The Experts below are selected from a list of 22632 Experts worldwide ranked by ideXlab platform
Harry P Warren - One of the best experts on this subject based on the ideXlab platform.
-
modeling coronal response in decaying active regions with magnetic flux transport and Steady Heating
The Astrophysical Journal, 2017Co-Authors: Ignacio Ugarteurra, Harry P Warren, Lisa Upton, P R YoungAbstract:We present new measurements of the dependence of the Extreme Ultraviolet radiance on the total magnetic flux in active regions as obtained from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO). Using observations of nine active regions tracked along different stages of evolution, we extend the known radiance - magnetic flux power-law relationship ($I\propto\Phi^{\alpha}$) to the AIA 335 A passband, and the Fe XVIII 93.93 A spectral line in the 94 A passband. We find that the total unsigned magnetic flux divided by the polarity separation ($\Phi/D$) is a better indicator of radiance for the Fe XVIII line with a slope of $\alpha=3.22\pm0.03$. We then use these results to test our current understanding of magnetic flux evolution and coronal Heating. We use magnetograms from the simulated decay of these active regions produced by the Advective Flux Transport (AFT) model as boundary conditions for potential extrapolations of the magnetic field in the corona. We then model the hydrodynamics of each individual field line with the Enthalpy-based Thermal Evolution of Loops (EBTEL) model with Steady Heating scaled as the ratio of the average field strength and the length ($\bar{B}/L$) and render the Fe XVIII and 335 A emission. We find that Steady Heating is able to partially reproduce the magnitudes and slopes of the EUV radiance - magnetic flux relationships and discuss how impulsive Heating can help reconcile the discrepancies. This study demonstrates that combined models of magnetic flux transport, magnetic topology and Heating can yield realistic estimates for the decay of active region radiances with time.
-
using a differential emission measure and density measurements in an active region core to test a Steady Heating model
The Astrophysical Journal, 2011Co-Authors: Amy R Winebarger, Harry P Warren, J T Schmelz, Steve Saar, V KashyapAbstract:The frequency of Heating events in the corona is an important constraint on the coronal Heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively Steady, suggesting that Heating events occur rapidly enough to keep high-temperature active region loops close to equilibrium. In this paper, we couple observations of active region (AR) 10955 made with the X-Ray Telescope and the EUV Imaging Spectrometer on board Hinode to test a simple Steady Heating model. First we calculate the differential emission measure (DEM) of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3 MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the Heating, we build a Steady Heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 < log T < 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. Wemore » find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with Steady Heating. We also find, however, that the Steady Heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the Heating in the core is more complicated. Different Heating scenarios must be tested to determine if they have the same level of agreement.« less
-
using a differential emission measure and density measurements in an active region core to test a Steady Heating model
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Amy R Winebarger, Harry P Warren, J T Schmelz, Steve Saar, V KashyapAbstract:The frequency of Heating events in the corona is an important constraint on the coronal Heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively Steady, suggesting that Heating events occur rapidly enough to keep high temperature active region loops close to equilibrium. In this paper, we couple observations of Active Region 10955 made with XRT and EIS on \textit{Hinode} to test a simple Steady Heating model. First we calculate the differential emission measure of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3\,MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the Heating, we build a Steady Heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 $<$ Log T $<$ 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. We find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with Steady Heating. We also find, however, that the Steady Heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the Heating in the core is more complicated. Different Heating scenarios must be tested to determine if they have the same level of agreement.
-
evidence for Steady Heating observations of an active region core with hinode and trace
The Astrophysical Journal, 2010Co-Authors: Harry P Warren, Amy R Winebarger, David H BrooksAbstract:The timescale for energy release is an important parameter for constraining the coronal Heating mechanism. Observations of 'warm' coronal loops ({approx}1 MK) have indicated that the Heating is impulsive and that coronal plasma is far from equilibrium. In contrast, observations at higher temperatures ({approx}3 MK) have generally been consistent with Steady Heating models. Previous observations, however, have not been able to exclude the possibility that the high temperature loops are actually composed of many small-scale threads that are in various stages of Heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer and X-ray Telescope (XRT) on Hinode we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for Steady Heating. We find that the emission observed in XRT is generally Steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive Heating events are observed, but they appear to be unrelated to the Steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlatedmore » with the hot emission, as would be expected if the high temperature loops are the result of impulsive Heating. Finally, we also find that intensities in the 'moss', the footpoints of high temperature loops, are consistent with Steady Heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the Heating in the core of an active region is effectively Steady, that is, the time between Heating events is short relative to the relevant radiative and conductive cooling times.« less
-
evidence for Steady Heating observations of an active region core with hinode and trace
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Harry P Warren, Amy R Winebarger, David H BrooksAbstract:Previous observations have not been able to exclude the possibility that high temperature active region loops are actually composed of many small scale threads that are in various stages of Heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS) and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for Steady Heating. We find that the emission observed in XRT is generally Steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive Heating events are observed, but they appear to be unrelated to the Steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive Heating. Finally, we also find that intensities in the "moss", the footpoints of high temperature loops, are consistent with Steady Heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the Heating in the core of an active region is effectively Steady, that is, the time between Heating events is short relative to the relevant radiative and conductive cooling times.
