A protocometary cloud around HR 4796A?

We report both ROSAT observations and ground-based 10.8 mu m imaging of the wide binary HR 4796, which consists of a main-sequence A-type star with a large amount of circumstellar dust, HR 4796A, and, at a separation of 7." 7, a pre-main-sequence M-type companion, HR 4796B. From the ROSAT data, we find that the X-ray emission is centered on HR 4796B, with L-x/L-bol approximate to 3 x 10(-4). The 10.8 mu m flux, which arises from HR 4796A, displays an excess over the photospheric emission of 0.08 +/- 0.02 Jy, a result consistent with the previous characterization of the emission from the circumstellar dust in the wavelength range 12 mu m less than or equal to lambda less than or equal to 100 mu m as a 110 K blackbody. The Hipparcos data can be used to argue that the three main-sequence A-type stars in the Bright Star Catalogue with L-IR/L-bol > 10(-3) (HR 4796A, beta Pic, and 49 Cet) all have low luminosities for their colors. We argue that approximately 20% of all A-type stars pass through an early phase where they possess an amount of circumstellar dust comparable to that found around HR 4796A or beta Pie. In order to explain the result that the grain emission can be approximated by a 110 K blackbody, we propose that the circumstellar grains are largely composed of ice particles with a typical radius near 100 mu m, and that they sublimate rapidly when they are closer than similar to 35 AU to HR 4796A. This swarm of ice particles might be a protocometary cloud.