English: Abstract:

We present images of the Vega planetary debris disk obtained at 15.5, 23, and 25.5 microns with the Mid-Infrared Instrument (MIRI) on JWST. The debris system is remarkably symmetric and smooth, and centered accurately on the star. There is a broad Kuiper-belt-analog ring at 80 to 170 au that coincides with the planetesimal belt detected with ALMA at 1.34 mm. The interior of the broad belt is filled with warm debris that shines most efficiently at mid-infrared along with a shallow flux dip/gap at 60 au from the star. These qualitative characteristics argue against any Saturn-mass planets orbiting the star outside of about 10 au assuming the unseen planet would be embedded in the very broad planetesimal disk from a few to hundred au. We find that the distribution of dust detected interior to the broad outer belt is consistent with grains being dragged inward by the Poynting-Robertson effect. Tighter constraints can be derived for planets in specific locations, for example any planet shepherding the inner edge of the outer belt is likely to be less than 6 Earth masses. The disk surface brightness profile along with the available infrared photometry suggest a disk inner edge near 3-5 au, disconnected from the sub-au region that gives rise to the hot near-infrared excess. The gap between the hot, sub-au zone and the inner edge of the warm debris might be shepherded by a modest mass, Neptune-size planet.

Figure 1:

The bottom row shows the three MIRI images of the Vega debris system at the same orientation and field of view. Slight artifacts from the coronagraph persist in the 15.5 μm image, while it and the 23 μm image have the central region eliminated by the coronagraphs; the 25.5 μm image is missing the core because of saturation. The millimeter disk emission detected by ALMA (Matr`a et al. 2020) is superimposed as contours on the 25.5 μm image for comparison. The top panel is the enlarged disk image at 25.5 μm with the major disk features labeled for reference as they are discussed further in this paper. These features are: (1) the halo, visible at 25.5 μm to a radius of ∼33′′ (∼250 au); (2) the outer disk (Kuiper-belt analog) extending from ∼10′′ to 22′′ (∼78 to ∼170 au) and the dominant feature in the ALMA image at 1.34 mm; (3) the inner disk extending from the inner edge of the outer disk to as close as the images penetrate to the star; and (4) the dip in surface brightness of the inner disk from ∼5′′ to 10′′ (∼40−78 au).