1. Introduction 2. Radial velocities 3. Astrometry 4. Timing 5. Microlensing 6. Transits 7. Imaging 8. Host stars 9. Brown dwarfs and free-floating planets 10. Formation and evolution 11. Interiors and atmospheres 12. The Solar System Appendixes References Index.

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The Exoplanet Handbook

We investigate shock structure and particle acceleration in relativistic magnetized collisionless electron-ion shocks by means of 2.5-dimensional particle-in-cell simulations with ion-to-electron mass ratios (m i /m e ) ranging from 16 to 1000. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. In "subluminal" shocks, where relativistic particles can escape ahead of the shock along the magnetic field lines, ions are efficiently accelerated via the first-order Fermi process. The downstream ion spectrum consists of a relativistic Maxwellian and a high-energy power-law tail, which contains ~5% of ions and ~30% of ion energy. Its slope is -2.1 ± 0.1. The scattering is provided by short-wavelength non-resonant modes produced by Bell's instability, whose growth is seeded by the current of shock-accelerated ions that propagate ahead of the shock. Upstream electrons enter the shock with lower energy than ions (albeit by only a factor of ~5 << m i /m e ), so they are more strongly tied to the field. As a result, only ~ 1% of the incoming electrons are accelerated at the shock before being advected downstream, where they populate a steep power-law tail (with slope -3.5 ± 0.1). For "superluminal" shocks, where relativistic particles cannot outrun the shock along the field, the self-generated turbulence is not strong enough to permit efficient Fermi acceleration, and the ion and electron downstream spectra are consistent with thermal distributions. The incoming electrons are heated up to equipartition with ions, due to strong electromagnetic waves emitted by the shock into the upstream. Thus, efficient electron heating (≳15% of the upstream ion energy) is the universal property of relativistic electron-ion shocks, but significant nonthermal acceleration of electrons (≳2% by number, ≳10% by energy, with slope flatter than -2.5) is hard to achieve in magnetized flows and requires weakly magnetized shocks (magnetization σ ≲ 10- 3 ), where magnetic fields self-generated via the Weibel instability are stronger than the background field. These findings place important constraints on the models of gamma-ray bursts and jets from active galactic nuclei that invoke particle acceleration in relativistic magnetized electron-ion shocks.

https://iopscience.iop.org/article/10.1088/0004-637X/726/2/75/pdf

Particle acceleration in relativistic magnetized collisionless electron-ion shocks

We present empirical measurements of the radii of 116 stars that host transiting planets. These radii are determined using only direct observables-the bolometric flux at Earth, the effective temperature, and the parallax provided by the Gaia first data release-and thus are virtually model independent, extinction being the only free parameter. We also determine each star's mass using our newly determined radius and the stellar density, itself a virtually model independent quantity from previously published transit analyses. These stellar radii and masses are in turn used to redetermine the transiting planet radii and masses, again using only direct observables. The median uncertainties on the stellar radii and masses are ~8% and ~30%, respectively, and the resulting uncertainties on the planet radii and masses are ~9% and ~22%, respectively. These accuracies are generally larger than previously published model-dependent precisions of ~5% and ~6% on the planet radii and masses, respectively, but the newly determined values are purely empirical. We additionally report radii for 242 stars hosting radial-velocity (non-transiting) planets, with median achieved accuracy of ~2%. Using our empirical stellar masses we verify that the majority of putative "retired A stars" in the sample are indeed more massive than ~1.2 Msun. Most importantly, the bolometric fluxes and angular radii reported here for a total of 498 planet host stars-with median accuracies of 1.7% and 1.8%, respectively-serve as a fundamental dataset to permit the re-determination of transiting planet radii and masses with the Gaia second data release to ~3% and ~5% accuracy, better than currently published precisions, and determined in an entirely empirical fashion.

