Abstract

The dispersal of primordial gas and dust from debris disks sets the timescale for giant planet formation and is closely intertwined with our understanding of the physical processes that shape planetary systems. While it is generally assumed that molecular gas dissipates before the debris disk stage, the nearby A star 49 Ceti is one of only a handful of systems known to host a tenuous, second-generation debris disk while still retaining a substantial molecular gas reservoir. It is the closest, best-studied, and oldest of the group of objects, with the most recent estimates placing its age at 40 Myr. We present ALMA observations that spatially resolve the outer dusty debris belt for the first time, and improve upon previous molecular gas observations by an order of magnitude in both sensitivity and spectral resolution. A combined analysis of the two CO transitions probed by ALMA and SMA provide new measurements of the gas temperature and mass, which allows us to infer the lifetime of the molecular gas. We also examine the disk kinematics in exquisite detail, following up on deviations from Keplerian rotation hinted at by previous SMA observations. We place the 49 Ceti system in context by comparing it with the other known gas-rich debris disks. We discuss the implications of the new ALMA observations for the origins of the gas in these systems, in particular whether they imply a primordial or second-generation (i.e. cometary) source.

Presentation

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