Based in part on observations made with ESO telescopes at Paranal and APEX Observatories, under ESO programs 083.C-0459(A), 085.C-0571(D), 083.F-0162(A). This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory. AbstractTransition 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 SED morphology, have disk masses ranging from < ∼ 1 to 10 M JUP and accretion rates ranging from < ∼ 10 −11 to 10 −7.7 M yr −1 . Of the 17 bona fide transition disks in our sample, 3, 9, 3, and 2 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 AGB 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.. Subject headings: accretion disk -binaries: general -line: identification -planetary systems: protoplanetary disks -stars: pre-main sequence a b " · · · " implies that the signal to noise in this region of the spectrum is too low to measure the width or establish the presence of the line c "-1" implies that Hα is seen in absorption. d "<" implies upper limits value (3 σ) e Sources # 1, 3, 4, and 9 have been identified as binaries by WFI observations . The binary nature of source # 14 was discovered using speckle interferometry at the NTT (La Silla) revealing a projected separation of 0.132 ± 0.009 (Köhler et al. 2008). Sources # 11, 13 are triple systems with tight binary components consistent with two equally bright objects and a projected separation of ∼0.05 .f The spectral type derived by us is significantly later than the previously obtained value. We consider our estimate of M5.25 based on a high quality optical spectrum to be more reliable than the rather rough guess of Merín et...

As part of an ongoing program aiming to characterize a large number of Spitzer -selected transition disks (disks with reduced levels of near-IR and/or mid-IR excess emission), we have obtained (sub)millimeter wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 31 transition objects located in the Perseus, Taurus, and Auriga molecular clouds. We use these ground-based data to estimate disk masses, multiplicity, and accretion rates in order to investigate the mechanisms potentially responsible for their inner holes. Following our previous studies in other regions, we combine disk masses, accretion rates and multiplicity data with other information, such as SED morphology and fractional disk luminosity to classify the disks as strong candidates for the following categories: grain-growth dominated disks (7 objects), giant planet-forming disks (6 objects), photoevaporating disks (7 objects), debris disks (11 objects), and cicumbinary disks (1 object, which was also classified as a photoeavaporating disk). Combining our sample of 31 transition disks with those from our previous studies results in a sample of 74 transition objects that have been selected, characterized, and classified in an homogenous way. We discuss this combined high-quality sample in the context of the current paradigm of the evolution and dissipation of protoplanetary disks and use its properties to constrain different aspects of the key processes driving their evolution. We find that the age distribution of disks that are likely to harbor recently formed giant planets favors core accretion as the main planet formation mechanism and a ∼2-3 Myr formation timescale. Subject headings: circumstellar matter -binaries: general -planetary systems: protoplanetary disks -stars: pre-main sequence -4are still quite massive (Najita et al. 2007). Even though the broadest aspects of disk evolution summarized above are relatively well established (see Williams & Cieza, 2011 for a recent review on protoplanetary disks and their evolution), we are still far from developing a comprehensive disk evolution theory, for which additional observational constraints are much needed. The so-called "transition" objects (broadly defined as disks with inner opacity holes) are particularly useful disk evolution laboratories as they are the systems where the key physical processes mentioned above have the clearest observational signatures. This is so simply because grain growth, photevaporation, and dynamical clearing all result in reduced levels of near-and/or mid-IR excess emission, which is the defining feature of transition objects.This paper is the third part of a series from an ongoing project aiming to characterize ∼100 Spitzer -selected transition disks located in nearby star-forming regions. This coordinated project has two main goals: 1) provide observational constraints on the evolution of primordial disks, their dissipation, and the primordial to debris disk transition, and 2) identify systems with stro...