The Surprisingly Low Carbon Mass in the Debris Disk around HD 32297
Gianni Cataldi, Yanqin Wu, A. Brandeker, Nagayoshi Ohashi, A. Moór, G. Olofsson, P. Ábrahám, R. Asensio-Torres, Maria Cavallius, William R. F. Dent, C. A. Grady, Thomas Henning, Aya E. Higuchi, A. Meredith Hughes, M. Janson, I. Kamp, Á. Kóspál, Seth Redfield, Aki Roberge, Alycia J. Weinberger, Barry Y. Welsh
Abstract
Abstract 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 C 0 is located in a ring at ∼110 au with an 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 photodissociation in a time as short as ∼10 4 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 C 0 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 rerelease. 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.