Variable red giants exploration with MASTER robotic net: main algorithms and study of three Mira-type targets

Abstract 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.