Photometric and spectrophotometric observations of the classical symbioticstar YY Her during its return to quiescence

We present new photometric UBVRI and spectroscopic observations of the symb iotic star YY Her during its return to quiescence after a strong outburst i n 1993. High-resolution spectra of YY Her at similar phases at outburst max imum (phi = 0.48) and in quiescence ( phi = 0.37) are presented for the fir st time. The ephemeris of YY Her has been refined (P = 586(d)). The last tw o observed minima (in 1999 and 2000) differed radically in shape from the 1 997 minimum described previously. Both were sharp and deep (DeltaU similar to 1.(m)6, DeltaV similar to 0.(m)9). To explain this shape of the V light curve, which is only slightly affected by nebular emission, it should be as sumed that the cool component of YY Her fills much of its Roche lobe and ha s a hot spot on the hemisphere facing the hot component. The emission spect rum rich in Fe II lines, which is characteristic of symbiotic stars, was ob served during the outburst, but high-ionization lines (He II lambda 4686) w ere also observed. The He I lambda lambda 5876, 7065 lines exhibit distinct P Cyg profiles; the centers of the absorption components are shifted from the emission ones by V-r approximate to 100 km s(-1), suggesting moderate o utflow velocities. (C) 2001 MAIK "Nauka/Interperiodica".