1,121 research outputs found
Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS
We present Hubble Space Telescope near-infrared transit photometry of the
nearby hot-Jupiter HD189733b. The observations were taken with the NICMOS
instrument during five transits, with three transits executed with a narrowband
filter at 1.87 microns and two performed with a narrowband filter at 1.66
microns. Our observing strategy using narrowband filters is insensitive to the
usual HST intra-orbit and orbit-to-orbit measurement of systematic errors,
allowing us to accurately and robustly measure the near-IR wavelength
dependance of the planetary radius. Our measurements fail to reproduce the
Swain et al. absorption signature of atmospheric water below 2 microns at a
5-sigma confidence level. We measure a planet-to-star radius contrast of
0.15498+/-0.00035 at 1.66 microns and a contrast of 0.15517+/-0.00019 at 1.87
microns. Both of our near-IR planetary radii values are in excellent agreement
with the levels expected from Rayleigh scattering by sub-micron haze particles,
observed at optical wavelengths, indicating that upper-atmospheric haze still
dominates the near-IR transmission spectra over the absorption from gaseous
molecular species at least below 2 microns.Comment: 9 pages, 7 figures. Accepted for publication in A&
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
We present a direct method for isolating the component of the starlight
blocked by a planet as it transits its host star, and apply it to spectra of
the bright transiting planet HD 189733b. We model the global shape of the
stellar cross-correlation function as the convolution of a limb-darkened
rotation profile and a gaussian representing the Doppler core of the average
photospheric line profile. The light blocked by the planet during the transit
is a gaussian of the same intrinsic width, whose trajectory across the line
profile yields a precise measure of the misalignment angle and an independent
measure of v sin I. We show that even when v sin I is less than the width of
the intrinsic line profile, the travelling Doppler "shadow" cast by the planet
creates an identifiable distortion in the line profiles which is amenable to
direct modelling. Direct measurement of the trajectory of the missing starlight
yields self-consistent measures of the projected stellar rotation rate, the
intrinsic width of the mean local photospheric line profile, the projected
spin-orbit misalignment angle, and the system's centre-of-mass velocity.
Combined with the photometric rotation period, the results give a geometrical
measure of the stellar radius which agrees closely with values obtained from
high-precision transit photometry if a small amount of differential rotation is
present in the stellar photosphere.Comment: 8 pages, 5 figures, 2 tables; accepted by MNRA
Tailoring morphology and mechanical properties of PLA/PBSA blends optimizing the twin-screw extrusion processing parameters aided by a 1D simulation software
To promote sustainability, the adoption of biobased and biodegradable plastics is a compelling solution. However, the successful utilization of these materials is contingent upon achieving desired properties and the ability to scale up production processes. Particularly in the case of blend systems, synergising the advantages of different polymers is essential. Moreover, assessing processing behavior and optimizing parameters are pivotal. This study aims to improve the extrusion process parameters selection using a 1D software-assisted Design of Experiments (DoE) approach. Polylactic acid (PLA) and polybutylene succinate-co-adipate (PBSA), varying PLA/PBSA ratios, were analysed simplifying and expediting the parameters selection. Remarkably, even in the absence of compatibility agents, this work demonstrates the potential to modify the structure, thereby influencing properties and performance by manipulating the process conditions
Transit spectrophotometry of the exoplanet HD189733b. II. New Spitzer observations at 3.6 microns
We present a new primary transit observation of the hot-jupiter HD189733b,
obtained at 3.6 microns with the Infrared Array Camera (IRAC) onboard the
Spitzer Space Telescope. Previous measurements at 3.6 microns suffered from
strong systematics and conclusions could hardly be obtained with confidence on
the water detection by comparison of the 3.6 and 5.8 microns observations. We
use a high S/N Spitzer photometric transit light curve to improve the precision
of the near infrared radius of the planet at 3.6 microns. The observation has
been performed using high-cadence time series integrated in the subarray mode.
