Brown dwarf disks with Herschel: Linking far-infrared and (sub)-mm fluxes | Astronomy & Astrophysics (A&A)

Brown dwarf disks with Herschel: Linking far-infrared and (sub)-mm fluxes⋆

Sebastian Daemgen1,2, Antonella Natta3,4, Alexander Scholz5, Leonardo Testi6,3,7, Ray Jayawardhana8, Jane Greaves9 and Daniel Eastwood10

A&A 594, A83 (2016)

1 ETH Zürich, Institut für Astronomie, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland

e-mail: [email protected]

2 Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5H 3H4, Canada

3 INAF/Osservatorio Astrofisico of Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy

4 School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliams Place, Dublin 2, Ireland

5 SUPA School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, UK

6 European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching, Germany

7 Excellence Cluster “Universe”, Boltzmannstr. 2, 85748 Garching bei München, Germany

8 Faculty of Science, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada

9 School of Physics & Astronomy, Cardiff University, Queen’s Buildings, Cardiff CF24 3AA, UK

10 Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

Received: 4 March 2016
Accepted: 22 July 2016

Abstract

Brown dwarf disks are excellent laboratories to test our understanding of disk physics in an extreme parameter regime. In this paper we investigate a sample of 29 well-characterized brown dwarfs and very low-mass stars, for which Herschel far-infrared fluxes and (sub)-mm fluxes are available. We measured new Herschel/PACS fluxes for 11 objects and complement these with (sub)-mm data and Herschel fluxes from the literature. We analyze their spectral energy distributions in comparison with results from radiative transfer modeling. Fluxes in the far-infrared are strongly affected by the shape and temperature of the disk (and hence stellar luminosity), whereas the (sub)-mm fluxes mostly depend on disk mass. Nevertheless, there is a clear correlation between far-infrared and (sub)-mm fluxes. We argue that the link results from the combination of the stellar mass-luminosity relation and a scaling between disk mass and stellar mass. We find strong evidence of dust settling to the disk midplane. The spectral slopes between near- and far-infrared are mostly between −0.5 and −1.2 in our sample, which is comparable to more massive T Tauri stars; this may imply that the disk shapes are similar as well, although highly flared disks are rare among brown dwarfs. We find that dust temperatures in the range of 7−15 K, calculated with T ≈ 25 (L/L⊙)0.25 K, are appropriate for deriving disk masses from (sub)-mm fluxes for these low luminosity objects. About half of our sample hosts disks with at least one Jupiter mass, confirming that many brown dwarfs harbor sufficient material for the formation of Earth-mass planets in their midst.

Key words: brown dwarfs / circumstellar matter / stars: pre-main sequence / infrared: stars / submillimeter: stars

⋆

Herschel is a ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.