Posts Tagged internal structure

Recent Postings from internal structure

The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet

Kepler-10b was the first rocky planet detected by the Kepler satellite and con- firmed with radial velocity follow-up observations from Keck-HIRES. The mass of the planet was measured with a precision of around 30%, which was insufficient to constrain models of its internal structure and composition in detail. In addition to Kepler-10b, a second planet transiting the same star with a period of 45 days was sta- tistically validated, but the radial velocities were only good enough to set an upper limit of 20 Mearth for the mass of Kepler-10c. To improve the precision on the mass for planet b, the HARPS-N Collaboration decided to observe Kepler-10 intensively with the HARPS-N spectrograph on the Telescopio Nazionale Galileo on La Palma. In to- tal, 148 high-quality radial-velocity measurements were obtained over two observing seasons. These new data allow us to improve the precision of the mass determina- tion for Kepler-10b to 15%. With a mass of 3.33 +/- 0.49 Mearth and an updated radius of 1.47 +0.03 -0.02 Rearth, Kepler-10b has a density of 5.8 +/- 0.8 g cm-3, very close to the value -0.02 predicted by models with the same internal structure and composition as the Earth. We were also able to determine a mass for the 45-day period planet Kepler-10c, with an even better precision of 11%. With a mass of 17.2 +/- 1.9 Mearth and radius of 2.35 +0.09 -0.04 Rearth, -0.04 Kepler-10c has a density of 7.1 +/- 1.0 g cm-3. Kepler-10c appears to be the first strong evidence of a class of more massive solid planets with longer orbital periods.

Phenomenology of hadron structure --- why low energy physics matters

The description of the internal structure of hadrons is one of the main goal of QCD. At moderate energy scales, the hadronic representation succeeds to the partonic description, rendering challenging the description of the dynamics of scattering processes and hadronic structure. The information on the hadron structure is embodied in the long distance contributions which are defined as Parton Distribution Functions (PDFs). PDFs are a key framework for connecting the low and high-energy regimes, in that the knowledge on non- perturbative QCD carries important consequences at the high-energy level. We here review recent progress in the description of the proton, from complementary approaches such as fits of PDFs, phenomenological analyses and experimental predictions in view of the JeffersonLab upgrade and applications for high-energy colliders.

Density, porosity, mineralogy, and internal structure of cosmic dust and alteration of its properties during high velocity atmospheric entry [Replacement]

X-ray microtomography (XMT), X-ray diffraction (XRD) and magnetic hysteresis measurements were used to determine micrometeorite internal structure, mineralogy, crystallography, and physical properties at ~{\mu}m resolution. The study samples include unmelted, partially melted (scoriaceous) and completely melted (cosmic spherules) micrometeorites. This variety not only allows comparison of the mineralogy and porosity of these three micrometeorite types, but also reveals changes in meteoroid properties during atmospheric entry at various velocities. At low entry velocities, meteoroids do not melt, and their physical properties do not change. The porosity of unmelted micrometeorites varies considerably (0-12%) with one friable example having porosity around 50%. At higher velocities, the range of meteoroid porosity narrows, but average porosity increases (to 16-27%) due to volatile evaporation and partial melting (scoriaceous phase). Metal distribution seems to be mostly unaffected at this stage. At even higher entry velocities, complete melting follows the scoriaceous phase. Complete melting is accompanied by metal oxidation and redistribution, loss of porosity (1 $\pm$ 1%), and narrowing of the bulk (3.2 $\pm$ 0.5 g/cm$^{3}$) and grain (3.3 $\pm$ 0.5 g/cm$^{3}$) density range. Melted cosmic spherules with a barred olivine structure show an oriented crystallographic structure, whereas other subtypes do not.

Density, porosity, mineralogy, and internal structure of cosmic dust and alteration of its properties during high velocity atmospheric entry

X-ray microtomography (XMT), X-ray diffraction (XRD) and magnetic hysteresis measurements were used to determine micrometeorite internal structure, mineralogy, crystallography, and physical properties at ~{\mu}m resolution. The study samples include unmelted, partially melted (scoriaceous) and completely melted (cosmic spherules) micrometeorites. This variety not only allows comparison of the mineralogy and porosity of these three micrometeorite types, but also reveals changes in meteoroid properties during atmospheric entry at various velocities. At low entry velocities, meteoroids do not melt, and their physical properties do not change. The porosity of unmelted micrometeorites varies considerably (0-12%) with one friable example having porosity around 50%. At higher velocities, the range of meteoroid porosity narrows, but average porosity increases (to 16-27%) due to volatile evaporation and partial melting (scoriaceous phase). Metal distribution seems to be mostly unaffected at this stage. At even higher entry velocities, complete melting follows the scoriaceous phase. Complete melting is accompanied by metal oxidation and redistribution, loss of porosity (1 $\pm$ 1%), and narrowing of the bulk (3.2 $\pm$ 0.5 g/cm3) and grain (3.3 $\pm$ 0.5 g/cm3) density range. Melted cosmic spherules with a barred olivine structure show an oriented crystallographic structure, whereas other subtypes do not.

Dissecting the Red Sequence: The Bulge and Disc Colours of Early-Type Galaxies in the Coma Cluster

We explore the internal structure of red sequence galaxies in the Coma cluster across a wide range of luminosities ($-17>M_g>-22$) and cluster-centric radii ($0<r_{\rm{cluster}}<1.3 r_{200}$). We present the 2D bulge-disc decomposition of galaxies in deep Canada-France-Hawaii Telescope $u,g,i$ imaging using GALFIT. Rigorous filtering is applied to identify an analysis sample of 200 galaxies which are well described by an `archetypal’ S0 structure (central bulge + outer disc). We consider internal bulge and/or disc colour gradients by allowing component sizes to vary between bands. Gradients are required for $30\%$ of analysis sample galaxies. Bulge half-light radii are found to be uncorrelated with galaxy luminosity ($R_e \sim 1$ kpc, $n\sim2$) for all but the brightest galaxies ($M_g<-20.5$). The S0 discs are brighter (at fixed size, or smaller at fixed luminosity) than those of star-forming spirals. A similar colour-magnitude relation is found for both bulges and discs. The global red sequence for S0s in Coma hence results from a combination of both component trends. We measure an average bulge $-$ disc colour difference of $0.09\pm0.01$ mag in $g-i$, and $0.16\pm0.01$ mag in $u-g$. Using simple stellar population models, bulges are either $\sim2$-$3\times$ older, or $\sim2\times$ more metal-rich than discs. The trend towards bluer global S0 colours observed further from Coma’s core is driven by a significant correlation in disc colour with cluster-centric radius. An equivalent trend is detected in bulge colours at a marginal significance level. Our results therefore favour environment-mediated mechanisms of disc fading as the dominant factor in S0 formation.

