Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide. (arXiv:2104.03210v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Roth_N/0/1/0/all/0/1">Nathan X. Roth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Milam_S/0/1/0/all/0/1">Stefanie N. Milam</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cordiner_M/0/1/0/all/0/1">Martin A. Cordiner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bockelee_Morvan_D/0/1/0/all/0/1">Dominique Bockelée-Morvan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Biver_N/0/1/0/all/0/1">Nicolas Biver</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Boissier_J/0/1/0/all/0/1">Jérémie Boissier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lis_D/0/1/0/all/0/1">Dariusz C. Lis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Remijan_A/0/1/0/all/0/1">Anthony J. Remijan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Charnley_S/0/1/0/all/0/1">Steven B. Charnley</a>
We report the first survey of molecular emission from cometary volatiles
using standalone Atacama Compact Array (ACA) observations of the Atacama Large
Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS)
carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst.
These measurements of HCN, CS, CH$_3$OH, H$_2$CO, and HNC (along with continuum
emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric
outgassing and discerning parent from daughter/distributed source species. This
work presents spectrally integrated flux maps, autocorrelation spectra,
production rates, and parent scale lengths for each molecule, and a stringent
upper limit for CO. HCN is consistent with direct nucleus release in C/2015
ER61, whereas CS, H$_2$CO, HNC, and potentially CH$_3$OH are associated with
distributed sources in the coma. Adopting a Haser model, parent scale lengths
determined for H$_2$CO (L$_p$ $sim$ 2200 km) and HNC (L$_p$ $sim$ 3300 km)
are consistent with previous work in comets, whereas significant extended
source production (L$_p$ $sim$ 2000 km) is indicated for CS, suggesting
production from an unknown parent in the coma. The continuum presents a
point-source distribution, with a flux density implying an excessively large
nucleus, inconsistent with other estimates of the nucleus size. It is best
explained by the thermal emission of slowly-moving outburst ejectas, with total
mass 5–8 $times$ 10$^{10}$ kg. These results demonstrate the power of the ACA
for revealing the abundances, spatial distributions, and locations of molecular
production for volatiles in moderately bright comets such as C/2015 ER61.
We report the first survey of molecular emission from cometary volatiles
using standalone Atacama Compact Array (ACA) observations of the Atacama Large
Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS)
carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst.
These measurements of HCN, CS, CH$_3$OH, H$_2$CO, and HNC (along with continuum
emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric
outgassing and discerning parent from daughter/distributed source species. This
work presents spectrally integrated flux maps, autocorrelation spectra,
production rates, and parent scale lengths for each molecule, and a stringent
upper limit for CO. HCN is consistent with direct nucleus release in C/2015
ER61, whereas CS, H$_2$CO, HNC, and potentially CH$_3$OH are associated with
distributed sources in the coma. Adopting a Haser model, parent scale lengths
determined for H$_2$CO (L$_p$ $sim$ 2200 km) and HNC (L$_p$ $sim$ 3300 km)
are consistent with previous work in comets, whereas significant extended
source production (L$_p$ $sim$ 2000 km) is indicated for CS, suggesting
production from an unknown parent in the coma. The continuum presents a
point-source distribution, with a flux density implying an excessively large
nucleus, inconsistent with other estimates of the nucleus size. It is best
explained by the thermal emission of slowly-moving outburst ejectas, with total
mass 5–8 $times$ 10$^{10}$ kg. These results demonstrate the power of the ACA
for revealing the abundances, spatial distributions, and locations of molecular
production for volatiles in moderately bright comets such as C/2015 ER61.
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