Asteroseismology of the Kepler field DBV White Dwarf - It's a hot one!

We present an asteroseismic analysis of the helium atmosphere white dwarf (a DBV) recently found in the field of view of the Kepler satellite. We analyze the 5-mode pulsation spectrum that was produced based on one month of high cadence Kepler data. The pulsational characteristics of the star and the asteroseismic analysis strongly suggest that the star is hotter (29200 K) than the 24900 K suggested by model fits to the low S/N survey spectrum of the object. This result has profound and exciting implications for tests of the Standard Model of particle physics. Hot DBVs are expected to lose over half of their energy through the emission of plasmon neutrinos. Continuous monitoring of the star with the Kepler satellite over the course of 3 to 5 years is not only very likely to yield more modes to help constrain the asteroseismic fits, but also allow us to obtain a rate of change of any stable mode and therefore measure the emission of plasmon neutrinos.Comment: 5 pages, 3 figures, accepted for publication in ApJ

Silicon Sensors implemented on p-type substrates for high radiation resistance applications

Silicon based micropattern detectors are essential elements of modern high energy physics experiments. Cost effectiveness and high radiation resistance are two important requirements for technologies to be used in inner tracking devices. Processes based on p-type substrates have very strong appeal for these applications. Recent results and prototype efforts under way are reviewed.Comment: 7 pages, 2 figures; invited paper at Vertex 2006, Perugia, Italy, september 200

Excitation of stellar p-modes by turbulent convection: 1. Theoretical formulation

Stochatic excitation of stellar oscillations by turbulent convection is investigated and an expression for the power injected into the oscillations by the turbulent convection of the outer layers is derived which takes into account excitation through turbulent Reynolds stresses and turbulent entropy fluctuations. This formulation generalizes results from previous works and is built so as to enable investigations of various possible spatial and temporal spectra of stellar turbulent convection. For the Reynolds stress contribution and assuming the Kolmogorov spectrum we obtain a similar formulation than those derived by previous authors. The entropy contribution to excitation is found to originate from the advection of the Eulerian entropy fluctuations by the turbulent velocity field. Numerical computations in the solar case in a companion paper indicate that the entropy source term is dominant over Reynold stress contribution to mode excitation, except at high frequencies.Comment: 14 pages, accepted for publication in A&

Has a star enough energy to excite the thousand of modes observed with CoRoT?

The recent analyses of the light curves provided by CoRoT have revealed pulsation spectra of unprecedented richness and precision, in particular, thousands of pulsating modes, and a clear distribution of amplitudes with frequency. In the community, some scientists have started doubting about the validity of the classical tools to analyze these very accurate light curves. This work provides the asteroseismic community with answers to this question showing that (1) it is physically possible for a star to excite at a time and with the observed amplitudes such a large number of modes; and (2) that the kinetic energy accumulated in all those modes does not destroy the equilibrium of the star. Consequently, mathematical tools presently applied in the analyses of light curves can a priori be trusted. This conclusion is even more important now, when a large amount of space data coming from Kepler are currently being analyzed. The power spectrum of different stellar cases, and the non-adiabatic code GraCo have been used to estimate the upper limit of the energy per second required to excite all the observed modes, and their total kinetic energy. A necessary previous step for this study is to infer the relative radial pulsational amplitude from the observed photometric amplitude, scaling our linear pulsational solutions to absolute values. The derived upper limits for the required pulsational energy were compared with 1) the luminosity of the star; and 2) the gravitational energy. We obtained that both upper energy limits are orders of magnitude smaller.Comment: 18 pages, 2 figures, accepted by ApJ Letters Dec 15, 200

Photofluid Instabilities of Hot Stellar Envelopes

Beginning from a relatively simple set of dynamical equations for a fluid permeated by a radiative field strong enough to produce significant forces, we find the structure of plane-parallel equilibria and study their stability to small acoustic disturbances. In doing this, we neglect viscous effects and complications of nongreyness. We find that acoutic instabilities occur over a wide range of conditions below the Eddington limit. This result is in line with findings reported twenty years ago but it contradicts some more recent reports of the absence of instabilities. We briefly attempt to identify the causes of the discrepancies and then close with a discussion of the possible astrophysical interest of such instabilities.Comment: 10 pages, LaTeX, 5 postscript figures, to be published in Physics Report

Interactively Picking Real-World Objects with Unconstrained Spoken Language Instructions

