Dying SiO masers in the V407 Cyg system

Abstract

The symbiotic nova, V407 Cyg, is a system having a Mira-type cool stellar component with circumstellar SiO maser emission (Deguchi et al. 2005; PASJ 57, 939). The nova outburst occurred in the V407 Cyg system can significantly influence the structure of the circumstellar shell of the cool star in a short time scale. We have been monitoring the time variation of SiO maser emission in the V407 Cyg system with the Nobeyama 45m telescope every few days since March 16, 2010. The intensity of the J=1-0 v=2 line at 42.821 GHz is currently about 0.5 Jy (March 28), while the J=1-0 v=1 line at 43.122 GHz is considerably weaker than the J=1-0 v=2 line. The line profile of the J=1-0 v=2 line changes rapidly in a time scale of a few days, though the V(LSR)=-20 km/s component seems to be relatively stable in the last two weeks. The -27 km/s component, which was found to be the strongest (~0.9 Jy) on March 16, has disappeared on March 19, while the -31 km/s (~0.3 Jy) component newly appeared on March 22. No H2O maser line at 22.235 GHz has been detected. The variation of the line profile of SiO masers in the V407 Cyg system provides us a clear picture of the physical interaction between the nova outburst and circumstellar matter at a scale of 10 AU.