The seven known Radio-Quiet Isolated Compact Objects (RICOs) are characterized by a blackbody-like spectral energy distribution (kT ~ 100 eV) in the X-rays, and excess emission above the extrapolated Rayleigh-Jeans tail at long wavelengths. Isothermal heavy element atmospheres can naturally explain the broadband spectral energy distributions and the optical excesses. However, the two brightest RICOs do not differ significantly from a continuous spectral energy distribution - there are no absorption lines or edges, contrary to expectations for stars with gaseous atmospheres. Solid surface models can explain the absence of narrow features, but require fine tuning to reproduce the optical fluxes. We will discuss our explorations of modified stellar atmospheres - atmospheres with non-zero pressures at the top, or extended atmospheres - as a solution to the observed lack of spectral features. (Work performed in collaboration with Jose Pons)
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