53 research outputs found
The evolution of collision debris near the secular resonance and its role in the origin of terrestrial water
This work presents novel findings that broadens our understanding of the
amount of water that can be transported to Earth. The key innovation lies in
the combined usage of Smoothed Particle Hydrodynamics (SPH) and -body codes
to assess the role of collision fragments in water delivery. We also present a
method for generating initial conditions that enables the projectile to impact
at the designated location on the target's surface with the specified velocity.
The primary objective of this study is to simulate giant collisions between two
Ceres-sized bodies by SPH near the secular resonance and follow the
evolution of the ejected debris by numerical -body code. With our method 6
different initial conditions for the collision were determined and the
corresponding impacts were simulated by SPH. Examining the orbital evolution of
the debris ejected after collisions, we measured the amount of water delivered
to Earth, which is broadly 0.001 ocean equivalents of water, except in one case
where one large body transported 7\% oceans of water to the planet. Based on
this, and taking into account the frequency of collisions, the amount of
delivered water varies between 1.2 and 8.3 ocean's worth of water, depending on
the primordial disk mass. According to our results, the prevailing external
pollution model effectively accounts for the assumed water content on Earth,
whether it's estimated at 1 or 10 ocean's worth of water.Comment: 15 pages, 13 figure
Dynamics of the fast solar tachocline: II. Migrating field
We present detailed numerical calculations of the fast solar tachocline based
on the assumption that the dynamo field dominates over the dynamics of the
tachocline. In the present paper of the series, we focus on three shortfalls of
the earlier models. First, instead of the simple oscillating dipole poloidal
field we study the more general magnetic field structures reminiscent of the
butterfly diagram. The migrating field is prescribed as the observed
axisymmetric radial magnetic field Stenflo (1988, 1994). Our results are in
good agreement with our analitical estimate and our previous works in
Forgacs-Dajka & Petrovay (2001,2002), but the polar "dip" in isorotational
surfaces is strongly reduced in this case. On the other hand, a more realistic
model should have a magnetic diffusivity decreasing significantly inside the
radiative interior, so we also explore the effect of diffusivity and magnetic
Prandtl number varying with depth. We found that the downwards decreasing
magnetic diffusivity and Prandtl number have no significant effect on the
solution, although the temporal variation of the tachocline thickness has
decreased.Comment: 9 page
A fast method to identify mean motion resonances
The identification of mean motion resonances in exoplanetary systems or in
the Solar System might be cumbersome when several planets and large number of
smaller bodies are to be considered. Based on the geometrical meaning of the
resonance variable, an efficient method is introduced and described here, by
which mean motion resonances can be easily find without any a priori knowledge
on them. The efficiency of this method is clearly demonstrated by using known
exoplanets engaged in mean motion resonances, and also some members of
different families of asteroids and Kuiper-belt objects being in mean motion
resonances with Jupiter and Neptune respectively.Comment: 7 pages, 13 figures, accepted by Monthly Notices of the Royal
Astronomical Societ
Dynamics of the fast solar tachocline: I. Dipolar field
One possible scenario for the origin of the solar tachocline, known as the
"fast tachocline", assumes that the turbulent diffusivity exceeds eta>10^9
cm^2/s. In this case the dynamics will be governed by the dynamo-generated
oscillatory magnetic field on relatively short timescales. Here, for the first
time, we present detailed numerical models for the fast solar tachocline with
all components of the magnetic field calculated explicitly, assuming axial
symmetry and a constant turbulent diffusivity eta and viscosity nu. We find
that a sufficiently strong oscillatory poloidal field with dipolar latitude
dependence at the tachocline-convective zone boundary is able to confine the
tachocline. Exploring the three-dimensional parameter space defined by the
viscosity in the range log(nu)=9-11, the magnetic Prandtl number in the range
Prm=0.1-10, and the meridional flow amplitude (-3 to +3 cm/s), we also find
that the confining field strength B_conf, necessary to reproduce the observed
thickness of the tachocline, increases with viscosity nu, with magnetic Prandtl
number nu/eta, and with equatorward meridional flow speed. Nevertheless, the
resulting B_conf values remain quite reasonable, in the range 10^3-10^4 G, for
all parameter combinations considered here. The thickness of the tachocline
shows a marked dependence on both time and latitude. A comparison with seismic
constraints suggests that best agreement with our models is achieved for the
highest values of nu and Prm considered here.Comment: 11 page
A BABCOCK-LEIGHTON SOLAR DYNAMO MODEL WITH MULTI-CELLULAR MERIDIONAL CIRCULATION IN ADVECTION- AND DIFFUSION-DOMINATED REGIMES
Babcock-Leighton type solar dynamo models with single-celled meridional
circulation are successful in reproducing many solar cycle features. Recent
observations and theoretical models of meridional circulation do not indicate a
single-celled flow pattern. We examine the role of complex multi-cellular
circulation patterns in a Babcock-Leighton solar dynamo in advection- and
diffusion-dominated regimes. We show from simulations that presence of a weak,
second, high-latitude reverse cell speeds up the cycle and slightly enhances
the poleward branch in butterfly diagram, whereas the presence of a second cell
in depth reverses the tilt of butterfly wing to an anti-solar type. A butterfly
diagram constructed from middle of convection zone yields a solar-like pattern,
but this may be difficult to realize in the Sun because of magnetic buoyancy
effects. Each of the above cases behaves similarly in higher and lower magnetic
diffusivity regimes. However, our dynamo with a meridional circulation
containing four cells in latitude behaves distinctly differently in the two
regimes, producing solar-like butterfly diagrams with fast cycles in the higher
diffusivity regime, and complex branches in butterfly diagrams in the lower
diffusivity regime. We also find that dynamo solutions for a four-celled
pattern, two in radius and two in latitude, prefer to quickly relax to
quadrupolar parity if the bottom flow-speed is strong enough, of similar order
of magnitude as the surface flow-speed.Comment: 40 pages, 19 figures, accepted in Ap
Time-dependent properties of sunspot groups. I. Lifetime and asymmetric evolution
Aims. In this paper, we aim to study the time dependence of sunspot group areas in a large sample composed of various databases spanning over 130 years, used state-of-the-art statistical methods.
