A search for cool molecular gas in GK Persei and other classical novae

Vol. 659
6. Interstellar and circumstellar matter

A search for cool molecular gas in GK Persei and other classical novae

Null results, though too often consigned to a desk drawer, can sometimes provide basic insights, and this is one such example. The authors conducted a deep spectroscopic survey of CO and HCN emission in a sample of more than one hundred Galactic novae, covering about 350 years and spanning the various subclasses of outbursts. Their conclusion is that no emission intrinsic to the ejecta is detected, but interstellar lines were. The lack of CO emission adds support to chemical models for molecular formation and persistence in the ejecta. For those novae for which light echos were historically seen, such as the prototypical outburst of GK Per 1901, the interstellar matter may be associated with the scattering, and they discuss several cases.