The Next Possible Outburst of P Cygni

Abstract

On the basis of long-term UBV observations of P Cygni, which were made by Eugene Kharadze and Nino Magalashvili between 1951-1983, is evident that P Cygni undergone reddening during those observations. P cygni is a LBV and a supernova impostor. Corrected on the reddening B-V color has values between about -0.4 (at the beginning of 1950-ies) and -0.1 (for the 1980-ies). It means that the star probably had earlier spectral type at the beginning of 20-th century and accordingly, we are witnesses of its evolutionary changes. It means also that on the HR diagram the star moves gradually to the instability strip of LBVs in Outburst. So, if the rate of the reddening of the P Cygni will the same in near future then the star will have the next eruption (or even supernova explosion) after approximately 80-120 years.

The long (approximately 1500 d, 1160 d, 760 d, 580 d) quasi-periods and the shorter ones (approximatelly 130 d, 68 d and 15-18 days) were revealed using the above observations.

We observed P Cygni on July 23 - October 20, 2014 with the 48 cm Cassegrain telescope and standard B,V,R,I filters. HD 228793 has been used as a comparison star. We revealed that during our observations the star underwent light variations with the mean amplitude of approximately 0.1 magnitudes in all pass-bands and the period of this change was approximately 68 days. There is also a relation between brightness and the Hα EW variability. Therefore, we think that the cause of this behavior may be a variability of rate of the stellar wind that is very strong in this star. Changes in the rate of the stellar wind, on the other hand, maybe due to the pulsation of the star. It seems that quasi-periods of the brightness variability are almost the exact multiples of each other which probably also indicates on pulsation of the star. According to the new photometric observations of 2014 the star continues reddening.