UBV PHOTOMETRIC PROPERTIES OF THE SYMBIOTIC STAR V443 HERCULIS

We present extensive UBV photoelectric photometry of the symbiotic sta r V443 Her covering the period 1979-1993. It is found that the mean br ightness of V443 Her has remained constant at a level of 2-3 % in any of the UBV bands over the last 40 years. This suggests that both the r adiation output of the white dwarf and the mass loss of the M5 III com panion have remained constant over the last 40 years. No flickering as sociated with accretion processes has been observed. Two short duratio n, Delta U similar to 0.5 mag phases and an irregular Delta V similar to 0.1 mag intrinsic variability of the cool giant have been discovere d. V443 Her presents a marked modulation of the brightness along the o rbital cycle which is ascribed to the heating effect frequently observ ed in symbiotic stars. The orbital period is found to be 594(+/-3) day s and the amplitude of the heating effect Delta U=0.9, Delta B=0.4 and Delta V=0.1 mag. No evidence for an eclipse scenario of the WD or a c ompact nebular region surrounding the latter is found in the optical p hotometry. The V band lightcurve along the orbital period indicates th at the M5 III star is well inside its Roche Lobe and thus V443 Her is a detached system. The color evolution of V443 Her along the orbital p eriod is very similar to that exhibited by the yellow symbiotic star H e2-467. Given the large differences between the wind outflow regimes o f the cool giants of these two systems, this similarity suggests that the basic characteristics of the heating effect in symbiotic stars are not strongly affected by the details of the cool giant mass loss. A l ower limit to the amount of energy deposited by the WD radiation field onto the LTG facing side for impacting photons with energies greater than or equal to 0.01 keV is obtained in a direct, assumption-free way .