David H Brooks - One of the best experts on this subject based on the ideXlab platform.
-
evidence for Steady Heating observations of an active region core with hinode and trace
The Astrophysical Journal, 2010Co-Authors: Harry P Warren, Amy R Winebarger, David H BrooksAbstract:The timescale for energy release is an important parameter for constraining the coronal Heating mechanism. Observations of 'warm' coronal loops ({approx}1 MK) have indicated that the Heating is impulsive and that coronal plasma is far from equilibrium. In contrast, observations at higher temperatures ({approx}3 MK) have generally been consistent with Steady Heating models. Previous observations, however, have not been able to exclude the possibility that the high temperature loops are actually composed of many small-scale threads that are in various stages of Heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer and X-ray Telescope (XRT) on Hinode we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for Steady Heating. We find that the emission observed in XRT is generally Steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive Heating events are observed, but they appear to be unrelated to the Steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlatedmore » with the hot emission, as would be expected if the high temperature loops are the result of impulsive Heating. Finally, we also find that intensities in the 'moss', the footpoints of high temperature loops, are consistent with Steady Heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the Heating in the core of an active region is effectively Steady, that is, the time between Heating events is short relative to the relevant radiative and conductive cooling times.« less
-
evidence for Steady Heating observations of an active region core with hinode and trace
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Harry P Warren, Amy R Winebarger, David H BrooksAbstract:Previous observations have not been able to exclude the possibility that high temperature active region loops are actually composed of many small scale threads that are in various stages of Heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS) and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for Steady Heating. We find that the emission observed in XRT is generally Steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive Heating events are observed, but they appear to be unrelated to the Steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive Heating. Finally, we also find that intensities in the "moss", the footpoints of high temperature loops, are consistent with Steady Heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the Heating in the core of an active region is effectively Steady, that is, the time between Heating events is short relative to the relevant radiative and conductive cooling times.
-
flows and motions in moss in the core of a flaring active region evidence for Steady Heating
The Astrophysical Journal, 2009Co-Authors: David H Brooks, Harry P WarrenAbstract:We present new measurements of the time variability of intensity, Doppler, and nonthermal velocities in moss in an active region core observed by the EUV Imaging Spectrometer on Hinode in 2007 June. The measurements are derived from spectral profiles of the Fe XII 195 A line. Using the 2'' slit, we repeatedly scanned 150'' by 150'' in a few minutes. This is the first time it has been possible to make such velocity measurements in the moss, and the data presented are the highest cadence spatially resolved maps of moss Doppler and nonthermal velocities ever obtained in the corona. The observed region produced numerous C- and M-class flares with several occurring in the core close to the moss. The magnetic field was therefore clearly changing in the active region core, so we ought to be able to detect dynamic signatures in the moss if they exist. Our measurements of moss intensities agree with previous studies in that a less than 15% variability is seen over a period of 16 hr. Our new measurements of Doppler and nonthermal velocities reveal no strong flows or motions in the moss, nor any significant variability in these quantities. The results confirm that moss atmore » the bases of high temperature coronal loops is heated quasi-steadily. They also show that quasi-Steady Heating can contribute significantly even in the core of a flare productive active region. Such Heating may be impulsive at high frequency, but if so it does not give rise to large flows or motions.« less
-
flows and motions in moss in the core of a flaring active region evidence for Steady Heating