Dissecting the Red Sequence: The Bulge and Disc Colours of Early-Type Galaxies in the Coma Cluster [Replacement]

We explore the internal structure of red sequence galaxies in the Coma cluster across a wide range of luminosities ($-17>M_g>-22$) and cluster-centric radii ($0<r_{\rm{cluster}}<1.3 r_{200}$). We present the 2D bulge-disc decomposition of galaxies in deep Canada-France-Hawaii Telescope $u,g,i$ imaging using GALFIT. Rigorous filtering is applied to identify an analysis sample of 200 galaxies which are well described by an `archetypal’ S0 structure (central bulge + outer disc). We consider internal bulge and/or disc colour gradients by allowing component sizes to vary between bands. Gradients are required for $30\%$ of analysis sample galaxies. Bulge half-light radii are found to be uncorrelated with galaxy luminosity ($R_e \sim 1$ kpc, $n\sim2$) for all but the brightest galaxies ($M_g<-20.5$). The S0 discs are brighter (at fixed size, or smaller at fixed luminosity) than those of star-forming spirals. A similar colour-magnitude relation is found for both bulges and discs. The global red sequence for S0s in Coma hence results from a combination of both component trends. We measure an average bulge $-$ disc colour difference of $0.09\pm0.01$ mag in $g-i$, and $0.16\pm0.01$ mag in $u-g$. Using simple stellar population models, bulges are either $\sim2$-$3\times$ older, or $\sim2\times$ more metal-rich than discs. The trend towards bluer global S0 colours observed further from Coma’s core is driven by a significant correlation in disc colour with cluster-centric radius. An equivalent trend is detected in bulge colours at a marginal significance level. Our results therefore favour environment-mediated mechanisms of disc fading as the dominant factor in S0 formation.

Exotic hadron production in hard exclusive reactions

We consider hard exclusive production of exotic hadrons to study their internal structure. Revisiting the constituent-counting rule for the large-angle exclusive scattering, we discuss general features expected for the production cross section of exotic hadrons whose leading Fock states are given by multi-quark states other than the ordinary baryon ($qqq$) or meson ($q\bar{q}$) states.We take the production of $\Lambda(1405)$ as an example and propose to study its partonic configuration from the asymptotic scaling of the cross section, which is measurable at J-PARC. We also discuss the production of a pair of the light-hadrons such as $f_0(980)$s and $a_0(980)$s in $\gamma^*\gamma$ collisions in the framework of QCD factorization, in which the cross section is expressed as a convolution of the perturbative coefficients and the generalized distribution amplitudes (GDAs). We demonstrate how the internal structure of $f_0(980)$ or $a_0(980)$ can be explored by measuring the GDAs at $e^+e^-$ experiments such as the B-factories.

Exotic hadron production in hard exclusive reactions [Replacement]

We consider hard exclusive production of exotic hadrons to study their internal structure. Revisiting the constituent-counting rule for the large-angle exclusive scattering, we discuss general features expected for the production cross section of exotic hadrons whose leading Fock states are given by multi-quark states other than the ordinary baryon ($qqq$) or meson ($q\bar{q}$) states.We take the production of $\Lambda(1405)$ as an example and propose to study its partonic configuration from the asymptotic scaling of the cross section, which is measurable at J-PARC. We also discuss the production of a pair of the light-hadrons such as $f_0(980)$s and $a_0(980)$s in $\gamma^*\gamma$ collisions in the framework of QCD factorization, in which the cross section is expressed as a convolution of the perturbative coefficients and the generalized distribution amplitudes (GDAs). We demonstrate how the internal structure of $f_0(980)$ or $a_0(980)$ can be explored by measuring the GDAs at $e^+e^-$ experiments such as the B-factories.

Systematic Problems With Using Dark Matter Simulations to Model Stellar Halos

The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be "painted" onto dark matter particles in progenitor satellites; (2) pure dark matter simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted dark matter particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure dark matter simulation that does not form a baryonic disk. We find that the "painting" simplification reduces the halo concentration and internal structure, predominantly because painted dark matter particles have different kinematics than star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure dark matter simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on dark matter only simulations when such differences are less than an order of magnitude.

Inferring mode inertias in evolved solar-like stars

Asteroseismology of evolved solar-like stars is experiencing a growing interest due to the wealth of observational data from space-borne instruments such as the \emph{CoRoT} and \emph{Kepler} spacecraft. In particular, the recent detection of mixed modes, which probe both the innermost and uppermost layers of stars, paves the way for inferring the internal structure of stars along their evolution through the subgiant and red giant phases. Mixed modes can also place stringent constraints on the physics of such stars and on their global properties (mass, age, etc…). Here, using two \emph{Kepler} stars (KIC 4351319 and KIC 6442183), we demonstrate that measurements of mixed mode characteristics allow us to estimate the mode inertias, providing a new and additional diagnostics on the mode trapping and subsequently on the internal structure of evolved stars. We however stress that the accuracy may be sensitive to non-adiabatic effects.

Three-Hair Newtonian Relations for Rotating Stars

Astrophysical black holes can be completely described by their mass and spin due to the no-hair theorem. This was not expected to hold for stars because of their internal structure. We analytically find that arbitrarily uniformly rotating stars can still be completely described by only three numbers (mass, spin and quadrupole moment) in the Newtonian limit. Surprisingly, this description is approximately universal (independent of internal structure) for low multipole order, analytically confirming previous numerical results in full general relativity.

Three-Hair Newtonian Relations for Rotating Stars [Cross-Listing]

Astrophysical black holes can be completely described by their mass and spin due to the no-hair theorem. This was not expected to hold for stars because of their internal structure. We analytically find that arbitrarily uniformly rotating stars can still be completely described by only three numbers (mass, spin and quadrupole moment) in the Newtonian limit. Surprisingly, this description is approximately universal (independent of internal structure) for low multipole order, analytically confirming previous numerical results in full general relativity.

Direct detection of dark matter in universal bound states [Replacement]

We study the signatures for internal structure of dark matter in direct detection experiments in the context of asymmetric self-interacting dark matter. The self-interaction cross section of two dark matter particles at low energies is assumed to come close to saturating the S-wave unitarity bound, which requires the presence of a resonance near their scattering threshold. The universality of S-wave near-threshold resonances then implies that the low-energy scattering properties of a two-body bound state of dark matter particles are completely determined by its binding energy, irrespective of the underlying microphysics. The form factor for elastic scattering of the bound state from a nucleus and the possibility of breakup of the bound state produce new signatures in the nuclear recoil energy spectrum. If these features are observed in experiments, it will give a smoking-gun signature for the internal structure of dark matter.

