UBV photometric properties of the symbiotic star V443 Herculis.

We present extensive UBV photoelectric photometry of the symbiotic star V443 Her covering the period 1979-1993. It is found that the mean brightness 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 radiation output of the white dwarf and the mass loss of the M5 III companion have remained constant over the last 40 years. No flickering associated with accretion processes has been observed. Two short duration, {DELTA}U~0.5mag phases and an irregular {DELTA}V~0.1mag intrinsic variability of the cool giant have been discovered. V443 Her presents a marked modulation of the brightness along the orbital cycle which is ascribed to the heating effect frequently observed in symbiotic stars. The orbital period is found to be 594(+/-3) days and the amplitude of the heating effect {DELTA}U=0.9, {DELTA}B=0.4 and {DELTA}V=0.1mag. No evidence for an eclipse scenario of the WD or a compact nebular region surrounding the latter is found in the optical photometry. The V band lightcurve along the orbital period indicates that 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 period is very similar to that exhibited by the yellow symbiotic star He2-467. Given the large differences between the wind outflow regimes of 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 lower limit to the amount of energy deposited by the WD radiation field onto the LTG facing side for impacting photons with energies >=0.01keV is obtained in a direct, assumption-free way.