68 research outputs found
Application of the MEGNO technique to the dynamics of Jovian irregular satellites
We apply the MEGNO (Mean Exponential Growth of Nearby Orbits) technique to
the dynamics of Jovian irregular satellites. We demonstrate the efficiency of
applying the MEGNO indicator to generate a mapping of relevant phase-space
regions occupied by observed jovian irregular satellites. The construction of
MEGNO maps of the Jovian phase-space region within its Hill-sphere is addressed
and the obtained results are compared with previous studies regarding the
dynamical stability of irregular satellites. Since this is the first time the
MEGNO technique is applied to study the dynamics of irregular satellites we
provide a review of the MEGNO theory. We consider the elliptic restricted
three-body problem in which Jupiter is orbited by a massless test satellite
subject to solar gravitational perturbations. The equations of motion of the
system are integrated numerically and the MEGNO indicator computed from the
systems variational equations. An unprecedented large set of initial conditions
are studied to generate the MEGNO maps. The chaotic nature of initial
conditions are demonstrated by studying a quasi-periodic orbit and a chaotic
orbit. As a result we establish the existence of several high-order mean-motion
resonances detected for retrograde orbits along with other interesting
dynamical features. The computed MEGNO maps allows to qualitatively
differentiate between chaotic and quasi-periodic regions of the irregular
satellite phase-space given only a relatively short integration time. By
comparing with previous published results we can establish a correlation
between chaotic regions and corresponding regions of orbital instability.Comment: 15 pages, 13 figures, 2 tables, submitted to MNRA
A Planet in a 0.6-AU Orbit Around the K0 Giant HD 102272
We report the discovery of one or more planet-mass companions to the K0-giant
HD 102272 with the Hobby-Eberly Telescope. In the absence of any correlation of
the observed periodicities with the standard indicators of stellar activity,
the observed radial velocity variations are most plausibly explained in terms
of a Keplerian motion of at least one planet-mass body around the star. With
the estimated stellar mass of 1.9M, the minimum mass of the confirmed
planet is 5.9M. The planet's orbit is characterized by a small but nonzero
eccentricity of =0.05 and the semi-major axis of 0.61 AU, which makes it the
most compact one discovered so far around GK-giants. This detection adds to the
existing evidence that, as predicted by theory, the minimum size of planetary
orbits around intermediate-mass giants is affected by both planet formation
processes and stellar evolution. The currently available evidence for another
planet around HD 102272 is insufficient to obtain an unambiguous two-orbit
solution.Comment: 10 pages, 5 figure
Resonances of low orders in the planetary system of HD37124
The full set of published radial velocity data (52 measurements from Keck +
58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed.
Two families of dynamically stable high-eccentricity orbital solutions for the
planetary system are found. In the first one, the outer planets c and d are
trapped in the 2/1 mean-motion resonance. The second family of solutions
corresponds to the 5/2 mean-motion resonance between these planets. In both
families, the planets are locked in (or close to) an apsidal corotation
resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation
(with the difference between the longitudes of periastra ), whereas in the case of the 5/2 MMR it is a symmetric antialigned
one ().
