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

¹ Centro de Astrobiología (INTA-CSIC); LAEFF, P.O. Box 78, 28691 Villanueva de la Cañada, Spain
e-mail: nhuelamo@cab.inta-csic.es
² Laboratoire d’Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
³ Astronomy Dpt., 601 Campbell Hall, UC Berkeley, CA 94720 Berkeley, USA
⁴ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁵ Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, 18080 Granada, Spain
⁶ Calar Alto Observatory, Centro Astronómico Hispano Alemán, Almería, Spain
⁷ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Vitacura, Santiago, Chile
⁸ Atacama Large Millimeter/Submillimeter Array, Joint ALMA Office, Av. Apoquindo 3650, Piso 18, Las Condes, Santiago, Chile
⁹ Max-Planck-Institut für Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany

Received: 10 June 2008
Accepted: 27 August 2010

Abstract

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, R_in ≤ 0.05 AU, which is very close to the dust sublimation radius, and the maximum size of the dust grains, a_max ≥ 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.