Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk

TL;DR

This study analyzes the volatile-rich circumstellar gas in the 49 Ceti debris disk using Hubble UV spectra, revealing a gas composition rich in carbon but lacking CO absorption, indicating a unique volatile environment.

Contribution

First detailed UV spectroscopic analysis of 49 Ceti's debris disk revealing its volatile-rich gas composition and unusual absence of CO absorption.

Findings

High C/Fe ratio indicating volatile-rich gas

Absence of CO absorption along the line-of-sight

Presence of atomic lines from circumstellar gas

Abstract

We present Hubble Space Telescope STIS far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing sub-mm CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight CI column density, estimated the total carbon column density, and set limits on the OI column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of Beta Pictoris.