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Title: C{sub 60} in photodissociation regions

Recent studies have confirmed the presence of buckminsterfullerene (C{sub 60}) in different interstellar and circumstellar environments. However, several aspects regarding C{sub 60} in space are not yet well understood, such as the formation and excitation processes, and the connection between C{sub 60} and other carbonaceous compounds in the interstellar medium, in particular polycyclic aromatic hydrocarbons (PAHs). In this paper, we study several photodissociation regions (PDRs) where C{sub 60} and PAHs are detected and the local physical conditions are reasonably well constrained to provide observational insights into these questions. C{sub 60} is found to emit in PDRs where the dust is cool (T{sub d} = 20-40 K) and even in PDRs with cool stars. These results exclude the possibility for C{sub 60} to be locked in grains at thermal equilibrium in these environments. We observe that PAH and C{sub 60} emission are spatially uncorrelated and that C{sub 60} is present in PDRs where the physical conditions (in terms of radiation field and hydrogen density) allow for full dehydrogenation of PAHs, with the exception of Ced 201. We also find trends indicative of an increase in C{sub 60} abundance within individual PDRs, but these trends are not universal. These results support modelsmore » where the dehydrogenation of carbonaceous species is the first step toward C{sub 60} formation. However, this is not the only parameter involved and C{sub 60} formation is likely affected by shocks and PDR age.« less
Authors:
;  [1] ;  [2] ; ;  [3]
  1. Leiden Observatory, P.O. Box 9513, 2300 RA Leiden (Netherlands)
  2. Université de Toulouse, UPS-OMP, IRAP, F-31400 Toulouse (France)
  3. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
Publication Date:
OSTI Identifier:
22370440
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 794; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DEHYDROGENATION; DENSITY; DISSOCIATION; EMISSION; EXCEPTIONS; EXCITATION; FULLERENES; HYDROGEN; MOLECULES; PHOTOLYSIS; PHOTONS; POLYCYCLIC AROMATIC HYDROCARBONS; SPACE; THERMAL EQUILIBRIUM