269 research outputs found
The GTC exoplanet transit spectroscopy survey. VII. An optical transmission spectrum of WASP-48b
We obtained long-slit optical spectroscopy of one transit of WASP-48b with
the Optical System for Imaging and low-Intermediate-Resolution Integrated
Spectroscopy (OSIRIS) spectrograph at the 10.4 m Gran Telescopio Canarias
(GTC). We integrated the spectrum of WASP-48 and one reference star in several
channels with different wavelength ranges, creating numerous color light curves
of the transit. We fit analytic transit curves to the data taking into account
the systematic effects present in the time series in an effort to measure the
change of the planet-to-star radius ratio () across wavelength. After
removing the transit model and systematic trends to the curves we reached
precisions between 261 ppm and 455-755 ppm for the white and spectroscopic
light curves, respectively. We obtained uncertainty values between
and for all the curves analyzed in
this work. The measured transit depth for the curves made by integrating the
wavelength range between 530 nm and 905 nm is in agreement with previous
studies. We report a relatively flat transmission spectrum for WASP-48b with no
statistical significant detection of atmospheric species, although the
theoretical models that fit the data more closely include of TiO and VO.Comment: 8 pages, 8 figures. Accepted for publication in Astronomy and
Astrophysic
Implications of Geographic Information System in Mapping Solid Waste Collection Points in New Owerri, Imo State
The unsanitary condition in which solid waste is temporarily dumped and disposed of has generated environmental concern through pollutions and health hazards. This calls for a need to map out suitable collection points and disposal point for effective and efficient management of solid waste to promote hygienic environment. Therefore, GIS offers solution in this regard as a decision support system for most suitable site selection. Consequently, different layers (roads, stream and land use) were created to serve the purpose of manipulation and analyses to procure most suitable site for collection point of solid waste generated in New Owerri, Imo State using Arc view 3.2a software
The Interiors of Giant Planets: Models and Outstanding Questions
We know that giant planets played a crucial role in the making of our Solar
System. The discovery of giant planets orbiting other stars is a formidable
opportunity to learn more about these objects, what is their composition, how
various processes influence their structure and evolution, and most importantly
how they form. Jupiter, Saturn, Uranus and Neptune can be studied in detail,
mostly from close spacecraft flybys. We can infer that they are all enriched in
heavy elements compared to the Sun, with the relative global enrichments
increasing with distance to the Sun. We can also infer that they possess dense
cores of varied masses. The intercomparison of presently caracterised
extrasolar giant planets show that they are also mainly made of hydrogen and
helium, but that they either have significantly different amounts of heavy
elements, or have had different orbital evolutions, or both. Hence, many
questions remain and are to be answered for significant progresses on the
origins of planets.Comment: 43 pages, 11 figures, 3 tables. To appear in Annual Review of Earth
and Planetary Sciences, vol 33, (2005
Spitzer 3.6 micron and 4.5 micron full-orbit lightcurves of WASP-18
We present new lightcurves of the massive hot Jupiter system WASP-18 obtained
with the Spitzer spacecraft covering the entire orbit at 3.6 micron and 4.5
micron. These lightcurves are used to measure the amplitude, shape and phase of
the thermal phase effect for WASP-18b. We find that our results for the thermal
phase effect are limited to an accuracy of about 0.01% by systematic noise
sources of unknown origin. At this level of accuracy we find that the thermal
phase effect has a peak-to-peak amplitude approximately equal to the secondary
eclipse depth, has a sinusoidal shape and that the maximum brightness occurs at
the same phase as mid-occultation to within about 5 degrees at 3.6 micron and
to within about 10 degrees at 4.5 micron. The shape and amplitude of the
thermal phase curve imply very low levels of heat redistribution within the
atmosphere of the planet. We also perform a separate analysis to determine the
system geometry by fitting a lightcurve model to the data covering the
occultation and the transit. The secondary eclipse depths we measure at 3.6
micron and 4.5 micron are in good agreement with previous measurements and
imply a very low albedo for WASP-18b. The parameters of the system (masses,
radii, etc.) derived from our analysis are in also good agreement with those
from previous studies, but with improved precision. We use new high-resolution
imaging and published limits on the rate of change of the mean radial velocity
to check for the presence of any faint companion stars that may affect our
results. We find that there is unlikely to be any significant contribution to
the flux at Spitzer wavelengths from a stellar companion to WASP-18. We find
that there is no evidence for variations in the times of eclipse from a linear
ephemeris greater than about 100 seconds over 3 years.Comment: 17 pages, 10 figures. Accpeted for publication in MNRA
The impact of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.We investigate the effects of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b. We use a simplified dynamical model and a robust chemical network, as opposed to previous studies which have used a three dimensional circulation model coupled to a simple chemical kinetics scheme. The temperature structure and distribution of the main atmospheric constituents are calculated in the limit of an atmosphere that rotates as a solid body with an equatorial rotation rate of 1 km/s. Such motion mimics a uniform zonal wind which resembles the equatorial superrotation structure found by three dimensional circulation models. The uneven heating of this tidally locked planet causes, even in the presence of such a strong zonal wind, large temperature contrasts between the dayside and nightside, of up to 800 K. This would result in important longitudinal variations of some molecular abundances if the atmosphere were at chemical equilibrium. The zonal wind, however, acts as a powerful disequilibrium process. We identify the existence of a pressure level of transition between two regimes, which may be located between 100 and 0.1 mbar depending on the molecule. Below this transition layer, chemical equilibrium holds, while above it, the zonal wind tends to homogenize the chemical composition of the atmosphere, bringing molecular abundances in the limb and nightside regions close to chemical equilibrium values characteristic of the dayside, i.e. producing an horizontal quenching effect in the abundances. Reasoning based on timescales arguments indicates that horizontal and vertical mixing are likely to compete in HD 209458b's atmosphere, producing a complex distribution where molecular abundances are quenched horizontally to dayside values and vertically to chemical equilibrium values characteristic of deep layers.M.A., O.V., F.S., and E.H. acknowledge support from the European Research Council (ERC Grant 209622: E3ARTHs). Computer time for this study was provided by the computing facilities MCIA (Mésocentre de Calcul Intensif Aquitain) of the Université de Bordeaux and of the Université de Pau et des Pays de l’Adour. We thank the anonymous referee for a constructive report that helped to improve this manuscript