https://iopscience.iop.org/article/10.3847/1538-3881/aa5df3/pdf

Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes

We study super-Eddington accretion flows onto black holes using a global three-dimensional radiation magneto-hydrodynamical simulation. We solve the time-dependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magneto-rotational instability provides self-consistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ∼220 L {sub Edd}/c {sup 2} and forms a radiation-driven outflow along the rotation axis. The mechanical energy flux carried by the outflow is ∼20% of the radiative energy flux. The total mass flux lost in the outflow is about 29% of the net accretion rate. The radiative luminosity of this flow is ∼10 L {sub Edd}. This yields a radiative efficiency ∼4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in most models, such as the slim disk model, which neglect vertical advection. Our inferred radiative efficiencies also exceed publishedmore » results from previous global numerical simulations, which did not attribute a significant role to vertical advection. We briefly discuss the implications for the growth of supermassive black holes in the early universe and describe how these results provided a basis for explaining the spectrum and population statistics of ultraluminous X-ray sources.« less

https://iopscience.iop.org/article/10.1088/0004-637X/796/2/106/pdf

A Global Three Dimensional Radiation Magneto-hydrodynamic Simulation of Super-Eddington Accretion Disks

Astrophysical fluid bodies that orbit close to one another induce tidal distortions and flows that are subject to dissipative processes. The spin and orbital motions undergo a coupled evolution over astronomical timescales, which is relevant for many types of binary star, short-period extrasolar planetary systems, and the satellites of the giant planets in the Solar System. I review the principal mechanisms that have been discussed for tidal dissipation in stars and giant planets in both linear and nonlinear regimes. I also compare the expectations based on theoretical models with recent observational findings.

Tidal Dissipation in Stars and Giant Planets

Asynchronous rotation and orbital eccentricity lead to time-dependent irradiation of the close-in gas giant exoplanets—the hot Jupiters. This time-dependent surface heating gives rise to fluid motions which propagate throughout the planet. We investigate the ability of this "thermal tide" to produce a quadrupole moment which can couple to the stellar gravitational tidal force. While previous investigations discussed planets with solid surfaces, here we focus on entirely fluid planets in order to understand gas giants with small cores. The Coriolis force, thermal diffusion, and self-gravity of the perturbations are ignored for simplicity. First, we examine the response to thermal forcing through analytic solutions of the fluid equations which treat the forcing frequency as a small parameter. In the "equilibrium tide" limit of zero frequency, fluid motion is present but does not induce a quadrupole moment. In the next approximation, finite frequency corrections to the equilibrium tide do lead to a nonzero quadrupole moment, the sign of which torques the planet away from synchronous spin. We then numerically solve the boundary value problem for the thermally forced, linear response of a planet with neutrally stratified interior and a stably stratified envelope. The numerical results find quadrupole moments in agreement with the analytic non-resonant result at a sufficiently long forcing period. Surprisingly, in the range of forcing periods of 1-30 days, the induced quadrupole moments can be far larger than the analytic result due to response of internal gravity waves which propagate in the radiative envelope. We discuss the relevance of our results for the spin, eccentricity, and thermal evolution of hot Jupiters.

https://iopscience.iop.org/article/10.1088/0004-637X/714/1/1/pdf

Thermal tides in fluid extrasolar planets

A hard power-law component dominates the radiation spectra of many of the brightest ultraluminous X-ray sources (ULXs). Therefore, a hot, optically thin corona likely powers the emission by Comptonizing seed photons emitted by a cooler, optically thick accretion disk. Before its dissipation and conversion into coronal radiation, the randomized gravitational binding energy responsible for powering ULXs must separate from the mass of its origin by a means quicker than electron-scattering-mediated radiative diffusion. Therefore, the accretion power released in ULXs is not necessarily subject to photon trapping, as long as it occurs in a corona. Motivated by these considerations, we present a model of ULXs powered by geometrically thin accretion onto stellar-mass black holes. In the innermost region of the disk, where the majority of the binding energy is released, an adjacent corona covering the entire disk surface Comptonizes the cool thermal radiation. The intense photoionizing flux and subsequent high ionization level produces an albedo near unity for X-ray photons. Therefore, the amount of reprocessed emission in this region is small relative to the non-thermal output. If dissipation takes place within an optically thin corona, Compton drag and the wind's low optical depth hamper the driving of a wind. If the magnetic field geometry of the corona is primarily closed, then fields of modest strength can, in principle, prevent the launching of a wind. In the outer region, the albedo is lower, and the surface area is larger. Therefore, the disk emits lower temperature thermal radiation resulting from both viscous dissipation within the body of the disk and reprocessed coronal power. Thus, this model qualitatively reproduces the main features of most highly luminous ULX spectra.

