Effects of dust evolution on protoplanetary disks in the mid-infrared

¹ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
e-mail: greenwood@astro.rug.nl
² SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
³ Anton Pannekoek Institute for Astronomy, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands
⁴ SUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
⁵ Max Planck Institute for Extraterrestrial Physics, Gießenbachstraße 1, 85741 Garching, Germany

Received: 3 October 2018
Accepted: 25 March 2019

Abstract

In this paper, we couple the dust evolution code two-pop-py with the thermochemical disk modelling code ProDiMo. We create a series of thermochemical disk models that simulate the evolution of dust over time from 0.018 to 10 Myr, including the radial drift, growth, and settling of dust grains. We examine the effects of this dust evolution on mid-infrared gas emission, focusing on the mid-infrared spectral lines of C₂H₂, CO₂, HCN, NH₃, OH, and H₂O, which are readily observable with Spitzer and the upcoming E-ELT and JWST. The addition of dust evolution acts to increase line fluxes by reducing the population of small dust grains. We find that the spectral lines of all species except C₂H₂ respond strongly to dust evolution; line fluxes increase by more than an order of magnitude across the model series as the density of small dust grains decreases over time. The C₂H₂ line fluxes are extremely low because of a low abundance in the infrared line-emitting regions, even though C₂H₂ is commonly detected with Spitzer, suggesting that warm chemistry in the inner disk may need further investigation. Finally, we find that the CO₂ flux densities increase more rapidly than the other species as the dust disk evolves. This suggests that the flux ratios of CO₂ to other species may be lower in disks with less-evolved dust populations.