The central star of LoTr5 revisited.

Abstract

We report on new photometric and spectroscopic observations carried out in 1994 of the late-type star HD112313 in the binary nucleus of the planetary nebula LoTr5. From comparison with model spectra we derive a gravity logg=2.7+/-0.5 and an effective temperature T_eff_=5250+/-200K, in full agreement with a spectral type G5III. Iron is found to be nearly solar: [Fe/H]_sun_^*^=-0.25+/-0.20dex. We estimate a projected rotational velocity of 60+/-5km/s. No variations in the spectral continuum of the G-star have been detected within 5 observing nights with exposure times of 4mn. In addition, no eclipses of the hot central star appear in the SWP spectra extracted from the IUE Uniform Low Dispersion Archive. Our photometric observations confirm the existence of two possible periods: P_0_=5.9d and its alias P_1_=1.2d, interpreted as the rotational period. By assuming a typical mass of M_G_=1.1M_sun_ for the giant and of M_SD_=0.6M_sun_ for the hot central star, we find that the rotational period P_0_ is more realistic, and that the G-star is near break-up. We suggest that the rotational and orbital planes are not coplanar.