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  • The Surprisingly Low Carbon...
    Cataldi, Gianni; Wu, Yanqin; Brandeker, Alexis; Ohashi, Nagayoshi; Moór, Attila; Olofsson, Göran; Ábrahám, Péter; Asensio-Torres, Ruben; Cavallius, Maria; Dent, William R. F.; Grady, Carol; Henning, Thomas; Higuchi, Aya E.; Hughes, A. Meredith; Janson, Markus; Kamp, Inga; Kóspál, Ágnes; Redfield, Seth; Roberge, Aki; Weinberger, Alycia; Welsh, Barry

    Astrophysical journal/˜The œAstrophysical journal, 04/2020, Volume: 892, Issue: 2
    Journal Article

    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 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 ∼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 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.