7,651 research outputs found
- A tool for multiband light curve modeling of planetary transits and stellar spots
Several studies have shown that stellar activity features, such as occulted
and non-occulted starspots, can affect the measurement of transit parameters
biasing studies of transit timing variations and transmission spectra. We
present , which we designed to model multiband transit
light curves showing starspot anomalies, inferring both transit and spot
parameters. The code follows a pixellation approach to model the star with its
corresponding limb darkening, spots, and transiting planet on a two dimensional
Cartesian coordinate grid. We combine with an MCMC
framework to study and derive exoplanet transmission spectra, which provides
statistically robust values for the physical properties and uncertainties of a
transiting star-planet system. We validate 's performance
by analyzing eleven synthetic light curves of four different star-planet
systems and 20 transit light curves of the well-studied WASP-41b system. We
also investigate the impact of starspots on transit parameters and derive
wavelength dependent transit depth values for WASP-41b covering a range of
6200-9200 , indicating a flat transmission spectrum.Comment: 17 pages, 22 figures; accepted for publication in Astronomy &
Astrophysic
Multivariate calibration of a water and energy balance model in the spectral domain
The objective of this paper is to explore the possibility of using multiple variables in the calibration of hydrologic models in the spectral domain. A simple water and energy balance model was used, combined with observations of the energy balance and the soil moisture profile. The correlation functions of the model outputs and the observations for the different variables have been calculated after the removal of the diurnal cycle of the energy balance variables. These were transformed to the frequency domain to obtain spectral density functions, which were combined in the calibration algorithm. It has been found that it is best to use the square root of the spectral densities in the parameter estimation. Under these conditions, spectral calibration performs almost equally as well as time domain calibration using least squares differences between observed and simulated time series. Incorporation of the spectral coefficients of the cross-correlation functions did not improve the results of the calibration. Calibration on the correlation functions in the time domain led to worse model performance. When the meteorological forcing and model calibration data are not overlapping in time, spectral calibration has been shown to lead to an acceptable model performance. Overall, the results in this paper suggest that, in case of data scarcity, multivariate spectral calibration can be an attractive tool to estimate model parameters
Primordial features and Planck polarization
With the Planck 2015 Cosmic Microwave Background (CMB) temperature and
polarization data, we search for possible features in the primordial power
spectrum (PPS). We revisit the Wiggly Whipped Inflation (WWI) framework and
demonstrate how generation of some particular primordial features can improve
the fit to Planck data. WWI potential allows the scalar field to transit from a
steeper potential to a nearly flat potential through a discontinuity either in
potential or in its derivatives. WWI offers the inflaton potential
parametrizations that generate a wide variety of features in the primordial
power spectra incorporating most of the localized and non-local inflationary
features that are obtained upon reconstruction from temperature and
polarization angular power spectrum. At the same time, in a single framework it
allows us to have a background parameter estimation with a nearly free-form
primordial spectrum. Using Planck 2015 data, we constrain the primordial
features in the context of Wiggly Whipped Inflation and present the features
that are supported both by temperature and polarization. WWI model provides
more than improvement in fit to the data with respect to the best
fit power law model considering combined temperature and polarization data from
Planck and B-mode polarization data from BICEP and Planck dust map. We use 2-4
extra parameters in the WWI model compared to the featureless strict slow roll
inflaton potential. We find that the differences between the temperature and
polarization data in constraining background cosmological parameters such as
baryon density, cold dark matter density are reduced to a good extent if we use
primordial power spectra from WWI. We also discuss the extent of bispectra
obtained from the best potentials in arbitrary triangular configurations using
the BI-spectra and Non-Gaussianity Operator (BINGO).Comment: v1: 22 pages, 7 figures and 1 table; v2: 23 pages, 7 figures and 1
table, minor changes, references added, matches published version in JCA
High-contrast imaging at small separation: impact of the optical configuration of two deformable mirrors on dark holes
The direct detection and characterization of exoplanets will be a major
scientific driver over the next decade, involving the development of very large
telescopes and requires high-contrast imaging close to the optical axis. Some
complex techniques have been developed to improve the performance at small
separations (coronagraphy, wavefront shaping, etc). In this paper, we study
some of the fundamental limitations of high contrast at the instrument design
level, for cases that use a combination of a coronagraph and two deformable
mirrors for wavefront shaping. In particular, we focus on small-separation
point-source imaging (around 1 /D). First, we analytically or
semi-analytically analysing the impact of several instrument design parameters:
actuator number, deformable mirror locations and optic aberrations (level and
frequency distribution). Second, we develop in-depth Monte Carlo simulation to
compare the performance of dark hole correction using a generic test-bed model
to test the Fresnel propagation of multiple randomly generated optics static
phase errors. We demonstrate that imaging at small separations requires large
setup and small dark hole size. The performance is sensitive to the optic
aberration amount and spatial frequencies distribution but shows a weak
dependence on actuator number or setup architecture when the dark hole is
sufficiently small (from 1 to 5 /D).Comment: 13 pages, 18 figure
A Comparison of Cosmological Parameters Determined from CMB Temperature Power Spectra from the South Pole Telescope and the Planck Satellite
The Planck cosmic microwave background (CMB) temperature data are best fit
with a LCDM model that is in mild tension with constraints from other
cosmological probes. The South Pole Telescope (SPT) 2540 SPT-SZ
survey offers measurements on sub-degree angular scales (multipoles ) with sufficient precision to use as an independent check of
the Planck data. Here we build on the recent joint analysis of the SPT-SZ and
Planck data in \citet{hou17} by comparing LCDM parameter estimates using the
temperature power spectrum from both data sets in the SPT-SZ survey region. We
also restrict the multipole range used in parameter fitting to focus on modes
measured well by both SPT and Planck, thereby greatly reducing sample variance
as a driver of parameter differences and creating a stringent test for
systematic errors. We find no evidence of systematic errors from such tests.
When we expand the maximum multipole of SPT data used, we see low-significance
shifts in the angular scale of the sound horizon and the physical baryon and
cold dark matter densities, with a resulting trend to higher Hubble constant.
When we compare SPT and Planck data on the SPT-SZ sky patch to Planck full-sky
data but keep the multipole range restricted, we find differences in the
parameters and . We perform further checks, investigating
instrumental effects and modeling assumptions, and we find no evidence that the
effects investigated are responsible for any of the parameter shifts. Taken
together, these tests reveal no evidence for systematic errors in SPT or Planck
data in the overlapping sky coverage and multipole range and, at most, weak
evidence for a breakdown of LCDM or systematic errors influencing either the
Planck data outside the SPT-SZ survey area or the SPT data at .Comment: 14 pages, 7 figures. Updated 1 figure and expanded on the reasoning
for fixing the affect of lensing on the power spectrum instead of varying
Alen
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