327 research outputs found
Effect of core--mantle and tidal torques on Mercury's spin axis orientation
The rotational evolution of Mercury's mantle and its core under conservative
and dissipative torques is important for understanding the planet's spin state.
Dissipation results from tides and viscous, magnetic and topographic
core--mantle interactions. The dissipative core--mantle torques take the system
to an equilibrium state wherein both spins are fixed in the frame precessing
with the orbit, and in which the mantle and core are differentially rotating.
This equilibrium exhibits a mantle spin axis that is offset from the Cassini
state by larger amounts for weaker core--mantle coupling for all three
dissipative core--mantle coupling mechanisms, and the spin axis of the core is
separated farther from that of the mantle, leading to larger differential
rotation. The relatively strong core--mantle coupling necessary to bring the
mantle spin axis to its observed position close to the Cassini state is not
obtained by any of the three dissipative core--mantle coupling mechanisms. For
a hydrostatic ellipsoidal core--mantle boundary, pressure coupling dominates
the dissipative effects on the mantle and core positions, and dissipation
together with pressure coupling brings the mantle spin solidly to the Cassini
state. The core spin goes to a position displaced from that of the mantle by
about 3.55 arcmin nearly in the plane containing the Cassini state. With the
maximum viscosity considered of if the coupling is
by the circulation through an Ekman boundary layer or for purely viscous coupling, the core spin lags the
precessing Cassini plane by 23 arcsec, whereas the mantle spin lags by only
0.055 arcsec. Larger, non hydrostatic values of the CMB ellipticity also result
in the mantle spin at the Cassini state, but the core spin is moved closer to
the mantle spin.Comment: 35 pages, 7 figure
Relativistic Resonant Relations between Massive Black Hole Binary and Extreme Mass Ratio Inspiral
One component of a massive black hole binary (MBHB) might capture a small
third body, and then a hierarchical, inclined triple system would be formed.
With the post-Newtonian approximation including radiation reaction, we analyzed
the evolution of the triple initially with small eccentricities. We found that
an essentially new resonant relation could arise in the triple system. Here
relativistic effects are crucial. Relativistic resonances, including the new
one, stably work even for an outer MBHB of comparable masses, and significantly
change the orbit of the inner small body.Comment: 9 pages, 5 figures, to appear in PR
Dynamics and Origin of the 2:1 Orbital Resonances of the GJ 876 Planets
(Abridged) A dynamical fit has placed the two planets about the star GJ 876
in coplanar orbits deep in 3 resonances at the 2:1 mean-motion commensurability
with small libration amplitudes. The libration of both lowest order mean-motion
resonance variables, theta_1 and theta_2, and the secular resonance variable,
theta_3, about 0 deg. differs from the familiar geometry of the Io-Europa pair,
where theta_2 and theta_3 librate about 180 deg. By considering a condition for
stable simultaneous librations of theta_1 and theta_2, we show that the GJ 876
geometry results because of the large orbital eccentricities e_i, whereas the
very small e_i in the Io-Europa system lead to the latter's geometry.
Surprisingly, the GJ 876 resonance configuration remains stable for e_1 up to
0.86 and for amplitude of libration of theta_1 approaching 45 deg. with the
current e_i. We find that inward migration of the outer planet of the GJ 876
system results in certain capture into the observed resonances if initially e_1
<0.06 and e_2<0.03 and the migration rate |(da_2/dt)/a_2| < 0.03(a_2/AU)^{-3/2}
yr^{-1}. The bound on the migration rate is easily satisfied by migration due
to planet-nebula interaction. If there is no eccentricity damping, eccentricity
growth is rapid with continued migration within the resonance, with e_i
exceeding the observed values after a further reduction in the semi-major axes
a_i of only 7%. With eccentricity damping (de_i/dt)/e_i = -K|(da_i/dt)/a_i|,
the e_i reach equilibrium values that remain constant for arbitrarily long
migration within the resonances. The equilibrium e_i are close to the observed
e_i for K=100 (K=10) if there is migration and damping of the outer planet only
(of both planets). It is as yet unclear that planet-nebula interaction can
produce the large value of K required to obtain the observed eccentricities.Comment: 23 pages, including 8 figures; uses AASTeX v5.0; minor additions;
accepted for publication in Ap
Origin of Tidal Dissipation in Jupiter: II. the Value of Q
The process of tidal dissipation inside Jupiter is not yet understood. Its
tidal quality factor () is inferred to lie between and . We
examine effects of inertial-modes on tidal dissipation in a neutrally bouyant,
core-less, uniformly rotating planet. The rate of dissipation caused by
resonantly excited inertial-modes depends on the following three parameters:
how well they are coupled to the tidal potential, how strongly they are
dissipated (by the turbulent viscosity), and how densely distributed they are
in frequency. We find that as a function of tidal frequency, the value
exhibits large fluctuations, with its maximum value set by the group of
inertial-modes that have a typical offset from an exact resonance of order
their turbulent damping rates. In our model, inertial-modes shed their tidally
acquired energy very close to the surface within a narrow latitudinal zone (the
'singularity belt'), and the tidal luminosity escapes freely out of the planet.
