Asteroseismic Signatures of Stellar Magnetic Activity Cycles

Observations of stellar activity cycles provide an opportunity to study magnetic dynamos under many different physical conditions. Space-based asteroseismology missions will soon yield useful constraints on the interior conditions that nurture such magnetic cycles, and will be sensitive enough to detect shifts in the oscillation frequencies due to the magnetic variations. We derive a method for predicting these shifts from changes in the Mg II activity index by scaling from solar data. We demonstrate this technique on the solar-type subgiant beta Hyi, using archival International Ultraviolet Explorer spectra and two epochs of ground-based asteroseismic observations. We find qualitative evidence of the expected frequency shifts and predict the optimal timing for future asteroseismic observations of this star.Comment: 5 pages including 3 figures and 1 table, MNRAS Letters accepte

Removal of Spectro-Polarimetric Fringes by 2D Pattern Recognition

We present a pattern-recognition based approach to the problem of removal of polarized fringes from spectro-polarimetric data. We demonstrate that 2D Principal Component Analysis can be trained on a given spectro-polarimetric map in order to identify and isolate fringe structures from the spectra. This allows us in principle to reconstruct the data without the fringe component, providing an effective and clean solution to the problem. The results presented in this paper point in the direction of revising the way that science and calibration data should be planned for a typical spectro-polarimetric observing run.Comment: ApJ, in pres

'This is what democracy looks like' : New Labour's blind spot and peripheral vision

New Labour in government since 1997 has been roundly criticized for not possessing a clear, coherent and consistent democratic vision. The absence of such a grand vision has resulted, from this critical perspective, in an absence of 'joined-up' thinking about democracy in an evolving multi-level state. Tensions have been all too apparent between the government's desire to exert central direction - manifested in its most pathological form as 'control freakery' - and its democratising initiatives derived from 'third-way' obsessions with 'decentralising', 'empowering' and 'enabling'. The purpose of this article is to examine why New Labour displayed such apparently impaired democratic vision and why it appeared incapable of conceiving of democratic reform 'in the round'. This article seeks to explain these apparent paradoxes, however, through utilising the notion of 'macular degeneration'. In this analysis, the perceived democratic blind spot of New Labour at Westminster is connected to a democratic peripheral vision, which has envisaged innovative participatory and decentred initiatives in governance beyond Westminster

Solar Atmospheric Oscillations and the Chromospheric Magnetic Topology

We investigate the oscillatory properties of the quiet solar chromosphere in relation to the underlying photosphere, with particular regard to the effects of the magnetic topology. We perform a Fourier analysis on a sequence of line-of-sight velocities measured simultaneously in a photospheric (Fe I 709.0 nm) and a chromospheric line (Ca II 854.2 nm). The velocities were obtained from full spectroscopic data acquired at high spatial resolution with the Interferometric BIdimensional Spectrometer (IBIS). The field of view encompasses a full supergranular cell, allowing us to discriminate between areas with different magnetic characteristics. We show that waves with frequencies above the acoustic cut-off propagate from the photosphere to upper layers only in restricted areas of the quiet Sun. A large fraction of the quiet chromosphere is in fact occupied by ``magnetic shadows'', surrounding network regions, that we identify as originating from fibril-like structures observed in the core intensity of the Ca II line. We show that a large fraction of the chromospheric acoustic power at frequencies below the acoustic cut-off, residing in the proximity of the magnetic network elements, directly propagates from the underlying photosphere. This supports recent results arguing that network magnetic elements can channel low-frequency photospheric oscillations into the chromosphere, thus providing a way to input mechanical energy in the upper layers.Comment: 4 pages, 3 figure, A&A Letters in pres

Charge-exchange limits on low-energy α-particle fluxes in solar flares

This paper reports on a search for flare emission via charge-exchange radiation in the wings of the Lyα line of He II at 304 Å, as originally suggested for hydrogen by Orrall and Zirker. Via this mechanism a primary α particle that penetrates into the neutral chromosphere can pick up an atomic electron and emit in the He II bound-bound spectrum before it stops. The Extreme-ultraviolet Variability Experiment on board the Solar Dynamics Observatory gives us our first chance to search for this effect systematically. The Orrall-Zirker mechanism has great importance for flare physics because of the essential roles that particle acceleration plays; this mechanism is one of the few proposed that would allow remote sensing of primary accelerated particles below a few MeV nucleon<sup>–1</sup>. We study 10 events in total, including the γ-ray events SOL2010-06-12 (M2.0) and SOL2011-02-24 (M3.5) (the latter a limb flare), seven X-class flares, and one prominent M-class event that produced solar energetic particles. The absence of charge-exchange line wings may point to a need for more complete theoretical work. Some of the events do have broadband signatures, which could correspond to continua from other origins, but these do not have the spectral signatures expected from the Orrall-Zirker mechanism

