Identification of transitional disks in Chamaeleon with Herschel^⋆,⋆⋆

¹ ESAC-ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid Spain
e-mail: aribas@cab.inta-csic.es
² Centro de Astrobiología, INTA−CSIC, PO Box − Apdo. de correos 78, Villanueva de la Cañada, Madrid 28691, Spain
³ Ingeniería y Servicios Aeroespaciales−ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴ Herschel Science Centre, ESAC−ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁵ NASA Herschel Science Center, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁶ Research and Scientific Support Department, ESTEC−ESA, PO Box 299, 2200 AG, Noordwijk, The Netherlands
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748, Garching bei München, Germany
⁸ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁹ Laboratoire AIM Paris – Saclay, CEA/DSM – CNRS – Université Paris Diderot, IRFU, Service d’Astrophysique, Centre d’Études de Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
¹⁰ School of Physics, Trinity College Dublin, Dublin 2, Ireland

Received: 19 December 2012
Accepted: 11 March 2013

Abstract

Context. Transitional disks are circumstellar disks with inner holes that in some cases are produced by planets and/or substellar companions in these systems. For this reason, these disks are extremely important for the study of planetary system formation.

Aims. The Herschel Space Observatory provides an unique opportunity for studying the outer regions of protoplanetary disks. In this work we update previous knowledge on the transitional disks in the Chamaeleon I and II regions with data from the Herschel Gould Belt Survey.

Methods. We propose a new method for transitional disk classification based on the WISE 12 μm − PACS 70 μm color, together with inspection of the Herschel images. We applied this method to the population of Class II sources in the Chamaeleon region and studied the spectral energy distributions of the transitional disks in the sample. We also built the median spectral energy distribution of Class II objects in these regions for comparison with transitional disks.

Results. The proposed method allows a clear separation of the known transitional disks from the Class II sources. We find six transitional disks, all previously known, and identify five objects previously thought to be transitional as possibly non-transitional. We find higher fluxes at the PACS wavelengths in the sample of transitional disks than those of Class II objects.

Conclusions. We show the Herschel 70 μm band to be a robust and efficient tool for transitional disk identification. The sensitivity and spatial resolution of Herschel reveals a significant contamination level among the previously identified transitional disk candidates for the two regions, which calls for a revision of previous samples of transitional disks in other regions. The systematic excess found at the PACS bands could be either a result of the mechanism that produces the transitional phase, or an indication of different evolutionary paths for transitional disks and Class II sources.