The Circumstellar Environments of Born-Again Giants

When a solar-mass star reaches the end of its main sequence life, has shed a planetary nebula or become a proto-planetary nebula, and is heading towards the white dwarf phase of its evolution, the star may reignite residual surface helium and be "reborn". It retraces its path on the HR diagram and once again becomes a giant: it undergoes a Very Late Thermal Pulse (VLTP) and becomes a "Born-Again Giant" (BAG). This alternate scenario for the demise of low mass stars may occur in as many as 20% of cases. During this phase the star may become a prolific dust producer such that the star is completely obscured and the only means of monitoring its evolution is by observing the ejected dust.Over the past 10-20 years we have used ground-based, spaceborne and airborne infrared (IR) facilities to monitor the spectral energy distributions of the dust shells of stars that have recently undergone VLTPs. Covering a time period from ~1996 to the present, and with recent SOFIA observations that extend the spectral coverage from 1 - 38 microns, we have been able to determine mass-loss rates from the stars, and the physical state, nature and extent of their circumstellar dust shells.Our observations throw light on a phase of the evolution of low mass stars that is very rare, poorly observed, and little understood. Understanding these phenomena can potentially give us a glimpse of the ultimate fate of the Sun.