the evolution of a system with M dwarfs
components is rather slow, and indicates as well a possible reason why systems
similar to BW3 V38 are so rare.
