Transition disk objects are pre-main-sequence stars with little or no near-IR
excess and significant far-IR excess, implying inner opacity holes in their
disks. Here we present a multifrequency study of transition disk candidates
located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius.
Complementing the information provided by Spitzer with adaptive optics (AO)
imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy
(Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and
accretion rate for each object in our sample in order to identify the mechanism
potentially responsible for its inner hole. We find that our transition disks
show a rich diversity in their spectral energy distribution morphology, have
disk masses ranging from lsim1 to 10 M JUP, and accretion rates ranging from
lsim10-11 to 10-7.7 M \odot yr-1. Of the 17 bona fide transition disks in our
sample, three, nine, three, and two objects are consistent with giant planet
formation, grain growth, photoevaporation, and debris disks, respectively. Two
disks could be circumbinary, which offers tidal truncation as an alternative
origin of the inner hole. We find the same heterogeneity of the transition disk
population in Lupus III, IV, and Corona Australis as in our previous analysis
of transition disks in Ophiuchus while all transition disk candidates selected
in Lupus V, VI turned out to be contaminating background asymptotic giant
branch stars. All transition disks classified as photoevaporating disks have
small disk masses, which indicates that photoevaporation must be less efficient
than predicted by most recent models. The three systems that are excellent
candidates for harboring giant planets potentially represent invaluable
laboratories to study planet formation with the Atacama Large
Millimeter/Submillimeter Array.Comment: 62 pages, 13 figure
