Abstract

The advent of ALMA has recently delivered detection of CO gas in debris disks, which were thought to be predominantly gas-poor objects. Its origin is still unconstrained: is it the product of collisions between cometary bodies? Does it represent a gaseous remnant of protoplanetary disks? In order to understand the role played by gas in both the disk dynamics and the planet formation process itself, searching for its presence in such relatively old systems is needed. We therefore analysed ALMA Cycle-0 data of the nearby Fomalhaut debris ring searching for CO J=3-2 emission, and defined a rigorous way to achieve detection and model ALMA line data for debris disks. In the Fomalhaut case, no emission is detected. We build a simple model to obtain an upper limit estimate on the total mass of CO in the ring, and show that the commonly adopted assumption of local thermodynamic equilibrium (LTE) should not hold at low densities typical of debris disks. This implies that determination of gas mass from CO line emission has to take into account the local gas density, as well as its temperature. With this in mind, we set constraints on the CO mass present in the Fomalhaut ring, and discuss possible improvements through future ALMA observations.

Presentation

Poster