We are able to derive accurate system parameters, including planet-to-star
radius ratio, impact parameter, scale of the system, and central time of the
transit from the fits of the transit light curve. We compare the results with
transmission spectroscopic models and with results from previous observations
at the same wavelength. We obtained the following system parameters:
R_p/R_\star=0.15566+0.00011-0.00024, b=0.661+0.0053-0.0050, and
a/R_\star=8.925+0.0490-0.0523 at 3.6 microns. These measurements are three
times more accurate than previous studies at this wavelength because they
benefit from greater observational efficiency and less statistic and systematic
errors. Nonetheless, we find that the radius ratio has to be corrected for
stellar activity and present a method to do so using ground-based long-duration
photometric follow-up in the V-band. The resulting planet-to-star radius ratio
corrected for the stellar variability is in agreement with the previous
measurement obtained in the same bandpass (Desert et al. 2009). We also discuss
that water vapour could not be evidenced by comparison of the planetary radius
measured at 3.6 and 5.8 microns, because the radius measured at 3.6 microns is
affected by absorption by other species, possibly Rayleigh scattering by haze.Comment: 19 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Kinematics of Tycho-2 Red Giant Clump Stars
Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633
red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort
constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc.
Using 3632 RGC stars with known proper motions, radial velocities, and
photometric distances, we show that, apart from the star centroid velocity
components relative to the Sun, only the model parameters that describe the
stellar motions in the XY plane differ significantly from zero. We have studied
the contraction (a negative K-effect) of the system of RGC stars as a function
of their heliocentric distance and elevation above the Galactic plane. For a
sample of distant (500--1000 pc) RGC stars located near the Galactic plane
(|Z|<200 pc) with an average distance of d=0.7 kpc, the contraction velocity is
shown to be Kd= -3.5+-0.9 km/s; a noticeable vertex deviation, lxy = 9.1+-0.5
degrees, is also observed for them. For stars located well above the Galactic
plane (|Z|>=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and
lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the
Galactic X axis directed toward the Galactic center with an angular velocity of
-2.5+-0.3 km/s/kpc, which we associate with the warp of the Galactic
stellar-gaseous disk.Comment: 23 pages, 7 figures, 4 table
Direct radiative effect of the Russian wildfires and its impact on air temperature and atmospheric dynamics during August 2010
International audienceIn this study, we investigate the shortwave aerosol direct radiative forcing (ADRF) and its feedback on air temperature and atmospheric dynamics during a major fire event that occurred in Russia during August 2010. The methodology is based on an offline coupling between the CHIMERE chemistry-transport and the Weather Research and Forecasting (WRF) models. First, simulations for the period 5â12 August 2010 have been evaluated by using AERONET (AErosol RObotic NETwork) and satellite measurements of the POLarization and Directionality of the Earth's Reflectance (POLDER) and the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) sensors. During this period, elevated POLDER aerosol optical thickness (AOT) is found over a large part of eastern Europe, with values above 2 (at 550 nm) in the aerosol plume. According to CALIOP observations, particles remain confined to the first five kilometres of the atmospheric layer. Comparisons with satellite measurements show the ability of CHIMERE to reproduce the regional and vertical distribution of aerosols during their transport from the source region. Over Moscow, AERONET measurements indicate an important increase of AOT (340 nm) from 0.7 on 5 August to 2â4 between 6 and 10 August when the aerosol plume was advected over the city. Particles are mainly observed in the fine size mode (radius in the range 0.2â0.4 ÎŒm) and are characterized by elevated single-scattering albedo (SSA) (0.95â0.96 between 440 and 1020 nm). Comparisons of simulations with AERONET measurements show that aerosol physicalâoptical properties (size distribution, AOT, SSA) have been well simulated over Moscow in terms of intensity and/or spectral dependence. Secondly, modelled aerosol optical properties have been used as input in the radiative transfer code of WRF to evaluate their direct radiative impact. Simulations indicate a significant reduction of solar radiation at the ground (up to 80â150 W mâ2 in diurnal averages over a large part of eastern Europe due to the presence of the