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arXiv:1904.07215 [astro-ph.EP]AbstractReferencesReviewsResources

The surprisingly low carbon mass in the debris disk around HD 32297

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

Published 2019-04-15Version 1

Gas has been detected in a number of debris disks. It is likely secondary in nature and produced by the colliding solids in these disks. Here, we used ALMA Band 8 to observe emission from neutral carbon at 492 GHz 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 $\sim$110 au with a FWHM of $\sim$80 au, and with a surprisingly small mass of $(3.5\pm0.2)\times10^{-3}$ M$_\oplus$. An order of magnitude estimate shows that such a mass can be produced by CO photo-dissociation in a time no longer than $10,000$ yr. We develop a simple evolutionary model to properly account for the reduction in CO photo-dissociation by CO self-shielding and shielding by neutral carbon, following the suggestion by Kral et al (2018). When adopting the commonly used intensity of the interstellar radiation field, to simultaneously reproduce the observed C$^0$ and the previously determined C$^{18}$O masses with our model, a high CO production rate by the debris disk is required, and that gas production started only $\sim$3000 yr ago around this star. By association, its dusty debris disk must also be similarly short-lived. We discuss various scenarios where our conclusion may fail. We conclude that the gas observed around HD 32297 is the result of a recent event, similar to the debris disk around $\beta$ Pictoris.

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