Direct detection of dark matter in universal bound states [Replacement]

We study the signatures for internal structure of dark matter in direct detection experiments in the context of asymmetric self-interacting dark matter. The self-interaction cross section of two dark matter particles at low energies is assumed to come close to saturating the S-wave unitarity bound, which requires the presence of a resonance near their scattering threshold. The universality of S-wave near-threshold resonances then implies that the low-energy scattering properties of a two-body bound state of dark matter particles are completely determined by its binding energy, irrespective of the underlying microphysics. The form factor for elastic scattering of the bound state from a nucleus and the possibility of breakup of the bound state produce new signatures in the nuclear recoil energy spectrum. If these features are observed in experiments, it will give a smoking-gun signature for the internal structure of dark matter.

Impact of the frequency dependence of tidal Q on the evolution of planetary systems

Context. Tidal dissipation in planets and in stars is one of the key physical mechanisms that drive the evolution of planetary systems. Aims. Tidal dissipation properties are intrisically linked to the internal structure and the rheology of studied celestial bodies. The resulting dependence of the dissipation upon the tidal frequency is strongly different in the cases of solids and fluids. Methods. We compute the tidal evolution of a two-body coplanar system, using the tidal quality factor’s frequency-dependencies appropriate to rocks and to convective fluids. Results. The ensuing orbital dynamics comes out smooth or strongly erratic, dependent on how the tidal dissipation depends upon frequency. Conclusions. We demonstrate the strong impact of the internal structure and of the rheology of the central body on the orbital evolution of the tidal perturber. A smooth frequency-dependence of the tidal dissipation renders a smooth orbital evolution while a peaked dissipation can furnish erratic orbital behaviour.

Giant Planet Formation, Evolution, and Internal Structure

The large number of detected giant exoplanets offers the opportunity to improve our understanding of the formation mechanism, evolution, and interior structure of gas giant planets. The two main models for giant planet formation are core accretion and disk instability. There are substantial differences between these formation models, including formation timescale, favorable formation location, ideal disk properties for planetary formation, early evolution, planetary composition, etc. First, we summarize the two models including their substantial differences, advantages, and disadvantages, and suggest how theoretical models should be connected to available (and future) data. We next summarize current knowledge of the internal structures of solar- and extrasolar- giant planets. Finally, we suggest the next steps to be taken in giant planet exploration.

Stellar Magnetic Dynamos and Activity Cycles

Using a new uniform sample of 824 solar and late-type stars with measured X-ray luminosities and rotation periods we have studied the relationship between rotation and stellar activity that is believed to be a probe of the underlying stellar dynamo. Using an unbiased subset of the sample we calculate the power law slope of the unsaturated regime of the activity — rotation relationship as $L_X/L_{bol}\propto Ro^\beta$, where $\beta=-2.70\pm0.13$. This is inconsistent with the canonical $\beta = -2$ slope to a confidence of 5$\sigma$ and argues for an interface-type dynamo. We map out three regimes of coronal emission as a function of stellar mass and age, using the empirical saturation threshold and theoretical super-saturation thresholds. We find that the empirical saturation timescale is well correlated with the time at which stars transition from the rapidly rotating convective sequence to the slowly rotating interface sequence in stellar spin-down models. This may be hinting at fundamental changes in the underlying stellar dynamo or internal structure. We also present the first discovery of an X-ray unsaturated, fully convective M star, which may be hinting at an underlying rotation – activity relationship in fully convective stars hitherto not observed. Finally we present early results from a blind search for stellar X-ray cycles that can place valuable constraints on the underlying ubiquity of solar-like activity cycles.

Kinematic Morphology of Large-scale Structure: Evolution from Potential to Rotational Flow

As an alternative way of describing the cosmological velocity field, we discuss the evolution of rotational invariants constructed from the velocity gradient tensor. Compared with the traditional divergence-vorticity decomposition, these invariants, defined as coefficients of characteristic equation of the velocity gradient tensor, enable a complete classification of all possible flow patterns in the dark-matter comoving frame, including both potential and vortical flows. Before shell-crossing, different categories of potential flow are highly associated with cosmic web structure, because of the coherent evolution of density and velocity. This correspondence is even preserved at some level when vorticity is generated after shell-crossing. The evolution from the potential to vortical flow can be traced continuously by these invariants. With the help of this tool, we show that the vorticity is generated in a particular way that is highly correlated with the large-scale structure. This includes a distinct spatial distribution and different types of alignment between cosmic web and vorticity direction for various vortical flows. Incorporating shell-crossing into closed dynamical systems is highly non-trivial, but we propose a possible statistical explanation for some of these phenomena relating to the internal structure of the three-dimensional invariants space.

Flux-tube structure from vertical magnetic flux concentrations

Strongly stratified hydromagnetic turbulence has previously been found to produce magnetic flux concentrations if the domain is large enough compared with the size of turbulent eddies. Mean-field simulations (MFS) using parameterizations of the Reynolds and Maxwell stresses show a negative effective magnetic pressure instability and have been able to reproduce many aspects of direct numerical simulations (DNS) regarding the growth rate of this large-scale instability, shape of the resulting magnetic structures, and their height as a function of magnetic field strength. Unlike the case of an imposed horizontal field, for a vertical one, magnetic flux concentrations of equipartition strength with the turbulence can be reached. This results in magnetic spots that are reminiscent of sunspots. Here we want to find out under what conditions magnetic flux concentrations with vertical field occur and what their internal structure is. We use a combination of MFS, DNS, and implicit large-eddy simulations to characterize the resulting magnetic flux concentrations in forced isothermal turbulence with an imposed vertical magnetic field. We confirm earlier results that in the kinematic stage of the large-scale instability the horizontal wavelength of structures is about 10 times the density scale height. At later times, even larger structures are being produced in a fashion similar to inverse spectral transfer in helically driven turbulence. Using turbulence simulations, we find that magnetic flux concentrations occur for different values of the Mach number between 0.1 and 0.7. DNS and MFS show magnetic flux tubes with mean-field energies comparable to the turbulent kinetic energy. The resulting vertical magnetic flux tubes are being confined by downflows along the tubes and corresponding inflow from the sides, which keep the field concentrated.

Double mode radial pulsations among RR Lyrae stars

The detection of a second radial mode in the RR Lyr type star puts strong constrain on its internal structure. We present 59 new Galactic double mode RR Lyr stars found in the LINEAR survey data with the fundamental radial mode and the first overtone exited (RRd stars). These stars may be useful for constraining the mass-metallicity relation for field horizontal branch stars. We present the updated Petersen diagram and the distribution of the fundamental mode periods in the Galactic RRd stars.

