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Published July 1, 2013 | Submitted + Published
Journal Article Open

Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk

Abstract

We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the "Gas in Protoplanetary Systems" (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 μm; 49 Cet is significantly extended in the 70 μm image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O I] 63 μm and [C II] 158 μm. The C II line was detected at the 5σ level—the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the O I line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C II emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.

Additional Information

© 2013 American Astronomical Society. Received 2012 December 21; accepted 2013 May 12; published 2013 June 17. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Support for this work was provided by the NASA Herschel Science Center through an award issued by JPL/Caltech. A. Roberge also acknowledges support by the Goddard Center for Astrobiology, part of the NASA Astrobiology Institute. J.-C. Augereau thanks the CNES-PNP for financial support. C. Eiroa, G. Meeus, and B. Montesinos were partly supported by Spanish grant AYA 2011-26202. Facilities: Herschel (PACS, SPIRE), Spitzer (IRS, MIPS), HIPPARCOS, CTIO:2MASS, WISE, IRAS, JCMT, SMA

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Submitted - 1305.2894v1.pdf

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