3,098 research outputs found
Tidally-driven Roche-Lobe Overflow of Hot Jupiters with MESA
Many exoplanets have now been detected in orbits with ultra-short periods,
very close to the Roche limit. Building upon our previous work, we study the
possibility that mass loss through Roche lobe overflow (RLO) may affect the
evolution of these planets, and could possibly transform a hot Jupiter into a
lower-mass planet (hot Neptune or super-Earth). We focus here on systems in
which the mass loss occurs slowly ("stable mass transfer" in the language of
binary star evolution) and we compute their evolution in detail with the binary
evolution code MESA. We include the effects of tides, RLO, irradiation and
photo-evaporation of the planet, as well as the stellar wind and magnetic
braking. Our calculations all start with a hot Jupiter close to its Roche
limit, in orbit around a sun-like star. The initial orbital decay and onset of
RLO are driven by tidal dissipation in the star. We confirm that such a system
can indeed evolve to produce lower-mass planets in orbits of a few days. The
RLO phase eventually ends and, depending on the details of the mass transfer
and on the planetary core mass, the orbital period can remain around a few days
for several Gyr. The remnant planets have a rocky core and some amount of
envelope material, which is slowly removed via photo-evaporation at nearly
constant orbital period; these have properties resembling many of the observed
super-Earths and sub-Neptunes. For these remnant planets we also predict an
anti-correlation between mass and orbital period; very low-mass planets
() in ultra-short periods (<1d) cannot be produced through this type of evolution.Comment: 14 pages, 7 figures, 2 tables. Accepted by ApJ. The manuscript has
been revised significantly to address the referee's comments. A link to MESA
inlist files is now provided on page
The Dynamics of the Multi-planet System Orbiting Kepler-56
Kepler-56 is a multi-planet system containing two coplanar inner planets that
are in orbits misaligned with respect to the spin axis of the host star, and an
outer planet. Various mechanisms have been proposed to explain the broad
distribution of spin-orbit angles among exoplanets, and these theories fall
under two broad categories. The first is based on dynamical interactions in a
multi-body system, while the other assumes that disk migration is the driving
mechanism in planetary configuration and that the star (or disk) is titled with
respect to the planetary plane. Here we show that the large observed obliquity
of Kepler-56 system is consistent with a dynamical origin. In addition, we use
observations by Huber et al. (2013) to derive the obliquity's probability
distribution function, thus improving the constrained lower limit. The outer
planet may be the cause of the inner planets' large obliquities, and we give
the probability distribution function of its inclination, which depends on the
initial orbital configuration of the planetary system. We show that even in the
presence of precise measurement of the true obliquity, one cannot distinguish
the initial configurations. Finally we consider the fate of the system as the
star continues to evolve beyond the main sequence, and we find that the
obliquity of the system will not undergo major variations as the star climbs
the red giant branch. We follow the evolution of the system and find that the
innermost planet will be engulfed in ~129 Myr. Furthermore we put an upper
limit of ~155 Myr for the engulfment of the second planet. This corresponds to
~ 3% of the current age of the star.Comment: 9 pages, 6 figures. Accepted for publication in Ap
Characterisation of the Thermal Damage in a Martensitic Steel Substrate Consequent to Laser Cladding Process
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Visual-cortical enhancement by acoustic distractors: The effects of endogenous spatial attention and visual working memory load
Past work has shown that when a peripheral sound captures our attention, it activates the contralateral visual cortex as revealed by an event-related potential component labelled the auditory-evoked contralateral occipital positivity (ACOP). This cross-modal activation of the visual cortex has been observed even when the sounds were not relevant to the ongoing task (visual or auditory), suggesting that peripheral sounds automatically activate the visual cortex. However, it is unclear whether top-down factors such as visual working memory (VWM) load and endogenous attention, which modulate the impact of task-irrelevant information, may modulate this spatially-specific component. Here, we asked participants to perform a lateralized VWM task (change detection), whose performance is supported by both endogenous spatial attention and VWM storage. A peripheral sound that was unrelated to the ongoing task was delivered during the retention interval. The amplitude of sound-elicited ACOP was analyzed as a function of the spatial correspondence with the cued hemifield, and of the memory array set-size. The typical ACOP modulation was observed over parieto-occipital sites in the 280–500 ms time window after sound onset. Its amplitude was not affected by VWM load but was modulated when the location of the sound did not correspond to the hemifield (right or left) that was cued for the change detection task. Our results suggest that sound-elicited activation of visual cortices, as reflected in the ACOP modulation, is unaffected by visual working memory load. However, endogenous spatial attention affects the ACOP, challenging the hypothesis that it reflects an automatic process
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