Methods. For a carefully selected but unbiased sample, we use Bayesian modelling to fit the temporal evolution of the combined umbral and penumbral area of spot groups with a skew-normal function to determine the existence of any asymmetry in spot growth or decay. Our primary selection criteria guaranteed that only spot groups with a well-defined maximum area were taken into account. We also analysed the covariance of the resulting model parameters and their correlations with the physical parameters of the sunspots and the ongoing solar cycle.
Results. Our results show that the temporal evolution of well-observed sunspot groups that reach at least 50 millionths of a solar hemisphere at their maximum can be fitted surprisingly well with our model. Furthermore, we show significant asymmetry – described by a skew parameter of fitted curves – between the growing and decaying phases of analysed sunspot groups. In addition, we found a weak correlation between the values of skew parameters and the maximum area of sunspot groups and their hemispherical latitude
Eclipse timing variation analysis of OGLE-IV eclipsing binaries towards the Galactic Bulge – I. Hierarchical triple system candidates
We report a study of the eclipse timing variation (ETV) of short period
() eclipsing binaries (EB) monitored during the photometric survey
OGLE-IV. From the 425\,193 EBs we selected approximately 80\,000 binaries that
we found suitable for further examination. Among them we identified 992
potential hierarchical triple (or multiple ) system candidates exhibiting
light-travel-time effect (LTTE). Besides, we obtained the orbital parameters of
these systems and carried out statistical analyses on the properties of these
candidates. We found that (i) there is a significant lack of triple systems
where the outer period is less than 500 days; (ii) the distribution of the
outer eccentricities has a maximum around ; (iii) the outer mass
ratio calculated from an estimated minimum mass of the third component is lower
than for the majority of the sample. We also present some systems
that deserve special attention. (i) There are four candidates that show double
periodic ETV, which we explain by the presence of a fourth companion. (ii) For
two systems the perturbations of the third component are also found to be
significant therefore we give a combined dynamical and LTTE ETV solution. (iii)
For one system the third component is found to be probably in the substellar
mass domain.Comment: Accepted for publication in MNRA
Long-term variation in distribution of sunspot groups
We studied the relation between the distribution of sunspot groups and the
Gleissberg cycle. As the magnetic field is related to the area of the sunspot
groups, we used area-weighted sunspot group data. On the one hand, we confirm
the previously reported long-term cyclic behaviour of the sum of the northern
and southern sunspot group mean latitudes, although we found a somewhat longer
period (P~104 years). We introduced the difference between the ensemble average
area of sunspot groups for the two hemispheres, which turns out to show similar
behaviour. We also investigated a further aspect of the Gleissberg cycle where
while in the 19th century the consecutive Schwabe cycles are sharply separated
from each other, one century later the cycles overlap each other more and more.Comment: 4 page
On the compatibility of a flux transport dynamo with a fast tachocline scenario
The compatibility of the fast tachocline scenario with a flux transport
dynamo model is explored. We employ a flux transport dynamo model coupled with
simple feedback formulae relating the thickness of the tachocline to the
amplitude of the magnetic field or to the Maxwell stress. The dynamo model is
found to be robust against the nonlinearity introduced by this simplified fast
tachocline mechanism. Solar-like butterfly diagrams are found to persist and,
even without any parameter fitting, the overall thickness of the tachocline is
well within the range admitted by helioseismic constraints. In the most
realistic case of a time and latitude dependent tachocline thickness linked to
the value of the Maxwell stress, both the thickness and its latitude dependence
are in excellent agreement with seismic results. In the nonparametric models,
cycle related temporal variations in tachocline thickness are somewhat larger
than admitted by helioseismic constraints; we find, however, that introducing a
further parameter into our feedback formula readily allows further fine tuning
of the thickness variations.Comment: Accepted in Solar Physic
KIC 7177553: a quadruple system of two close binaries
KIC 7177553 was observed by the Kepler satellite to be an eclipsing eccentric binary star system with an 18-day orbital period. Recently, an eclipse timing study of the Kepler binaries has revealed eclipse timing variations (ETVs) in this object with an amplitude of ~100 s and an outer period of 529 days. The implied mass of the third body is that of a super-Jupiter, but below the mass of a brown dwarf. We therefore embarked on a radial velocity (RV) study of this binary to determine its system configuration and to check the hypothesis that it hosts a giant planet. From the RV measurements, it became immediately obvious that the same Kepler target contains another eccentric binary, this one with a 16.5-day orbital period. Direct imaging using adaptive optics reveals that the two binaries are separated by 0”.4 (~167 AU) and have nearly the same magnitude (to within 2%). The close angular proximity of the two binaries and very similar γ velocities strongly suggest that KIC 7177553 is one of the rare SB4 systems consisting of two eccentric binaries where at least one system is eclipsing. Both systems consist of slowly rotating, nonevolved, solar-like stars of comparable masses. From the orbital separation and the small difference in γ velocity, we infer that the period of the outer orbit most likely lies in the range of 1000–3000 yr. New images taken over the next few years, as well as the high-precision astrometry of the Gaia satellite mission, will allow us to set much narrower constraints on the system geometry. Finally, we note that the observed ETVs in the Kepler data cannot be produced by the second binary. Further spectroscopic observations on a longer timescale will be required to prove the existence of the massive planet
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