Comprehension of spoken natural language is an essential component for robots to communicate with human effectively. However, handling unconstrained spoken instructions is challenging due to (1) complex structures including a wide variety of expressions used in spoken language and (2) inherent ambiguity in interpretation of human instructions. In this paper, we propose the first comprehensive system that can handle unconstrained spoken language and is able to effectively resolve ambiguity in spoken instructions. Specifically, we integrate deep-learning-based object detection together with natural language processing technologies to handle unconstrained spoken instructions, and propose a method for robots to resolve instruction ambiguity through dialogue. Through our experiments on both a simulated environment as well as a physical industrial robot arm, we demonstrate the ability of our system to understand natural instructions from human operators effectively, and how higher success rates of the object picking task can be achieved through an interactive clarification process.Comment: 9 pages. International Conference on Robotics and Automation (ICRA) 2018. Accompanying videos are available at the following links: https://youtu.be/_Uyv1XIUqhk (the system submitted to ICRA-2018) and http://youtu.be/DGJazkyw0Ws (with improvements after ICRA-2018 submission

Modelling turbulent fluxes due to thermal convection in rectilinear shearing flow

We revisit a phenomenological description of turbulent thermal convection along the lines proposed originally by Gough (1965) in which eddies grow solely by extracting energy from the unstably stratified mean state and are subsequently destroyed by internal shear instability. This work is part of an ongoing investigation for finding a procedure to calculate the turbulent fluxes of heat and momentum in the presence of a shearing background flow in stars.Comment: 2 pages, 1 figure, accepted for publication in IAU Symposium 271 "Astrophysical Dynamics: From Galaxies to Stars", Nice, 201

Thermal Tides in Fluid Extrasolar Planets

Asynchronous rotation and orbital eccentricity lead to time-dependent irradiation of the close-in gas giant exoplanets -- the hot Jupiters. This time-dependent surface heating gives rise to fluid motions which propagate throughout the planet. We investigate the ability of this "thermal tide" to produce a quadrupole moment which can couple to the stellar gravitational tidal force. While previous investigations discussed planets with solid surfaces, here we focus on entirely fluid planets in order to understand gas giants with small cores. The Coriolis force, thermal diffusion and self-gravity of the perturbations are ignored for simplicity. First, we examine the response to thermal forcing through analytic solutions of the fluid equations which treat the forcing frequency as a small parameter. In the "equilibrium tide" limit of zero frequency, fluid motion is present but does not induce a quadrupole moment. In the next approximation, finite frequency corrections to the equilibrium tide do lead to a nonzero quadrupole moment, the sign of which torques the planet {\it away} from synchronous spin. We then numerically solve the boundary value problem for the thermally forced, linear response of a planet with neutrally stratified interior and stably stratified envelope. The numerical results find quadrupole moments in agreement with the analytic non-resonant result at sufficiently long forcing period. Surprisingly, in the range of forcing periods of 1-30 days, the induced quadrupole moments can be far larger than the analytic result due to response of internal gravity waves which propagate in the radiative envelope. We discuss the relevance of our results for the spin, eccentricity and thermal evolution of hot Jupiters.Comment: 12 pages, 7 figures, submitted to Ap

Pulsations in the atmosphere of the roAp star HD 24712 II. Theoretical models

We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR 1217) based on nonadiabatic analyses taking into account the effect of dipole magnetic fields. We have found that all the pulsation modes appropriate for HD 24712 are damped; i.e., the kappa-mechanism excitation in the hydrogen ionization layers is not strong enough to excite high-order p-modes with periods consistent with observed ones, all of which are found to be above the acoustic cut-off frequencies of our models. The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with modified $l=2$ and $l=3$ modes, respectively. The large frequency separation ($\approx 68 \mu$Hz) is reproduced by models which lay within the error box of HD 24712 on the HR diagram. The nearly equally spaced frequencies of HD 24712 indicate the small frequency separation to be as small as $\approx 0.5\mu$Hz. However, the small separation derived from theoretical $l=1$ and 2 modes are found to be larger than $\sim 3\mu$Hz. The problem of equal spacings could be resolved by assuming that the spacings correspond to pairs of $l=2$ and $l=0$ modes. The amplitude distribution on the stellar surface is strongly affected by the magnetic field resulting in the predominant concentration at the polar regions. Amplitudes and phases of radial-velocity variations for various spectral lines are converted to relations of amplitude/phase versus optical depth in the atmosphere. Oscillation phase delays gradually outward in the outermost layers indicating the presence of waves propagating outward. The phase changes steeply around $\log\tau\sim-3.5$, which supports a $T-\tau$ relation having a small temperature inversion there.Comment: 11 pages, 13 figures, accepted for publication in MNRA