Theory of Stellar Oscillations

In recent years, astronomers have witnessed major progresses in the field of stellar physics. This was made possible thanks to the combination of a solid theoretical understanding of the phenomena of stellar pulsations and the availability of a tremendous amount of exquisite space-based asteroseismic data. In this context, this chapter reviews the basic theory of stellar pulsations, considering small, adiabatic perturbations to a static, spherically symmetric equilibrium. It starts with a brief discussion of the solar oscillation spectrum, followed by the setting of the theoretical problem, including the presentation of the equations of hydrodynamics, their perturbation, and a discussion of the functional form of the solutions. Emphasis is put on the physical properties of the different types of modes, in particular acoustic (p-) and gravity (g-) modes and their propagation cavities. The surface (f-) mode solutions are also discussed. While not attempting to be comprehensive, it is hoped that the summary presented in this chapter addresses the most important theoretical aspects that are required for a solid start in stellar pulsations research.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Cosmological models with linearly varying deceleration parameter

We propose a new law for the deceleration parameter that varies linearly with time and covers Berman's law where it is constant. Our law not only allows one to generalize many exact solutions that were obtained assuming constant deceleration parameter, but also gives a better fit with data (from SNIa, BAO and CMB), particularly concerning the late time behavior of the universe. According to our law only the spatially closed and flat universes are allowed; in both cases the cosmological fluid we obtain exhibits quintom like behavior and the universe ends with a big-rip. This is a result consistent with recent cosmological observations.Comment: 12 pages, 7 figures; some typo corrections; to appear in International Journal of Theoretical Physic

Porto Oscillation Code (POSC)

The Porto Oscillation Code (POSC) has been developed in 1995 and improved over the years, with the main goal of calculating linear adiabatic oscillations for models of solar-type stars. It has also been used to estimate the frequencies and eigenfunctions of stars from the pre-main sequence up to the sub-giant phase, having a mass between 0.8 and 4 solar masses. The code solves the linearised perturbation equations of adiabatic pulsations for an equilibrium model using a second order numerical integration method. The possibility of using Richardson extrapolation is implemented. Several options for the surface boundary condition can be used. In this work we briefly review the key ingredients of the calculations, namely the equations, the numerical scheme and the output.Comment: Accepted for publication in Astrophysics and Space Science

K2 observations of the rapidly oscillating Ap star 33 Lib (HD 137949): new frequencies and unique non-linear interactions

We present the analysis of K2 short cadence data of the rapidly oscillating Ap (roAp) star, 33 Librae (HD 137949). The precision afforded to the K2 data allow us to identify at least 11 pulsation modes in this star, compared to the three previously reported. Reoccurring separations between these modes leads us to suggest a large frequency separation, ∆ν, of 78.9 µHz, twice that reported in the literature. Other frequency separations we detect may represent the small frequency separation, δν, but this is inconclusive at this stage due to magnetic perturbation of the frequencies. Due to the highly non-linear pulsation in 33 Lib, we identify harmonics to four times the principal frequency. Furthermore, we note a unique occurrence of non-linear interactions of the 11 identified modes. The frequency separations of the modes around the principal frequency are replicated around the first harmonic, with some interaction with the second harmonic also. Such a phenomenon has not been seen in roAp stars before. With revised stellar parameters, linear non-adiabatic modelling of 33 Lib shows that the pulsations are not greater than the acoustic cutoff frequency, and that the κ-mechanism can excite the observed modes. Our observations are consistent with 33 Lib having a rotation period much larger than 88 d as presented in the literature

Generating mass and topological terms to the antisymmetric tensor matter field by Higgs mechanism

The interaction between the complex antisymmetric tensor matter field and a scalar field is constructed. We analyze the Higgs mechanism and show the generation of mass and topological terms by spontaneous symmetry breaking.Comment: Accepted for publication in Phys. Lett.

