EPoS Contribution
EPoS Contribution
Evolving ices - understanding observations of complex organics around protostars

Karin I. Öberg
Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
The past decade realized the first observations of complex organic molecules (e.g. HCOOCH3) around low-mass protostars. Thought to reside close to the protostar, in so called 'hot cores/corinos', the detected organics provide constraints on the physical conditions in protostellar regions which are not accessible by smaller, more conventional molecular probes. The 'hot core' molecules may also provide the basis of even more complexity as stars and planets form. A key unknown in both areas is how the observed molecules form. Both gas-phase and icy grain-surface reaction pathways have been suggested; it is mainly the large uncertainties in how ices evolve have prevented progress, so far. Building on recent developments in experiments, theory and observations (from Spitzer IRS and the IRAM 30m telescope), I will discuss the significant advances made in our understanding of where these complex molecules come from. Specifically, our experiments show that UV irradiation of astrophysical relevant ices efficiently produces the observed 'hot core' molecules. The molecular abundance ratios seen in the experiment can be used to predict abundance ratios in space under different conditions, especially as a function of ice temperature. From previous experiments we also know that UV photodesorption should be efficient enough to release observable amounts of the produced organic ices into the gas-phase non-thermally, providing fingerprints of the ice composition as it evolves in the protostellar envelope. Addressing these predictions, I will share the results from a new search for cold complex organics -- HCOOCH3, CH3CHO, CH3OCH3, C2H5OH and HCOCH2OH -- towards a protostar with previous evidence for non-thermal ice desorption. The findings will be discussed in view of the complex chemistry evolution and the possibilities of using complex chemistry to trace the physics, e.g. collapse time scales and thermal histories, of protostars.
Caption: Reaction scheme of a UV-induced CH3OH-based ice chemistry adapted from Oberg et al. 2009. CH3OH is photodissociated into CH2OH, CH3O, CH3 and OH fragments, which then recombine to form more complex molecules. Adding large amounts of CO to a cold (20 K) ice results in an overproduction of specific HCO-bearing species (dashed boxes) compared to molecules such as C2H5OH, CH3OCH3 and (CH2OH)2. The latter three instead dominate among the pure CH3OH-photochemistry products (solid and dotted boxes). (CH2OH)2 and HOCH2CHO (dotted boxes) are only produced abundantly 50 K and warmer, in the laboratory.
Collaborators:
R.T. Garrod, Cornell University, USA
S. Bottinelli, CESR, France
E.C. Fayolle, Leiden Observatory, Netherlands
J.K. Jorgensen, University of Bonn, Germany
H. Linnartz, Leiden Observatory, Netherlands
E.F. van Dishoeck, Leiden Observatory, Netherlands
Key publication

Suggested Session: Chemistry