It remains also possible that the two outer planets are not trapped in an
orbital resonance. Then their orbital eccentricities should be relatively small
(less than, say, 0.15) and the ratio of their orbital periods is unlikely to
exceed .Comment: 28 pages, 10 figures, 3 tables; Accepted to Celestial Mechanics and
Dynamical Astronom
New Light-Travel Time Models and Orbital Stability Study of the Proposed Planetary System HU Aquarii
In this work we propose a new orbital architecture for the two proposed
circumbinary planets around the polar eclipsing binary HU Aquarii. We base the
new two-planet, light-travel time model on the result of a Monte Carlo
simulation driving a least-squares Levenberg-Marquardt minimisation algorithm
on the observed eclipse egress times. Our best-fitting model with
resulted in high final eccentricities for the two companions
leading to an unstable orbital configuration. From a large ensemble of initial
guesses we examined the distribution of final eccentricities and semi-major
axes for different parameter intervals and encountered
qualitatively a second population of best-fitting parameters. The main
characteristic of this population is described by low-eccentric orbits
favouring long-term orbital stability of the system. We present our
best-fitting model candidate for the proposed two-planet system and demonstrate
orbital stability over one million years using numerical integrations.Comment: 9 Figures (B/W) and 2 tables, accepted for publication in MNRAS, this
is pre-proof versio
The Debris Disk Around HR 8799
We have obtained a full suite of Spitzer observations to characterize the
debris disk around HR 8799 and to explore how its properties are related to the
recently discovered set of three massive planets orbiting the star. We
distinguish three components to the debris system: (1) warm dust (T ~150 K)
orbiting within the innermost planet; (2) a broad zone of cold dust (T ~45 K)
with a sharp inner edge, orbiting just outside the outermost planet and
presumably sculpted by it; and (3) a dramatic halo of small grains originating
in the cold dust component. The high level of dynamical activity implied by
this halo may arise due to enhanced gravitational stirring by the massive
planets. The relatively young age of HR 8799 places it in an important early
stage of development and may provide some help in understanding the interaction
of planets and planetary debris, an important process in the evolution of our
own solar system.Comment: emulateapj format, 13 pages, 10 figures, accepted to Ap
LBT observations of the HR 8799 planetary system: First detection of HR8799e in H band
We have performed H and Ks band observations of the planetary system around
HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES
Camera. The excellent instrument performance (Strehl ratios up to 80% in H
band) enabled detection the inner planet HR8799e in the H band for the first
time. The H and Ks magnitudes of HR8799e are similar to those of planets c and
d, with planet e slightly brighter. Therefore, HR8799e is likely slightly more
massive than c and d. We also explored possible orbital configurations and
their orbital stability. We confirm that the orbits of planets b, c and e are
consistent with being circular and coplanar; planet d should have either an
orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c.
Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion
resonances with c and d, while coplanar and circular orbits are allowed for a
5:2 resonance. The analysis of dynamical stability shows that the system is
highly unstable or chaotic when planetary masses of about 5 MJup for b and 7
MJup for the other planets are adopted. Significant regions of dynamical
stability for timescales of tens of Myr are found when adopting planetary
masses of about 3.5, 5, 5, and 5 Mjup for HR 8799 b, c, d, and e respectively.
These masses are below the current estimates based on the stellar age (30 Myr)
and theoretical models of substellar objects.Comment: 13 pages, 10 figures, A&A, accepte
Orbital and dynamical analysis of the system around HR 8799. New astrometric epochs from VLT/SPHERE and LBT/LUCI
HR\,8799 is a young planetary system composed of 4 planets and a double
debris belt. Being the first multi-planetary system discovered with the direct
imaging technique, it has been observed extensively since 1998. This wide
baseline of astrometric measurements, counting over 50 observations in 20
years, permits a detailed orbital and dynamical analysis of the system. To
explore the orbital parameters of the planets, their dynamical history, and the
planet-to-disk interaction, we made follow-up observations of the system during
the VLT/SPHERE GTO program. We obtained 21 observations, most of them in
favorable conditions. In addition, we observed HR\,8799 with the instrument
LBT/LUCI. All the observations were reduced with state-of-the-art algorithms
implemented to apply the spectral and angular differential imaging method. We
re-reduced the SPHERE data obtained during the commissioning of the instrument
and in 3 open-time programs to have homogeneous astrometry. The precise
position of the 4 planets with respect to the host star was calculated by
exploiting the fake negative companions method. To improve the orbital fitting,
we also took into account all of the astrometric data available in the
literature. From the photometric measurements obtained in different
wavelengths, we estimated the planets' masses following the evolutionary
models. We obtained updated parameters for the orbits with the assumption of
coplanarity, relatively small eccentricities, and periods very close to the 2:1
resonance. We also refined the dynamical mass of each planet and the parallax
of the system (24.49 0.07 mas). We also conducted detailed -body
simulations indicating possible positions of a~putative fifth innermost planet
with a mass below the present detection limits of ~\MJup.Comment: 27 pages, 15 figures, A&A in pres
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