Photometric and spectrophotometric observations of the evolution of a strong outburst of the classical symbiotic star YY Herculis

We present spectrophotometric (3400-7500 Angstrom) observations of the evol ution of a strong outburst of the classical symbiotic star YY Her in 1993 a nd photoelectric UBV observations of the star's eclipse in 1997. The durati on of the phase of lowest brightness, when the U brightness had decreased b y similar to 1.3(m), was similar to 0.17P(orb) (P-orb is the orbital period ). if this phase is due to the total eclipse of similar to 70% of the radia tion of the circumstellar envelope, this duration implies that the cool com ponent of YY Her fills its Roche lobe, the bulk of the envelope's volume em ission measure is concentrated around the hot component in a region with ra ther sharp boundaries r much less than R-giant (R-giant is the giant's radi us), and the line of sight is close to the binary orbital plane. We model f it the spectral energy distribution of YY Her to obtain estimates of the pa rameters of several structural components of the system. The red giant's sp ectral type correlates with its visual brightness and does not correlate wi th the hot component's brightness. At minimum brightness, the hot component 's luminosity fluctuates about that of its cool companion (L-h,L- bol/L-c,L - bol approximate to 0.9), and its temperature is T-h approximate to (9-11) x 10(4) K. Activity of the hot component of YY Her is accompanied by incre ased brightness and reduced temperature (L-h,L- bol (proportional to) T-h(- 5)), though the relation between these parameters is not unique. At maximum brightness, L-h,L- bol/L-c,L- bol approximate to 10 and T-h approximate to 6.0 x 10(4) K. if the red giant fills its Roche lobe, the hot component's luminosity is similar to 3.3 x 10(4)L(circle dot). The active period of YY Her lasted about 5 years, and the activity decrease was not monotonic. (C) 2000 MAIK "Nauka/lnterperiodica".