A Radially Broad Collisional Cascade in the Debris Disk of γ Ophiuchi Observed by JWST

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Abstract The A1V star γ Oph, at a distance of 29.7 pc, is known from Spitzer imaging to host a debris disk with a large radial extent and from its spectral energy distribution to host inner warm dust. We imaged γ Oph with the James Webb Space Telescope (JWST)/Mid-InfraRed Instrument at 15 and 25.5 μ m, revealing smooth and radially broad emission that extends to a radius of at least 250 au at 25.5 μ m. In contrast to JWST findings of an inner small-grain component with distinct ringed structures in Fomalhaut and Vega, the mid-infrared radial profile combined with prior Atacama Large Millimeter/submillimeter Array imaging suggests a radially broad steady-state collisional cascade with the same grain size distribution throughout the disk. This further suggests that the system is populated by a radially broad planetesimal belt from tens of astronomical units or less to well over 200 au, rather than a narrow planetesimal belt from which the observed dust is displaced to appear broad. The disk is also found to be asymmetric, which could be modeled by a stellocentric offset corresponding to a small eccentricity of ∼0.03. Such a disk eccentricity could be induced by a mildly eccentric <10 M Jup giant planet outside 10 au, or a more eccentric companion up to stellar mass at a few astronomical units, without producing a resolvable radial gap in the disk.

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