P-modes in rapidly rotating stars -- looking for regular patterns in synthetic asymptotic spectra

According to a recent ray-based asymptotic theory, the high-frequency p-mode spectrum of rapidly rotating stars is a superposition of frequency subsets associated with dynamically independent regions of the ray-dynamics phase space. At high rotation rates corresponding to typical $\delta$ Scuti stars, two frequency subsets are expected to be visible : a regular frequency subset described by a Tassoul like formula and an irregular frequency subset with specific statistical properties. In this paper, we investigate whether the regular patterns can be detected in the resulting spectrum. We compute the autocorrelation function of synthetic spectra where the frequencies follow the asymptotic theory, the relative amplitudes are simply given by the modes' disk-averaging factors, and the frequency resolution is that of a CoRoT long run. Our first results are that (i) the detection of regular patterns strongly depends on the ratio of regular over irregular modes, (ii) low inclination angle configurations are more favorable than near equator-on configurations, (iii) in the absence of differential rotation, the $2 \Omega$ rotational splitting between $m=1$ and $m=-1$ modes is an easy feature to detect.Comment: 4 pages, 4 figures, proceedings of the HELAS-IV International Conference, accepted for publication in Astronomische Nachrichte

The Prison Education Project in Scotland

The Prison Education Project (PEP) is the largest prison education program of its kind in the United States. With the assistance of 2,400 university student and faculty volunteers, PEP has served approximately 7,000 inmates in 14 correctional facilities in California since 2011. By providing academic, life skills, and career development programming, PEP aims to educate, empower, and transform the lives of incarcerated individuals. Since 2014, this program has taken a group of veteran volunteers to an international destination to teach courses in prisons in Uganda, England, and Scotland. This article will focus on the PEP-Scotland experience. Eleven PEP instructors traveled to Edinburgh, Scotland to teach courses in HMP Addiewell. There were 10 African American and one Asian American instructors on the PEP team. Nearly 100% of the inmates in their classes were white. This added an interesting dynamic to the experience. There were eleven 105-minute courses taught over a five-day period. This article will briefly discuss the genesis of this project, the content of the courses that were taught, the international prison education movement, the spirit of volunteerism, and the post-course outcome data. At the end of the courses, the in-custody students were given a survey, which contained three closed-ended questions and one open-ended question. The in-custody students\u27 responses to the open-ended survey question describe this experience in ways in which this author could not--with vivid clarity, depth, and breadth

Water, water, everywhere, Nor any drop to drink?

With the world’s population set to exceed nine billion by the end of the century, the demand for fresh water will become ever more acute. Applying nanotechnology to filter seawater in coastal areas could provide part of the answer, as Jason Reese explain

Stable higher order finite-difference schemes for stellar pulsation calculations

Context: Calculating stellar pulsations requires a sufficient accuracy to match the quality of the observations. Many current pulsation codes apply a second order finite-difference scheme, combined with Richardson extrapolation to reach fourth order accuracy on eigenfunctions. Although this is a simple and robust approach, a number of drawbacks exist thus making fourth order schemes desirable. A robust and simple finite-difference scheme, which can easily be implemented in either 1D or 2D stellar pulsation codes is therefore required. Aims: One of the difficulties in setting up higher order finite-difference schemes for stellar pulsations is the so-called mesh-drift instability. Current ways of dealing with this defect include introducing artificial viscosity or applying a staggered grids approach. However these remedies are not well-suited to eigenvalue problems, especially those involving non-dissipative systems, because they unduly change the spectrum of the operator, introduce supplementary free parameters, or lead to complications when applying boundary conditions. Methods: We propose here a new method, inspired from the staggered grids strategy, which removes this instability while bypassing the above difficulties. Furthermore, this approach lends itself to superconvergence, a process in which the accuracy of the finite differences is boosted by one order. Results: This new approach is shown to be accurate, flexible with respect to the underlying grid, and able to remove mesh-drift.Comment: 15 pages, 11 figures, accepted for publication in A&

