Herschel-PACS observations of [OI] and H2O in Chamaeleon II⋆
Kapteyn Astronomical Institute, University of Groningen,
PO Box 800,
2 Depto. de Física Teórica, Fac. de Ciencias, UAM Campus Cantoblanco, 28049 Madrid, Spain
3 European Space Astronomy Centre (ESA), PO Box 78, 28691 Villanueva de la Cañada, Spain
4 Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
5 Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
6 Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822, USA
7 Centro de Astrobiología (INTA–CSIC) – Depto. Astrofísica, POB 78, ESAC Campus, 28691 Villanueva de la Cañada, Spain
8 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
9 University of Hawaii, Department of Physics and Astronomy, 2505 Correa Rd. Honolulu, Hawaii 96822, USA
10 Astronomy Department, University of California, Berkeley, CA 94720-3411, USA
11 University Grenoble Alpes, IPAG, 38000 Grenoble, France
12 CNRS, IPAG, 38000 Grenoble, France
13 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
14 ALMA, Avda Apoquindo 3846, Piso 19, Edificio Alsacia, Las Condes, Santiago, Chile
Received: 27 June 2014
Accepted: 11 November 2014
Context. Gas plays a major role in the dynamical evolution of protoplanetary discs. Its coupling with the dust is the key to our understanding of planetary formation. Studying the gas content is therefore a crucial step towards understanding protoplanetary discs evolution. Such a study can be made through spectroscopic observations of emission lines in the FIR, where some of the most important gas coolants emit, such as the [OI] 3P1 → 3P2 transition at 63.18 μm.
Aims. We aim at characterising the gas content of protoplanetary discs in the intermediate-aged (from the perspective of the disc lifetime) Chamaeleon II (Cha II) star forming region. We also aim at characterising the gaseous detection fractions within this age range, which is an essential step tracing gas evolution with age in different star forming regions. This evolutionary study can be used to tackle the problem of the gas dispersal timescale in future studies.
Methods. We obtained Herschel-PACS line scan spectroscopic observations at 63 μm of 19 Cha II Class I and II stars. The observations were used to trace [OI] and o-H2O at 63 μm. The analysis of the spatial distribution of [OI], when extended, can be used to understand the origin of the emission.
Results. We have detected [OI] emission toward seven out of the nineteen systems observed, and o-H2O emission at 63.32 μm in just one of them, Sz 61. Cha II members show a correlation between [OI] line fluxes and the continuum at 70 μm, similar to what is observed in Taurus. We analyse the extended [OI] emission towards the star DK Cha and study its dynamical footprints in the PACS Integral Field Unit (IFU). We conclude that there is a high velocity component from a jet combined with a low velocity component with an origin that may be a combination of disc, envelope and wind emission. The stacking of spectra of objects not detected individually in [OI] leads to a marginal 2.6σ detection that may indicate the presence of gas just below our detection limits for some, if not all, of them.
Key words: circumstellar matter / stars: evolution / astrochemistry / protoplanetary disks
© ESO, 2015