Ultraluminous X-Ray Sources Powered by Radiatively Efficient Two-Phase Super-Eddington Accretion onto Stellar-Mass Black Holes

We present a feedback mechanism for supermassive black holes and their host bulges that operates during epochs of radio-loud quasar activity. In the radio cores of relativistic quasar jets, internal shocks convert a fraction of ordered bulk kinetic energy into randomized relativistic ions, or in other words cosmic rays. By employing a phenomenologically-motivated jet model, we show that enough 1-100 GeV cosmic rays escape the radio core into the host galaxy to break the Eddington limit in cosmic rays. As a result, hydrostatic balance is lost and a cosmic ray momentum-driven wind develops, expelling gas from the host galaxy and thus self-limiting the black hole and bulge growth. Although the interstellar cosmic ray power is much smaller than the quasar photon luminosity, cosmic rays provide a stronger feedback than UV photons, since they exchange momentum with the galactic gas much more efficiently. The amount of energy released into the host galaxy as cosmic rays, per unit of black hole rest mass energy, is independent of black hole mass. It follows that radio-loud jets should be more prevalent in relatively massive systems since they sit in galaxies with relatively deep gravitational potentials. Therefore, jet-powered cosmic ray feedback not only self-regulates the black hole and bulge growth, but also provides an explanation for the lack of radio-loud activity in relatively small galaxies. By employing basic known facts regarding the physical conditions in radio cores, we approximately reproduce both the slope and the normalization of the M_{BH}-M_{Bulge} relation.

The Eddington Limit in Cosmic Rays: An Explanation for the Observed Lack of Low-Mass Radio-Loud Quasars and the M_{BH}-M_{Bulge} Relation

Time-dependent insolation in a planetary atmosphere induces a mass quadrupole upon which the stellar tidal acceleration can exert a force This "thermal tide" force can give rise to secular torques on the planet and orbit as well as radial forces causing eccentricity evolution We apply this idea to the close-in gas giant exoplanets ("hot Jupiters") The response of radiative atmospheres is computed in a hydrostatic model which treats the insolation as a time-dependent heat source, and solves for thermal radiation using flux-limited diffusion Fully nonlinear numerical simulations are compared to solutions of the linearized equations, as well as analytic approximations, all of which are in good agreement We find generically that thermal tide density perturbations {\it lead} the semi-diurnal forcing As a result thermal tides can generate asynchronous spin and eccentricity Our results are as follows: (1) Departure from synchronous spin is significant for hot Jupiters, and increases with orbital period (2) Ongoing gravitational tidal dissipation in spin equilibrium leads to steady-state internal heating rates up to $\sim 10^{28} {\rm erg\ s^{-1}}$ If deposited sufficiently deep, these heating rates may explain the anomalously large radii of many hot Jupiters in terms of a "tidal main sequence" where cooling balances tidal heating At fixed stellar type, planet mass and tidal $Q$, planetary radius increases strongly toward the star inside orbital periods $\la 2$ weeks (3) There exists a narrow window in orbital period where small eccentricities, $e$, grow exponentially with a large rate This window may explain the $\sim 1/4$ of hot Jupiters which should have been circularized by the gravitational tide long ago, but are observed to have significant nonzero $e$(Abridged)

Thermal Tides in Short Period Exoplanets

Bright star-forming galaxies radiate well below their Eddington limits. The value of the flux-mean opacity that mediates the radiation force onto matter is orders of magnitude smaller than the UV or optical dust opacity. On empirical grounds, it is shown that high-redshift ULIRGs radiate at two orders of magnitude below their Eddington limits, while the local starbursters M82 and Arp 220 radiate at a few percent of their Eddington limits. A model for the radiative transfer of UV and optical light in dust-rich environments is considered. Radiation pressure on dust does not greatly affect the large-scale gas dynamics of star-forming galaxies.

http://iopscience.iop.org/article/10.1088/2041-8205/772/2/L21/pdf

Aristotle Socrates

Papers

Thermal tides in fluid extrasolar planets

Ultraluminous X-Ray Sources Powered by Radiatively Efficient Two-Phase Super-Eddington Accretion onto Stellar-Mass Black Holes

The Eddington Limit in Cosmic Rays: An Explanation for the Observed Lack of Low-Mass Radio-Loud Quasars and the M_{BH}-M_{Bulge} Relation

Thermal Tides in Short Period Exoplanets

Photon feedback: screening and the eddington limit