Evidence of Resource Procurement and Manufacturing Techniques in Caddoan Ceramic Assemblages from the Sabine, Cypress, and Sulphur River Drainage Basins, Rusk and Titus Counties, Texas

Texas Utilities Services and Espey, Huston & Associates, Inc. have conducted ongoing archaeological investigations of cultural resources in Northeast Texas for the past 15 years. As a part of these studies, prehistoric Caddoan ceramic assemblages were recovered from 13 sites in three distinct drainage basins: three sites from the Sabine River drainage; three sites from the Cypress Creek drainage; and seven sites from the Sulphur River drainage. Recent research on the ceramic collections has emphasized variability in surface treatment, vessel form, and paste composition by means of a detailed attribute analysis and petrographic examination of a sample of the Caddoan sherds. This paper focuses on the paste composition of a sherd sample selected to undergo petrographic analysis. The sample contains representatives among the sherds of the major tempering agents identified during a macroscopic examination of the pastes. The initial goal of the analyses was establishment of a baseline for paste composition in the study areas. A detailed point count, and grain size measurements, allowed for the identification of constituents in a range of frequencies from among the sites located in each of the three drainage basins. Upon completion of the initial studies, the results of the analyses from the three studies were compared. This paper presents a discussion of preliminary patterns identified in Caddoan ceramic assemblages of resource procurement and manufacturing techniques observed among the site samples

Internal rapid rotation and its implications for stellar structure and pulsations

Massive and intermediate mass stars play a crucial role in astrophysics. Indeed, massive stars are the main producers of heavy elements, explode in supernovae at the end of their short lifetimes, and may be the progenitors of gamma ray bursts. Intermediate mass stars, although not destined to explode in supernovae, display similar phenomena, are much more numerous, and have some of the richest pulsation spectra. A key to understanding these stars is understanding the effects of rapid rotation on their structure and evolution. These effects include centrifugal deformation and gravity darkening which can be observed immediately, and long terms effects such as rotational mixing due to shear turbulence, which prolong stellar lifetime, modify chemical yields, and impact the stellar remnant at the end of their lifetime. In order to understand these effects, a number of models have been and are being developed over the past few years. These models lead to increasingly sophisticated predictions which need to be tested through observations. A particularly promising source of constraints is seismic observations as these may potentially lead to detailed information on their internal structure. However, before extracting such information, a number of theoretical and observational hurdles need to be overcome, not least of which is mode identification. The present proceedings describe recent progress in modelling these stars and show how an improved understanding of their pulsations, namely frequency patterns, mode visibilities, line profile variations, and mode excitation, may help with deciphering seismic observations.Comment: Proceedings for the CoRoT 3/KASC 7 meeting in Toulous

Inequalities on stellar rotational splittings derived from assumptions on the rotation profile

Context: A number of pulsating stars with rotational splittings have been observed thanks to the CoRoT and Kepler missions. This is particularly true of evolved (sub-giant and giant) stars, and has led various groups to investigate their rotation profiles via different methods. Aims: We would like to set up some criteria which will help us to know whether a decreasing rotation profile, or one which satisfies Rayleigh's stability criterion, is compatible with a set of observed rotational splittings for a given reference model. Methods: We derive inequalities on the rotational splittings using a reformulated version of the equation which relates the splittings to the rotation profile and kernels. Results: These inequalities are tested out on some simple examples. The first examples show how they are able to reveal when a rotation profile is increasing somewhere or inconsistent with Rayleigh's criterion in a main sequence star, depending on the profile and the $\ell$ values of the splittings. The next example illustrates how a slight mismatch between an observed evolved star and a reference model can lead to erroneous conclusions about the rotation profile. We also show how frequency differences between the star and the model, which should normally reveal this mismatch, can be masked by frequency corrections for near-surface effects.Comment: 15 pages, 19 figures, accepted for publication in A&