DUNES: DUst around NEarby Stars
A Herschel Key Programme

             TRANSPORT-DOMINATED DEBRIS DISKS:
          PROPERTIES AND IMPLICATIONS FOR HERSCHEL

         Alexander V. Krivov, Christian Vitense, Martin Reidemeister,
         Jonathan Marshall, Carlos Eiroa, Jean-Charles Augereau,
         and the DUNES team

Most of the debris disks discovered so far are believed to be collision-dominated. This means that visible dust must be removed (and continually replenished) by collisions before it can be transported inward by Poynting-Robertson and stellar wind drag and get lost in the inner system. With Herschel, we are starting to enter the realm of transport-dominated disks where the opposite is true. One obvious class of transport-dominated disks are tenuous disks with fractional luminosities well below ~1e-5, exemplified by the presumed Kuiper belt dust disk in the solar system. Another, less obvious, class of transport-dominated disks includes disks around late-type stars, many of which are also targeted by Herschel. Since radiation pressure they exert on the dust grains is too weak, the radiation pressure blowout limit no longer exists; on the other hand, they possess strong stellar winds leading to strong drag forces. We will demonstrate that these two circumstances together make disks transport-dominated even at high fractional luminosities, on the order of ~1e-3. An example is the disk of epsilon Eridani. We will show that properties of transport-dominated debris disks in either category are different from those of collision-dominated ones, and will discuss implications for Herschel.