Intermediate- and high-resolution optical spectroscopy on the nascent planetary nebula Vy 2-2: Evidence of binary-star evolution
Spectroscopy of nascent planetary nebula Vy 2-2 revealed subsolar chemical abundances and a high Abundance Discrepancy Factor (ADF) of 13.6±2.6, suggesting it belongs to a unique class of PNe. Internal structure analysis shows a high-excitation central region and bipolar lobes, with no shock excitation in the main shell. These features strongly imply Vy 2-2 formed through a post-common-envelope binary system.