Strength of coupling between the tidal potential and inertial-modes is
sensitive to the presence of density discontinuities inside Jupiter. In the
case of a discreet density jump (as may be caused by the transition between
metallic and molecular hydrogen), we find a time-averaged . Even
though it remains unclear whether tidal dissipation due to resonant
inertial-modes is the correct answer to the problem, it is impressive that our
simple treatment here already leads to three to five orders of magnitude
stronger damping than that from the equilibrium tide. Moreover, our conclusions
are not affected by the presence of a small solid core, a different
prescription for the turbulent viscosity, or nonlinear mode coupling, but they
depend critically on the static stability in the upper atmosphere of Jupiter.Comment: 27 pages, incl. 11 figures, ApJ in print, expanded discussions
(nonlinearity, radiative envelope
Concentration of atomic hydrogen diffused into silicon in the temperature range 900–1300 °C
Boron-doped Czochralski silicon samples with [B]~1017 cm−3 have been heated at various temperatures in the range 800–1300 °C in an atmosphere of hydrogen and then quenched. The concentration of [H-B] pairs was measured by infrared localized vibrational mode spectroscopy. It was concluded that the solubility of atomic hydrogen is greater than [Hs] = 5.6 × 1018 exp( − 0.95 eV/kT)cm−3 at the temperatures investigated
Obliquity Tides on Hot Jupiters
Obliquity tides are a potentially important source of heat for extrasolar
planets on close-in orbits. Although tidal dissipation will usually reduce the
obliquity to zero, a nonzero obliquity can persist if the planet is in a
Cassini state, a resonance between spin precession and orbital precession.
Obliquity tides might be the cause of the anomalously large size of the
transiting planet HD 209458b.Comment: To appear in ApJ Letters [9 pages, 2 figures
On the evolution of mean motion resonances through stochastic forcing: Fast and slow libration modes and the origin of HD128311
Aims. We clarify the response of extrasolar planetary systems in a 2:1 mean
motion commensurability with masses ranging from the super Jovian range to the
terrestrial range to stochastic forcing that could result from protoplanetary
disk turbulence. The behaviour of the different libration modes for a wide
range of system parameters and stochastic forcing magnitudes is investigated.
The growth of libration amplitudes is parameterized as a function of the
relevant physical parameters. The results are applied to provide an explanation
of the configuration of the HD128311 system.
Methods. We first develop an analytic model from first principles without
making the assumption that both eccentricities are small. We also perform
numerical N-body simulations with additional stochastic forcing terms to
represent the effects of putative disk turbulence.
Results. Systems are quickly destabilized by large magnitudes of stochastic
forcing but some stability is imparted should systems undergo a net orbital
migration. The slow mode, which mostly corresponds to motion of the angle
between the apsidal lines of the two planets, is converted to circulation more
readily than the fast mode which is associated with oscillations of the
semi-major axes. This mode is also vulnerable to the attainment of small
eccentricities which causes oscillations between periods of libration and
circulation.
Conclusions. Stochastic forcing due to disk turbulence may have played a role
in shaping the configurations of observed systems in mean motion resonance. It
naturally provides a mechanism for accounting for the HD128311 system.Comment: 15 pages, 8 figures, added discussion in h and k coordinates,
recommended for publicatio
Site-Selective Spectroscopy And Crystal-Field Analysis For Nd3+ In Strontium Fluorovanadate
Site‐selective spectroscopy reveals that Nd3+ ions occupy more than 40 different crystal‐field environments in Sr5(VO4)3F. Preferential energy transfer to the site responsible for 1 μm lasing occurs but becomes less complete with increasing temperature. The 4I and 4F3/2 Stark levels of the lasing site have been determined and an analysis of the crystal field performed. From the crystal‐field fitting parameters Bkq, a calculated energy‐level spectrum is determined up to 17 500 cm−1 with a rms deviation from the available experimental levels of 6 cm−1
- …