[O I] disk emission in the Taurus star-forming region

¹ Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
e-mail: giambattista.aresu@gmail.com
² INAF, Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius, Italy
³ Leiden Observatory, Leiden University, PO Box, 2300 RA Leiden, The Netherlands
⁴ SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK
⁵ UJF-Grenoble, CNRS-INSU, Institute de Planétologie et d’Astrophysique (IPAG), UMR, 5274, France
⁶ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁷ UMI-FCA (UMI 3386), CNRS/INSU France and Universidad de Chile, 1058 Santiago, Chile
⁸ University of Vienna, Department of Astronomy, Türkenschanzstrasse 17, 1180 Vienna, Austria

Received: 6 August 2013
Accepted: 11 February 2014

Abstract

Context. The structure of protoplanetary disks is thought to be linked to the temperature and chemistry of their dust and gas. Whether the disk is flat or flaring depends on the amount of radiation that it absorbs at a given radius and on the efficiency with which this is converted into thermal energy. The understanding of these heating and cooling processes is crucial for providing a reliable disk structure for interpreting dust continuum emission and gas line fluxes. Especially in the upper layers of the disk, where gas and dust are thermally decoupled, the infrared line emission is strictly related to the gas heating/cooling processes.

Aims. We aim to study the thermal properties of the disk in the oxygen line emission region and to investigate the relative importance of X-ray (1–120 Å) and far-UV radiation (FUV, 912–2070 Å) for the heating balance there.

Methods. We use [O i] 63 μm line fluxes observed in a sample of protoplanetary disks of the Taurus/Auriga star-forming region and compare it to the model predictions presented in our previous work. The data were obtained with the PACS instrument on board the Herschel Space Observatory as part of the Herschel open time key program GAS in Protoplanetary diskS (GASPS).

Results. Our theoretical grid of disk models can reproduce the [O i] absolute fluxes and predict a correlation between [O i] and the sum L_X + L_FUV. The data show no correlation between the [O i] line flux and the X-ray luminosity, the FUV luminosity or their sum.

Conclusions. The data show that the FUV or X-ray radiation has no notable impact on the region where the [O i] line is formed. This contrasts with what is predicted from our models. Possible explanations are that the disks in Taurus are less flaring than the hydrostatic models predict and/or that other disk structure aspects that were left unchanged in our models are important. Disk models should include flat geometries, varying parameters such as outer radius, dust settling, and the dust-to-gas mass ratio, which might play an equally important role for the [O i] emission. To improve statistics and draw more robust conclusions on the thermal processes that dominate the atmosphere of protoplanetary disks surrounding T Tauri stars, more L_FUV and L_X measurements are needed. High spatial and spectra resolution data is required to disentangle the fraction of [O i] flux emitted by the disk in outflow sources.