NUCLEAR VARIABILITY OF NGC-4151 IN UBV AND JHKL - A NEW CYCLE OF ACTIVITY

The coordinated UBV and JHKL observations of the Seyfert Galaxy NGC 41 51 during a new cycle of activity (1985-1997) after the deep minimum o f 1984 are analyzed. The variability amplitude is approximate to 2.(m) 5 in U and similar to 1(m) in K; the light variations are correlated i n all bands. The emission from a variable source in the nucleus has be en separated in the wavelength range 0.36-3.5 mu m by subtracting the constant flux from the underlying galaxy that was obtained from multia perture photometry. The emission of the underlying galaxy through a 12 '' aperture (14 Mpc for H-0 = 75) has been decomposed: similar to 80% of the light comes from stars, and the remaining emission is produced by gas and dust at temperatures of approximate to 1100 add approximat e to 420 K, respectively. The contribution of the variable source is v ery small in UBV at minimum light (1985-1988) and almost zero in JHKL. At maximum light (1995-1996), three variable sources are clearly sepa rated in the spectral energy distribution: (i) a compact hot source (a radius of similar to 7 x 10(14) cm, a temperature of similar to 30 00 8 K, L0.36-3.5 similar to 2.4 x 10(44) erg s(-1)); (2) an intermediate source (similar to 3 x 10(15), similar to 7000, L0.36-3.5 similar to 3 x 10(43)); and (3) a cold source (similar to 4 x 10(16), similar to 1500, L0.36-3.5 similar to 1 x 10(43)). If the infrared emission is th e reradiation of energy of the compact hot source, then the infrared s ource cannot be spherically symmetric, but rather has a flattened stru cture with h/r similar to 0.15.