846 research outputs found
Electron density distribution and solar plasma correction of radio signals using MGS, MEX and VEX spacecraft navigation data and its application to planetary ephemerides
The Mars Global Surveyor (MGS), Mars Express (MEX), and Venus Express (VEX)
experienced several superior solar conjunctions. These conjunctions cause
severe degradations of radio signals when the line of sight between the Earth
and the spacecraft passes near to the solar corona region. The primary
objective of this work is to deduce a solar corona model from the spacecraft
navigation data acquired at the time of solar conjunctions and to estimate its
average electron density. The corrected or improved data are then used to fit
the dynamical modeling of the planet motions, called planetary ephemerides. We
analyzed the radio science raw data of the MGS spacecraft using the orbit
determination software GINS. The range bias, obtained from GINS and provided by
ESA for MEX and VEX, are then used to derive the electron density profile.
These profiles are obtained for different intervals of solar distances: from
12Rs to 215Rs for MGS, 6Rs to 152Rs for MEX, and form 12Rs to 154Rs for VEX.
They are acquired for each spacecraft individually, for ingress and egress
phases separately and both phases together, for different types of solar winds
(fast, slow), and for solar activity phases (minimum, maximum). We compared our
results with the previous estimations that were based on in situ measurements,
and on solar type III radio and radio science studies made at different phases
of solar activity and at different solar wind states. Our results are
consistent with estimations obtained by these different methods. Moreover,
fitting the planetary ephemerides including complementary data that were
corrected for the solar corona perturbations, noticeably improves the
extrapolation capability of the planetary ephemerides and the estimation of the
asteroids masses.Comment: Accepted for publication in A&
A Potential Bio-sorbent for Heavy Metals in the Remediation of Waste Water
Bay leaves are used for flavoring in cold drinks production, in bakery goods, sauces, confectionary products and liquors. The waste generated from these sources has been valorized by attempting the remediation of waste water. Hence, adsorption of toxic metals onto Bay leaves has been investigated after optimizing the experimental parameters, namely the pH, contact time, adsorbent and Zn(II) concentrations as well as the temperature of the equilibrium mixture (consisting of the metal solution in contact with the adsorbent). The participation of the constituent functional groups, of the adsorbent, was ascertained with Fourier transform spectroscopic studies. The mode of adsorption was examined by employing important isotherm models, namely Langmuir, Freundlich and Dubinin-Radushkevich models. The adsorption process was found to follow pseudo-first order kinetic model and also followed the intraparticle diffusion up to 60 minutes of contact time. The thermodynamic parameters suggest the spontaneous nature of adsorption
Comparison of different exoplanet mass detection limit methods using a sample of main-sequence intermediate-type stars
The radial velocity (RV) technique is a powerful tool for detecting
extrasolar planets and deriving mass detection limits that are useful for
constraining planet pulsations and formation models. Detection limit methods
must take into account the temporal distribution of power of various origins in
the stellar signal. These methods must also be able to be applied to large
samples of stellar RV time series We describe new methods for providing
detection limits. We compute the detection limits for a sample of ten main
sequence stars, which are of G-F-A type, in general active, and/or with
detected planets, and various properties. We use them to compare the
performances of these methods with those of two other methods used in the
litterature. We obtained detection limits in the 2-1000 day period range for
ten stars. Two of the proposed methods, based on the correlation between
periodograms and the power in the periodogram of the RV time series in specific
period ranges, are robust and represent a significant improvement compared to a
method based on the root mean square of the RV signal. We conclude that two of
the new methods (correlation-based method and local power analysis, i.e. LPA,
method) provide robust detection limits, which are better than those provided
by methods that do not take into account the temporal sampling.Comment: 18 pages, 15 figures Accepted in Astronomy & Astrophysic
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
Where are the Uranus Trojans?
The area of stable motion for fictitious Trojan asteroids around Uranus'
equilateral equilibrium points is investigated with respect to the inclination
of the asteroid's orbit to determine the size of the regions and their shape.
