Variable Red Giants Exploration with MASTER Robotic Net: Brightening of R CrB Variable and Pulsating Carbon Star With Long Term Trend

We report the discovery and present archival light curves for four optical transients, connected with long period variable red giants, based on MASTER Robotic Net all-sky survey observations and archival MASTER light curves at Lomonosov database storage. We demonstrate transient detection frames and light curves for three Mira-type variables: MASTER OT J083717.54-573411.1 , MASTER OT J190436.33+192828.7 and MASTER OT J07010810-6818548 . Spectroscopically validated carbon star candidate MASTER OT J07010810-6818548 shows mean magnitude growth but constant pulsation period which may indicate the presence of a long secondary period. We also present photometry of unusual brightening on known variable star V581 CrA (optical transient MASTER OT J18244346-4524439 . The star V581 CrA is classified in catalogs as R CrB type variable, but it suddenly flared up on more than 4 magnitudes. As the result of MASTER wide-field images analysis at Lomonosov supercomputer data storage we present the 8-years historical light curves for all four objects with period calculations for all three Mira-type variables and unusual brightening photometry for V581 CrA. Analysis of V581 CrA light curves has shown, that this object is probably not an R CrB type variable. We estimated fundamental astrophysical parameters for all three Mira-type variables: luminosities, radii, and zero age main sequence (ZAMS) masses.