5,376 research outputs found
Primary transit of the planet HD189733b at 3.6 and 5.8 microns
The hot Jupiter HD 189733b was observed during its primary transit using the
Infrared Array Camera on the Spitzer Space Telescope. The transit depths were
measured simultaneously at 3.6 and 5.8 microns. Our analysis yields values of
2.356 +- 0.019 % and 2.436 +- 0.020$ % at 3.6 and 5.8 microns respectively, for
a uniform source. We estimated the contribution of the limb-darkening and
star-spot effects on the final results. We concluded that although the limb
darkening increases by ~0.02-0.03 % the transit depths, and the differential
effects between the two IRAC bands is even smaller, 0.01 %. Furthermore, the
host star is known to be an active spotted K star with observed photometric
modulation. If we adopt an extreme model of 20 % coverage with spots 1000K
cooler of the star surface, it will make the observed transits shallower by
0.19 and 0.18 %. The difference between the two bands will be only of 0.01 %,
in the opposite direction to the limb darkening correction. If the transit
depth is affected by limb darkening and spots, the differential effects between
the 3.6 and 5.8 microns bands are very small. The differential transit depths
at 3.6 and 5.8 microns and the recent one published by Knutson et al.(2007) at
8 microns are in agreement with the presence of water vapour in the upper
atmosphere of the planet. This is the companion paper to Tinetti et al.
(2007b), where the detailed atmosphere models are presented.Comment: 6 pages, 4 figures, Astrophysical Journal 675. Accepted Nov 21,
20007, to appear on March 10, 200
The full spectral radiative properties of Proxima Centauri
The discovery of Proxima b, a terrestrial temperate planet, presents the
opportunity of studying a potentially habitable world in optimal conditions. A
key aspect to model its habitability is to understand the radiation environment
of the planet in the full spectral domain. We characterize the X-rays to mid-IR
radiative properties of Proxima with the goal of providing the
top-of-atmosphere fluxes on the planet. We also aim at constraining the
fundamental properties of the star. We employ observations from a large number
of facilities and make use of different methodologies to piece together the
full spectral energy distribution of Proxima. In the high-energy domain, we pay
particular attention to the contribution by rotational modulation, activity
cycle, and flares so that the data provided are representative of the overall
radiation dose received by the atmosphere of the planet. We present the full
spectrum of Proxima covering 0.7 to 30000 nm. The integration of the data shows
that the top-of-atmosphere average XUV irradiance on Proxima b is 0.293 W m^-2,
i.e., nearly 60 times higher than Earth, and that the total irradiance is
877+/-44 W m^-2, or 64+/-3% of the solar constant but with a significantly
redder spectrum. We also provide laws for the XUV evolution of Proxima
corresponding to two scenarios. Regarding the fundamental properties of
Proxima, we find M=0.120+/-0.003 Msun, R=0.146+/-0.007 Rsun, Teff=2980+/-80 K,
and L=0.00151+/-0.00008 Lsun. In addition, our analysis reveals a ~20% excess
in the 3-30 micron flux of the star that is best interpreted as arising from
warm dust in the system. The data provided here should be useful to further
investigate the current atmospheric properties of Proxima b as well as its past
history, with the overall aim of firmly establishing the habitability of the
planet.Comment: 12 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Cosmological model with non-minimally coupled fermionic field
A model for the Universe is proposed whose constituents are: (a) a dark
energy field modeled by a fermionic field non-minimally coupled with the
gravitational field, (b) a matter field which consists of pressureless baryonic
and dark matter fields and (c) a field which represents the radiation and the
neutrinos. The coupled system of Dirac's equations and Einstein field equations
is solved numerically by considering a spatially flat homogeneous and isotropic
Universe. It is shown that the proposed model can reproduce the expected
red-shift behaviors of the deceleration parameter, of the density parameters of
each constituent and of the luminosity distance. Furthermore, for small values
of the red-shift the constant which couples the fermionic and gravitational
fields has a remarkable influence on the density and deceleration parameters.Comment: Accepted for publication in Europhysics Letter
A new polyploid species of Mimosa (leguminosae, mimosoideae) from the highlands of Southern Brazil
Mimosa tucumensis (Leguminosae), a new species from M. sect. Mimosa ser. Mimosa subser. Mimosa is described and illustrated. This taxon is found in southern Brazil (Paran State), in "campos de altitude," an environment different from the typical habitat of other entities in this subseries. Mimosa tucumensis is morphologically close to M. debilis, M. velloziana, and M. sensibilis, but differs from these principally by the presence of humifuse stems with adventitious roots, considerably longer petioles and peduncles, and foliar venation. In addition, cytological characterization of this new taxon is provided and discussed in relation to the nearest species. This taxon appears to be narrowly restricted to grasslands on a handful of closely adjacent peaks in the Paran State adding to the notable endemism of this area. On the basis of morphological, cytological, and geographical data, some evolutionary considerations are inferred.Fil: Morales, Matias. Universidad de MorĂłn; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Ribas, Osmar S.. Museu Botanico Municipal de Curitiba; BrasilFil: Santos Silva, Juliana. Universidade Estadual de Campinas; Brasi
Performance of the Micromegas detector in the CAST experiment
The gaseous Micromegas detector designed for the CERN Axion search experiment
CAST, operated smoothly during Phase-I, which included the 2003 and 2004
running periods. It exhibited linear response in the energy range of interest
(1-10keV), good spatial sensitivity and energy resolution (15-19% FWHM at
5.9keV)as well as remarkable stability. The detector's upgrade for the 2004
run, supported by the development of advanced offline analysis tools, improved
the background rejection capability, leading to an average rate 5x10^-5
counts/sec/cm^2/keV with 94% cut efficiency. Also, the origin of the detected
background was studied with a Monte Carlo simulation, using the GEANT4 package.Comment: Prepared for PSD7: The Seventh International Conference on Position
Sensitive Detectors, Liverpool, United Kingdom, 12-16 Sep. 200
Noether symmetry for non-minimally coupled fermion fields
A cosmological model where a fermion field is non-minimally coupled with the
gravitational field is studied. By applying Noether symmetry the possible
functions for the potential density of the fermion field and for the coupling
are determined. Cosmological solutions are found showing that the non-minimally
coupled fermion field behaves as an inflaton describing an accelerated
inflationary scenario, whereas the minimally coupled fermion field describes a
decelerated period being identified as dark matter.Comment: Revised version accepted for publication in Classical and Quantum
Gravit
Spectroscopic characterisation of CARMENES target candidates from FEROS, CAFE and HRS high-resolution spectra
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with
Near-infrared and optical Echelle Spectrographs) started a new planet survey on
M-dwarfs in January this year. The new high-resolution spectrographs are
operating in the visible and near-infrared at Calar Alto Observatory. They will
perform high-accuracy radial-velocity measurements (goal 1 m s-1) of about 300
M-dwarfs with the aim to detect low-mass planets within habitable zones. We
characterised the candidate sample for CARMENES and provide fundamental
parameters for these stars in order to constrain planetary properties and
understand star-planet systems. Using state-of-the-art model atmospheres
(PHOENIX-ACES) and chi2-minimization with a downhill-simplex method we
determine effective temperature, surface gravity and metallicity [Fe/H] for
high-resolution spectra of around 480 stars of spectral types M0.0-6.5V taken
with FEROS, CAFE and HRS. We find good agreement between the models and our
observed high-resolution spectra. We show the performance of the algorithm, as
well as results, parameter and spectral type distributions for the CARMENES
candidate sample, which is used to define the CARMENES target sample. We also
present first preliminary results obtained from CARMENES spectra
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