A Comparison of the LVDP and {\Lambda}CDM Cosmological Models

We compare the cosmological kinematics obtained via our law of linearly varying deceleration parameter (LVDP) with the kinematics obtained in the {\Lambda}CDM model. We show that the LVDP model is almost indistinguishable from the {\Lambda}CDM model up to the near future of our universe as far as the current observations are concerned, though their predictions differ tremendously into the far future.Comment: 6 pages, 5 figures, 1 table, matches the version to be published in International Journal of Theoretical Physic

Cryptococcal Pneumonia and Meningitis in a Horse

AbstractGross and microscopic evidence of Cryptococcus neoformans in the lungs and central nervous system of a mature Thoroughbred horse presenting with granulomatous pneumonia and meningitis has been described in this article

On the oscillation spectrum of a magnetized core in a giant star

The spectrum of gravito-acoustic modes is depleted in dipolar modes for a significant fraction of the giant stars observed by the Kepler mission, a feature that has been explained by the presence of magnetic fields in the core of these stars (Fuller et al. 2015, Cantiello et al. 2016). We further investigate this possible scenario by considering first the oscillation spectrum of the core of a giant star modeled by a stably stratified, self-gravitating fluid of uniform density in a sphere pervaded by a uniform magnetic field. Our results show that the first effect of a magnetic field on the g-modes is to reduce their wavenumber and therefore reduce their damping. The magnetic effect, on this model, is therefore opposite Fuller’s et al scenario. Moreover, the model shows that it is not possible to change the damping rate without changing the frequency of the modes and this latter change is not observed. Because of the simplicity of our model, the magnetized core scenario cannot be dismissed but further investigations are needed, and other ways of explaining the presence of depressed modes should also be considered

Mariniblastus fucicola gen. nov., sp. nov. a novel planctomycete associated with macroalgae

One strain of a novel genus and species of the order Planctomycetes, designated FC18T, was isolated from the epiphytic community of Fucusspiralis. This strain was non-pigmented in medium M13 but was slightly pink pigmented on medium M14, containing four-fold the levels of glucose, peptone and yeast extract of M13. The organism was primarily spherical, with unicellular non-motile forms and rosettes. The optimal temperature for growth was about 25 C and the optimal pH was 7.5. FC18T was chemoorganotrophic and aerobic. Several sugars, polyols and amino acids were assimilated. The major fatty acids were C18: 1 ω 9c, C14: 0 and C16: 0. The major polar lipids were phosphatidylglycerol (PG) and two unknown lipids. Menaquinone 5 (MK-5) was the main respiratory quinone, but MK-6 was also present. The results of the 16S rRNA gene sequence analysis confirmed the affiliation of this organism to the order Planctomycetales, family Planctomycetaceae, with Blastopirellula marina as the closest relative with only 86% sequence similarity. On the basis of physiological, biochemical and chemotaxonomic characteristics we propose that FC18T (=LMG 29748T =DSM 26290T) represents a novel species of a novel genus of the family Planctomycetaceae for which we propose the name Mariniblastusfucicola gen. nov., sp. nov. © 2017 IUMS.This work was partially supported by the Strategic Funding UID/Multi/ 04423/2013 through national funds provided by FCT ? Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the programme PT2020 and by FEDER funds through the Operational Programme Competitiveness Factors ? COMPETE and the strategic project UID/NEU/04539/2013

Ricci-flat deformation of orbifolds and localized tachyonic modes

We study Ricci-flat deformations of orbifolds in type II theory. We obtain a simple formula for mass corrections to the twisted modes due to the deformations, and apply it to originally tachyonic and massless states in several examples. In the case of supersymmetric orbifolds, we find that tachyonic states appear when the deformation breaks all the supersymmetries. We also study nonsupersymmetric orbifolds C^2/Z_{2N(2N+1)}, which is T-dual to N type 0 NS5-branes. For N>=2, we compute mass corrections for states, which have string scale tachyonic masses. We find that the corrected masses coincide to ones obtained by solving the wave equation for the tachyon field in the smeared type 0 NS5-brane background geometry. For N=1, we show that the unstable mode representing the bubble creation is the unique tachyonic mode.Comment: 20 pages, minor collection