14468327
The radius and effective temperature of the binary Ap starβ CrB from CHARA/FLUOR and VLT/NACO observations ⋆
Context. The prospects for using the asteroseismology of rapidly oscillating Ap (roAp) stars are hampered by the large uncertainty in fundamental stellar parameters. Results in the literature for the effective temperature (Teff) often span a range of 1000 K. Aims. Our goal is to reduce systematic errors and improve the Teff calibration of Ap stars based on new interferometric measurements. Methods. We obtained long-baseline interferometric observations of β CrB using the CHARA/FLUOR instrument. To disentangle the flux contributions of the two components of this binary star, we obtained VLT/NACO adaptive optics images. Results. We determined limb-darkened angular diameters of 0.699 ± 0.017 mas for β CrB A (from interferometry) and 0.415 ± 0.017 mas for β CrB B (from surface brightness-colour relations), corresponding to radii of 2.63 ± 0.09 R� (3.4% uncertainty) and 1.56 ± 0.07 R� (4.5%). The combined bolometric flux of the A+B components was determined from satellite UV data, spectrophotometry in the visible, and broadband data in the infrared. The flux from the B component constitutes 16 ± 4% of the total flux and was determined by fitting an ATLAS9 model atmosphere to the broad-band NACO J and K magnitudes. By combining the flux of the A component with its measured angular diameter, we determined the effective temperature Teff (A) = 7980 ± 180 K (2.3%). Conclusions. Our new interferometric and imaging data enable nearly model-independent determination of the effective temperature of β CrB A. Including our recent study of α Cir, we now have direct Teff measurements of two of the brightest roAp stars, providing a strong benchmark for improved calibration of the Teff scale for Ap stars. This will support the use of potentially strong constraints imposed by asteroseismic studies of roAp stars.
14738827
Improved pulsating models of magnetic Ap stars ¿ I. Exploring different magnetic field configurations
Magnetic perturbations to the frequencies of low-degree, high radial order, axisymmetric pulsations in stellar models permeated by large-scale magnetic fields are presented. Magnetic fields with dipolar, quadrupolar and a superposition of aligned dipolar and quadrupolar components are considered. The results confirm that the magnetic field may produce strong anomalies in the power spectra of roAp stars. It is shown for the first time that anomalies may result both from a sudden decrease or a sudden increase of a mode frequency. Moreover, the results indicate that the anomalies depend essentially on the geometry of the problem, that is, on the configuration of the magnetic field and on the degree of the modes. This dependence opens the possibility of using these anomalies as a tool to learn about the magnetic field configuration in the magnetic boundary layer of pulsating stars permeated by large-scale magnetic fields.
16590095
Asteroseismology and interferometry
Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.
14857158
A search for rapid pulsations among nine luminous Ap stars
The rapidly oscillating Ap (roAp) stars are of importance for studying the atmospheric structure of stars where the process of chemical element diffusion is significant. We have performed a survey for rapid oscillations in a sample of nine luminous Ap stars, selected from their location in the colour‐magnitude diagram as more evolved main-sequence Ap stars that are inside the instability strip for roAp stars. Until recently this region was devoid of stars with observed rapid pulsations. We used the Very Large Telescope UV‐Visual Echelle Spectrograph to obtain high time resolution spectroscopy to make the first systematic spectroscopic search for rapid oscillations in this region of the roAp instability strip. We report nine null detections with upper limits for radial velocity amplitudes of 20‐65 m s −1 and precisions of σ = 7‐ 20 m s −1 for combinations of Nd and Pr lines. Cross-correlations confirm these null results. At least six stars are magnetic and we provide magnetic field measurements for four of them, of which three are newly discovered magnetic stars. It is found that four stars have magnetic fields smaller than ∼2 kG, which according to theoretical predictions might be insufficient for suppressing envelope convection around the magnetic poles for more evolved Ap stars. Suppression of convection is expected to be essential for the opacity mechanism acting in the hydrogen ionization zone to drive the high-overtone roAp pulsations efficiently. Our null results suggest that the more evolved roAp stars may require particularly strong magnetic fields to pulsate. Three of the studied stars do, however, have magnetic fields stronger than 5 kG.
59387646
Theory of rapidly oscillating Ap stars
I review recent theoretical work on rapidly oscillating Ap stars and discuss key aspects of the physics of the oscillations observed in this class of pulsators.
