The Nature of Transition Circumstellar Disks I :The Ophiuchus Molecular Cloud

LUCAS A. CIEZA; MATTHIAS R. SCHREIBER; GISELA A. ROMERO; MARCELO D. MORA; BRUNO MERIN; JONATHAN J. SWIFT; MARIANA ORELLANA; JONATHAN P. WILLIAMS; PAUL M. HARVEY; NEAL J. EVANS II

ASTROPHYSICAL JOURNAL

IOP Publishing

Año: 2010 vol. 712 p. 925 - 941

0004-637X

We have obtained millimeter wavelength photometry, high-resolution optical spectroscopy and adaptive optics near-infrared imaging for a sample of  26  Spitzer-selected transition circumstellar disks. All of our targets are located in the Ophiuchus molecular cloud  (d $sim$125 pc) and have Spectral Energy Distributions (SEDs) suggesting  the presence of inner opacity holes.We use these ground-based data to estimate  the disk mass,  multiplicity, and accretion rate for each object in our sample in order to  investigate the mechanisms potentially responsible for  their inner holes. We find that transition disks are a heterogeneous group of objects, with disk masses ranging from <0.6 to 40 MJUP and accretion rates ranging from <1.E-11 to 1.E-7 M sun per yr,   but most tend to have much lower masses and accretion rates than ``full disks´´ (i.e., disks without opacity holes). Eight of our targets have stellar companions: 6 of them are binaries and the other 2 are triple  systems. In four cases,  the  stellar companions are close enough to suspect they are responsible for the inferred inner holes. We find that  9 of our 26 targets have low disk mass ($<$ 2.5 MJUP) and negligible accretion ($<$ 10$^{-11}$ M$_{odot}$yr$^{-1}$), and are thus consistent with photoevaporating (or photoevaporated) disks. Four of these 9 non-accreting objects have fractional disk luminosities $<$ 10$^{-3}$ and could already be in a debris disk stage. Seventeen of our transition disks are accreting. Thirteen of these  accreting objects are consistent with  grain growth.The remaining 4  accreting objects have SEDs suggesting the presence of sharp inner holes, and thus are  excellent candidates for harboring giant planets.