The Astrophysical Journal, 2009Co-Authors: David H Brooks, Harry P WarrenAbstract:We present new measurements of the time variability of intensity, Doppler, and nonthermal velocities in moss in an active region core observed by the EUV Imaging Spectrometer on Hinode in 2007 June. The measurements are derived from spectral profiles of the Fe XII 195 A line. Using the 2'' slit, we repeatedly scanned 150'' by 150'' in a few minutes. This is the first time it has been possible to make such velocity measurements in the moss, and the data presented are the highest cadence spatially resolved maps of moss Doppler and nonthermal velocities ever obtained in the corona. The observed region produced numerous C- and M-class flares with several occurring in the core close to the moss. The magnetic field was therefore clearly changing in the active region core, so we ought to be able to detect dynamic signatures in the moss if they exist. Our measurements of moss intensities agree with previous studies in that a less than 15% variability is seen over a period of 16 hr. Our new measurements of Doppler and nonthermal velocities reveal no strong flows or motions in the moss, nor any significant variability in these quantities. The results confirm that moss atmore » the bases of high temperature coronal loops is heated quasi-steadily. They also show that quasi-Steady Heating can contribute significantly even in the core of a flare productive active region. Such Heating may be impulsive at high frequency, but if so it does not give rise to large flows or motions.« less
-
flows and motions in moss in the core of a flaring active region evidence for Steady Heating
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: David H Brooks, Harry P WarrenAbstract:We present new measurements of the time variability of intensity, Doppler and non-thermal velocities in moss in an active region core observed by the EUV Imaging Spectrometer on Hinode in 2007, June. The measurements are derived from spectral profiles of the Fe 12 195A line. Using the 2" slit, we repeatedly scanned 150" by 150" in a few mins. This is the first time it has been possible to make such velocity measurements in the moss, and the data presented are the highest cadence spatially resolved maps of moss Doppler and non-thermal velocities ever obtained in the corona. The observed region produced numerous C- and M- class flares with several occurring in the core close to the moss. The magnetic field was therefore clearly changing in the active region core, so we ought to be able to detect dynamic signatures in the moss if they exist. Our measurements of moss intensities agree with previous studies in that a less than 15% variability is seen over a period of 16 hours. Our new measurements of Doppler and non-thermal velocities reveal no strong flows or motions in the moss, nor any significant variability in these quantities. The results confirm that moss at the bases of high temperature coronal loops is heated quasi-steadily. They also show that quasi-Steady Heating can contribute significantly even in the core of a flare productive active region. Such Heating may be impulsive at high frequency, but if so it does not give rise to large flows or motions.
Amy R Winebarger - One of the best experts on this subject based on the ideXlab platform.
-
bright points multithermal analysis as a test of Steady Heating models
The Astrophysical Journal, 2013Co-Authors: J T Schmelz, Amy R Winebarger, J A Kimble, S Pathak, L Golub, B S Jenkins, B T WorleyAbstract:X-ray bright points are small, million-degree features in the solar atmosphere composed of short coronal loops. They are magnetically driven structures associated with photospheric magnetic bipoles. Their relatively small size and simple structure suggest they are ideal candidates for comparisons with coronal Heating models. In this paper, we present the analysis of 12 bright points using data from the EUV Imaging Spectrometer on Hinode and the Michelson Doppler Imager on Solar and Heliospheric Observatory. Using the spectroscopy data, we construct differential emission measure (DEM) curves, calculate the electron density, and find DEM-weighted temperatures. In addition, we determine the most likely ionization balance. Using the magnetic field observations, we complete potential field extrapolations of the magnetograms and estimate the loop lengths. Using this information, we construct models assuming the bright points are formed of hundreds of strands, each heated steadily and uniformly. We formulate the models so that the observed emission measure distribution is matched within a few percent. We then compare the densities determined from the models, (1.4-5.0) × 109, to those calculated from spectral data, (0.6-2.0) × 109. We find the majority of bright points do not agree with Steady uniform Heating models; instead they are underdense relative to their expected density by a factor of 0.16-0.82.
