A survey of C2H, HCN, and C18O in protoplanetary disks. (arXiv:1904.09315v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bergner_J/0/1/0/all/0/1">Jennifer B. Bergner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oberg_K/0/1/0/all/0/1">Karin I. Oberg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bergin_E/0/1/0/all/0/1">Edwin A. Bergin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Loomis_R/0/1/0/all/0/1">Ryan A. Loomis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pegues_J/0/1/0/all/0/1">Jamila Pegues</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Qi_C/0/1/0/all/0/1">Chunhua Qi</a>
Molecular lines observed towards protoplanetary disks carry information about
physical and chemical processes associated with planet formation. We present
ALMA Band 6 observations of C2H, HCN, and C18O in a sample of 14 disks spanning
a range of ages, stellar luminosities, and stellar masses. Using C2H and HCN
hyperfine structure fitting and HCN/H13CN isotopologue analysis, we extract
optical depth, excitation temperature, and column density radial profiles for a
subset of disks. C2H is marginally optically thick (tau ~1-5) and HCN is quite
optically thick (tau ~ 5-10) in the inner 200 AU. The extracted temperatures
of both molecules are low (10-30K), indicative of either sub-thermal emission
from the warm disk atmosphere or substantial beam dilution due to chemical
substructure. We explore the origins of C2H morphological diversity in our
sample using a series of toy disk models, and find that disk-dependent overlap
between regions with high UV fluxes and high atomic carbon abundances can
explain a wide range of C2H emission features (e.g. compact vs. extended and
ringed vs. ringless emission). We explore the chemical relationship between
C2H, HCN, and C18O and find a positive correlation between C2H and HCN fluxes,
but no relationship between C2H or HCN with C18O fluxes. We also see no
evidence that C2H and HCN are enhanced with disk age. C2H and HCN seem to share
a common driver, however more work remains to elucidate the chemical
relationship between these molecules and the underlying evolution of C, N, and
O chemistries in disks.
Molecular lines observed towards protoplanetary disks carry information about
physical and chemical processes associated with planet formation. We present
ALMA Band 6 observations of C2H, HCN, and C18O in a sample of 14 disks spanning
a range of ages, stellar luminosities, and stellar masses. Using C2H and HCN
hyperfine structure fitting and HCN/H13CN isotopologue analysis, we extract
optical depth, excitation temperature, and column density radial profiles for a
subset of disks. C2H is marginally optically thick (tau ~1-5) and HCN is quite
optically thick (tau ~ 5-10) in the inner 200 AU. The extracted temperatures
of both molecules are low (10-30K), indicative of either sub-thermal emission
from the warm disk atmosphere or substantial beam dilution due to chemical
substructure. We explore the origins of C2H morphological diversity in our
sample using a series of toy disk models, and find that disk-dependent overlap
between regions with high UV fluxes and high atomic carbon abundances can
explain a wide range of C2H emission features (e.g. compact vs. extended and
ringed vs. ringless emission). We explore the chemical relationship between
C2H, HCN, and C18O and find a positive correlation between C2H and HCN fluxes,
but no relationship between C2H or HCN with C18O fluxes. We also see no
evidence that C2H and HCN are enhanced with disk age. C2H and HCN seem to share
a common driver, however more work remains to elucidate the chemical
relationship between these molecules and the underlying evolution of C, N, and
O chemistries in disks.
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