118476277
Probing tiny convective cores with the acoustic modes of lowest degree
Solar-like oscillations are expected to be excited in stars of up to about 1.6 solar masses. Most of these stars will have convective cores during their main-sequence evolution. At the edges of these convective cores, there is a rapid variation in the sound speed, which influences the frequencies of acoustic oscillations. In this paper we build on earlier work to investigate the impact that these rapid structural variations have on different p-mode frequency combinations, involving modes of low degree. In particular, we adopt a different expression to describe the sound speed variation at the edge of the core, which we show more closely reproduces the profiles derived from the equilibrium models. We analyse the impact of this change on the frequency perturbation derived for radial modes. Moreover, we consider three different small frequency separations involving modes of degree l = 0, 1, 2, 3, l = 0, 1, and l = 0, 2, and show that they are all significantly affected by the sharp sound speed variation at the edge of the core. In particular, we confirm that the frequency derivative of the diagnostic tool that combines modes of degree up to 3 can potentially be used to infer the amplitude of the relative sound speed variation directly at the edge of the core. We show that at high frequencies the other two diagnostic tools can be up to a few μHz smaller than what would be expected in the absence of the rapid structural variation at the edge of the core. Also, we show that the absolute values of their frequency derivatives are significantly increased, in a manner that strongly depends on stellar age.
119612595
Energy eigenfunctions for position-dependent mass particles in a new class of molecular Hamiltonians
Based on recent results on quasi-exactly solvable Schrodinger equations, we review a new phenomenological potential class lately reported. In the present paper, we consider the quantum differential equations resulting from position-dependent mass (PDM) particles. We first focus on the PDM version of the hyperbolic potential V(x) = asech2x + bsech4x, which we address analytically with no restrictioon the parameters and the energies. This is the celebrated Manning potential, a double-well widely used in molecular physics, until now not investigated for PDM. We also evaluate the PDM version of the sixth power hyperbolic potential V(x) = asech6x + bsech4x for which we could find exact expressions under some special settings. Finally, we address a triple-well case V(x) = asech6x + bsech4x + csech2x of particular interest for its connection to the new trends in atomtronics. The PDM Schrodinger equations studied in the present paper yield analytical eigenfunctions in terms of local Heun functions in its confluen...
119097979
Solutions to position-dependent mass quantum mechanics for a new class of hyperbolic potentials
We analytically solve the position-dependent mass (PDM) 1D Schrodinger equation for a new class of hyperbolic potentials Vqp(x)=−V0sinhpxcoshqx,p=−2,0,⋯q [see C. A. Downing, J. Math. Phys. 54, 072101 (2013)] among several hyperbolic single- and double-wells. For a solitonic mass distribution, m(x)=m0sech2(x), we obtain exact analytic solutions to the resulting differential equations. For several members of the class, the quantum mechanical problems map into confluent Heun differential equations. The PDM Poschl-Teller potential is considered and exactly solved as a particular case.
16040629
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.
118935596
Hořava-Lifshitz gravity effects on Casimir energy in weak field approximation and infrared regime
We calculate the renormalized vacuum energy of a massless scalar field confined between two nearby parallel plates formed by ideal uncharged conductors, placed tangentially to the surface of a sphere with mass $M$ and radius $R$. This study will take into account the static and spherically symmetric solution of Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity found by Kehagias-Sfetsos (KS), in both weak field and infrared limits. A slight amplification of the Casimir force between the conducting plates is found. Thermal corrections to the Casimir energy are analyzed. Based on current Casimir effect measurements, a constraint on the $\ensuremath{\omega}$ parameter of KS metric is also obtained.
13913247
N = 2 MAXWELL–CHERN–SIMONS MODEL WITH ANOMALOUS MAGNETIC MOMENT COUPLING VIA DIMENSIONAL REDUCTION
An N = 1-supersymmetric version of the Cremmer–Scherk–Kalb–Ramond model with nonminimal coupling to matter is built up both in terms of superfields and in a component-field formalism. By adopting a dimensional reduction procedure, the (N = 2)-(D = 3) counterpart of the model comes out, with two main features: a genuine (diagonal) Chern–Simons term and an anomalous magnetic moment coupling between matter and the gauge potential.