149 research outputs found
Analytic orbit propagation for transiting circumbinary planets
The herein presented analytical framework fully describes the motion of
coplanar systems consisting of a stellar binary and a planet orbiting both
stars on orbital as well as secular timescales. Perturbations of the Runge-Lenz
vector are used to derive short period evolution of the system, while octupole
secular theory is applied to describe its long term behaviour. A post Newtonian
correction on the stellar orbit is included. The planetary orbit is initially
circular and the theory developed here assumes that the planetary eccentricity
remains relatively small (e_2<0.2). Our model is tested against results from
numerical integrations of the full equations of motion and is then applied to
investigate the dynamical history of some of the circumbinary planetary systems
discovered by NASA's Kepler satellite. Our results suggest that the formation
history of the systems Kepler-34 and Kepler-413 has most likely been different
from the one of Kepler-16, Kepler-35, Kepler-38 and Kepler-64, since the
observed planetary eccentricities for those systems are not compatible with the
assumption of initially circular orbits.Comment: Accepted for publication in Ap
Sublimation-induced orbital perturbations of extrasolar active asteroids and comets: application to white dwarf systems
The metal budgets in some white dwarf (WD) atmospheres reveal that
volatile-rich circumstellar bodies must both exist in extrasolar systems and
survive the giant branch phases of stellar evolution. The resulting behaviour
of these active asteroids or comets which orbit WDs is not well-understood, but
may be be strongly influenced by sublimation due to stellar radiation. Here we
develop a model, generally applicable to any extrasolar system with a main
sequence or WD star, that traces sublimation-induced orbital element changes in
approximately km-sized extrasolar minor planets and comets traveling within
hundreds of au. We derive evolution equations on orbital timescales and for
arbitrarily steep power-law sublimation dependencies on distance, and place our
model in a Solar system context. We also demonstrate the importance of coupling
sublimation and general relativity, and the orbital consequences of outgassing
in arbitrary directions. We prove that nongravitational accelerations alone
cannot result in orbit crossing with the WD disruption radius, but may shrink
or expand the orbit by up to several au after a single pericentre passage,
potentially affecting subsequent interactions with remnant debris and planets.
Our analysis suggests that extant planets must exist in polluted WD systems.Comment: Accepted for publication in MNRA
Detectability of Earth-like Planets in Circumstellar Habitable Zones of Binary Star Systems with Sun-like Components
Given the considerable percentage of stars that are members of binaries or
stellar multiples in the Solar neighborhood, it is expected that many of these
binaries host planets, possibly even habitable ones. The discovery of a
terrestrial planet in the alpha Centauri system supports this notion. Due to
the potentially strong gravitational interaction that an Earth-like planet may
experience in such systems, classical approaches to determining habitable
zones, especially in close S-Type binary systems, can be rather inaccurate.
Recent progress in this field, however, allows to identify regions around the
star permitting permanent habitability. While the discovery of alpha Cen Bb has
shown that terrestrial planets can be detected in solar-type binary stars using
current observational facilities, it remains to be shown whether this is also
the case for Earth analogues in habitable zones. We provide analytical
expressions for the maximum and RMS values of radial velocity and astrometric
signals, as well as transit probabilities of terrestrial planets in such
systems, showing that the dynamical interaction of the second star with the
planet may indeed facilitate the planets detection. As an example, we discuss
the detectability of additional Earth-like planets in the averaged, extended,
and permanent habitable zones around both stars of the alpha Centauri system.Comment: accepted for publication in The Astrophysical Journa
The orbital evolution of asteroids, pebbles and planets from giant branch stellar radiation and winds
The discovery of over 50 planets around evolved stars and more than 35 debris
discs orbiting white dwarfs highlight the increasing need to understand small
body evolution around both early and asymptotic giant branch (GB) stars.
