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Wang Y.-M.,U.S. Navy | Robbrecht E.,Royal Observatory of Belgium | Muglach K.,NASA | Muglach K.,ARTEP Inc.
Astrophysical Journal | Year: 2011

As observed in spectral lines originating from the chromosphere, transition region, and low corona, active regions are surrounded by an extensive "circumfacular" area which is darker than the quiet Sun. We examine the properties of these dark moat- or canopy-like areas using Fe IX 17.1 nm images and line-of-sight magnetograms from the Solar Dynamics Observatory. The 17.1 nm canopies consist of fibrils (horizontal fields containing extreme-ultraviolet-absorbing chromospheric material) clumped into featherlike structures. The dark fibrils initially form a quasiradial or vortical pattern as the low-lying field lines fanning out from the emerging active region connect to surrounding network and intranetwork elements of opposite polarity. The area occupied by the 17.1 nm fibrils expands as supergranular convection causes the active-region flux to spread into the background medium; the outer boundary of the dark canopy stabilizes where the diffusing flux encounters a unipolar region of opposite sign. The dark fibrils tend to accumulate in regions of weak longitudinal field and to become rooted in mixed-polarity flux. To explain the latter observation, we note that the low-lying fibrils are more likely to interact with small loops associated with weak, opposite-polarity flux elements in close proximity, than with high loops anchored inside strong unipolar network flux. As a result, the 17.1 nm fibrils gradually become concentrated around the large-scale polarity inversion lines (PILs), where most of the mixed-polarity flux is located. Systematic flux cancellation, assisted by rotational shearing, removes the field component transverse to the PIL and causes the fibrils to coalesce into long PIL-aligned filaments. © 2011. The American Astronomical Society. All rights reserved..

Young P.R.,George Mason University | Feldman U.,Artep Inc. | Lobel A.,Royal Observatory of Belgium
Astrophysical Journal, Supplement Series | Year: 2011

Ultraviolet and visible spectra of the symbiotic nova RR Telescopii are used to derive reference wavelengths for many forbidden and intercombination transitions of ions +1 to +6 of elements C, N, O, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca. The wavelengths are then used to determine new energy values for the levels within the ions' ground configurations or first excited configuration. The spectra were recorded by the Space Telescope Imaging Spectrograph of the Hubble Space Telescope and the Ultraviolet Echelle Spectrograph of the European Southern Observatory in 2000 and 1999, respectively, and cover 1140-6915 Å. Particular care was taken to assess the accuracy of the wavelength scale between the two instruments. An investigation of the profiles of the emission lines reveals that the nebula consists of at least two plasma components at different velocities. The components have different densities, and a simple model of the lines' emissions demonstrates that most of the lines principally arise from the high density component. Only these lines were used for the wavelength study. © 2011. The American Astronomical Society. All rights reserved.

Balthasar H.,Leibniz Institute for Astrophysics Potsdam | Muglach K.,Artep. Inc.
Astronomy and Astrophysics | Year: 2010

Aims: Many sunspots are surrounded by a radial outflow called the moat flow. We investigate the moat flow at two different heights of the solar atmosphere for a sunspot whose magnetic properties were reported in the first paper of this series. Methods: We use two simultaneous time series taken with the Transition Region And Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The field-of-view is centered on the small sunspot NOAA10886 located near disk center. Horizontal velocities are derived by applying two different local correlation tracking techniques. Results: Outflows are found everywhere in the moat. In the inner moat, the velocities from the UV series are larger than those from white light, whereas in the outer part of the moat we find the converse result. Conclusions. The results imply that the white light velocities represent a general outflow of the quiet sun plasma in the moat, while UV velocities are dominated by small bright points that move faster than the general plasma flow. © 2010 ESO.

The graduated cylindrical shell (GCS) model developed by Thernisien etal. has been used with the goal of studying the three-dimensional morphology, position, and kinematics of coronal mass ejections observed by coronagraphs. These studies focused more on the results rather than the details of the model itself. As more researchers begin to use the model, it becomes necessary to provide a deeper discussion on how it is derived, which is the purpose of this paper. The model is built using the following features and constraints: (1) the legs are conical, (2) the front is pseudo-circular, (3) the cross section is circular, and (4) it expands in a self-similar way. We derive the equation of the model from these constraints. We also show that the ice-cream cone model is a limit of the GCS when the two legs overlap completely. Finally, we provide formulae for the calculation of various geometrical dimensions, such as angular width and aspect ratio, as well as the pseudo-code that is used for its computer implementation. © Copyright is not claimed for this article..

Young P.R.,George Mason University | Muglach K.,NASA | Muglach K.,ARTEP Inc.
Solar Physics | Year: 2014

A blowout jet occurred within the south coronal hole on 9 February 2011 at 09:00 UT and was observed by the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory, and by the EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) onboard the Hinode spacecraft during coronal-hole monitoring performed as part of Hinode Operations Program No. 177. Images from AIA show expanding hot and cold loops from a small bright point with plasma ejected in a curtain up to 30 Mm wide. The initial intensity front of the jet had a projected velocity of 200 km s-1, and the line-of-sight (LOS) velocities measured by EIS are between 100 and 250 km s-1. The LOS velocities increased along the jet, implying that an acceleration mechanism operates within the body of the jet. The jet plasma had a density of 2.7×108 cm-3 and a temperature of 1.4 MK. During the event a number of bright kernels were seen at the base of the bright point. The kernels have sizes of ≈ 1000 km, are variable in brightness, and have lifetimes of 1 - 15 minutes. An XRT filter ratio yields temperatures of 1.5 - 3.0 MK for the kernels. The bright point existed for at least ten hours, but disappeared within two hours after the jet, which lasted for 30 minutes. HMI data reveal converging photospheric flows at the location of the bright point, and the mixed-polarity magnetic flux canceled over a period of four hours on either side of the jet. © 2014 Springer Science+Business Media Dordrecht.

