Sunday, October 16, 2016

Tau Ceti's Debris Disk is NOT Like the Solar System's Kuiper Belt

ALMA Observations of the Debris Disk of Solar Analogue Tau Ceti


MacGregor et al


We present 1.3 mm observations of the Sun-like star τ Ceti with the Atacama Large Millimeter/submillimeter Array (ALMA) that probe angular scales of ∼1'' (4 AU). This first interferometric image of the τ Ceti system, which hosts both a debris disk and possible multiplanet system, shows emission from a nearly face-on belt of cold dust with a position angle of 90∘ surrounding an unresolved central source at the stellar position. To characterize this emission structure, we fit parametric models to the millimeter visibilities. The resulting best-fit model yields an inner belt edge of 6.2+9.8−4.6 AU, consistent with inferences from lower resolution, far-infrared Herschel observations. While the limited data at sufficiently short baselines preclude us from placing stronger constraints on the belt properties and its relation to the proposed five planet system, the observations do provide a strong lower limit on the fractional width of the belt, ΔR/R>0.75 with 99% confidence. This fractional width is more similar to broad disks such as HD 107146 than narrow belts such as the Kuiper Belt and Fomalhaut. The unresolved central source has a higher flux density than the predicted flux of the stellar photosphere at 1.3 mm. Given previous measurements of an excess by a factor of ∼2 at 8.7 mm, this emission is likely due to a hot stellar chromosphere.

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