Formation and internal structure of superdense dark matter clumps and ultracompact minihaloes

We discuss the formation mechanisms and structure of the superdense dark matter clumps (SDMC) and ultracompact minihaloes (UCMH) and outline the differences between these types of DM objects. We define as SDMC the gravitationally bounded DM objects which have come into virial equilibrium at the radiation-dominated (RD) stage of the universe evolution. Such objects can form from the isocurvature (entropy) density perturbations or from the peaks in the spectrum of curvature (adiabatic) perturbation. The axion miniclusters (Kolb and Tkachev 1994) are the example of the former model. The system of central compact mass (e.g. in the form of SDMC or primordial black hole (PBH)) with the outer DM envelope formed in the process of secondary accretion we refer to as UCMH. Therefore, the SDMC can serve as the seed for the UCMH in some scenarios. Recently, the SDMC and UCMH were considered in the many works, and we try to systematize them here. We consider also the effect of asphericity of the initial density perturbation in the gravitational evolution, which decreases the SDMC amount and, as the result, suppresses the gamma-ray signal from DM annihilation.

Non-isothermal filaments in equilibrium

The physical properties of the so-called Ostriker isothermal filament (Ostriker 1964) have been classically used as benchmark to interpret the stability of the filaments observed in nearby clouds. However, recent continuum studies have shown that the internal structure of the filaments depart from the isothermality, typically exhibiting radially increasing temperature gradients. The presence of internal temperature gradients within filaments suggests that the equilibrium configuration of these objects should be therefore revisited. The main goal of this work is to theoretically explore how the equilibrium structure of a filament changes in a non-isothermal configuration. We solve the hydrostatic equilibrium equation assuming temperature gradients similar to those derived from observations. We obtain a new set of equilibrium solutions for non-isothermal filaments with both linear and asymptotically constant temperature gradients. Our results show that, for sufficiently large internal temperature gradients, a non-isothermal filament could present significantly larger masses per unit length and shallower density profiles than the isothermal filament without collapsing by its own gravity. We conclude that filaments can reach an equilibrium configuration under non-isothermal conditions. Detailed studies of both the internal mass distribution and temperature gradients within filaments are then needed in order to judge the physical state of filaments.

Remapping dark matter halo catalogues between cosmological simulations

We present and test a method for modifying the catalogue of dark matter haloes produced from a given cosmological simulation, so that it resembles the result of a simulation with an entirely different set of parameters. This extends the method of Angulo & White (2010), which rescales the full particle distribution from a simulation. Working directly with the halo catalogue offers an advantage in speed, and also allows modifications of the internal structure of the haloes to account for nonlinear differences between cosmologies. Our method can be used directly on a halo catalogue in a self contained manner without any additional information about the overall density field: although the large-scale displacement field is required by the method, this can be inferred from the halo catalogue alone. We show proof of concept of our method by rescaling a matter-only simulation with no baryon acoustic oscillation (BAO) features to a more standard LCDM model containing a cosmological constant and a BAO signal. In conjunction with the halo occupation approach, this method provides a basis for the rapid generation of mock galaxy samples spanning a wide range of cosmological parameters.

Rotating hybrid compact stars

Starting from equations of state of nucleonic and color-superconducting quark matter and assuming a first-order phase transition between these, we construct an equation of state of stellar matter which contains three phases: a nucleonic phase, as well as two-flavor and three-flavor color-superconducting phases of quarks. Static sequences of the corresponding hybrid stars include massive members with masses $\sim 2 M_{\odot}$ and radii in the range $13\le R\le 16$ km. We investigate the integral parameters of rapidly rotating stars, and obtain evolutionary sequences that correspond to constant rest-mass stars spinning down by electromagnetic and gravitational radiation. Physically new "transitional" sequences are revealed that are distinguished by a phase transition from nucleonic to color-superconducting matter for some configurations that are located between the static and Keplerian limits. The "snapshots" of internal structure of the star, displaying the growth or shrinkage of superconducting volume as the star’s spin changes, are displayed for constant rest mass stars. We further obtain evolutionary sequences of rotating supermassive compact stars and construct pre-collapse models that can be used as initial data to simulate a collapse of color-superconducting hybrid stars to a black hole.

Constraining white dwarf viscosity through tidal heating in detached binary systems

Although the internal structure of white dwarfs is considered to be generally well understood, the source and entity of viscosity is still very uncertain. We propose here to study white dwarf viscous properties using short period (< 1 hr), detached white dwarf binaries, such as the newly discovered ~12.8 min system. These binaries are wide enough that mass transfer has not yet started but close enough that the least massive component is subject to a measurable tidal deformation. The associated tidal torque transfers orbital energy, which is partially converted into heat by the action of viscosity within the deformed star. As a consequence, its outer non-degenerate layers expand, and the star puffs up. We self-consistently calculate the fractional change in radius, and the degree of asynchronism (ratio of stellar to orbital spin) as a function of the viscous time. Specializing our calculations to J0651, we find that the discrepancy between the measured radius of the secondary star and He white dwarf model predictions can be interpreted as tidal inflation if the viscous timescale is either ~2 10^5 yr or ~10^4 yr. Such values point to a non-microscopic viscosity, possibly given by tidally induced turbulence, or by magnetic field stresses with a magnetic field strength of 10-100 Gauss. Fortunately, these two timescales produce very different degree of asynchronism, with the shortest one, bringing the system much closer to synchronisation. A measurement of the stellar spin can thus univocally determined the mean viscosity. Extrapolating the secondary’s radial expansion, we predict that the star will fill is Roche lobe at a separation which is 1.2-1.3 smaller than the current one. Applying this method to a future sample of systems can allow us to learn whether viscosity changes with mass and/or nuclear composition.

Theoretical models of planetary system formation: mass vs semi-major axis

Planet formation models have been developed during the last years in order to try to reproduce the observations of both the solar system, and the extrasolar planets. Some of these models have partially succeeded, focussing however on massive planets, and for the sake of simplicity excluding planets belonging to planetary systems. However, more and more planets are now found in planetary systems. This tendency, which is a result of both radial velocity, transit and direct imaging surveys, seems to be even more pronounced for low mass planets. These new observations require the improvement of planet formation models, including new physics, and considering the formation of systems. In a recent series of papers, we have presented some improvements in the physics of our models, focussing in particular on the internal structure of forming planets, and on the computation of the excitation state of planetesimals, and their resulting accretion rate. In this paper, we focus on the concurrent effect of the formation of more than one planet in the same protoplanetary disc, and show the effect, in terms of global architecture and composition of this multiplicity. We use a N-body calculation including collision detection to compute the orbital evolution of a planetary system. Moreover, we describe the effect of competition for accretion of gas and solids, as well as the effect of gravitational interactions between planets. We show that the masses and semi-major axis of planets are modified by both the effect of competition and gravitational interactions. We also present the effect of the assumed number of forming planets in the same system (a free parameter of the model), as well as the effect of the inclination and eccentricity damping.