For this task we used the results of extensive numerical integrations of orbits
for a grid of initial conditions around the points L4 and L5, and analyzed the
stability of the individual orbits. Our basic dynamical model was the Outer
Solar System (Jupiter, Saturn, Uranus and Neptune). We integrated the equations
of motion of fictitious Trojans in the vicinity of the stable equilibrium
points for selected orbits up to the age of the Solar system of 5 billion
years. One experiment has been undertaken for cuts through the Lagrange points
for fixed values of the inclinations, while the semimajor axes were varied. The
extension of the stable region with respect to the initial semimajor axis lies
between 19.05 < a < 19.3 AU but depends on the initial inclination. In another
run the inclination of the asteroids' orbit was varied in the range 0 < i < 60
and the semimajor axes were fixed. It turned out that only four 'windows' of
stable orbits survive: these are the orbits for the initial inclinations 0 < i
< 7, 9 < i < 13, 31 < i < 36 and 38 < i < 50. We postulate the existence of at
least some Trojans around the Uranus Lagrange points for the stability window
at small and also high inclinations.Comment: 15 pages, 12 figures, submitted to CMD
The role of chaotic resonances in the solar system
Our understanding of the Solar System has been revolutionized over the past
decade by the finding that the orbits of the planets are inherently chaotic. In
extreme cases, chaotic motions can change the relative positions of the planets
around stars, and even eject a planet from a system. Moreover, the spin axis of
a planet-Earth's spin axis regulates our seasons-may evolve chaotically, with
adverse effects on the climates of otherwise biologically interesting planets.
Some of the recently discovered extrasolar planetary systems contain multiple
planets, and it is likely that some of these are chaotic as well.Comment: 28 pages, 9 figure
Measuring the mixing efficiency in a simple model of stirring:some analytical results and a quantitative study via Frequency Map Analysis
We prove the existence of invariant curves for a --periodic Hamiltonian
system which models a fluid stirring in a cylindrical tank, when is small
and the assigned stirring protocol is piecewise constant. Furthermore, using
the Numerical Analysis of the Fundamental Frequency of Laskar, we investigate
numerically the break down of invariant curves as increases and we give a
quantitative estimate of the efficiency of the mixing.Comment: 10 figure
Inverse Compton X-rays from Giant Radio Galaxies at z~1
We report XMM-Newton observations of three FR II radio galaxies at redshifts
between 0.85 and 1.34, which show extended diffuse X-ray emission within the
radio lobes, likely due to inverse-Compton up-scattering of the cosmic
microwave background. Under this assumption, through spectrum-fitting together
with archival VLA radio observations, we derive an independent estimate of the
magnetic field in the radio lobes of 3C 469.1 and compare it with the
equipartition value. We find concordance between these two estimates as long as
the turnover in the energy distribution of the particles occurs at a Lorentz
factor in excess of ~ 250. We determine the total energy in relativistic
particles in the radio emitting lobes of all three sources to range between
3e59 and 8e59 erg. The nuclei of these X-ray sources are heavily-absorbed
powerful AGN.Comment: 5 pages, 7 figures, 2 tables. Accepted for publication in MNRA
Constructing the secular architecture of the solar system II: The terrestrial planets
We investigate the dynamical evolution of the terrestrial planets during the
planetesimal-driven migration of the giant planets. A basic assumption of this
work is that giant planet migration occurred after the completion of
terrestrial planet formation, such as in the models that link the former to the
origin of the Late Heavy Bombardment. The divergent migration of Jupiter and
Saturn causes the g5 eigenfrequency to cross resonances of the form g5=gk with
k ranging from 1 to 4. Consequently these secular resonances cause
large-amplitude responses in the eccentricities of the terrestrial planets. We
show that the resonances g5=g_4 and g5=g3 do not pose a problem if Jupiter and
Saturn have a fast approach and departure from their mutual 2:1 mean motion
resonance. On the other hand, the resonance crossings g5=g2 and g5=g1 are more
of a concern as they tend to yield a terrestrial system incompatible with the
current one. We offer two solutions to this problem. The first uses the fact
that a secular resonance crossing can also damp the amplitude of a Fourier mode
if the latter is large originally. A second scenario involves a 'jumping
Jupiter' in which encounters between an ice giant and Jupiter, without ejection
of the former, cause the latter to migrate away from Saturn much faster than if
migration is driven solely by encounters with planetesimals. In this case, the
g5=g2 and g5=g1 resonances can be jumped over, or occur very briefly.Comment: Astronomy & Astrophysics (2009) in pres
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