-
using a differential emission measure and density measurements in an active region core to test a Steady Heating model
The Astrophysical Journal, 2011Co-Authors: Amy R Winebarger, Harry P Warren, J T Schmelz, Steve Saar, V KashyapAbstract:The frequency of Heating events in the corona is an important constraint on the coronal Heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively Steady, suggesting that Heating events occur rapidly enough to keep high-temperature active region loops close to equilibrium. In this paper, we couple observations of active region (AR) 10955 made with the X-Ray Telescope and the EUV Imaging Spectrometer on board Hinode to test a simple Steady Heating model. First we calculate the differential emission measure (DEM) of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3 MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the Heating, we build a Steady Heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 < log T < 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. Wemore » find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with Steady Heating. We also find, however, that the Steady Heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the Heating in the core is more complicated. Different Heating scenarios must be tested to determine if they have the same level of agreement.« less
-
using a differential emission measure and density measurements in an active region core to test a Steady Heating model
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Amy R Winebarger, Harry P Warren, J T Schmelz, Steve Saar, V KashyapAbstract:The frequency of Heating events in the corona is an important constraint on the coronal Heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively Steady, suggesting that Heating events occur rapidly enough to keep high temperature active region loops close to equilibrium. In this paper, we couple observations of Active Region 10955 made with XRT and EIS on \textit{Hinode} to test a simple Steady Heating model. First we calculate the differential emission measure of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3\,MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the Heating, we build a Steady Heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 $<$ Log T $<$ 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. We find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with Steady Heating. We also find, however, that the Steady Heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the Heating in the core is more complicated. Different Heating scenarios must be tested to determine if they have the same level of agreement.
-
evidence for Steady Heating observations of an active region core with hinode and trace
The Astrophysical Journal, 2010Co-Authors: Harry P Warren, Amy R Winebarger, David H BrooksAbstract:The timescale for energy release is an important parameter for constraining the coronal Heating mechanism. Observations of 'warm' coronal loops ({approx}1 MK) have indicated that the Heating is impulsive and that coronal plasma is far from equilibrium. In contrast, observations at higher temperatures ({approx}3 MK) have generally been consistent with Steady Heating models. Previous observations, however, have not been able to exclude the possibility that the high temperature loops are actually composed of many small-scale threads that are in various stages of Heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer and X-ray Telescope (XRT) on Hinode we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for Steady Heating. We find that the emission observed in XRT is generally Steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive Heating events are observed, but they appear to be unrelated to the Steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlatedmore » with the hot emission, as would be expected if the high temperature loops are the result of impulsive Heating. Finally, we also find that intensities in the 'moss', the footpoints of high temperature loops, are consistent with Steady Heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the Heating in the core of an active region is effectively Steady, that is, the time between Heating events is short relative to the relevant radiative and conductive cooling times.« less
-
evidence for Steady Heating observations of an active region core with hinode and trace
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Harry P Warren, Amy R Winebarger, David H BrooksAbstract:Previous observations have not been able to exclude the possibility that high temperature active region loops are actually composed of many small scale threads that are in various stages of Heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS) and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for Steady Heating. We find that the emission observed in XRT is generally Steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive Heating events are observed, but they appear to be unrelated to the Steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive Heating. Finally, we also find that intensities in the "moss", the footpoints of high temperature loops, are consistent with Steady Heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the Heating in the core of an active region is effectively Steady, that is, the time between Heating events is short relative to the relevant radiative and conductive cooling times.
James A. Klimchuk - One of the best experts on this subject based on the ideXlab platform.
-
Signatures of Steady Heating in Time Lag Analysis of Coronal Emission
The Astrophysical Journal, 2016Co-Authors: Nicholeen M. Viall, James A. KlimchukAbstract:Among the multitude of methods used to investigate coronal Heating, the time lag method of Viall & Klimchuk is becoming increasingly prevalent as an analysis technique that is complementary to those that are traditionally used. The time lag method cross correlates light curves at a given spatial location obtained in spectral bands that sample different temperature plasmas. It has been used most extensively with data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. We have previously applied the time lag method to entire active regions and surrounding the quiet Sun and created maps of the results. We find that the majority of time lags are consistent with the cooling of coronal plasma that has been impulsively heated. Additionally, a significant fraction of the map area has a time lag of zero. This does not indicate a lack of variability. Rather, strong variability must be present, and it must occur in phase between the different channels. We have previously shown that these zero time lags are consistent with the transition region response to coronal nanoflares, although other explanations are possible. A common misconception is that the zero time lag indicates Steady emission resulting from Steady Heating. Using simulated and observed light curves, we demonstrate here that highly correlated light curves at zero time lag are not compatible with equilibrium solutions. Such light curves can only be created by evolution.
