Mm-wave and far-IR Molecular line survey of OH 231.8+4.2: Hard-boiled rotten eggs
Résumé
Envelopes around evolved stars are extraordinarily efficient factories of complex molecules and dust particles that will eventually enrich the ISM. To date, most chemistry studies have focused on C-rich envelopes, expected to show the largest molecular variety and abundances. Recent observations suggest that O-rich shells may be as chemically diverse as their Carbon counterparts, however, no serious attempt has been made yet to perform a full frequency scan of such objects. In this conference, I will report the first results from our spectral line surveys with the IRAM 30m telescope (~80-345 GHz) and Herschel/HIFI (~479-1244 GHz) of the well known, O-rich pre-PN OH 231.8+4.2 (a.k.a. The Rotten Egg nebula after the high abundance of Hydrogen sulfide, H2S, in its envelope). This object displays fast (>400 km/s), bipolar outflows and a molecular richness unparalleled amongst O-rich AGB and post-AGB stars. These surveys have led to the detection of hundreds of lines from different species, many of them detected for the first time in O-rich CSEs, that clearly confirm OH231.8+4.2 as the ''The Rosetta-stone'' for studying non-equilibrium, shock-induced molecule formation processes in O-rich environments. HIFI data have been particularly crucial to trace the physico-chemical conditions in the warm, dense circumstellar layers, which are not proved by lower-energy/frequency transitions. At these high frequencies, H2O and S-containing species are, together with CO, the dominant contributors to the total line flux observed. The main product from these surveys, is a molecular inventory and unprecentedly detailed chemical study (in progress) of an O-rich molecular flow accelerated by fast shocks.