Tuesday, 11 June 2013

The debris disk of 49 Ceti.

49 Ceti is a bright star in the constellation of Cetus, 194 light years from the Earth, with a mass slightly over 2 times that of the Sun. It is a young star, only about 40 million years in age, and is surrounded by a large debris disk, which has been shown to be rich in Carbon Monoxide. In an system this old it would generally be assumed that such a disk was made of comet-type bodies, with the detectable free Carbon Monoxide being the shed from these either in cometary halos and or as a result of collisions, but the shear volume of material in the 49 Ceti debris disk (roughly 400 times the mass of the Earth) has led some astronomers to conclude that this is unlikely, and that the disk may represent residual material left over from the formation of the system, with important implications for our understanding of how stars and planetary systems form.

In a paper published on the online arXiv database at Cornell University Library on 13 May 2013, a team of scientists led by Aki Roberge of the Exoplanets & Stellar Astrophysics Laboratory at NASA's Goddard Space Flight Center, describe the results of a study of the 49 Ceti system by the Herschel Space Observatory, which scanned the system at a number of different infrared wavelengths, in order to gain a better understanding of the system.

Herschel image of the 49 Ceti showing the intensity of electromagnetic radiation in the 70 μm wavelength (mid-infrared) band. Roberge et al. (2013).

Roberge et al. conclude that 49 Ceti actually has two debris rings, one with an inner edge at around 11 AU (11 times the distance at which the Earth orbit's the Sun), with a mean temperature of about 175 K and the other at around 89 AU with a mean temperature of 62 K. These differentiated disks do not appear to be remnant material from the formation of the system; comets and comet debris is a far more likely explanation.


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