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

1. A new Herschel view of the young star T54: not a transitional disk? • L. Matrà1,2, B. Merín1, C. Alves de Oliveira1, N. Huélamo3, Á. Kóspál4, N. L.J. Cox5, Á. Ribas1,3, • E. Puga1, R. Vavrek1, P. Royer5, T. Prusti4, G. L. Pilbratt4, and P. André6 • 1 ESA – ESAC Herschel Science Centre, 2 TCD - School of Physics, 3 Centro de Astrobiología, 4 ESA - ESTEC, 5 K.U. Leuven, 6 Saclay SED analysis: downscaled excess The SED of T54 nowpresents a reduction in the excessat the source position: the amount of materialpresent in itscircumstellarenvironmentisscaled down significantly. Introduction Transitional disks (TDs) are circumstellar disks that present inner clearings or gaps induced by different physical processes, which cause a wide range of spectral energy distribution (SED) properties to be observed. This makes TDs not easy to disentangle from sources of different nature, such as systems with nebulosity in their surroundings. Herschel, with its high spatial resolution, can greatly serve the purpose of detecting contamination at far-IR and sub-mm wavelengths. The young T54 binary system, in the Chamaeleon I star-forming region, was classified as a transitional/circumbinary disk, but new Herschel images revealed something unexpected. IC 348 Perseus Rho Ophiuchi Herschel and ancillary images NGC 1333 Perseus Serpens Core Figure 2: SED of T54, with the blue solid triangles representing Herschel fluxes not attributed to T54 but to off-source extended emission. The dashed line is a NEXTGEN stellar model for spectral type G8. The red line is the Spitzer IRS spectrum. The green solid line represents a T = 94 K blackbody curve fit to the mid-IR fluxes. We obtain a stellar luminosity of ~3.66 L that with a temperature of 5520 K from Kim et al. (2009) leads to a mass of approximately 1.5 M and an age between 3 and 10 Myr. The blackbody fit (green line in Fig. 2) to remaining excess yields a dust temperature of ~94 K and a fractional luminosity value of 0.005. Conclusions • A significant part of the excess in the T54 systemdoes not originate from a transitional disk at the source position, but to extended emission offset from it, likely associated with the small reflection nebula BRAN341E (Brand et al. 1986). • Regarding the remaining excess, T54 shows no silicate feature at 10 μm and PAH emission at 11.3 μm, setting it among other examples of dubious disks. One such example (see Fig. 3) is the strikingly similar system DoAr 21. Figure 1: The T54 (northern cross) system at different wavelengths. North is up, east is left. Herschel images show extended emission offset from it, resolved at 70 μm (arrows) and causing most of the emission at longer wavelengths (dashed ellipse). This is not observed at shorter wavelengths. The southern cross represents the unrelated object 2MASS J11124076-7722378. The diameter of the circles in the bottom left of each image represents the FWHM of the different PSFs. Figure 3: High-resolution images of DoAr 21 from Jensen et al. 2009. Analogous extended emission at these scales could explain the remaining unresolved excess in T54. Surprisingly, extendedemissionisdiscovered and spatiallyresolved in the PACS 70 μm image ~6’’ south-west of the system. In longerwavelength images, most of the fluxisshown to originate from it and not from the source position. Inspectionof optical, near- and mid-infrared images of T54 (up to 24 μm) shows no counterpart for thisextendedemissionatshorterwavelengths. • However, if a disk is to be present, itwouldfall under the definition of debris disk from Wyatt (2008). In suchpicture, the calculated disk radiuswouldmake T54 an interesting case of an evolved disk around a single binary component. Get the full paper!Matrà et al. (2012), A&A, in press. http://arxiv.org/abs/1210.7679 Luca Matrà: luca.matra@sciops.esa.int Figure 4: Possible configuration if an evolved disk was to be present in the T54 binary system (not to scale) Acknowledgements This work was partially made possible thanks to the ESA Trainee and Research Fellowship programs at ESAC (Spain). Support was also provided by the Enterprise Ireland Space Education Program, and by the Belgian Federal Science Policy Office via the PRODEX Programme of ESA.