393 research outputs found
Na I and H absorption features in the atmosphere of MASCARA-2b/KELT-20b
We have used the HARPS-North high resolution spectrograph (=115
000) at TNG to observe one transit of the highly irradiated planet
MASCARA-2b/KELT-20b. Using only one transit observation, we are able to clearly
resolve the spectral features of the atomic sodium (Na I) doublet and the
H line in its atmosphere, measuring absorption depths of
0.170.03 and 0.590.08 for a 0.75 passband,
respectively. These absorptions are corroborated with the transmission measured
from their respective transmission light curves, which show a large
Rossiter-McLaughlin effect. In case of H, this absorption corresponds
to an effective radius of =1.200.04. While the S/N of the
final transmission spectrum is not sufficient to adjust different temperature
profiles to the lines, we find that higher temperatures than the equilibrium
are needed to explain the lines contrast. Particularly, we find that the Na I
lines core require a temperature of T=4210180K and that H requires
T=4330520K. MASCARA-2b, like other planets orbiting A-type stars, receives
a large amount of UV energy from its host star. This energy excites the atomic
hydrogen and produces H absorption, leading to the expansion and
abrasion of the atmosphere. The study of other Balmer lines in the transmission
spectrum would allow the determination of the atmospheric temperature profile
and the calculation of the lifetime of the atmosphere. In the case of
MASCARA-2b, residual features are observed in the H and H lines,
but they are not statistically significant. More transit observations are
needed to confirm our findings in Na I and H, and to build up enough
S/N to explore the presence of H and H planetary absorptions.Comment: 14 pages, 12 figure
Naked Singularity in a Modified Gravity Theory
The cosmological constant induced by quantum fluctuation of the graviton on a
given background is considered as a tool for building a spectrum of different
geometries. In particular, we apply the method to the Schwarzschild background
with positive and negative mass parameter. In this way, we put on the same
level of comparison the related naked singularity (-M) and the positive mass
wormhole. We discuss how to extract information in the context of a f(R)
theory. We use the Wheeler-De Witt equation as a basic equation to perform such
an analysis regarded as a Sturm-Liouville problem . The application of the same
procedure used for the ordinary theory, namely f(R)=R, reveals that to this
approximation level, it is not possible to classify the Schwarzschild and its
naked partner into a geometry spectrum.Comment: 8 Pages. Contribution given to DICE 2008. To appear in the
proceeding
Detection efficiency and photometry in supernova surveys - the Stockholm VIMOS Supernova Survey I
The aim of the work presented in this paper is to test and optimise supernova
detection methods based on the optimal image subtraction technique. The main
focus is on applying the detection methods to wide field supernova imaging
surveys and in particular to the Stockholm VIMOS Supernova Survey (SVISS). We
have constructed a supernova detection pipeline for imaging surveys. The core
of the pipeline is image subtraction using the ISIS 2.2 package. Using real
data from the SVISS we simulate supernovae in the images, both inside and
outside galaxies. The detection pipeline is then run on the simulated frames
and the effects of image quality and subtraction parameters on the detection
efficiency and photometric accuracy are studied. The pipeline allows efficient
detection of faint supernovae in the deep imaging data. It also allows
controlling and correcting for possible systematic effects in the SN detection
and photometry. We find such a systematic effect in the form of a small
systematic flux offset remaining at the positions of galaxies in the subtracted
frames. This offset will not only affect the photometric accuracy of the
survey, but also the detection efficiencies. Our study has shown that ISIS 2.2
works well for the SVISS data. We have found that the detection efficiency and
photometric accuracy of the survey are affected by the stamp selection for the
image subtraction and by host galaxy brightness. With our tools the subtraction
results can be further optimised, any systematic effects can be controlled and
photometric errors estimated, which is very important for the SVISS, as well as
for future SN searches based on large imaging surveys such as Pan-STARRS and
LSST.Comment: 17 pages, 10 figure, accepted for publication in A&
Testing homogeneity with galaxy number counts : light-cone metric and general low-redshift expansion for a central observer in a matter dominated isotropic universe without cosmological constant
As an alternative to dark energy it has been suggested that we may be at the
center of an inhomogeneous isotropic universe described by a
Lemaitre-Tolman-Bondi (LTB) solution of Einstein's field equations. In order to
test this hypothesis we calculate the general analytical formula to fifth order
for the redshift spherical shell mass. Using the same analytical method we
write the metric in the light-cone by introducing a gauge invariant quantity
which together with the luminosity distance completely
determine the light-cone geometry of a LTB model.Comment: 13 page
Averaging inhomogeneities in scalar-tensor cosmology
The backreaction of inhomogeneities on the cosmic dynamics is studied in the
context of scalar-tensor gravity. Due to terms of indefinite sign in the
non-canonical effective energy tensor of the Brans-Dicke-like scalar field,
extra contributions to the cosmic acceleration can arise. Brans-Dicke and
metric f(R) gravity are presented as specific examples. Certain representation
problems of the formalism peculiar to these theories are pointed out.Comment: Comments and references added. 14 page
SALT: a Spectral Adaptive Light curve Template for Type Ia Supernovae
We present a new method to parameterize Type Ia Supernovae (SN Ia)
multi-color light curves. The method was developed in order to analyze the
large number of SN Ia multi-color light curves measured in current
high-redshift projects. The technique is based on empirically modeling SN Ia
luminosity variations as a function of phase, wavelength, a shape parameter,
and a color parameter. The model is trained with a sample of well measured