The SL2S Galaxy-scale Lens Sample. IV. The dependence of the total mass density profile of early-type galaxies on redshift, stellar mass, and size

We present optical and near infrared spectroscopy obtained at Keck, VLT, and Gemini for a sample of 36 secure strong gravitational lens systems and 17 candidates identified as part of the SL2S survey. The deflectors are massive early-type galaxies in the redshift range z_d=0.2-0.8, while the lensed sources are at z_s=1-3.5. We combine this data with photometric and lensing measurements presented in the companion paper III and with lenses from the SLACS and LSD surveys to investigate the cosmic evolution of the internal structure of massive early-type galaxies over half the age of the universe. We study the dependence of the slope of the total mass density profile \gamma’ (\rho(r)\propto r^{-\gamma’}) on stellar mass, size, and redshift. We find that two parameters are sufficent to determine \gamma’ with less than 6% residual scatter. At fixed redshift, \gamma’ depends solely on the surface stellar mass density \partial \gamma’/ \partial \Sigma_*=0.38\pm 0.07, i.e. galaxies with denser stars also have steeper slopes. At fixed M_* and R_{eff}, \gamma’ depends on redshift, in the sense that galaxies at a lower redshift have steeper slopes (\partial \gamma’ / \partial z = -0.31\pm 0.10). However, the mean redshift evolution of \gamma’ for an individual galaxy is consistent with zero d\gamma’/dz=-0.10\pm0.12. This result is obtained by combining our measured dependencies of \gamma’ on z,M_*,R_{eff} with the evolution of the R_{eff}-M_* taken from the literature, and is broadly consistent with current models of the formation and evolution of massive early-type galaxies. Detailed quantitative comparisons of our results with theory will provide qualitatively new information on the detailed physical processes at work.

Influence of Rotation on Stellar Evolution

The Sun has been known to rotate for more than 4 centuries, and evidence is also available through direct measurements, that almost all stars rotate. In this lecture, I will propose a review of the different physical processes associated to rotation that are expected to impact the evolution of stars. I will describe in detail the way these physical processes are introduced in 1D stellar evolution codes and how their introduction in the modelling has impacted our understanding of the internal structure, nucleosynthesis and global evolution of stars.

Influence of Rotation on Stellar Evolution [Replacement]

The Sun has been known to rotate for more than 4 centuries, and evidence is also available through direct measurements, that almost all stars rotate. In this lecture, I will propose a review of the different physical processes associated to rotation that are expected to impact the evolution of stars. I will describe in detail the way these physical processes are introduced in 1D stellar evolution codes and how their introduction in the modelling has impacted our understanding of the internal structure, nucleosynthesis and global evolution of stars.

Clumps and triggered star formation in ionised molecular clouds

Infrared shells and bubbles are ubiquitous in the Galaxy and can generally be associated with HII regions formed around young, massive stars. In this paper, we use high-resolution 3D SPH simulations to explore the effect of a single O7 star emitting photons at 10^49 1/s and located at the centre of a molecular cloud with mass 10^4 M_sun and radius 6.4 pc; the internal structure of the cloud is characterised by its fractal dimension, D (with 2.0 <= D <= 2.8), and the variance of its (log-normal) density distribution, sigma_0^2 (with 0.36 <= sigma_0^2 <= 1.42). Our study focuses on the morphology of the swept-up cold gas and the distribution and statistics of the resulting star formation. If the fractal dimension is low, the border of the HII region is dominated by extended shell-like structures, and these break up into a small number of massive high-density clumps which then spawn star clusters; star formation occurs relatively quickly, and delivers somewhat higher stellar masses. Conversely, if the fractal dimension is high, the border of the HII region is dominated by a large number of pillars and cometary globules, which contain compact dense clumps and tend to spawn single stars or individual multiple systems; star formation occurs later, the stellar masses are somewhat lower, and the stars are more widely distributed.

Thirteenth Marcel Grossmann Meeting, Summary of the session, White Dwarf Pulsars and Rotating White Dwarf Theory

This is the summary of the parallel session entitled "White Dwarf Pulsars and Rotating White Dwarf Theory", chaired by Yukikatsu Terada in Thirteenth Marcel Grossmann Meeting. The origin of cosmic rays remains a mystery, even over 100 years since their discovery. Neutron stars (NSs) are considered textbook cases of particle acceleration sites in our Galaxy, but many unresolved numerical problems remain. Searches for new acceleration sites are crucial for astrophysics. The magnetized white dwarfs (MWDs) have the same kind of rotating magnetosphere as NSs, and may be the source of up to 10% of galactic cosmic ray electrons. In the parallel session of the "white dwarf pulsars and rotating white dwarf theory", we focus on the current observational results on white dwarf pulsars, related theories of the radiation process both in white dwarfs and neutron stars, and the origin and rule of white dwarf pulsars, as well as surveying on the current theories of the internal structure and the equation of state of white dwarfs.

Thirteenth Marcel Grossmann Meeting, Summary of the session, White Dwarf Pulsars and Rotating White Dwarf Theory [Replacement]

This is the summary of the parallel session entitled "White Dwarf Pulsars and Rotating White Dwarf Theory", chaired by Yukikatsu Terada in Thirteenth Marcel Grossmann Meeting. The origin of cosmic rays remains a mystery, even over 100 years since their discovery. Neutron stars (NSs) are considered textbook cases of particle acceleration sites in our Galaxy, but many unresolved numerical problems remain. Searches for new acceleration sites are crucial for astrophysics. The magnetized white dwarfs (MWDs) have the same kind of rotating magnetosphere as NSs, and may be the source of up to 10% of galactic cosmic ray electrons. In the parallel session of the "white dwarf pulsars and rotating white dwarf theory", we focus on the current observational results on white dwarf pulsars, related theories of the radiation process both in white dwarfs and neutron stars, and the origin and rule of white dwarf pulsars, as well as surveying on the current theories of the internal structure and the equation of state of white dwarfs.

