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An irradiated brown dwarf companion to an accreting white dwarf

Hernandez Santisteban, Juan, Knigge, Christian, Littlefair, Stuart, Breton, Rene, Dhillon, Vik, Gänsicke, Boris, Marsh, Thomas, Pretorius, Magaretha, Southworth, John and Hauschildt, Peter (2016) An irradiated brown dwarf companion to an accreting white dwarf. Nature, 533, 366-368.

Record type: Article

Abstract

Brown dwarfs and giant planets orbiting close to a host star are subjected to significant irradiation that can modify the properties of their atmospheres. In order to test the atmospheric models that are used to describe these systems, it is necessary to obtain accurate observational estimates of their physical properties (masses, radii, temperatures, albedos). Interacting compact binary systems provide a natural laboratory for studying strongly irradiated sub-stellar objects. As the mass-losing secondary in these systems makes a critical, but poorly understood transition from the stellar to the sub-stellar regime, it is also strongly irradiated by the compact accretor. In fact, the internal and external energy fluxes are both expected to be comparable in these objects, providing access to an unexplored irradiation regime. However, the atmospheric properties of such donors have so far remained largely unknown. Here, we report the direct spectroscopic detection and characterisation of an irradiated sub-stellar donor in an accreting white dwarf binary system. Our near-infrared observations allow us to determine a model-independent mass estimate for the donor of $M_2=0.055\pm0.008M_{\odot}$ and an average spectral type of ${\rm L1}\pm{\rm1}$, supporting both theoretical predictions and model-dependent observational constraints. Our time-resolved data also allow us to estimate the average irradiation-induced temperature difference between the day and night sides on the sub-stellar donor, $\Delta {\rm T} \simeq 57$~K, and the maximum difference between the hottest and coolest parts of its surface, of $\Delta {\rm T}_{max} \simeq 200$~K. The observations are well described by a simple geometric reprocessing model with a bolometric (Bond) albedo of $A_B < 0.54$ at the 2-$\sigma$ confidence level, consistent with high reprocessing efficiency, but poor lateral heat redistribution in the donor's atmosphere.

Text
manuscript_imag.pdf - Accepted Manuscript

Submitted date: 17 April 2015
Accepted/In Press date: 14 March 2016
e-pub ahead of print date: 18 May 2016
Published date: 19 May 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 390805
URI: http://eprints.soton.ac.uk/id/eprint/390805
ISSN: 0028-0836
PURE UUID: 21bd390c-28f5-42aa-acfd-bb96672c9933

Catalogue record

Date deposited: 07 Apr 2016 15:52

Contributors

Author: Juan Hernandez Santisteban
Author: Stuart Littlefair
Author: Rene Breton
Author: Vik Dhillon
Author: Boris Gänsicke
Author: Thomas Marsh
Author: Magaretha Pretorius
Author: John Southworth
Author: Peter Hauschildt