Pebbles and asteroids are susceptible to strong accelerations from the intense
luminosity and winds of GB stars. Here, we establish equations that can model
time-varying GB stellar radiation, wind drag and mass loss. We derive the
complete three-dimensional equations of motion in orbital elements due to (1)
the Epstein and Stokes regimes of stellar wind drag, (2) Poynting-Robertson
drag, and (3) the Yarkovsky drift with seasonal and diurnal components. We
prove through averaging that the potential secular eccentricity and inclination
excitation due to Yarkovsky drift can exceed that from Poynting-Robertson drag
and radiation pressure by at least three orders of magnitude, possibly flinging
asteroids which survive YORP spin-up into a widely dispersed cloud around the
resulting white dwarf. The GB Yarkovsky effect alone may change an asteroid's
orbital eccentricity by ten per cent in just one Myr. Damping perturbations
from stellar wind drag can be just as extreme, but are strongly dependent on
the highly uncertain local gas density and mean free path length. We conclude
that GB radiative and wind effects must be considered when modelling the
post-main-sequence evolution of bodies smaller than about 1000 km.Comment: Corrected Fig. 3 and Eq. 14 (In Press, MNRAS
Climate variations on Earth-like circumbinary planets
The discovery of planets orbiting double stars at close distances has sparked increasing scientific interest in determining whether Earth-analogues can remain habitable in such environments and how their atmospheric dynamics is influenced by the rapidly changing insolation. In this work we present results of the first three-dimensional numerical experiments of a water-rich planet orbiting a double star. We find that the periodic forcing of the atmosphere has a noticeable impact on the planet’s climate. Signatures of the forcing frequencies related to the planet’s as well as to the binary’s orbital periods are present in a variety of climate indicators such as temperature and precipitation, making the interpretation of potential observables challenging. However, for Earth-like greenhouse gas concentrations, the variable forcing does not change the range of insolation values allowing for habitable climates substantially
Spectral properties of near-Earth and Mars-crossing asteroids using Sloan photometry
The nature and origin of the asteroids orbiting in near-Earth space,
including those on a potentially hazardous trajectory, is of both scientific
interest and practical importance. We aim here at determining the taxonomy of a
large sample of near-Earth (NEA) and Mars-crosser (MC) asteroids and analyze
the distribution of these classes with orbit. We use this distribution to
identify their source regions and to study the strength of planetary encounters
to refresh asteroid surfaces. We measure the photometry of these asteroids over
four filters at visible wavelengths on images taken by the SDSS. These colors
are used to classify the asteroids into a taxonomy consistent with the widely
used Bus-DeMeo taxonomy based on spectroscopy. We report here on the taxonomic
classification of 206 NEAs and 776 MCs determined from SDSS photometry,
representing an increase of 40% and 663% of known taxonomy classifications in
these populations. Using the source region mapper by Greenstreet et al. (2012),
we compare the taxonomic distribution among NEAs and main-belt asteroids of
similar diameters. Both distributions agree at the few percent level for the
inner part of the Main Belt and we confirm this region as a main source of
near-Earth objects. The effect of planetary encounters on asteroid surfaces are
also studied by developing a simple model of forces acting on a surface grain
during planetary encounter, which provides the minimum distance at which a
close approach should occur to trigger resurfacing events. By integrating
numerically the orbit of the 519 S-type and 46 Q-type asteroids back in time
and monitoring their encounter distance with planets, we seek to understand the
conditions for resurfacing events. The population of Q-type is found to present
statistically more encounters with Venus and the Earth than S-types, although
both types present the same amount of encounters with Mars.Comment: Accepted for publication in Icarus. 45 pages, 11 figures, 4 tables, 2
tables in appendix (supplementary material
An Analytic Method to determine Habitable Zones for S-Type Planetary Orbits in Binary Star Systems
With more and more extrasolar planets discovered in and around binary star
systems, questions concerning the determination of the classical Habitable Zone
arise. Do the radiative and gravitational perturbations of the second star
influence the extent of the Habitable Zone significantly, or is it sufficient
to consider the host-star only? In this article we investigate the implications
of stellar companions with different spectral types on the insolation a
terrestrial planet receives orbiting a Sun-like primary. We present time
independent analytical estimates and compare these to insolation statistics
gained via high precision numerical orbit calculations. Results suggest a
strong dependence of permanent habitability on the binary's eccentricity, as
well as a possible extension of Habitable Zones towards the secondary in close
binary systems.Comment: submitted to ApJ, status: accepte
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