90 research outputs found
The Temperature Dependence of Solar Active Region Outflows
Spectroscopic observations with the EUV Imaging Spectrometer (EIS) on Hinode
have revealed large areas of high speed outflows at the periphery of many solar
active regions. These outflows are of interest because they may connect to the
heliosphere and contribute to the solar wind. In this Letter we use slit
rasters from EIS in combination with narrow band slot imaging to study the
temperature dependence of an active region outflow and show that it is more
complicated than previously thought. Outflows are observed primarily in
emission lines from Fe XI - Fe XV. Observations at lower temperatures (Si VII),
in contrast, show bright fan-like structures that are dominated by downflows.
The morphology of the outflows is also different than that of the fans. This
suggests that the fan loops, which often show apparent outflows in imaging
data, are contained on closed field lines and are not directly related to the
active region outflows.Comment: Movies are available online at:
http://tcrb.nrl.navy.mil/~hwarren/temp/papers/flow_temperatures/ To be
submitted to ApJ
Solar prominences line profiles
A numerical code to calculate the line profiles for different elements present in the solar atmosphere was developed for the particular case of solar prominences. The objective is to compare the calculated with the observed profiles in order to limit the range of variation of the physical parameters, as temperature, pressure, electronic density, total density and turbulence velocity, which characterize these phenomena.Asociación Argentina de AstronomÃ
2D and 3D Polar Plume Analysis from the Three Vantage Positions of STEREO/EUVI A, B, and SOHO/EIT
Polar plumes are seen as elongated objects starting at the solar polar
regions. Here, we analyze these objects from a sequence of images taken
simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and
SOHO/EIT. We establish a method capable of automatically identifying plumes in
solar EUV images close to the limb at 1.01 - 1.39 R in order to study their
temporal evolution. This plume-identification method is based on a multiscale
Hough-wavelet analysis. Then two methods to determined their 3D localization
and structure are discussed: First, tomography using the filtered
back-projection and including the differential rotation of the Sun and,
secondly, conventional stereoscopic triangulation. We show that tomography and
stereoscopy are complementary to study polar plumes. We also show that this
systematic 2D identification and the proposed methods of 3D reconstruction are
well suited, on one hand, to identify plumes individually and on the other
hand, to analyze the distribution of plumes and inter-plume regions. Finally,
the results are discussed focusing on the plume position with their
cross-section area.Comment: 22 pages, 10 figures, Solar Physics articl
Magnetic topology of active regions and coronal holes: implications for coronal outflows and the solar wind
During 2-18 January 2008 a pair of low-latitude opposite-polarity coronal holes (CHs) were observed on the Sun with two active regions (ARs) and the heliospheric plasma sheet located between them. We use the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows and measure their velocities. Solar-Terrestrial Relations Observatory (STEREO) imaging is also employed, as are the Advanced Composition Explorer (ACE) in-situ observations, to assess the resulting impacts on the solar wind (SW) properties. Magnetic-field extrapolations of the two ARs confirm that AR plasma outflows observed with EIS are co-spatial with quasi-separatrix layer locations, including the separatrix of a null point. Global potential-field source-surface modeling indicates that field lines in the vicinity of the null point extend up to the source surface, enabling a part of the EIS plasma upflows access to the SW. We find that similar upflow properties are also observed within closed-field regions that do not reach the source surface. We conclude that some of plasma upflows observed with EIS remain confined along closed coronal loops, but that a fraction of the plasma may be released into the slow SW. This suggests that ARs bordering coronal holes can contribute to the slow SW. Analyzing the in-situ data, we propose that the type of slow SW present depends on whether the AR is fully or partially enclosed by an overlying streamer. © 2012 Springer Science+Business Media B.V
The kinematics of coronal mass ejections using multiscale methods
The diffuse morphology and transient nature of coronal mass ejections (CMEs)
make them difficult to identify and track using traditional image processing
techniques. We apply multiscale methods to enhance the visibility of the faint
CME front. This enables an ellipse characterisation to objectively study the
changing morphology and kinematics of a sample of events imaged by the Large
Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO) and the Sun Earth Connection Coronal and Heliospheric
Investigation (SECCHI) onboard the Solar Terrestrial Relations Observatory
(STEREO). The accuracy of these methods allows us to test the CMEs for
non-constant acceleration and expansion.
We exploit the multiscale nature of CMEs to extract structure with a
multiscale decomposition, akin to a Canny edge detector. Spatio-temporal
filtering highlights the CME front as it propagates in time. We apply an
ellipse parameterisation of the front to extract the kinematics (height,
velocity, acceleration) and changing morphology (width, orientation).
The kinematic evolution of the CMEs discussed in this paper have been shown
to differ from existing catalogues. These catalogues are based upon
running-difference techniques that can lead to over-estimating CME heights. Our
resulting kinematic curves are not well-fitted with the constant acceleration
model. It is shown that some events have high acceleration below 5
R_{\sun}. Furthermore, we find that the CME angular widths measured by these
catalogues are over-estimated, and indeed for some events our analysis shows
non-constant CME expansion across the plane-of-sky.Comment: 10 pages, 13 figures, accepted for publicatio
Characterizing Abundances of Volatiles in Comets Through Multiwavelength Observations
Recently, there have been complimentary observations from multiple facilities to try to unravel the chemical complexity of comets. Incorporating results from various techniques, including: single-dish millimeter wavelength observations, interferometers, and/or IR spectroscopy, one can gain further insight into the abundances, production rates, distributions, and formation mechanisms of molecules in these objects [I]. Such studies have provided great detail towards molecules with a-typical chemistries, such as H2CO [2]. We report spectral observations of C/2007 N3 (Lulin), C/2009 R1 (McNaught), 103P/Hartley 2, and C/2009 P1 (Garradd) with the Arizona Radio Observatory's SMT and 12-m telescopes, as well as the NRAO Greenbank telescope and IRTF-CSHELL. Multiple parent volatiles (HCN, CH3OH, CO, CH4, C2H6, and H2O) as well as a number of daughter products (CS and OH) have been detected in these objects. We will present a comparison of molecular abundances in these comets to those observed in others, supporting a long-term effort of building a comet taxonomy based on composition. Previous work has revealed a range of abundances of parent species (from "organics-poor" to "organics-rich") with respect to water among comets [3,4,5], however the statistics are still poorly constrained and interpretations of the observed compositional diversity are uncertain. We gratefully acknowledge support from the NSF Astronomy and Astrophysics Program, the NASA Planetary Astronomy Program, NASA Planetary Atmospheres Program, and the NASA Astrobiology Program
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