Saturday, September 2, 2017

HD far infrared emission as a measure of protoplanetary disk mass

HD far infrared emission as a measure of protoplanetary disk mass


Trapman et al

Protoplanetary disks around young stars are the sites of planet formation. While the dust mass can be estimated using standard methods, determining the gas mass - and thus the amount of material available to form giant planets - has proven to be very difficult. Hydrogen deuteride (HD) is a promising alternative to the commonly-used gas mass tracer, CO. We aim to examine the robustness of HD as tracer of the disk gas mass, specifically the effect of gas mass on the HD FIR emission and its sensitivity to the vertical structure. Deuterium chemistry reactions relevant for HD were implemented in the thermochemical code DALI and models were run for a range of disk masses and vertical structures. The HD J=1-0 line intensity depends directly on the gas mass through a sublinear power law relation with a slope of ~0.8. Assuming no prior knowledge about the vertical structure of a disk and using only the HD 1-0 flux, gas masses can be estimated to within a factor of 2 for low mass disks (Mdisk<10 1.8="" 2-1="" 2016b="" 5="" 6="" a="" about="" adding="" al.="" all="" an="" and="" can="" constrain="" disk="" disks="" et="" factor="" for="" from="" future="" gas="" hd="" hya="" increases="" independent="" information="" kama="" line="" m="" magnitude.="" mass="" masses.="" massive="" mdisk="" more="" observations="" of="" or="" order="" power="" r="" radial="" reduce="" require="" resolving="" sensitivity="" spectral="" structure="" than="" the="" this="" to="" tw="" uncertainty="" using="" vertical="" w=""> 300 (1000) to detect HD 1-0 (HD 2-1) for all disk masses above 10−5 M⊙ with a line-to-continuum ratio > 0.01. These results show that HD can be used as an independent gas mass tracer with a relatively low uncertainty and should be considered as an important science goal for future FIR missions.

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