A new Herschel view of the young star T54: not a transitional disk?^⋆

¹ Herschel Science Centre, ESAC-ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
e-mail: lmatra@sciops.esa.int
² School of Physics, Trinity College Dublin, Dublin 2, Ireland
³ Centro de Astrobiología, INTA-CSIC, PO Box - Apdo. de correos 78, Villanueva de la Cañada, 28691 Madrid, Spain
⁴ Research and Scientific Support Department, ESTEC-ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁵ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁶ 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

Received: 28 September 2012
Accepted: 25 October 2012

Abstract

Context. Observations of transitional disks give us an understanding of the formation of planets and planetary systems such as our own. But care must be taken in identifying such sources: the higher spatial resolution of the Herschel Space Observatory provides a new view of the origin of the far-infrared and submillimeter excesses observed.

Aims. We review the nature of previously known transitional disks in the Chamaeleon I star-forming region with Herschel data.

Methods. We analyze Herschel PACS and SPIRE images of the young star T54, together with ancillary images. We also analyze its spectral energy distribution and indications from optical and mid-infrared spectroscopy.

Results. We detect extended emission in the PACS 70 μm image  ~6′′ off source at a position angle of 196° from T54. The emission detected at longer wavelengths (PACS 100, 160, SPIRE 250 and 350 μm) is also offset from the position of the star. This suggests that the excess observed in the far-infrared part of the SED is not fully associated with T54.

Conclusions.Herschel images show that the far-infrared excess seen in T54 is not due to a transitional disk but to extended emission southwest of the source. The object still shows point-like and now downscaled excess at mid-infrared wavelengths, but its origin cannot be constrained without higher spatial resolution data. However, different indications point towards an evolved disk or extended unresolved emission close to the source.