Gas has been detected in a number of debris disks. It is likely secondary, i.e. produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15--30 Myr old A-type star HD 32297. We find that C0 is located in a ring at ∼110 au with a FWHM of ∼80 au, and has a mass of (3.5±0.2)×10−3 M⊕. Naively, such a surprisingly small mass can be accumulated from CO photo-dissociation in a time as short as ∼104 yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C0 and CO observations, is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of ∼15 M⊕ Myr−1, much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and re-release. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.
@article{arxiv.1904.07215,
title = {The surprisingly low carbon mass in the debris disk around HD 32297},
author = {Gianni Cataldi and Yanqin Wu and Alexis Brandeker and Nagayoshi Ohashi and Attila Moór and Göran Olofsson and Péter Ábrahám and Ruben Asensio-Torres and Maria Cavallius and William R. F. Dent and Carol Grady and Thomas Henning and Aya E. Higuchi and A. Meredith Hughes and Markus Janson and Inga Kamp and Ágnes Kóspál and Seth Redfield and Aki Roberge and Alycia Weinberger and Barry Welsh},
journal= {arXiv preprint arXiv:1904.07215},
year = {2020}
}