ICE LINES IN CIRCUMBINARY PROTOPLANETARY DISKS

I examine the position of the ice line in circumbinary disks heated by steady mass accretion and stellar irradiation and compare with the critical semimajor axis, interior to which planetary orbits are unstable. There is a critical binary separation, dependent on the binary parameters and disk properties, for which binaries with separations larger than this critical value have ice lines that lie interior to the boundary of stability. For an equal-mass binary comprised of 1 M-circle dot components, this critical separation is approximate to 1.04 AU, and scales weakly with mass accretion rate and Rosseland mean opacity (alpha [(M) over dot(kappa R)](2/9)). Assuming a steady mass accretion rate of (M) over dot similar to 10(-8) M-circle dot yr(-1) and a Rosseland mean opacity of kappa(R) similar to 1 cm(2) g(-1), I show that greater than or similar to 80% of all binary systems with component masses M-* less than or similar to 2.0 M-circle dot have ice lines that lie interior to the critical semimajor axis. This suggests that rocky planets should not form in these systems, a prediction which can be tested by looking for planets around binaries with separations larger than the critical separation with Kepler (difficult) and with microlensing.