Shape functions of dipolar ferromagnets at the Curie point
We present a complete mode coupling theory for the critical dynamics of ferromagnets above the Curie point with both short range exchange and long range dipolar interaction. This theory allows us to determine the full Kubo relaxation functions at the critical point. In particular, we are able to explain recent spin echo measurements
Habitability and multistability in earth-like planets
We explore the potential multistability of the climate for a planet around the habitable zone. We focus on conditions reminiscent to those of the Earth system, but our investigation aims at presenting a general methodology for dealing with exoplanets. We provide a thorough analysis of the non-equilibrium thermodynamical properties of the climate system and explore, using a a flexible climate model, how such properties depend on the energy input of the parent star, on the infrared atmospheric opacity, and on the rotation rate. It is possible to reproduce the multi-stability properties reminiscent of the paleoclimatologically relevant snowball (SB) - warm (W) conditions. We then study the thermodynamics of the W and SB states, clarifying the role of the hydrological cycle in shaping the irreversibility and the efficiency of the W states, and emphasizing the extreme diversity of the SB states, where dry conditions are realized. Thermodynamics provides the clue for studying the tipping points of the system and leads us to constructing parametrizations where the main thermodynamic properties are expressed as functions of the emission temperature of the planet only. Such functions are rather robust with respect to changing the rotation rate of the planet from the current terrestrial one to half of it. We then explore the dynamical range of slowy rotating and phase locked planets. There is a critical rotation rate below which the multi-stability properties are lost. Such critical rotation rate corresponds roughly to the phase lock 2:1 condition. Therefore, if an Earth-like planet is 1:1 phase locked with respect to the parent star, only one climatic state would be compatible with a given set of astronomical and astrophysical parameters. These results have relevance for the general theory of planetary circulation and for the definition of necessary and sufficient conditions for habitability
Effect of structural defects on anomalous ultrasound propagation in solids during second-order phase transitions
The effect of structural defects on the critical ultrasound attenuation and
ultrasound velocity dispersion in Ising-like three-dimensional systems is
studied. A field-theoretical description of the dynamic effects of
acoustic-wave propagation in solids during phase transitions is performed with
allowance for both fluctuation and relaxation attenuation mechanisms. The
temperature and frequency dependences of the scaling functions of the
attenuation coefficient and the ultrasound velocity dispersion are calculated
in a two-loop approximation for pure and structurally disordered systems, and
their asymptotic behavior in hydrodynamic and critical regions is separated. As
compared to a pure system, the presence of structural defects in it is shown to
cause a stronger increase in the sound attenuation coefficient and the sound
velocity dispersion even in the hydrodynamic region as the critical temperature
is reached. As compared to pure analogs, structurally disordered systems should
exhibit stronger temperature and frequency dependences of the acoustic
characteristics in the critical region.Comment: 7 RevTeX pages, 4 figure
A low fraction of nitrogen in molecular form in a dark cloud
Nitrogen is the fifth most abundant element in the Universe. In the interstellar medium, it has been thought to be mostly molecular (N-2)(1). However, N-2 has no observable rotational or vibrational transitions, so its abundance in the interstellar medium remains poorly known. In comets, the N-2 abundance is very low(2,3), while the elemental nitrogen abundance is deficient with respect to the solar value. Moreover, large nitrogen isotopic anomalies are observed in meteorites and interstellar dust particles(4). Here we report the N2H+ (and by inference the N-2) abundance inside a cold dark molecular cloud. We find that only a small fraction of nitrogen in the gas phase is molecular, with most of it being atomic. Because the compositions of comets probably reflect those of dark clouds(5), this result explains the low N-2 abundance in comets. We argue that the elemental nitrogen abundance deficiency in comets can be understood if the atomic oxygen abundance is lower than predicted by present chemical models. Furthermore, the lack of molecular nitrogen in molecular clouds explains the nitrogen anomalies in meteorites and interstellar dust particles, as nitrogen fractionation is enhanced if gaseous nitrogen is atomic(6).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62670/1/nature04919.pd
Radiative Transfer for Exoplanet Atmospheres
Remote sensing of the atmospheres of distant worlds motivates a firm
understanding of radiative transfer. In this review, we provide a pedagogical
cookbook that describes the principal ingredients needed to perform a radiative
transfer calculation and predict the spectrum of an exoplanet atmosphere,
including solving the radiative transfer equation, calculating opacities (and
chemistry), iterating for radiative equilibrium (or not), and adapting the
output of the calculations to the astronomical observations. A review of the
state of the art is performed, focusing on selected milestone papers.
Outstanding issues, including the need to understand aerosols or clouds and
elucidating the assumptions and caveats behind inversion methods, are
discussed. A checklist is provided to assist referees/reviewers in their
scrutiny of works involving radiative transfer. A table summarizing the
methodology employed by past studies is provided.Comment: 7 pages, no figures, 1 table. Filled in missing information in
references, main text unchange
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