Thirteenth Marcel Grossmann Meeting, Summary of the session, White Dwarf Pulsars and Rotating White Dwarf Theory [Replacement]

This is the summary of the parallel session entitled "White Dwarf Pulsars and Rotating White Dwarf Theory", chaired by Yukikatsu Terada in Thirteenth Marcel Grossmann Meeting. The origin of cosmic rays remains a mystery, even over 100 years since their discovery. Neutron stars (NSs) are considered textbook cases of particle acceleration sites in our Galaxy, but many unresolved numerical problems remain. Searches for new acceleration sites are crucial for astrophysics. The magnetized white dwarfs (MWDs) have the same kind of rotating magnetosphere as NSs, and may be the source of up to 10% of galactic cosmic ray electrons. In the parallel session of the "white dwarf pulsars and rotating white dwarf theory", we focus on the current observational results on white dwarf pulsars, related theories of the radiation process both in white dwarfs and neutron stars, and the origin and rule of white dwarf pulsars, as well as surveying on the current theories of the internal structure and the equation of state of white dwarfs.

Thirteenth Marcel Grossmann Meeting, Summary of the session, White Dwarf Pulsars and Rotating White Dwarf Theory [Replacement]

This is the summary of the parallel session entitled "White Dwarf Pulsars and Rotating White Dwarf Theory", chaired by Yukikatsu Terada in Thirteenth Marcel Grossmann Meeting. The origin of cosmic rays remains a mystery, even over 100 years since their discovery. Neutron stars (NSs) are considered textbook cases of particle acceleration sites in our Galaxy, but many unresolved numerical problems remain. Searches for new acceleration sites are crucial for astrophysics. The magnetized white dwarfs (MWDs) have the same kind of rotating magnetosphere as NSs, and may be the source of up to 10% of galactic cosmic ray electrons. In the parallel session of the "white dwarf pulsars and rotating white dwarf theory", we focus on the current observational results on white dwarf pulsars, related theories of the radiation process both in white dwarfs and neutron stars, and the origin and rule of white dwarf pulsars, as well as surveying on the current theories of the internal structure and the equation of state of white dwarfs.

Hydrogen lines in LAMOST low resolution spectra of RR Lyrae stars

The LAMOST spectroscopic survey for Galactic structure and evolution has been in operation since October 2012, following a one-year pilot survey. The pilot survey produced a data release containing over 600,000 stellar spectra. By cross-checking with a large time series photometric database of RR Lyrae stars in high Galactic latitude regions, we found a total number of 157 stars that have been observed with LAMOST. In this sample, we successfully captured three RR Lyrae stars in the fast expansion phase, all of them showing significant hypersonic shock wave features in the spectra. By fitting the H{\alpha} line shape, we determine that the emission features seen within the broader H{\alpha} absorption line suggest hypersonic relative motions in the atmospheres of these three objects. With a further LAMOST survey of millions of stars, we will capture a large sample of RR Lyrae stars in their hypersonic expansion phase, and therefore provide a large database for the study of the internal structure and pulsation mechanism of RR Lyrae stars.

Hydrogen lines in LAMOST low resolution spectra of RR Lyrae stars [Replacement]

The LAMOST spectroscopic survey for Galactic structure and evolution has been in operation since October 2012, following a one-year pilot survey. The pilot survey produced a data release containing over 600,000 stellar spectra. By cross-checking with a large time series photometric database of RR Lyrae stars in high Galactic latitude regions, we found a total number of 157 stars that have been observed with LAMOST. In this sample, we successfully captured three RR Lyrae stars in the fast expansion phase, all of them showing significant hypersonic shock wave features in the spectra. By fitting the H{\alpha} line shape, we determine that the emission features seen within the broader H{\alpha} absorption line suggest hypersonic relative motions in the atmospheres of these three objects. With a further LAMOST survey of millions of stars, we will capture a large sample of RR Lyrae stars in their hypersonic expansion phase, and therefore provide a large database for the study of the internal structure and pulsation mechanism of RR Lyrae stars.

Influence of an inner core on the long-period forced librations of Mercury

The planetary perturbations on Mercury’s orbit lead to long-period forced librations of Mercury’s mantle. These librations have previously been studied for a planet with two layers: a mantle and a liquid core. Here, we calculate how the presence of a solid inner core in the liquid outer core influences the long-period forced librations. Mantle-inner core coupling affects the long-period libration dynamics mainly by changing the free libration: first, it lengthens the period of the free libration of the mantle, and second, it adds a second free libration, closely related to the free gravitational oscillation between the mantle and inner core. The two free librations have periods between 2.5 and 18 y depending on the internal structure. We show that large amplitude long-period librations of 10′s of arcsec are generated when the period of a planetary forcing approaches one of the two free libration periods. These amplitudes are sufficiently large to be detectable by spacecraft measurements of the libration of Mercury. The amplitudes of the angular velocity of Mercury’s mantle at planetary forcing periods are also amplified by the resonances, but remain much smaller than the current precision of Earth-based radar observations unless the period is very close to a free libration period. The inclusion of mantle-inner core coupling in the rotation model does not significantly improve the fit to the radar observations. This implies that it is not yet possible to determine the size of the inner core of Mercury on the basis of available observations of Mercury’s rotation rate. Future observations of the long-period librations may be used to constrain the interior structure of Mercury, including the size of its inner core.

Bulk Composition of GJ 1214b and other sub-Neptune exoplanets [Replacement]

GJ1214b stands out among the detected low-mass exoplanets, because it is, so far, the only one amenable to transmission spectroscopy. Up to date there is no consensus about the composition of its envelope although most studies suggest a high molecular weight atmosphere. In particular, it is unclear if hydrogen and helium are present or if the atmosphere is water dominated. Here, we present results on the composition of the envelope obtained by using an internal structure and evolutionary model to fit the mass and radius data. By examining all possible mixtures of water and H/He, with the corresponding opacities, we find that the bulk amount of H/He of GJ1214b is at most 7% by mass. In general, we find the radius of warm sub-Neptunes to be most sensitive to the amount of H/He. We note that all (Kepler-11b,c,d,f, Kepler-18b, Kepler-20b, 55Cnc-e, Kepler-36c and Kepler-68b) but two (Kepler-11e and Kepler-30b) of the discovered low-mass planets so far have less than 10% H/He. In fact, Kepler-11e and Kepler-30b have 10-18% and 5-15% bulk H/He. Conversely, little can be determined about the H2O or rocky content of sub-Neptune planets. We find that although a 100% water composition fits the data for GJ1214b, based on formation constraints the presence of heavier refractory material on this planet is expected, and hence, so is a component lighter than water required. A robust determination by transmission spectroscopy of the composition of the upper atmosphere of GJ1214b will help determine the extent of compositional segregation between the atmosphere and envelope.

