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تسجيل مستخدم جديدThe Inner Debris Structure in the Fomalhaut Planetary System
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Kate Y. L. Su
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Fomalhaut plays an important role in the study of debris disks and small bodies in other planetary systems. The proximity and luminosity of the star make key features of its debris, like the water ice-line, accessible. Here we present ALMA cycle 1, 870 mu m (345 GHz) observations targeted at the inner part of the Fomalhaut system with a synthesized beam of 0.45x0.37 (~3 AU linear resolution at the distance of Fomalhaut) and a rms of 26 mu Jy/beam. The high angular resolution and sensitivity of the ALMA data enable us to place strong constraints on the nature of the warm excess revealed by Spitzer and Herschel observations. We detect a point source at the star position with a total flux consistent with thermal emission from the stellar photosphere. No structures that are brighter than 3sigma are detected in the central 15 AU x 15 AU region. Modeling the spectral energy distribution using parameters expected for a dust-producing planetesimal belt indicates a radial location in the range ~8-15 AU. This is consistent with the location where ice sublimates in Fomalhaut, i.e., an asteroid-belt analog. The 3sigma upper limit for such a belt is <1.3 mJy at 870 mu m. We also interpret the 2 and 8-13 mu m interferometric measurements to reveal the structure in the inner 10 AU region as dust naturally connected to this proposed asteroid belt by Poynting-Robertson drag, dust sublimation, and magnetically trapped nano grains.
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We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 $mu$Jy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform
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xcess emission in the close vicinity of Vega for the first time. The properties of the warm excess in Vega are further characterized with ancillary photometry in the mid infrared and resolved images in the far-infrared and submillimeter wavelengths. The Vega warm excess shares many similar properties with the one found around Fomalhaut. The emission shortward of ~30 um from both warm components is well described as a blackbody emission of ~170 K. Interestingly, two other systems, eps Eri and HR 8799, also show such an unresolved warm dust using the same approach. These warm components may be analogous to the solar systems zodiacal dust cloud, but of far greater. The dust temperature and tentative detections in the submillimeter suggest the warm excess arises from dust associated with a planetesimal ring located near the water-frost line and presumably created by processes occurring at similar locations in other debris systems as well. We also review the properties of the 2 um hot excess around Vega and Fomalhaut, showing that the dust responsible for the hot excess is not spatially associated with the dust we detected in the warm belt. We suggest it may arise from hot nano grains trapped in the magnetic field of the star. Finally, the separation between the warm and cold belt is rather large with an orbital ratio >~10 in all four systems. In light of the current upper limits on the masses of planetary objects and the large gap, we discuss the possible implications for their underlying planetary architecture, and suggest that multiple, low-mass planets likely reside between the two belts in Vega and Fomalhaut.
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