Co- and counter-helicity interaction between two adjacent laboratory prominences

The interaction between two side-by-side solar prominence-like plasmas has been studied using a four-electrode magnetized plasma source that can impose a wide variety of surface boundary conditions. When the source is arranged to create two prominences with the same helicity (co-helicity), it is observed that helicity transfer from one prominence to the other causes the receiving prominence to erupt sooner and faster than the transmitting prominence. When the source is arranged to create two prominences with opposite helicity (counter-helicity), it is observed that upon merging, prominences wrap around each other to form closely spaced, writhing turns of plasma. This is followed by appearance of a distinct bright region in the middle and order of magnitude higher emission of soft x rays. The four-electrode device has also been used to change the angle of the neutral line and so form more pronounced S-shapes

Search for Rapid Changes in the Visible-Light Corona during the 21 June 2001 Total Solar Eclipse

Some 8000 images obtained with the SECIS fast-frame CCD camera instrument located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been analyzed to search for short-period oscillations in intensity that could be a signature of solar coronal heating mechanisms by MHD wave dissipation. Images were taken in white- light and Fe XIV green-line (5303 A) channels over 205 seconds (frame rate 39 s-1), approximately the length of eclipse totality at this location, with a pixel size of four arcseconds square. The data are of considerably better quality than were obtained during the 11 August 1999 total eclipse, observed by us (Rudawy et al.: Astron. Astrophys. 416, 1179, 2004), in that the images are much better exposed and enhancements in the drive system of the heliostat used gave a much improved image stability. Classical Fourier and wavelet techniques have been used to analyze the emission at 29518 locations, of which 10714 had emission at reasonably high levels, searching for periodic fluctuations with periods in the range 0.1-17 seconds (frequencies 0.06-10 Hz). While a number of possible periodicities were apparent in the wavelet analysis, none of the spatially and time-limited periodicities in the local brightness curves was found to be physically important. This implies that the pervasive Alfven wave-like phenomena (Tomczyk et al.: Science 317, 1192, 2007) using polarimetric observations with the CoMP instrument do not give rise to significant oscillatory intensity fluctuations.Comment: Accepted by Solar Physics; 16 figure

Bessel beam illumination reduces random and systematic errors in quantitative functional studies using light-sheet microscopy

Light-sheet microscopy (LSM), in combination with intrinsically transparent zebrafish larvae, is a choice method to observe brain function with high frame rates at cellular resolution. Inherently to LSM, however, residual opaque objects cause stripe artifacts, which obscure features of interest and, during functional imaging, modulate fluorescence variations related to neuronal activity. Here, we report how Bessel beams reduce streaking artifacts and produce high-fidelity quantitative data demonstrating a fivefold increase in sensitivity to calcium transients and a 20 fold increase in accuracy in the detection of activity correlations in functional imaging. Furthermore, using principal component analysis, we show that measurements obtained with Bessel beams are clean enough to reveal in one-shot experiments correlations that can not be averaged over trials after stimuli as is the case when studying spontaneous activity. Our results not only demonstrate the contamination of data by systematic and random errors through conventional Gaussian illumination and but,furthermore, quantify the increase in fidelity of such data when using Bessel beams

Haro 11, Pox 186, and VCC 1313: The Enigmatic Behavior of HI Non-Emitters

We present neutral hydrogen (HI) observations from the Very Large Array (VLA) telescope of the galaxies Haro 11, Pox 186, and VCC 1313. 24 hours of deep spectral line observation at the 21 cm line were obtained from the program 17B-287 of Haro 11, the primary galaxy studied in this capstone, and 176 and 203 respective minutes of archival VLA data at the 21 cm line were obtained from the program AS0832 of Pox 186 and VCC 1313, the secondary and tertiary sources of study for this capstone. Haro 11 is one of a very small number of local dwarf galaxies to be both a Lyα and LyC emitter. While it harbors ongoing aggressive star formation (with sources reporting up to 32.8 M☉ yr-1), the neutral hydrogen gas in the system has been notoriously difficult to detect. Previous interferometric observations have resulted in non-detections, while a deep Green Bank Telescope (GBT) spectrum reveals a weak spectral line. Our emission result is a non-detection, while our absorption result is a detection, confirming the results of similar, previously conducted absorption work. Past interferometric research has additionally resulted in HI non-detections for both Pox 186 and VCC 1313. Our results from archival data are also two HI non-detections, confirming the results of past research. For all three systems, given their aggressive star formation rates, these HI non-detection results are surprising. The behavior of these systems remains highly enigmatic

The origins of X-ray emission from the hotspots of FRII radio sources

We use new and archival Chandra data to investigate the X-ray emission from a large sample of compact hotspots of FRII radio galaxies and quasars from the 3C catalogue. We find that only the most luminous hotspots tend to be in good agreement with the predictions of a synchrotron self-Compton model with equipartition magnetic fields. At low hotspot luminosities inverse-Compton predictions are routinely exceeded by several orders of magnitude, but this is never seen in more luminous hotspots. We argue that an additional synchrotron component of the X-ray emission is present in low-luminosity hotspots, and that the hotspot luminosity controls the ability of a given hotspot to produce synchrotron X-rays, probably by determining the high-energy cutoff of the electron energy spectrum. It remains plausible that all hotspots are close to the equipartition condition.Comment: 49 pages, 16 figures. ApJ accepted. Revised version fixes a typo in one of the Tables and corrects a statement about 3C27

Analysis and interpretation of a fast limb CME with eruptive prominence, C-flare and EUV dimming

Coronal Mass ejections or CMEs are large dynamical solar-corona events. The mass balance and kinematics of a fast limb CME, including its prominence progenitor and the associated flare, will be compared with computed magnetic structures to look for their origin and effect. Multi-wavelength ground-based and space-borne observations are used to study a fast W-limb CME event of December 2, 2003, taking into account both on and off disk observations. Its erupting prominence is measured at high cadence with the Pic du Midi full H-alpha line-flux imaging coronagraph. EUV images from space instruments are processed including difference imaging. SOHO/LASCO images are used to study the mass excess and motions. A fast bright expanding coronal loop is identified in the region recorded slightly later by GOES as a C7.2 flare, followed by a brightening and an acceleration phase of the erupting material with both cool and hot components. The total coronal radiative flux dropped by 5 percent in the EUV channels, revealing a large dimming effect at and above the limb. The typical 3-part structure observed 1 hour later shows a core shaped similarly to the eruptive filament/prominence. The total measured mass of the escaping CME (1.5x10to16 g from C2 LASCO observations) definitely exceeds the estimated mass of the escaping cool prominence material although assumptions made to analyse the Ha erupting prominence, as well as the corresponding EUV darkening of the filament observed several days before, made this evaluation uncertain by a factor of 2. From the current free extrapolation we discuss the shape of the magnetic neutral surface and a possible scenario leading to an instability, including the small scale dynamics inside and around the filament.Comment: 11 pages, 9 figure