From scattered-light to millimeter emission: A global view of the Gyr-old system of HD 202628 and its eccentric debris ring
Abstract
We present a collection of new observations of the cold eccentric debris ring surrounding the Gyr-old solar-type star HD 202628 in scattered light with HST/STIS, at far-infrared wavelengths with Herschel/PACS and SPIRE, and at millimeter wavelengths with ALMA. Similar to the debris disk of Fomalhaut, the ring appears much narrower at millimeter wavelengths than at optical wavelengths, while its inner edge is found to be consistent between ALMA and HST data. Best fit to the dust parent ring seen with ALMA is found to have inner and outer edges 143.8±2.3 AU and 165.3±2.2 AU, respectively, an inclination of 57.5°±0.6 from face-on, and a position angle of 129.8°±0.7. The offset of the ring centre of symmetry from the star allows us to quantify its eccentricity to be e=0.08±0.03. This eccentric feature reveals itself as well in low resolution Herschel/PACS observations, under the form of a pericenter-glow. Upper limits on the gas mass provided by ALMA data allow us to exclude this narrow eccentric ring results from gas-solid interactions, hence confirming the presence of a distant belt-shaping eccentric perturber in this system. From the combination of the ALMA and the Herschel photometry, we retrieve a disk grain size distribution index of ∼-3.5, and therefore exclude in-situ formation of the inferred perturber, for which we provide new dynamical constraints. Another feature consistent across both ALMA and HST datasets is an emission enhancement in the SE direction, which cannot be explained by the overdensity expected at apocenter in eccentric debris disks, as the apocenter lies in NE direction. Finally, ALMA images show a source just interior to the ring, although we can not exclude it to be a background object at that stage. We cannot exclude either that this source is circumplanetary material surrounding the eccentric belt-shaper, in which case degeneracies between its mass and orbital parameters could be lifted, allowing us to characterize the mass and orbital properties of a mature planet on a wide orbit for the very first time.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23316322F