The far-infrared behaviour of Herbig Ae/Be discs: Herschel PACS photometry^⋆

¹ Dept. Física Teórica, Universidad Autónoma de Madrid, Campus Cantoblanco, Spain
² Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
e-mail: natalia.pascual@open.ac.uk
³ Dept. of Astrophysics, CAB (CSIC-INTA), ESAC Campus, PO Box 78, 28691 Villanueva de la Cañada, Spain
⁴ School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
⁵ Australian Centre for Astrobiology, University of New South Wales, Sydney, NSW 2052, Australia
⁶ School of Physics & Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
⁷ SOFIA-USRA, NASA Ames Research Center, MS 232-12, Moffett Field, CA 94035-0001, USA

Received: 26 May 2015
Accepted: 17 November 2015

Abstract

Herbig Ae/Be objects are pre-main sequence stars surrounded by gas- and dust-rich circumstellar discs. These objects are in the throes of star and planet formation, and their characterisation informs us of the processes and outcomes of planet formation processes around intermediate mass stars. Here we analyse the spectral energy distributions of disc host stars observed by the Herschel open time key programme “Gas in Protoplanetary Systems”. We present Herschel/PACS far-infrared imaging observations of 22 Herbig Ae/Bes and 5 debris discs, combined with ancillary photometry spanning ultraviolet to sub-millimetre wavelengths. From these measurements we determine the diagnostics of disc evolution, along with the total excess, in three regimes spanning near-, mid-, and far-infrared wavelengths. Using appropriate statistical tests, these diagnostics are examined for correlations. We find that the far-infrared flux, where the disc becomes optically thin, is correlated with the millimetre flux, which provides a measure of the total dust mass. The ratio of far-infrared to sub-millimetre flux is found to be greater for targets with discs that are brighter at millimetre wavelengths and that have steeper sub-millimetre slopes. Furthermore, discs with flared geometry have, on average, larger excesses than flat geometry discs. Finally, we estimate the extents of these discs (or provide upper limits) from the observations.