Protostars and Planets VI, Heidelberg, July 15-20, 2013
Chemical tracers of episodic accretion
Visser, Ruud (University of Michigan)
Bergin, Ted (University of Michigan)
Kristensen, Lars (Harvard-Smithsonian CfA)
The embedded phase of low-mass star formation (Class 0/I) is when most of the mass is accreted. This appears to happen at a highly variable rate, with long periods of weak accretion punctuated by brief bursts of strong accretion. The luminosity is directly proportional to the accretion rate. Each accretion burst heats up the protostellar envelope for ~100 yr. This disrupts the chemical balance for up to ~10^4 yr. The corresponding time evolution of certain molecular line ratios allows us to measure the time since the last accretion burst.
Our conclusions are: (1) Episodic accretion in embedded protostars leaves a long-lasting imprint on the chemical profile of the envelope. (2) Line ratios like HCO+ 7-6/H13CO+ 3-2 can be used to measure the time passed since the most recent burst. (3) Normalization is required to filter out intrinsic source-to-source variations.
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