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تسجيل مستخدم جديدRadiative Hydrodynamic Simulations of HD209458b: Temporal Variability
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We present a new approach for simulating the atmospheric dynamics of the close-in giant planet HD209458b that allows for the decoupling of radiative and thermal energies, direct stellar heating of the interior, and the solution of the full 3D Navier Stokes equations. Simulations reveal two distinct temperature
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We present a time-dependent radiative model of the atmosphere of HD209458b and investigate its thermal structure and chemical composition. In a first step, the stellar heating profile and radiative timescales were calculated under planet-averaged ins
olation conditions. We find that 99.99% of the incoming stellar flux has been absorbed before reaching the 7 bar level. Stellar photons cannot therefore penetrate deeply enough to explain the large radius of the planet. We derive a radiative time constant which increases with depth and reaches about 8 hr at 0.1 bar and 2.3 days at 1 bar. Time-dependent temperature profiles were also calculated, in the limit of a zonal wind that is independent on height (i.e. solid-body rotation) and constant absorption coefficients. We predict day-night variations of the effective temperature of ~600 K, for an equatorial rotation rate of 1 km/s, in good agreement with the predictions by Showman &Guillot (2002). This rotation rate yields day-to-night temperature variations in excess of 600 K above the 0.1-bar level. These variations rapidly decrease with depth below the 1-bar level and become negligible below the ~5--bar level for rotation rates of at least 0.5 km/s. At high altitudes (mbar pressures or less), the night temperatures are low enough to allow sodium to condense into Na2S. Synthetic transit spectra of the visible Na doublet show a much weaker sodium absorption on the morning limb than on the evening limb. The calculated dimming of the sodium feature during planetary transites agrees with the value reported by Charbonneau et al. (2002).
We perform detailed variability analysis of two-dimensional viscous, radiation hydrodynamic numerical simulations of Shakura-Sunyaev thin disks around a stellar mass black hole. Disk models are initialized on both the gas-, as well as radiation-, pre
ssure-dominated branches of the thermal equilibrium curve, with mass accretion rates spanning the range from $dot{M} = 0.01 L_mathrm{Edd}/c^2$ to $10 L_mathrm{Edd}/c^2$. An analysis of temporal variations of the numerically simulated disk reveals multiple robust, coherent oscillations. Considering the local mass flux variability, we find an oscillation occurring at the maximum radial epicyclic frequency, $3.5times 10^{-3},t_mathrm{g}^{-1}$, a possible signature of a trapped fundamental ${it g}$-mode. Although present in each of our simulated models, the trapped ${it g}$-mode feature is most prominent in the gas-pressure-dominated case. The total pressure fluctuations in the disk suggest strong evidence for standing-wave ${it p}$-modes, some trapped in the inner disk close to the ISCO, others present in the middle/outer parts of the disk. Knowing that the trapped ${it g}$-mode frequency and maximum radial epicyclic frequency differ by only $0.01%$ in the case of a non-rotating black hole, we simulated an additional initially gas-pressure-dominated disk with a dimensionless black hole spin parameter $a_* = 0.5$. The oscillation frequency in the spinning black hole case confirms that this oscillation is indeed a trapped ${it g}$-mode. All the numerical models we report here also show a set of high frequency oscillations at the vertical epicyclic and breathing mode frequencies. The vertical oscillations show a 3:2 frequency ratio with oscillations occurring approximately at the radial epicyclic frequency, which could be of astrophysical importance in observed twin peak, high-frequency quasi-periodic oscillations.
The core accretion model of giant planet formation has been challenged by the discovery of recycling flows between the planetary envelope and the disc that can slow or stall envelope accretion. We carry out 3D radiation hydrodynamic simulations with
an updated opacity compilation to model the proto-Jupiters envelope. To isolate the 3D effects of convection and recycling, we simulate both isolated spherical envelopes and envelopes embedded in discs. The envelopes are heated at given rates to achieve steady states, enabling comparisons with 1D models. We vary envelope properties to obtain both radiative and convective solutions. Using a passive scalar, we observe significant mass recycling on the orbital timescale. For a radiative envelope, recycling can only penetrate from the disc surface until $sim$0.1-0.2 planetary Hill radii, while for a convective envelope, the convective motion can dredge up the deeper part of the envelope so that the entire convective envelope is recycled efficiently. This recycling, however, has only limited effects on the envelopes thermal structure. The radiative envelope embedded in the disc has identical structure as the isolated envelope. The convective envelope has a slightly higher density when it is embedded in the disc. We introduce a modified 1D approach which can fully reproduce our 3D simulations. With our updated opacity and 1D model, we recompute Jupiters envelope accretion with a 10 $M_{oplus}$ core, and the timescale to runaway accretion is shorter than the disc lifetime as in prior studies. Finally, we discuss the implications of the efficient recycling on the observed chemical abundances of the planetary atmosphere (especially for super-Earths and mini-Neptunes).
Ellerman bombs (EBs) and UV bursts are both small-scale solar activities that occur in active regions. They are now believed to form at different heights in the lower atmosphere. In this paper, we use one-dimensional radiative hydrodynamic simulation
s to calculate various line profiles in response to heating in different atmospheric layers. We confirm that heating in the upper photosphere to the lower chromosphere can generate spectral features of typical EBs, while heating in the mid to upper chromosphere can generate spectral features of typical UV bursts. The intensity evolution of the H$alpha$ line wing in EBs shows a rise--plateau pattern, while that of the Si IV 1403 r{A} line center in UV bursts shows a rise--fall pattern. However, the predicted enhancement of FUV continuum near 1400 r{A} for EBs is rarely reported and requires further observations to check it. With two heating sources or an extended heating source in the atmosphere, both EB and UV burst features could be reproduced simultaneously.
Transit observations in the MgI line of HD209458b revealed signatures of neutral magnesium escaping the upper atmosphere of the planet, while no atmospheric absorption was found in the MgII doublet. Here we present a 3D particle model of the dynamics
of neutral and ionized magnesium populations, coupled with an analytical modeling of the atmosphere below the exobase. Theoretical MgI absorption line profiles are directly compared with the absorption observed in the blue wing of the line during the planet transit. Observations are well-fitted with an escape rate of neutral magnesium in the range 2x10^7-3.4x10^7 g/s, an exobase close to the Roche lobe (Rexo in the range 2.1-4.3 Rp, where Rp is the planet radius) and a planetary wind velocity at the exobase vpl=25km/s. The observed velocities of the planet-escaping magnesium up to -60km/s are well explained by radiation pressure acceleration, provided that UV-photoionization is compensated for by electron recombination up to about 13Rp. If the exobase properties are constrained to values given by theoretical models of the deeper atmosphere (Rexo=2Rp and vpl=10km/s), the best fit to the observations is found at a similar electron density and escape rate within 2 sigma. In all cases, the mean temperature of the atmosphere below the exobase must be higher than about 6100 K. Simulations predict a redward expansion of the absorption profile from the beginning to the end of the transit. The spatial and spectral structure of the extended atmosphere is the result of complex interactions between radiation pressure, planetary gravity, and self-shielding, and can be probed through the analysis of transit absorption profiles in the MgI line.
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