RT VIR – A SEMIREGULAR STAR WITH MASER EMISSION: MATHEMATICAL MODELLING OF OPTICAL VARIABILITY

The historical light curve of the semiregular pulsating star RT Vir (SRb, Sp M8III) with a ma- 
ser emission is analyzed based on the AAVSO database. The star is extensively studied in the IR, radio and the optical ranges. The value of the period from the CCVS (155 d ) conflicts with some observational data. Signs of a systematic variability were also detected in the radio frequency range with a period that was close to 200 days. Studies of the period showed that the period of this star varies with time and the latest value was found to be roughly 136 days. Period analysis result of the visual data from 1904 May to 2016 August provided by AAVSO for RT Vir. Published databases of "virtual observatories" - AAVSOnet, Hipparcos, ASAS-SN, KWS were used. Periodogram analysis revealed that the star still has several periods (320, 280, 169 and 153 days). In fact, the variations are not truly periodic, there are large shifts in time, changes in amplitude, and these smaller periods occur as smaller-amplitude peaks in-between the main ones with 320 period. Two-color diagrams of gloss in I and color index (V-I) from V were constructed. Approximation of “Running parabola” was carried out, average values =8.457, =3.658, =+1.8 were determined.