THE CENTRAL STAR OF LOTR-5 REVISITED

We report on new photometric and spectroscopic observations carried ou t in 1994 of the late-type star HD 112313 in the binary nucleus of the planetary nebula LoTr5. From comparison with model spectra we derive a gravity log g = 2.7 +/- 0.5 and an effective temperature T-eff = 525 0 +/- 200 K, in full agreement with a spectral type G5III. Iron is fou nd to be nearly solar: [Fe/H]. = -0.25 +/- 0.20 dex. We estimate a pr ojected rotational velocity of 60 +/- 5 km s(-1). No variations in the spectral continuum of the G-star have been detected within 5 observin g nights with exposure times of 4mn. In addition, no eclipses of the h ot central star appear in the SWP spectra extracted from the IUE Unifo rm Low Dispersion Archive. Our photometric observations confirm the ex istence of two possible periods: P-0 = 5.9 d and its alias P-1 = 1.2 d , interpreted as the rotational period. By assuming a typical mass of M(G) = 1.1 M. for the giant and of M(SD) = 0.6M. for the hot central s tar, we find that the rotational period P-0 is more realistic, and tha t the G-star is near break-up. We suggest that the rotational and orbi tal planes are not coplanar.