TY - JOUR
T1 - An irradiated brown-dwarf companion to an accreting white dwarf
AU - Hernández Santisteban, Juan V.
AU - Knigge, Christian
AU - Littlefair, Stuart P.
AU - Breton, Rene P.
AU - Dhillon, Vikram S.
AU - Gänsicke, Boris T.
AU - Marsh, Thomas R.
AU - Pretorius, Magaretha L.
AU - Southworth, John
AU - Hauschildt, Peter H.
PY - 2016/5/19
Y1 - 2016/5/19
N2 - Interacting compact binary systems provide a natural laboratory in which
to study irradiated substellar objects. As the mass-losing secondary
(donor) in these systems makes a transition from the stellar to the
substellar regime, it is also irradiated by the primary (compact
accretor). The internal and external energy fluxes are both expected to
be comparable in these objects, providing access to an unexplored
irradiation regime. The atmospheric properties of donors are largely
unknown, but could be modified by the irradiation. To constrain models
of donor atmospheres, it is necessary to obtain accurate observational
estimates of their physical properties (masses, radii, temperatures and
albedos). Here we report the spectroscopic detection and
characterization of an irradiated substellar 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
0.055 ± 0.008 solar masses and an average spectral
type of L1 ± 1, supporting both theoretical
predictions and model-dependent observational constraints that suggest
that the donor is a brown dwarf. Our time-resolved data also allow us to
estimate the average irradiation-induced temperature difference between
the dayside and nightside of the substellar donor (57 kelvin) and the
maximum difference between the hottest and coolest parts of its surface
(200 kelvin). The observations are well described by a simple geometric
reprocessing model with a bolometric (Bond) albedo of less than 0.54 at
the 2σ confidence level, consistent with high reprocessing
efficiency, but poor lateral heat redistribution in the atmosphere of
the brown-dwarf donor. These results add to our knowledge of binary
evolution, in that the donor has survived the transition from the
stellar to the substellar regime, and of substellar atmospheres, in that
we have been able to test a regime in which the irradiation and the
internal energy of a brown dwarf are comparable.
AB - Interacting compact binary systems provide a natural laboratory in which
to study irradiated substellar objects. As the mass-losing secondary
(donor) in these systems makes a transition from the stellar to the
substellar regime, it is also irradiated by the primary (compact
accretor). The internal and external energy fluxes are both expected to
be comparable in these objects, providing access to an unexplored
irradiation regime. The atmospheric properties of donors are largely
unknown, but could be modified by the irradiation. To constrain models
of donor atmospheres, it is necessary to obtain accurate observational
estimates of their physical properties (masses, radii, temperatures and
albedos). Here we report the spectroscopic detection and
characterization of an irradiated substellar 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
0.055 ± 0.008 solar masses and an average spectral
type of L1 ± 1, supporting both theoretical
predictions and model-dependent observational constraints that suggest
that the donor is a brown dwarf. Our time-resolved data also allow us to
estimate the average irradiation-induced temperature difference between
the dayside and nightside of the substellar donor (57 kelvin) and the
maximum difference between the hottest and coolest parts of its surface
(200 kelvin). The observations are well described by a simple geometric
reprocessing model with a bolometric (Bond) albedo of less than 0.54 at
the 2σ confidence level, consistent with high reprocessing
efficiency, but poor lateral heat redistribution in the atmosphere of
the brown-dwarf donor. These results add to our knowledge of binary
evolution, in that the donor has survived the transition from the
stellar to the substellar regime, and of substellar atmospheres, in that
we have been able to test a regime in which the irradiation and the
internal energy of a brown dwarf are comparable.
U2 - 10.1038/nature17952
DO - 10.1038/nature17952
M3 - Article
SN - 0028-0836
VL - 533
SP - 366
EP - 368
JO - Nature
JF - Nature
IS - 7603
ER -