PREDNASAJUCI / LECTURER :

Vladyslava Marsakova

NAZOV / TITLE :

Multiwavelength research of the of orbital and pulsation variability of symbiotic nova PU Vul

ABSTRAKT / ABSTRACT :

Symbiotic variables, and especially symbiotic novae, with observable eclipses (due to the high inclination 
of the orbit, despite of large distances between the stellar components) are very rare stellar systems. 
But they are very important for understanding the processes of interaction between components and common 
envelope in the systems and for comparing these phenomena with the orbital motion of the components. 
One of such stellar systems is PU Vul. It exploded as a symbiotic nova in 1978, and soon after outburst 
the first deep eclipse (of brightened white dwarf and accretion structures near it) was observed. 
Then, during the slow brightness decreasing after explosion, the eclipses of white dwarf and accretion 
structures by red giant were repeated at least two times.

We present UBVRI light curves of PU Vul after the outburst (until the present time), composed of photometric 
observations made in AI SAS, Crimea and those compiled from open sources, as well as our estimates using 
photographic plates of Asiago Observatory (Italy). While three eclipses have been observed since the outburst, 
the last one (expected in 2021) was either not detected or had a very small amplitude, possibly due to low 
activity and brightness of the accretion structures in recent decades.

We rectified the orbital period of the system (13.4 years) and analyzed the red giant’s pulsation variability, 
which has a main cycle of about 208-219 days. The shape and amplitude of pulsation light curves change with 
1) passband (that is obviously due to the large contribution of the red giant to the luminosity in the long 
wavelength range of the spectrum, and the contribution of white dwarf and accretion structures in the short 
wavelength, especially at the outburst and shortly after it) as well as 
2) the phase of orbital variability, so the oscillations become more pronounced and regular before and after 
the observed eclipses. We studied these variations in five photometric passbands, with constructing the color 
indices curves, and testing the observations for period changes and multiperiodicity. In interval of much more 
chaotic pulsations with the low amplitude observations can be adequately fitted by two-period approximation 
(220 and 112 days).

Our hypothesis for these features are: 1) non-radial pulsations of the red giant caused by temperature 
differences between the two sides of its atmosphere - the side facing the white dwarf and accretion disk 
may be hotter due to heating by their radiation, which is less favorable for pulsatoing activity, and 
2) absorption in the common envelope of the stellar system - when the red giant is closer to us than the white 
dwarf, its radiation passes through a thinner layer of the envelope material and makes a larger contribution 
to the common luminosity (but this is but this does not agree well with the presence of complex multiperiodic 
oscillations at orbital phases near 0.5).