Bulk Composition of GJ 1214b and other sub-Neptune exoplanets

GJ1214b stands out among the detected low-mass exoplanets, because it is, so far, the only one amenable to transmission spectroscopy. Up to date there is no consensus about the composition of its envelope although most studies suggest a high molecular weight atmosphere. In particular, it is unclear if hydrogen and helium are present or if the atmosphere is water dominated. Here, we present results on the composition of the envelope obtained by using an internal structure and evolutionary model to fit the mass and radius data. By examining all possible mixtures of water and H/He, with the corresponding opacities, we find that the bulk amount of H/He of GJ1214b is at most 7% by mass. In general, we find the radius of warm sub-Neptunes to be most sensitive to the amount of H/He. We note that all (Kepler-11b,c,d,f, Kepler-18b, Kepler-20b, 55Cnc-e, Kepler-36c and Kepler-68b) but one (Kepler-11e) of the discovered low-mass planets so far have less than 10% H/He. In fact, Kepler-11e has 10-25% bulk H/He. Conversely, little can be determined about the H2O or rocky content of sub-Neptune planets. We find that although a 100% water composition fits the data for GJ1214b, based on formation constraints the presence of heavier refractory material on this planet is expected, and hence, so is a component lighter than water required. The same is true for Kepler-11f. A robust determination by transmission spectroscopy of the composition of the upper atmosphere of GJ1214b will help determine the extent of compositional segregation between the atmosphere and envelope.

Plasma Jets and Eruptions in Solar Coronal Holes: a 3D flux emergence experiment

A three-dimensional numerical experiment of the launching of a hot and fast coronal jet followed by several violent eruptions is analyzed in detail. These events are initiated through the emergence of a magnetic flux rope from the solar interior into a coronal hole. We explore the evolution of the emerging magnetically-dominated plasma dome surmounted by a current sheet and the ensuing pattern of reconnection. A hot and fast coronal jet with inverted-Y shape is produced that shows properties comparable to those frequently observed with EUV and X-Ray detectors. We analyze its 3D shape, its inhomogeneous internal structure, and its rise and decay phases, lasting for some 15-20 min each. Particular attention is devoted to the field-line connectivities and the reconnection pattern. We also study the cool and high-density volume that appears encircling the emerged dome. The decay of the jet is followed by a violent phase with a total of five eruptions. The first of them seems to follow the general pattern of tether-cutting reconnection in a sheared arcade, although modified by the field topology created by the preceding reconnection evolution. The two following eruptions take place near and above the strong field-concentrations at the surface. They show a twisted, \Omega-loop like rope expanding in height, with twist being turned into writhe, thus hinting at a kink instability (perhaps combined with a torus-instability) as the cause of the eruption. The succession of a main jet ejection and a number of violent eruptions that resemble mini-CME’s and their physical properties suggest that this experiment may provide a model for the blowout jets recently proposed in the literature.

The heating history of Vesta and the onset of differentiation

In this work we study the link between the evolution of the internal structure of Vesta and thermal heating due to 26Al and 60Fe and long-lived radionuclides, taking into account the chemical differentiation of the body and the affinity of 26Al with silicates. Differentiation takes place in all scenarios in which Vesta completes its accretion in less than 1.4 Ma after the injection of 26Al into the Solar Nebula. In all those scenarios where Vesta completes its formation in less than 1 Ma from the injection of 26Al, the degree of silicate melting reaches 100 vol. % throughout the whole asteroid. If Vesta completed its formation between 1 and 1.4 Ma after 26Al injection, the degree of silicate melting exceeds 50 vol. % over the whole asteroid but reaches 100 vol. % only in the hottest, outermost part of the mantle in all scenarios where the porosity is lower than 5 vol. %. If the formation of Vesta occurred later than 1.5 Ma after the injection of 26Al, the degree of silicate melting is always lower than 50 vol. % and is limited only to a small region of the asteroid. The radiation at the surface dominates the evolution of the crust which ranges in thickness from 8 to about 30 km after 5 Ma: a layer about 3-20 km thick is composed of primitive unmelted chondritic material while a layer of about 5-10 km is eucritic.

Saturn layered structure and homogeneous evolution models with different EOSs

The core mass of Saturn is commonly assumed to be 10-25 ME as predicted by interior models with various equations of state (EOSs) and the Voyager gravity data, and hence larger than that of Jupiter (0-10 ME). We here re-analyze Saturn’s internal structure and evolution by using more recent gravity data from the Cassini mission and different physical equations of state: the ab initio LM-REOS which is rather soft in Saturn’s outer regions but stiff at high pressures, the standard Sesame-EOS which shows the opposite behavior, and the commonly used SCvH-i EOS. For all three EOS we find similar core mass ranges, i.e. of 0-20 ME for SCvH-i and Sesame EOS and of 0-17 ME for LM-REOS. Assuming an atmospheric helium mass abundance of 18%, we find maximum atmospheric metallicities, Zatm of 7x solar for SCvH-i and Sesame-based models and a total mass of heavy elements, MZ of 25-30 ME. Some models are Jupiter-like. With LM-REOS, we find MZ=16-20 ME, less than for Jupiter, and Zatm less than 3x solar. For Saturn, we compute moment of inertia values lambda=0.2355(5). Furthermore, we confirm that homogeneous evolution leads to cooling times of only about 2.5 Gyr, independent on the applied EOS. Our results demonstrate the need for accurately measured atmospheric helium and oxygen abundances, and of the moment of inertia for a better understanding of Saturn’s structure and evolution.

Kronoseismology: Using density waves in Saturn's C ring to probe the planet's interior [Replacement]

Saturn’s C ring contains multiple spiral patterns that appear to be density waves driven by periodic gravitational perturbations. In other parts of Saturn’s rings, such waves are generated by Lindblad resonances with Saturn’s various moons, but most of the wave-like C-ring features are not situated near any strong resonance with any known moon. Using stellar occultation data obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we investigate the origin of six unidentified C-ring waves located between 80,900 and 87,200 km from Saturn’s center. By measuring differences in the waves’ phases among the different occultations, we are able to determine both the number of arms in each spiral pattern and the speeds at which these patterns rotate around the planet. We find that all six of these waves have between 2 and 4 arms and pattern speeds between 1660 degrees/day and 1861 degrees/day. These speeds are too large to be attributed to any satellite resonance. Instead they are comparable to the predicted pattern speeds of waves generated by low-order normal-mode oscillations within the planet [Marley & Porco 1993, Icarus 106, 508]. The precise pattern speeds associated with these waves should therefore provide strong constraints on Saturn’s internal structure. Furthermore, we identify multiple waves with the same number of arms and very similar pattern speeds, indicating that multiple m=3 and m=2 sectoral (l=m) modes may exist within the planet.

