14,985 research outputs found
Photospheric activity, rotation and magnetic interaction in LHS 6343 A
Context. The Kepler mission has recently discovered a brown dwarf companion
transiting one member of the M4V+M5V visual binary system LHS 6343 AB with an
orbital period of 12.71 days. Aims. The particular interest of this transiting
system lies in the synchronicity between the transits of the brown dwarf C
component and the main modulation observed in the light curve, which is assumed
to be caused by rotating starspots on the A component. We model the activity of
this star by deriving maps of the active regions that allow us to study stellar
rotation and the possible interaction with the brown dwarf companion. Methods.
An average transit profile was derived, and the photometric perturbations due
to spots occulted during transits are removed to derive more precise transit
parameters. We applied a maximum entropy spot model to fit the out-of-transit
optical modulation as observed by Kepler during an uninterrupted interval of
500 days. It assumes that stellar active regions consist of cool spots and
bright faculae whose visibility is modulated by stellar rotation. Results.
Thanks to the extended photometric time series, we refine the determination of
the transit parameters and find evidence of spots that are occulted by the
brown dwarf during its transits. The modelling of the out-of-transit light
curve of LHS 6343 A reveals several starspots rotating with a slightly longer
period than the orbital period of the brown dwarf, i.e., 13.13 +- 0.02 days. No
signature attributable to differential rotation is observed. We find evidence
of a persistent active longitude on the M dwarf preceding the sub- companion
point by 100 deg and lasting for at least 500 days. This can be relevant for
understanding how magnetic interaction works in low-mass binary and star-planet
systems.Comment: 14 pages, 16 figure
Doppler-beaming in the Kepler light curve of LHS 6343 A
Context. Kepler observations revealed a brown dwarf eclipsing the M-type star
LHS 6343 A with a period of 12.71 days. In addition, an out-of-eclipse light
modulation with the same period and a relative semi-amplitude of 2 x 10^-4 was
observed showing an almost constant phase lag to the eclipses produced by the
brown dwarf. In a previous work, we concluded that this was due to the light
modulation induced by photospheric active regions in LHS 6343 A. Aims. In the
present work, we prove that most of the out-of-eclipse light modulation is
caused by the Doppler-beaming induced by the orbital motion of the primary
star. Methods. We introduce a model of the Doppler-beaming for an eccentric
orbit and also considered the ellipsoidal effect. The data were fitted using a
Bayesian approach implemented through a Monte Carlo Markov chain method. Model
residuals were analysed by searching for periodicities using a Lomb-Scargle
periodogram. Results. For the first seven quarters of Kepler observations and
the orbit previously derived from the radial velocity measurements, we show
that the light modulation of the system outside eclipses is dominated by the
Doppler-beaming effect. A period search performed on the residuals shows a
significant periodicity of 42.5 +- 3.2 days with a false-alarm probability of 5
x 10^-4, probably associated with the rotational modulation of the primary
component.Comment: 6 pages, 7 figure
Using Wavelets to reject background in Dark Matter experiments
A method based on wavelet techniques has been developed and applied to
background rejection in the data of the IGEX dark matter experiment. The method
is presented and described in some detail to show how it efficiently rejects
events coming from noise and microphonism through a mathematical inspection of
their recorded pulse shape. The result of the application of the method to the
last data of IGEX is presented.Comment: 14 pages, 8 figures. Submitted to Astrop. Phy
Neutron background at the Canfranc Underground Laboratory and its contribution to the IGEX-DM dark matter experiment
A quantitative study of the neutron environment in the Canfranc Underground
Laboratory has been performed. The analysis is based on a complete set of
simulations and, particularly, it is focused on the IGEX-DM dark matter
experiment. The simulations are compared to the IGEX-DM low energy data
obtained with different shielding conditions. The results of the study allow us
to conclude, with respect to the IGEX-DM background, that the main neutron
population, coming from radioactivity from the surrounding rock, is practically
eliminated after the implementation of a suitable neutron shielding. The
remaining neutron background (muon-induced neutrons in the shielding and in the
rock) is substantially below the present background level thanks to the muon
veto system. In addition, the present analysis gives us a further insight on
the effect of neutrons in other current and future experiments at the Canfranc
Underground Laboratory. The comparison of simulations with the body of data
available has allowed to set the flux of neutrons from radioactivity of the
Canfranc rock, (3.82 +- 0.44) x 10^{-6} cm^{-2} s^{-1}, as well as the flux of
muon-induced neutrons in the rock, (1.73 +- 0.22(stat) \+- 0.69(syst)) x
10^{-9} cm^{-2} s^{-1}, or the rate of neutron production by muons in the lead
shielding, (4.8 +- 0.6 (stat) +- 1.9 (syst)) x 10^{-9} cm^{-3} s^{-1}.Comment: 17 pages, 8 figures, elsart document class; final version to appear
in Astroparticle Physic
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