The Stagger-grid: A grid of 3D stellar atmosphere models - V. Fe line shapes, shifts and asymmetries

We present a theoretical study of the effects and signatures of realistic velocity field and atmospheric inhomogeneities associated with convective motions at the surface of cool late-type stars on the emergent profiles of iron spectral lines for a large range in stellar parameters. We compute 3D spectral line flux profiles under the assumption of local thermodynamic equilibrium (LTE) by employing state-of-the-art, time-dependent, 3D, radiative-hydrodynamical atmosphere models from the Stagger-grid. A set of 35 real unblended, optical FeI and FeII lines of varying excitation potential are considered. Additionally, fictitious Fe i and Fe ii lines (5000A and 0, 2, 4 eV) are used to construct general curves of growth and enable comparison of line profiles with the same line strength to illustrate systematical trends stemming from the intrinsic structural differences among 3D model atmospheres with different stellar parameters. Theoretical line shifts and bisectors are derived to analyze the shapes, shifts, and asymmetries imprinted in the full 3D line profiles emerging self-consistently from the convective simulations with velocity fields and atmospheric inhomogeneities. We find systematic variations in line strength, shift, width, and bisectors, that can be related to the respective physical conditions at the height of the line formation in the stellar atmospheric environment, in particular the amplitude of the vertical velocity field. Line shifts and asymmetries arise due to the presence of convective velocities and the granulation pattern that are ubiquitously found in observed stellar spectra of cool stars.Comment: 11 pages, 8 figures, 2 tables, submitted to A&

The Stagger-grid: A grid of 3D stellar atmosphere models - IV. Limb darkening coefficients

We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. We have computed full 3D LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere models from the Stagger-grid. From the resulting intensities at different wavelength, we derived coefficients for the standard limb darkening laws considering a number of often-used photometric filters. Furthermore, we calculated theoretical transit light curves, in order to quantify the differences between predictions by the widely used 1D model atmosphere and our 3D models. The 3D models are often found to predict steeper limb darkening compared to the 1D models, mainly due to the temperature stratifications and temperature gradients being different in the 3D models compared to those predicted with 1D models based on the mixing length theory description of convective energy transport. The resulting differences in the transit light curves are rather small; however, these can be significant for high-precision observations of extrasolar transits, and are able to lower the residuals from the fits with 1D limb darkening profiles. We advocate the use of the new limb darkening coefficients provided for the standard four-parameter non-linear power law, which can fit the limb darkening more accurately than other choices.Comment: Accepted for publication in A&A, 10 pages, 9 figures, 1 tabl

The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - II. Horizontal and Temporal Averaging and Spectral Line Formation

We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmospheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as ) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from averages. We explore methods for computing mean stratifications from the Stagger-grid time-dependent 3D radiative hydro- dynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigate the influence of alternative averages (logarithmic or enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we compute curves of growth for Fe i and Fe ii lines in LTE . The resulting stratifications for the four reference depth scales can be considerably different. We find typically that in the upper atmosphere and in the superadiabatic region just below the optical surface, where the temperature and density fluctuations are highest, the differences become considerable and increase for higher Teff, lower logg, and lower [Fe/H]. The differential comparison of spectral line formation shows distinctive differences depending on which model is applied. The averages over layers of constant column-mass density yield the best mean representation for LTE line formation, while the averages on layers at constant geometrical height are the least appropriate. Unexpectedly, the usually preferred averages over layers of constant optical depth are prone to the increasing interference of the reversed granulation towards higher effective temperature, in particular at low metallicity.Comment: Accepted for publication in A&A, 18 pages, 16 figure

Exclusion Confusion? A Defense of the Federal Circuit\u27s Specific Exclusion Jurisprudence

Specific exclusion has become a controversial limitation on the doctrine of equivalents, which is itself an essential and controversial area of patent law. The doctrine of equivalents allows a patentee to successfully claim infringement against devices that are outside of the literal reach of the language used by the patentee in her patent to describe what she claims as her invention. The Supreme Court has prescribed some of the outer limits of the doctrine of equivalents and articulated the underlying policy concerns that inform its analysis-noting that courts should balance protection of the patentee\u27s intellectual property with the public\u27s reasonable expectations of the bounds of the patent-but has entrusted most of the doctrine\u27s development to the Federal Circuit. Critics argue that the Federal Circuit has applied specific exclusion, which precludes the doctrine of equivalents from reaching subject matter that is specifically excluded by the language used in the patent to describe the invention, in a way that does not adhere to the Supreme Court\u27s guidance on the doctrine of equivalents. The critics assert that the Federal Circuit has unduly narrowed the doctrine of equivalents by applying specific exclusion too aggressively. This Note demonstrates that the critics\u27 extreme characterization of Federal Circuit specific exclusion case law is unwarranted. The Federal Circuit has consistently and conscientiously applied specific exclusion, and their decisions conform to the Supreme Court\u27s guidance on the public notice function of patent claims. At the same time, the Federal Circuit has protected patentees by not allowing specific exclusion to reduce the doctrine of equivalents to another test for literal infringement

What Can be Taught in College in Prison? Reconciling Institutional Priorities in Clashes Over Incarcerated Students’ Access to Instructional Materials

This research was inspired by allegations of censorship of college curricula in an Illinois state penitentiary. This example highlights the confusion and controversy that may ensue when disagreements arise over what students in prison-based college programs are permitted to read and learn. Following this, my research considers these relevant questions: First, do many programs and prisons encounter disagreements over certain instructional materials? Next, to what extent are these rooted in clashing institutional values and priorities? And finally, what can be done to quell controversy, reduce confusion, and strengthen relationships between colleges and prisons? To shed light on these questions, I surveyed over forty practitioners from Higher Education in Prison (HEP) programs based in state penitentiaries across the United States. In particular, I asked about security clearance protocols for instructional materials, as well as institution-specific restrictions on modality and content. I report and discuss the findings and implications of this survey in the analysis that follows. As such, the intended audience for this report includes stakeholders in both academia and corrections, and others interested in strengthening relations between colleges and prisons that partner to educate incarcerated students

Planet transit and stellar granulation detection with interferometry

Aims. We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger-grid and synthetic images computed with the radiative transfer code Optim3D to provide interferometric observables to extract the signature of stellar granulation and transiting planets. Methods. We computed intensity maps from RHD simulations for twelve interferometric instruments covering wavelengths ranging from optical to infrared. The stellar surface asymmetries in the brightness distribution mostly affect closure phases. We compared the closure phases of the system star with a transiting planet and the star alone and considered the impact of magnetic spots constructing a hypothetical starspots image. Results. All the simulations show departure from the axisymmetric case at all wavelengths. We presented two possible targets (Beta Com and Procyon) and found that departures up to 16 deg can be detected on the 3rd lobe and higher. In particular, MIRC is the most appropriate instrument because it combines good UV coverage and long baselines. Moreover, we explored the impact of convection on interferometric planet signature for three prototypes of planets. It is possible to disentangle the signature of the planet at particular wavelengths (either in the infrared or in the optical) by comparing the closure phases of the star at difference phases of the planetary transit. Conclusions. The detection and characterisation of planets must be based on a comprehensive knowledge of the host star; this includes the detailed study of the stellar surface convection with interferometric techniques. In this context, RHD simulations are crucial to reach this aim. We emphasize that interferometric observations should be pushed at high spatial frequencies by accumulating observations on closure phases at short and long baselines.Comment: accepted in Astronomy and Astrophysics, 13 pages. Some figures have reduced resolution to decrease the size of the output file. Please contact [email protected] to have the high resolution version of the pape