The application of a Trous wave filtering and Monte Carlo analysis on SECIS 2001 solar eclipse observations

8000 images of the Solar corona were captured during the June 2001 total Solar eclipse. New software for the alignment of the images and an automated technique for detecting intensity oscillations using multi scale wavelet analysis were developed. Large areas of the images covered by the Moon and the upper corona were scanned for oscillations and the statistical properties of the atmospheric effects were determined. The a Trous wavelet transform was used for noise reduction and Monte Carlo analysis as a significance test of the detections. The effectiveness of those techniques is discussed in detail.Comment: 17 pages, 8 figures, accepted by Solar Physics Journal for publication in Topical Issue: "Frontiers in Solar Image Processing

Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling

We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5 yr. All four stars are found to be multiperiodic. The strongest secondary mode with frequency f2 has an amplitude of a few mmag, 20–45 times lower than the main radial mode with frequency f1. The two oscillations have a period ratio of P2/P1 = 0.612–0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is non-radial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P2/P1 ∼ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f2 at ∼1/2f2 and at ∼3/2f2. This is a signature of period doubling of the secondary oscillation, and is the first detection of period doubling in RRc stars. The amplitudes and phases of f2 and its subharmonics are variable on a time-scale of 10–200 d. The dominant radial mode also shows variations on the same time-scale, but with much smaller amplitude. In three Kepler RRc stars we detect additional periodicities, with amplitudes below 1 mmag, that must correspond to non-radial g-modes. Such modes never before have been observed in RR Lyrae variables

The complex case of V445 Lyr observed with Kepler: Two Blazhko modulations, a non-radial mode, possible triple mode RR Lyrae pulsation, and more

Rapid and strong changes in the Blazhko modulation of RR Lyrae stars, as they have recently been detected in high precision satellite data, have become a crucial topic in finding an explanation of the long-standing mystery of the Blazhko effect. We present here an analysis of the most extreme case detected so far, the RRab star V445 Lyr (KIC 6186029) which was observed with the Kepler space mission. V445 Lyr shows very strong cycle-to-cycle changes in its Blazhko modulation, which are caused both by a secondary long-term modulation period as well as irregular variations. In addition to the complex Blazhko modulation, V445 Lyr also shows a rich spectrum of additional peaks in the frequency range between the fundamental pulsation and the first harmonic. Among those peaks, the second radial overtone could be identified, which, combined with a metallicity estimate of [Fe/H]=-2.0 dex from spectroscopy, allowed to constrain the mass (0.55-0.65 M_sun) and luminosity (40-50 L_sun) of V445 Lyr through theoretical Petersen diagrams. A non-radial mode as well as possibly the first overtone are also excited. Furthermore, V445 Lyr shows signs of the period doubling phenomenon and a long term period change. A detailed Fourier analysis along with a study of the O-C variation of V445 Lyr is presented, and the origin of the additional peaks and possible causes of the changes in the Blazhko modulation are discussed. The results are then put into context with those of the only other star with a variable Blazhko effect for which a long enough set of high precision continuous satellite data has been published so far, the CoRoT star 105288363.Comment: 19 pages, 20 figuers, accepted for publication in MNRA

Period and light curve fluctuations of the Kepler Cepheid V1154 Cyg

We present a detailed period analysis of the bright Cepheid-type variable star V1154 Cygni (V =9.1 mag, P~4.9 d) based on almost 600 days of continuous observations by the Kepler space telescope. The data reveal significant cycle-to-cycle fluctuations in the pulsation period, indicating that classical Cepheids may not be as accurate astrophysical clocks as commonly believed: regardless of the specific points used to determine the O-C values, the cycle lengths show a scatter of 0.015-0.02 days over the 120 cycles covered by the observations. A very slight correlation between the individual Fourier parameters and the O-C values was found, suggesting that the O - C variations might be due to the instability of the light curve shape. Random fluctuation tests revealed a linear trend up to a cycle difference 15, but for long term, the period remains around the mean value. We compare the measurements with simulated light curves that were constructed to mimic V1154 Cyg as a perfect pulsator modulated only by the light travel time effect caused by low-mass companions. We show that the observed period jitter in V1154 Cyg represents a serious limitation in the search for binary companions. While the Kepler data are accurate enough to allow the detection of planetary bodies in close orbits around a Cepheid, the astrophysical noise can easily hide the signal of the light-time effect.Comment: published in MNRAS: 8 pages, 7 figure

A Scalable Parallel Approach for High-Fidelity Aerostructural Analysis and Optimization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97076/1/AIAA2012-1922.pd

Regime shifts and panarchies in regional scale social-ecological water systems

In this article we summarize histories of nonlinear, complex interactions among societal, legal, and ecosystem dynamics in six North American water basins, as they respond to changing climate. These case studies were chosen to explore the conditions for emergence of adaptive governance in heavily regulated and developed social-ecological systems nested within a hierarchical governmental system. We summarize resilience assessments conducted in each system to provide a synthesis and reference by the other articles in this special feature. We also present a general framework used to evaluate the interactions between society and ecosystem regimes and the governance regimes chosen to mediate those interactions. The case studies show different ways that adaptive governance may be triggered, facilitated, or constrained by ecological and/or legal processes. The resilience assessments indicate that complex interactions among the governance and ecosystem components of these systems can produce different trajectories, which include patterns of (a) development and stabilization, (b) cycles of crisis and recovery, which includes lurches in adaptation and learning, and (3) periods of innovation, novelty, and transformation. Exploration of cross scale (Panarchy) interactions among levels and sectors of government and society illustrate that they may constrain development trajectories, but may also provide stability during crisis or innovation at smaller scales; create crises, but may also facilitate recovery; and constrain system transformation, but may also provide windows of opportunity in which transformation, and the resources to accomplish it, may occur. The framework is the starting point for our exploration of how law might play a role in enhancing the capacity of social-ecological systems to adapt to climate change