Space-Time Distribution of G-Band and Ca II H-Line Intensity Oscillations in Hinode/SOT-FG Observations

We study the space-time distributions of intensity fluctuations in 2 - 3 hour sequences of multi-spectral, high-resolution, high-cadence broad-band filtergram images (BFI) made by the SOT-FG system aboard the Hinode spacecraft. In the frequency range 5.5 < f < 8.0 mHz both G-band and Ca II H-line oscillations are suppressed in the presence of magnetic fields, but the suppression disappears for f > 10 mHz. By looking at G-band frequencies above 10 mHz we find that the oscillatory power, both at these frequencies and at lower frequencies too, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly larger than normal granulation, and with correlation times on the order of hours. The mesh pattern lies in the dark lanes between stable cells found in time-integrated G-band intensity images. It also underlies part of the bright pattern in time-integrated H-line emission. This discovery may reflect dynamical constraints on the sizes of rising granular convection cells together with the turbulence created in strong intercellular downflows.Comment: 24 pages, 15 figure

Large-uncertainty intelligent states for angular momentum and angle

The equality in the uncertainty principle for linear momentum and position is obtained for states which also minimize the uncertainty product. However, in the uncertainty relation for angular momentum and angular position both sides of the inequality are state dependent and therefore the intelligent states, which satisfy the equality, do not necessarily give a minimum for the uncertainty product. In this paper, we highlight the difference between intelligent states and minimum uncertainty states by investigating a class of intelligent states which obey the equality in the angular uncertainty relation while having an arbitrarily large uncertainty product. To develop an understanding for the uncertainties of angle and angular momentum for the large-uncertainty intelligent states we compare exact solutions with analytical approximations in two limiting cases.Comment: 20 pages, 9 figures, submitted to J. Opt. B special issue in connection with ICSSUR 2005 conferenc

Minimum-Uncertainty Angular Wave Packets and Quantized Mean Values

Uncertainty relations between a bounded coordinate operator and a conjugate momentum operator frequently appear in quantum mechanics. We prove that physically reasonable minimum-uncertainty solutions to such relations have quantized expectation values of the conjugate momentum. This implies, for example, that the mean angular momentum is quantized for any minimum-uncertainty state obtained from any uncertainty relation involving the angular-momentum operator and a conjugate coordinate. Experiments specifically seeking to create minimum-uncertainty states localized in angular coordinates therefore must produce packets with integer angular momentum.Comment: accepted for publication in Physical Review

Two-Dimensional Helioseismic Power, Phase, and Coherence Spectra of {\it Solar Dynamics Observatory} Photospheric and Chromospheric Observables

While the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar Dynamics Observatory} (SDO) provides Doppler velocity [$V$], continuum intensity [$I_C$], and line-depth [$Ld$] observations, each of which is sensitive to the five-minute acoustic spectrum, the {\it Atmospheric Imaging Array} (AIA) also observes at wavelengths -- specifically the 1600 and 1700 Angstrom bands -- that are partly formed in the upper photosphere and have good sensitivity to acoustic modes. In this article we consider the characteristics of the spatio--temporal Fourier spectra in AIA and HMI observables for a 15-degree region around NOAA Active Region 11072. We map the spatio--temporal-power distribution for the different observables and the HMI Line Core [$I_L$], or Continuum minus Line Depth, and the phase and coherence functions for selected observable pairs, as a function of position and frequency. Five-minute oscillation power in all observables is suppressed in the sunspot and also in plage areas. Above the acoustic cut-off frequency, the behaviour is more complicated: power in HMI $I_C$ is still suppressed in the presence of surface magnetic fields, while power in HMI $I_L$ and the AIA bands is suppressed in areas of surface field but enhanced in an extended area around the active region, and power in HMI $V$ is enhanced in a narrow zone around strong-field concentrations and suppressed in a wider surrounding area. The relative phase of the observables, and their cross-coherence functions, are also altered around the active region. These effects may help us to understand the interaction of waves and magnetic fields in the different layers of the photosphere, and will need to be taken into account in multi-wavelength local helioseismic analysis of active regions.Comment: 18 pages, 15 figures, to be published in Solar Physic