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An irradiated brown dwarf companion to an accreting white dwarf

An irradiated brown dwarf companion to an accreting white dwarf
An irradiated brown dwarf companion to an accreting white dwarf
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.
0028-0836
366-368
Hernandez Santisteban, Juan
115e9657-d594-487b-b871-5c61cc32f692
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Littlefair, Stuart
10ffe59d-520f-47e5-ac4a-96c528d8bdf1
Breton, Rene
a7b5a5f7-c49e-4fae-8219-f381c85f9b4c
Dhillon, Vik
09777b02-39ce-45ba-a600-1c4858ce4f28
Gänsicke, Boris
cb2a21b2-cd91-4568-8911-181ec393b12a
Marsh, Thomas
470a9613-ad0b-4b31-bcd8-6dd6111dae36
Pretorius, Magaretha
a8f07349-cf0d-465c-95fc-9530ed8bd550
Southworth, John
4f5a5990-bee0-4e46-9d34-5c3855307f6e
Hauschildt, Peter
61654261-1da0-457c-aaf4-34484fe646ed
Hernandez Santisteban, Juan
115e9657-d594-487b-b871-5c61cc32f692
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Littlefair, Stuart
10ffe59d-520f-47e5-ac4a-96c528d8bdf1
Breton, Rene
a7b5a5f7-c49e-4fae-8219-f381c85f9b4c
Dhillon, Vik
09777b02-39ce-45ba-a600-1c4858ce4f28
Gänsicke, Boris
cb2a21b2-cd91-4568-8911-181ec393b12a
Marsh, Thomas
470a9613-ad0b-4b31-bcd8-6dd6111dae36
Pretorius, Magaretha
a8f07349-cf0d-465c-95fc-9530ed8bd550
Southworth, John
4f5a5990-bee0-4e46-9d34-5c3855307f6e
Hauschildt, Peter
61654261-1da0-457c-aaf4-34484fe646ed

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. (doi:10.1038/nature17952).

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.

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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

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Date deposited: 07 Apr 2016 15:52
Last modified: 14 Feb 2020 17:30

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