1,978 research outputs found
Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1
We present an XMM-Newton X-ray observation of TRAPPIST-1, which is an
ultracool dwarf star recently discovered to host three transiting and temperate
Earth-sized planets. We find the star is a relatively strong and variable
coronal X-ray source with an X-ray luminosity similar to that of the quiet Sun,
despite its much lower bolometric luminosity. We find L_x/L_bol=2-4x10^-4, with
the total XUV emission in the range L_xuv/L_bol=6-9x10^-4, and XUV irradiation
of the planets that is many times stronger than experienced by the present-day
Earth. Using a simple energy-limited model we show that the relatively close-in
Earth-sized planets, which span the classical habitable zone of the star, are
subject to sufficient X-ray and EUV irradiation to significantly alter their
primary and any secondary atmospheres. Understanding whether this high-energy
irradiation makes the planets more or less habitable is a complex question, but
our measured fluxes will be an important input to the necessary models of
atmospheric evolution.Comment: 5 pages, published as a letter in MNRAS (accepted 16 September 2016
Limits to the planet candidate GJ 436c
We report on H-band, ground-based observations of a transit of the hot
Neptune GJ 436b. Once combined to achieve sampling equivalent to archived
observations taken with Spitzer, our measurements reach comparable precision
levels. We analyze both sets of observations in a consistent way, and measure
the rate of orbital inclination change to be of 0.02+/-0.04 degrees in the time
span between the two observations (253.8 d, corresponding to 0.03+/-0.05
degrees/yr if extrapolated). This rate allows us to put limits on the relative
inclination between the two planets by performing simulations of planetary
systems, including a second planet, GJ 436c, whose presence has been recently
suggested (Ribas et al. 2008). The allowed inclinations for a 5 M_E super-Earth
GJ 436c in a 5.2 d orbit are within ~7 degrees of the one of GJ 436b; for
larger differences the observed inclination change can be reproduced only
during short sections (<50%) of the orbital evolution of the system. The
measured times of three transit centers of the system do not show any departure
from linear ephemeris, a result that is only reproduced in <1% of the simulated
orbits. Put together, these results argue against the proposed planet candidate
GJ 436c.Comment: Replaced with accepted version. Minor language corrections. 4 pages,
4 figures, to appear in A&A Letter
Relations entre niche trophique et habitat chez un peuplement de grillons, en mosaïque forêt-savane (Lamto, Côte d'Ivoire)
TRAPPIST photometry and imaging monitoring of comet C/2013 R1(Lovejoy): Implications for the origin of daughter species
We report the results of the narrow band photometry and imaging monitoring of
comet C/2013 R1 (Lovejoy) with the robotic telescope TRAPPIST (La Silla
observatory). We gathered around 400 images over 8 months pre- and
post-perihelion between September 12, 2013 and July 6, 2014. We followed the
evolution of the OH, NH, CN, C3 , and C2 production rates computed with the
Haser model as well as the evolution of the dust production. All five gas
species display an asymmetry about perihelion, the rate of brightening being
steeper than the rate of fading. The study of the coma morphology reveals gas
and dust jets which indicate one or several active zone(s) on the nucleus. The
dust, C2 , and C3 morphologies present some similarities while the CN
morphology is different. OH and NH are enhanced in the tail direction. The
study of the evolution of the comet activity shows that the OH, NH, and C2
production rates evolution with the heliocentric distance is correlated to the
dust evolution. The CN and, to a lesser extent, the C3 do not display such a
correlation with the dust. These evidences and the comparison with parent
species production rates indicate that C2 and C3 on one side and OH and NH on
the other side could be -at least partially- released from organic-rich grains
and icy grains. On the contrary, all evidences point to HCN being the main
parent of CN in this comet.Comment: Accepted for publication in Astronomy & Astrophysics, 10 page
Traits généraux et composition du peuplement des Grillons de la savane de Lamto (Côte d'Ivoire) brûlée et non brûlée (Orthoptera, Gryllidae)
The thermal emission of the young and massive planet CoRoT-2b at 4.5 and 8 microns
We report measurements of the thermal emission of the young and massive
planet CoRoT-2b at 4.5 and 8 microns with the Spitzer Infrared Array Camera
(IRAC). Our measured occultation depths are 0.510 +- 0.042 % and 0.41 +- 0.11 %
at 4.5 and 8 microns, respectively. In addition to the CoRoT optical
measurements, these planet/star flux ratios indicate a poor heat distribution
to the night side of the planet and are in better agreement with an atmosphere
free of temperature inversion layer. Still, the presence of such an inversion
is not definitely ruled out by the observations and a larger wavelength
coverage is required to remove the current ambiguity. Our global analysis of
CoRoT, Spitzer and ground-based data confirms the large mass and size of the
planet with slightly revised values (Mp = 3.47 +- 0.22 Mjup, Rp = 1.466 +-
0.044 Rjup). We find a small but significant offset in the timing of the
occultation when compared to a purely circular orbital solution, leading to e
cos(omega) = -0.00291 +- 0.00063 where e is the orbital eccentricity and omega
is the argument of periastron. Constraining the age of the system to be at most
of a few hundreds of Myr and assuming that the non-zero orbital eccentricity is
not due to a third undetected body, we model the coupled orbital-tidal
evolution of the system with various tidal Q values, core sizes and initial
orbital parameters. For log(Q_s') = 5 - 6, our modelling is able to explain the
large radius of CoRoT-2b if log(Q_p') <= 5.5 through a transient tidal
circularization and corresponding planet tidal heating event. Under this model,
the planet will reach its Roche limit within 20 Myr at most.Comment: 13 pages, 2 tables, 11 figures. Accepted for publication in Astronomy
and Astrophysic
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