The Kuwano-Honda's peculiar object (PU Vulpeculae) in 1983-1986.

Photometric, spectrophotometric, polarimetric, and spectroscopic observations of the peculiar object PU Vulpeculae, carried out in 1983-1986 in the wavelength range of 0.24 to 5 μm are presented. In addition to irregular brightness variations with a maximum amplitude ΔU ≈0^m.2 - 0^m.3, a systematic brightness decrease in the optical region as well as a decrease in the colour indices was observed. In two-colour diagrams, these systematic variations correspond to a drift of the exploded component of the binary along the supergiant branch from spectral class F to early A. Similar evolution was found from our spectrophotometric data, which means that in 1982 the photosphere of the exploded component attained a maximum in size and a mini- μm in temperature. After the extremum state, the component began to return back to the initial state of a hot dwarf. However, the cool giant component did not show any significant variations during the whole flare of PU Vul.

Variations of intrinsic polarimetric parameters p^*_λ and Θ^*_λ with time, as well as significant variety in their wavelength dependence were found. Three models were considered to interpret the observed polarization: 1) light scattering in a circumstellar dust envelope, 2) light scattering by free electrons in a magnetized stellar envelope, and 3) scattering in a spotty photo- sphere. However, none of them explain the whole variety of the observed wavelength dependence and none of them can be definitely rejected. Apparently the dust envelope which was responsible for the deep minimum in 1980-1981, is now dissipated and there have been no new episodes of dust formation. According to the spectroscopic observations, there were noticeable variations in the absorption spectrum after 1981. These can be explained with a change of the chemical composition in the outer layers of the exploded component to a photo spheric composition nearly identical with that of Am stars.

The hot component of PU Vul obviously ejects its envelope at a variable rate and/or anisotropically, which is seen from the unstable, P Cyg-type line profiles. Comparison with theoretical models shows that PU Vul is a binary system with an accreting white dwarf component of a mass lower than 1.1 M_sun and an accretion rate lower than 10^-8 5M_sun yr^-1. The burst in 1978 was quite unambiguously due to a temporary transition of the accreting component to a phase that could be called "supergiant mimicry".