-
signatures of Steady Heating in time lag analysis of coronal emission
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Nicholeen M. Viall, James A. KlimchukAbstract:Among the many ways of investigating coronal Heating, the time lag method of Viall & Klimchuk (2012) is becoming increasingly prevalent as an analysis technique complementary to those traditionally used. The time lag method cross correlates light curves at a given spatial location obtained in spectral bands that sample different temperature plasmas. It has been used most extensively with data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. We have previously applied the time lag method to entire active regions and surrounding quiet Sun and create maps of the results (Viall & Klimchuk 2012; Viall & Klimchuk 2015). We find that the majority of time lags are consistent with the cooling of coronal plasma that has been impulsively heated. Additionally, a significant fraction of the map area has a time lag of zero. This does not indicate a lack of variability. Rather, strong variability must be present, and it must occur in phase in the different channels. We have shown previously that these zero time lags are consistent with the transition region response to coronal nanoflares (Viall & Klimchuk 2015; Bradshaw & Viall 2016), but other explanations are possible. A common misconception is that the zero time lag indicates Steady emission resulting from Steady Heating. Using simulated and observed light curves, we demonstrate here that highly correlated light curves at zero time lag are not compatible with equilibrium solutions. Such light curves can only be created by evolution.
-
emission measure distribution and Heating of two active region cores
The Astrophysical Journal, 2011Co-Authors: James A. Klimchuk, Durgesh Tripathi, H E MasonAbstract:Using data from the Extreme-ultraviolet Imaging Spectrometer aboard Hinode, we have studied the coronal plasma in the core of two active regions. Concentrating on the area between opposite polarity moss, we found emission measure distributions having an approximate power-law form EM∝T 2.4 from log T = 5.5 up to a peak at log T = 6.55. We show that the observations compare very favorably with a simple model of nanoflare-heated loop strands. They also appear to be consistent with more sophisticated nanoflare models. However, in the absence of additional constraints, Steady Heating is also a viable explanation.
V Kashyap - One of the best experts on this subject based on the ideXlab platform.
-
using a differential emission measure and density measurements in an active region core to test a Steady Heating model
The Astrophysical Journal, 2011Co-Authors: Amy R Winebarger, Harry P Warren, J T Schmelz, Steve Saar, V KashyapAbstract:The frequency of Heating events in the corona is an important constraint on the coronal Heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively Steady, suggesting that Heating events occur rapidly enough to keep high-temperature active region loops close to equilibrium. In this paper, we couple observations of active region (AR) 10955 made with the X-Ray Telescope and the EUV Imaging Spectrometer on board Hinode to test a simple Steady Heating model. First we calculate the differential emission measure (DEM) of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3 MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the Heating, we build a Steady Heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 < log T < 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. Wemore » find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with Steady Heating. We also find, however, that the Steady Heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the Heating in the core is more complicated. Different Heating scenarios must be tested to determine if they have the same level of agreement.« less
-
using a differential emission measure and density measurements in an active region core to test a Steady Heating model
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Amy R Winebarger, Harry P Warren, J T Schmelz, Steve Saar, V KashyapAbstract:The frequency of Heating events in the corona is an important constraint on the coronal Heating mechanisms. Observations indicate that the intensities and velocities measured in active region cores are effectively Steady, suggesting that Heating events occur rapidly enough to keep high temperature active region loops close to equilibrium. In this paper, we couple observations of Active Region 10955 made with XRT and EIS on \textit{Hinode} to test a simple Steady Heating model. First we calculate the differential emission measure of the apex region of the loops in the active region core. We find the DEM to be broad and peaked around 3\,MK. We then determine the densities in the corresponding footpoint regions. Using potential field extrapolations to approximate the loop lengths and the density-sensitive line ratios to infer the magnitude of the Heating, we build a Steady Heating model for the active region core and find that we can match the general properties of the observed DEM for the temperature range of 6.3 $<$ Log T $<$ 6.7. This model, for the first time, accounts for the base pressure, loop length, and distribution of apex temperatures of the core loops. We find that the density-sensitive spectral line intensities and the bulk of the hot emission in the active region core are consistent with Steady Heating. We also find, however, that the Steady Heating model cannot address the emission observed at lower temperatures. This emission may be due to foreground or background structures, or may indicate that the Heating in the core is more complicated. Different Heating scenarios must be tested to determine if they have the same level of agreement.