nearby SN Ia and then tested with an independent set of supernovae by building
an optimal luminosity distance estimator combining the supernova rest-frame
luminosity, shape parameter and color reconstructed with the model. The
distances we measure using B- and V-band data show a dispersion around the
Hubble line comparable or lower than obtained with other methods. With this
model, we are able to measure distances using U- and B-band data with a
dispersion around the Hubble line of 0.16 +- 0.05.Comment: Accepted in A&A, June 23, 2005 (printer friendly replacement version,
includes language corrections
Scale-Free model for governing universe dynamics
We investigate the effects of scale-free model on cosmology, providing, in
this way, a statistical background in the framework of general relativity. In
order to discuss properties and time evolution of some relevant universe
dynamical parameters (cosmographic parameters), such as (Hubble
parameter), (deceleration parameter), (jerk parameter) and
(snap parameter), which are well re-defined in the framework of scale-free
model, we analyze a comparison between WMAP data. Hence the basic purpose of
the work is to consider this statistical interpretation of mass distribution of
universe, in order to have a mass density dynamics, not inferred from
Friedmann equations, via scale factor . This model, indeed, has been used
also to explain a possible origin and a viable explanation of cosmological
constant, which assumes a statistical interpretation without the presence of
extended theories of gravity; hence the problem of dark energy could be
revisited in the context of a classical probability distribution of mass, which
is, in particular, for the scale-free model, , with
. The CDM model becomes, with these considerations, a
consequence of the particular statistics together with the use of general
relativity.Comment: 7 pages, 4 figure
The GTC exoplanet transit spectroscopy survey IX. Detection of haze, Na, K, and Li in the super-Neptune WASP-127b
Exoplanets with relatively clear atmospheres are prime targets for detailed
studies of chemical compositions and abundances in their atmospheres. Alkali
metals have long been suggested to exhibit broad wings due to pressure
broadening, but most of the alkali detections only show very narrow absorption
cores, probably because of the presence of clouds. We report the strong
detection of the pressure-broadened spectral profiles of Na, K, and Li
absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1,
5.0, and 3.4, respectively. We performed a spectral retrieval
modeling on the high-quality optical transmission spectrum newly acquired with
the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed
optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope
(NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K,
and Li, which are super-solar at 3.7 for K and 5.1 for Li (and
only 1.8 for Na). We constrained the presence of haze coverage to be
around 52%. We also found a hint of water absorption, but cannot constrain it
with the global retrieval owing to larger uncertainties in the probed
wavelengths. WASP-127b will be extremely valuable for atmospheric
characterization in the era of James Webb Space Telescope
Observational Constraints of Modified Chaplygin Gas in Loop Quantum Cosmology
We have considered the FRW universe in loop quantum cosmology (LQC) model
filled with the dark matter (perfect fluid with negligible pressure) and the
modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter
in terms of the observable parameters , and
with the redshift and the other parameters like , , and .
From Stern data set (12 points), we have obtained the bounds of the arbitrary
parameters by minimizing the test. The best-fit values of the
parameters are obtained by 66%, 90% and 99% confidence levels. Next due to
joint analysis with BAO and CMB observations, we have also obtained the bounds
of the parameters () by fixing some other parameters and .
From the best fit of distance modulus for our theoretical MCG model in
LQC, we concluded that our model is in agreement with the union2 sample data.Comment: 14 pages, 10 figures, Accepted in EPJC. arXiv admin note: text
overlap with arXiv:astro-ph/0311622 by other author
Corrections to the apparent value of the cosmological constant due to local inhomogeneities
Supernovae observations strongly support the presence of a cosmological
constant, but its value, which we will call apparent, is normally determined
assuming that the Universe can be accurately described by a homogeneous model.
Even in the presence of a cosmological constant we cannot exclude nevertheless
the presence of a small local inhomogeneity which could affect the apparent
value of the cosmological constant. Neglecting the presence of the
inhomogeneity can in fact introduce a systematic misinterpretation of
cosmological data, leading to the distinction between an apparent and true
value of the cosmological constant. We establish the theoretical framework to
calculate the corrections to the apparent value of the cosmological constant by
modeling the local inhomogeneity with a solution. Our assumption
to be at the center of a spherically symmetric inhomogeneous matter
distribution correspond to effectively calculate the monopole contribution of
the large scale inhomogeneities surrounding us, which we expect to be the
dominant one, because of other observations supporting a high level of isotropy
of the Universe around us.
By performing a local Taylor expansion we analyze the number of independent
degrees of freedom which determine the local shape of the inhomogeneity, and
consider the issue of central smoothness, showing how the same correction can
correspond to different inhomogeneity profiles. Contrary to previous attempts
to fit data using large void models our approach is quite general. The
correction to the apparent value of the cosmological constant is in fact
present for local inhomogeneities of any size, and should always be taken
appropriately into account both theoretically and observationally.Comment: 16 pages,new sections added analyzing central smoothness and accuracy
of the Taylor expansion approach, Accepted for publication by JCAP. An essay
based on this paper received honorable mention in the 2011 Essay Context of
the Gravity Research Foundatio
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