Time resolved Hα spectroscopy of the SU UMajoris star TU Mensae in quiescence.

We have analyzed 67 spectra of TU Men in the λ 5800-7000A spectral region with 2A resolution covering a time range of =~14 hours. An orbital period of 2.813+/-0.005h was derived from the radial velocity variations of the Hα double emission line. This implies a not-evolved secondary mass M_2_=0.35+/-0.03M⊙. Unfortunately, our K semiamplitude diagnostic method gives two possible solutions: the most probable K is 108+/-10km/s. From that value and using measures on the emission profile, a system mass ratio q(M_2_/M_1_)=0.455+/-0.045, a primary mass M_1_=0.785+/-0.145M⊙ and an inclination angle i=52+/-5deg were calculated. However, a second K value arising from the analysis of the central parts of the Hα profile is K=87+/-2km/s. This solution yields to a mass ratio more compatible with the tidal disk instability model (q =~0.33, M_1_=~1.06M⊙ and i=~44deg). Periodic variations up to 100% of the Hα equivalent width characterized by two minima centered at phases 0.8 and 0.3 were observed. The FWHM of the Hα red and violet peak are anticorrelated and show a double wave behaviour during the orbital cycle. The peak separation and the V/R ratio between the intensities of the violet and the red peak and also the FWHM of the whole emission profile, oscillate with the orbital period. Two bright disk inhomogeneities could explain these results.