Resolving the multi-temperature debris disk around γ Doradus with Herschel




Broekhoven-Fiene, Hannah

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We present Herschel observations of the debris disk around γ Doradus (HD 27290, HIP 19893) from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free Reconnaissance in the Infrared/Submillimetre). The disk is well-resolved with PACS at 70, 100 and 160 micron and detected with SPIRE at 250 and 350 micron. The 250 micron image is only resolved along the disk's long axis. The SPIRE 500 micron 3 σ detection includes a nearby background source. γ Dor's spectral energy distribution (SED) is sampled in the submillimetre for the first time and modelled with multiple modified-blackbody functions to account for its broad shape. Two approaches are used, both of which reproduce the SED in the same way: a model of two narrow dust rings and a model of an extended, wide dust belt. The former implies the dust rings have temperatures of ~90 and ~40 K, corresponding to blackbody radii of 25 and 135 AU, respectively. The latter model suggests the dust lies in a wide belt extending from 15 to 230 AU. The resolved images, however, show dust extending beyond ~350 AU. This is consistent with other debris disks whose actual radii are observed to be a factor of 2 - 3 times larger than the blackbody radii. Although it is impossible to determine a preferred model from the SED alone, the resolved images suggest that the dust is located in a smooth continuous belt rather than discrete narrow rings. Both models estimate that the dust mass is 6.7 x 10^{-3} Earth masses and that fractional luminosity is 2.5 x 10^{-5}. This amount of dust is within the levels expected from steady state evolution given the age of γ Dor and therefore a transient event is not needed to explain the dust mass. No asymmetries that would hint at a planetary body are evident in the disk at Herschel's resolution. However, the constraints placed on the dust's location suggest that the most likely region to find planets is within 20 AU of the star.



planetary systems, Herschel Space Observatory, infrared/submillimetre astronomy, circumstellar disks, debris disks