Busquet M.,ARTEP Inc.
Optics Communications | Year: 2014

In this comment, we discuss the possibility of imaging the radiative precursor of a strong shock with a 21.2 nm soft x-ray laser probe and we analyze the data presented in C.Stehlé et al "New probing techniques of radiative shocks", (Optics Communications 285, 64, 2012) in order to derive some estimation of the achieved resolution. We show that the presented results are inconclusive for the existence of a radiative precursor. Furthermore, our best estimation of cold and warm Xenon VUV opacities tells that 21.2 nm backlighting would not be able to probe this radiative precursor. © 2012 Elsevier B.V.

Mariska J.T.,U.S. Navy | Muglach K.,U.S. Navy | Muglach K.,Artep Inc.
Astrophysical Journal | Year: 2010

Low-amplitude Doppler-shift oscillations have been observed in coronal emission lines in a number of active regions with the EUV Imaging Spectrometer (EIS) on the Hinode satellite. Both standing and propagating waves have been detected and many periods have been observed, but a clear picture of all the wave modes that might be associated with active regions has not yet emerged. In this study, we examine additional observations obtained with EIS in plage near an active region on 2007 August 22-23. We find Doppler-shift oscillations with amplitudes between 1 and 2kms-1 in emission lines ranging from Fe XI 188.23 , Å which is formed at log T = 6.07, to Fe XV 284.16 , which is formed at log T = 6.32. Typical periods are near 10minutes. We also observe intensity and density oscillations for some of the detected Doppler-shift oscillations. In the better-observed cases, the oscillations are consistent with upwardly propagating slow magnetoacoustic waves. Simultaneous observations of the Ca II H line with the Hinode Solar Optical Telescope Broadband Filter Imager show some evidence for 10 minute oscillations as well. © 2010 The American Astronomical Society. All rights reserved.

Feldman U.,Artep Inc.
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2016

CHIANTI is an atomic database with software for calculating emission properties. It is extensively used in deriving the atomic properties of spectra recorded from astrophysical and low density laboratory plasmas. In order to obtain an insight into the accuracy of the CHIANTI calculated level populations, a consistency check was conducted along the He i, Be i, B i, C i, N i, and O i isoelectronic sequences. In the evaluation process, levels of the ground configuration and the first and second excited configurations were considered. These are the levels responsible for most of the spectral lines used when deriving the plasma properties of astrophysical objects. As is documented below, the accuracy of the CHIANTI level population calculations depends on the particular ion, level and on the electron density. Under some conditions the calculations appear quite robust while in others they are not. © 2016 IOP Publishing Ltd.

Wang Y.-M.,U.S. Navy | Muglach K.,NASA | Muglach K.,ARTEP Inc.
Astrophysical Journal | Year: 2013

Filament channels coincide with large-scale polarity inversion lines of the photospheric magnetic field, where flux cancellation continually takes place. High-cadence Solar Dynamics Observatory (SDO) images recorded in He ii 30.4 nm and Fe ix 17.1 nm during 2010 August 22 reveal numerous transient brightenings occurring along the edge of a filament channel within a decaying active region, where SDO line-of-sight magnetograms show strong opposite-polarity flux in close contact. The brightenings are elongated along the direction of the filament channel, with linear extents of several arcseconds, and typically last a few minutes; they sometimes have the form of multiple two-sided ejections with speeds on the order of 100 km s-1. Remarkably, some of the brightenings rapidly develop into larger scale events, forming sheetlike structures that are eventually torn apart by the diverging flows in the filament channel and ejected in opposite directions. We interpret the brightenings as resulting from reconnections among filament-channel field lines having one footpoint located in the region of canceling flux. In some cases, the flow patterns that develop in the channel may bring successive horizontal loops together and cause a cascade to larger scales. © 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Klapisch M.,ARTEP Inc. | Busquet M.,ARTEP Inc.
New Journal of Physics | Year: 2013

We compare four models for the partial densities of the components of mixtures. These models yield different opacities as shown on polystyrene, acrylic and polyimide in local thermodynamical equilibrium (LTE). Two of these models, the 'whole volume partial pressure' model (M1) and its modification (M2) are not thermodynamically consistent (TC). The other two models are TC and minimize free energy. M3, the 'partial 7volume equal pressure' model, uses equality of chemical potential. M4 uses commonality of free electron density. The latter two give essentially identical results in LTE, but M4's convergence is slower. M4 is easily generalized to non-LTE conditions. Non-LTE effects are shown by the variation of the Planck mean opacity of the mixtures with temperature and density. © IOP Publishing and Deutsche Physikalische Gesellschaft.

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