UV Spectroscopy of Star-Grazing Comets within the 49 Ceti Debris Disk

Abstract

We present analysis of time-variable, shifted absorption features in far-UV spectra of the unusual 49 Ceti debris disk. This nearly edge-on disk is one of the brightest known, and is one of the very few containing detectable amounts of circumstellar gas as well as dust. In our two visits of Hubble Space Telescope STIS spectra, variable absorption features are seen on the wings of lines arising from C II and C IV, but not for any of the other circumstellar absorption lines. Similar variable features have long been seen in spectra of the well-studied $\beta$ Pictoris debris disk and attributed to the transits of star-grazing comets. We calculate the velocity ranges and apparent column densities of the 49 Cet variable gas, which appears to be moving at velocities of tens to hundreds of km s${}^{-1}$ relative to the central star. The velocities of the gas in the redshifted variable event in Visit 2 show that the maximum distances of the infalling gas at the time of transit are about 0.05 to 0.2 AU from the central star. A preliminary attempt at a composition analysis of the redshifted event suggests that the C/O ratio in the infalling gas may be super-solar, as it is in the bulk of the stable disk gas.

6 pages, 7 figures accepted to ApJ, figure 7 updated to most recent version

References in corpus (3)

• A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti
• Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk
• Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk

Cited by in corpus (12)

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• First scattered-light images of the gas-rich debris disk around 49 Ceti
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• A multi-wavelength study of the debris disc around 49 Cet
• Curves of growth for transiting exocomets: Application to Fe II lines in the Beta Pictoris system
• Comets in UV
• Population of excited levels of Fe+, Ni+ and Cr+ in exocomets gaseous tails
• A Radiatively Driven Wind from the eta Tel Debris Disk
• High resolution ALMA observation of the ${}^{12}$CO(3-2) and 350 GHz continuum emissions of the debris disc of 49 Ceti
• Search for exocomets transits in Kepler light curves: Ten new transits identified
• Transit distances and composition of low-velocity exocomets in the $\beta$ Pic system