Multi-wavelength study of the disk around the very low-mass star Par-Lup3-4

Huélamo, N.; Bouy, H.; Pinte, C.; Ménard, F.; Duchêne, G.; Comerón, F.; Fernández, M.; Barrado, D.; Bayo, A.; de Gregorio-Monsalvo, I.; Olofsson, J.
Astronomy and Astrophysics, Volume 523, id.A42, 9 pp.


Context. Par-Lup3-4 is a very low-mass star (spectral type M5) in the Lupus III star-forming region. It shows spectroscopic evidence of accretion and mass-loss. In the optical and near-infrared, the object is underluminous by ≈4 mag when compared to objects of similar mass in the same association.
Aims: The aim of this work is to characterize the circumstellar environment of Par-Lup3-4 to better understand the origin of its underluminosity.
Methods: We have analyzed high angular resolution near-IR observations and searched for extended emission from a disk and/or an envelope. We have studied the spectral energy distribution (SED) of the target from the optical to the sub-millimeter regime, and compared it to a grid of radiative transfer models of circumstellar disks. Since the target is strongly variable, we modeled two different near-infrared datasets.
Results: The SED of Par-Lup3-4 resembles that of objects with edge-on disks seen in scattered light, that is, a double peaked-SED and a dip at ~10 μm. The diffraction-limited infrared observations do not show obvious extended emission, allowing us to put an upper limit of ~20 AU to the disk outer radius. Par-Lup3-4 is probably in a Class II (rather than a Class I) evolutionary stage, which is indicated by the lack of extended emission together with the non detection of a strong 9.8 μm silicate in absorption. This last feature is indeed seen in emission. We fitted the whole SED of Par-Lup3-4 with a single disk model. Our modeling predicts a disk inclination of 81° ± 6°, which agrees well with previous estimates, and provides a natural explanation for the under-luminosity of the target. The detection of the silicate feature in emission at such a high inclination might be related to a more complex disk structure (e.g. asymmetries, inhomogeneities) than the one assumed here. Our analysis allows us to put constraints on the disk inner radius, Rin ≤ 0.05 AU, which is very close to the dust sublimation radius, and the maximum size of the dust grains, amax ≥ 10 μm, which indicates that dust processing has already taken place in Par-Lup3-4. Some of the derived disk parameters vary depending on the modeled near-infrared data-set, which emphasizes the importance of taking variability into account when modeling the SED of young stellar objects.

Based on observations obtained at the European Southern Observatory using the Very Large Telescope in Cerro Paranal, Chile, under programs 381.C-0283(A) and 71.C-0429(B).