aerosol plume. This ADRF causes an important reduction of the near-surface air temperature between 0.2 and 2.6° on a regional scale. Moscow has been affected by the aerosol plume, especially between 6 and 10 August. During this period, aerosol causes a significant reduction of surface shortwave radiation (up to 70â84 W mâ2 in diurnal averages) with a moderate part (20â30%) due to solar absorption within the aerosol layer. The resulting feedbacks lead to a cooling of the air up to 1.6° at the surface and 0.1° at an altitude of 1500â2000 m (in diurnal averages), that contribute to stabilize the atmospheric boundary layer (ABL). Indeed, a reduction of the ABL height of 13 to 65% has been simulated during daytime in presence of aerosols. This decrease is the result of a lower air entrainment as the vertical wind speed in the ABL is shown to be reduced by 5 to 80% (at midday) when the feedback of the ADRF is taken into account. However, the ADRF is shown to have a lower impact on the horizontal wind speed, suggesting that the dilution of particles would be mainly affected by the weakening of the ABL development and associated vertical entrainment. Indeed, CHIMERE simulations driven by the WRF meteorological fields including this ADRF feedback result in a large increase in the modelled near-surface PM10 concentrations (up to 99%). This is due to their lower vertical dilution in the ABL, which tend to reduce model biases with the ground PM10 values observed over Moscow during this specific period
Relationship of Mother Factors, Breastfeeding and Stunting Pattern in Central Sulawesi
Basic Health Research (Riskesdas), The Ministry of Health in Indonesia, reported a prevalence of stunting in 2013 is 37.2%, an increase of Compared to 2010 (35.6%) and 2007 (36.8%). Total stunting in Central Sulawesi in 2013 by 41% and the city of Palu at 21:42%. Stunting risk factors include maternal factors and patterns of breastfeeding. The purpose of this study to Determine the influence of maternal factors and patterns of breastfeeding against stunting in Central Sulawesi. The research was conducted in the city of Palu from August to November 2015. Retrospective cohort study design, the total sample of 65 Households with purposive sampling technique. The research instrument is a validated questionnaire. Data was Analyzed by univariate, bivariate and multivariate analyses. The results of the investigation with OR; 95% CI Showed that the factors that influence stunting in this study are no antenatal care with OR = 4.57 (3:05 to 6.85)
On the Influence of Pulse Shapes on Ionization Probability
We investigate analytical expressions for the upper and lower bounds for the
ionization probability through ultra-intense shortly pulsed laser radiation. We
take several different pulse shapes into account, including in particular those
with a smooth adiabatic turn-on and turn-off. For all situations for which our
bounds are applicable we do not find any evidence for bound-state
stabilization.Comment: 21 pages LateX, 10 figure
The Milky Way rotation curve in Horava - Lifshitz theory
The Horava - Lifshitz (HL) theory has recently attracted a lot of interest as
a viable solution to some quantum gravity related problems and the presence of
an effective cosmological constant able to drive the cosmic speed up. We show
here that, in the weak field limit, the HL proposal leads to a modification of
the gravitational potential because of two additive terms (scaling respectively
as and ) to the Newtonian potential. We then derive a
general expression to compute the rotation curve of an extended system under
the assumption that the mass density only depends on the cylindrical
coordinates showing that the HL modification induces a dependence of
the circular velocity on the mass function which is a new feature of the
theory. As a first exploratory analysis, we then try fitting the Milky Way
rotation curve using its visible components only in order to see whether the HL
modified potential can be an alternative to the dark matter framework. This
turns out not to be the case so that we argue that dark matter is still needed,
but the amount of dark matter and the dark halo density profile have to be
revised according to the new HL potential.Comment: 10 pages, 1 figure, accepted for publication on MNRA
A stellar flare during the transit of the extrasolar planet OGLE-TR-10b
We report a stellar flare occurring during a transit of the exoplanet OGLE-TR-10b, an event not previously reported in the literature. This reduces the observed transit depth, particularly in the u'-band, but flaring could also be significant in other bands and could lead to incorrect planetary parameters. We suggest that OGLE-TR-10a is an active planet-hosting star and has an unusually high X-ray luminosity
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