Kronoseismology: Using density waves in Saturn's C ring to probe the planet's interior

Saturn’s C ring contains multiple spiral patterns that appear to be density waves driven by periodic gravitational perturbations. In other parts of Saturn’s rings, such waves are generated by Lindblad resonances with Saturn’s various moons, but most of the wave-like C-ring features are not situated near any strong resonance with any known moon. Using stellar occultation data obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we investigate the origin of six unidentified C-ring waves located between 80,900 and 87,200 km from Saturn’s center. By measuring differences in the waves’ phases among the different occultations, we are able to determine both the number of arms in each spiral pattern and the speeds at which these patterns rotate around the planet. We find that all six of these waves have between 2 and 4 arms and pattern speeds between 1660 degrees/day and 1861 degrees/day. These speeds are too large to be attributed to any satellite resonance. Instead they are comparable to the predicted pattern speeds of waves generated by low-order normal-mode oscillations within the planet [Marley & Porco 1993, Icarus 106, 508]. The precise pattern speeds associated with these waves should therefore provide strong constraints on Saturn’s internal structure. Furthermore, we identify multiple waves with the same number of arms and very similar pattern speeds, indicating that multiple m=3 and m=2 sectoral (l=m) modes may exist within the planet.

BV technique for investigating 1-D interfaces

To investigate the internal structure of the magnetopause with spacecraft data, it is crucial to be able to determine its normal direction and to convert the measured time series into spatial profiles. We propose here a new single-spacecraft method, called the BV method, to reach these two objectives. Its name indicates that the method uses a combination of the magnetic field (B) and velocity (V) data. The method is tested on simulation and Cluster data, and a short overview of the possible products is given. We discuss its assumptions and show that it can bring a valuable improvement with respect to previous methods.

Observations of CMEs and Models of the Eruptive Corona

Current theoretical ideas on the internal structure of CMEs suggest that a flux rope is central to the CME structure, which has considerable observational support both from remote-sensing and in-situ observations. The flux-rope nature is also consistent with the post-eruption arcades with high-temperature plasmas and the charge states observed within CMEs arriving at Earth. The model involving magnetic loop expansion to explain CMEs without flux ropes is not viable because it contradicts CME kinematics and flare properties near the Sun. The flux rope is fast, it drives a shock, so the global picture of CMEs becomes complete if one includes the shock sheath to the CSHKP model.

Line Emission from Radiation-Pressurized HII Regions I: Internal Structure and Line Ratios

The emission line ratios [OIII]5007/H-beta and [NII]6584/H-alpha have been adopted as an empirical way to distinguish between the fundamentally different mechanisms of ionization in emission-line galaxies. However, detailed interpretation of these diagnostics requires calculations of the internal structure of the emitting HII regions, and these calculations depend on the assumptions one makes about the relative importance of radiation pressure and stellar winds. In this paper we construct a grid of quasi-static HII region models to explore how choices about these parameters alter HII regions’ emission line ratios. We find that, when radiation pressure is included in our models, HII regions reach a saturation point beyond which further increases in the luminosity of the driving stars does not produce any further increase in effective ionization parameter, and thus does not yield any further alteration in an HII region’s line ratio. We also show that, if stellar winds are assumed to be strong, the maximum possible ionization parameter is quite low. As a result of this effect, it is inconsistent to simultaneously assume that HII regions are wind-blown bubbles and that they have high ionization parameters; some popular HII region models suffer from this inconsistency. Our work in this paper provides a foundation for a companion paper in which we embed the model grids we compute here within a population synthesis code that enables us to compute the integrated line emission from galactic populations of HII regions.

Line Emission from Radiation-Pressurized HII Region II: Dynamics and Population Synthesis

Optical and infrared emission lines from HII regions are an important diagnostic used to study galaxies, but interpretation of these lines requires significant modeling of both the internal structure and dynamical evolution of the emitting regions. Most of the models in common use today assume that HII region dynamics are dominated by the expansion of stellar wind bubbles, and have neglected the contribution of radiation pressure to the dynamics, and in some cases also to the internal structure. However, recent observations of nearby galaxies suggest that neither assumption is justified, motivating us to revisit the question of how HII region line emission depends on the physics of winds and radiation pressure. In a companion paper we construct models of single HII regions including and excluding radiation pressure and winds, and in this paper we describe a population synthesis code that uses these models to simulate galactic collections of HII regions with varying physical parameters. We show that the choice of physical parameters has significant effects on galactic emission line ratios, and that in some cases the line ratios can exceed previously claimed theoretical limits. Our results suggest that the recently-reported offset in line ratio values between high-redshift star-forming galaxies and those in the local universe may be partially explained by the presence of large numbers of radiation pressured-dominated HII regions within them.

Arc Statistics

The existence of an arc statistics problem was at the center of a strong debate in the last fifteen years. With the aim to clarify if the optical depth for giant gravitational arcs by galaxy clusters in the so called concordance model is compatible with observations, several studies were carried out which helped to significantly improve our knowledge of strong lensing clusters, unveiling their extremely complex internal structure. In particular, the abundance and the frequency of strong lensing events like gravitational arcs turned out to be a potentially very powerful tool to trace the structure formation. However, given the limited size of observational and theoretical data-sets, the power of arc statistics as a cosmological tool has been only minimally exploited so far. On the other hand, the last years were characterized by significant advancements in the field, and several cluster surveys that are ongoing or planned for the near future seem to have the potential to make arc statistics a competitive cosmological probe. Additionally, recent observations of anomalously large Einstein radii and concentrations in galaxy clusters have reinvigorated the debate on the arc statistics problem. In this paper, we review the work done so far on arc statistics, focussing on what is the lesson we learned and what is likely to improve in the next years.

Internal Cluster Structure

The core structure of galaxy clusters is fundamentally important. Even though self-gravitating systems have no stable equilibrium state due to their negative heat capacity, numerical simulations find density profiles which are universal in the sense that they are fairly flat within a scale radius and gradually steepen farther outward, asymptotically approaching a logarithmic slope of $\approx-3$ near the virial radius. We argue that the reason for the formation of this profile is not satisfactorily understood. The ratio between the virial radius and the scale radius, the so-called concentration, is found in simulations to be closely related to the mass and the redshift and low for cluster-sized haloes, but observed to be substantially higher at least in a subset of observed clusters. Haloes formed from cold dark matter should furthermore be richly substructured. We review theoretical and observational aspects of cluster cores here, discuss modifications by baryonic physics and observables that can provide better insight into the internal structure of clusters.

 

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