scholarly journals DEM Analyses with the Utrecht Codes

1996 ◽  
Vol 152 ◽  
pp. 553-560
Author(s):  
R. Mewe ◽  
G.H.J. van den Oord ◽  
C.J. Schrijver ◽  
J.S. Kaastra
Keyword(s):  
Emission Measure ◽  
Resonant Scattering ◽  
Continuum Emission ◽  
Second Derivative ◽  
Inversion Problem ◽  
Differential Emission Measure ◽  
The Past ◽  
Cool Stars ◽  
Ill Posed ◽  
Thin Plasma

We address the inversion problem of deriving the differential emission measure (DEM) distribution D(T) = nenHdV/d log T from the spectrum of an optically thin plasma. In the past we have applied the iterative Withbroe-Sylwester technique and the Polynomial technique to the analysis of EXOSAT spectra of cool stars, but recently we have applied the inversion technique discussed by Craig & Brown (1986) and Press et al. (1992) in the analysis of EUVE spectra of cool stars. The inversion problem-a Fredholm equation of the first kind-is ill-posed and solutions tend to show large, unphysical oscillations. We therefore apply a second-order regularization, i.e., we select the specific DEM for which the second derivative is as smooth as is statistically allowed by the data. We demonstrate the importance of fitting lines and continuum simultaneously, discuss the effect on the DEM of continuum emission at temperatures where no line diagnostics are available, and address possible ways to check various model assumptions such as abundances and photon destruction induced by resonant scattering.

scholarly journals Are Some Stellar Coronae Optically Thick?

1996 ◽  
Vol 152 ◽  
pp. 121-128
Author(s):  
C.J. Schrijver ◽  
G.H.J. van den Oord ◽  
R. Mewe ◽  
J.S. Kaastra
Keyword(s):  
Extreme Ultraviolet ◽  
Formal Solution ◽  
Emission Measure ◽  
Resonant Scattering ◽  
Heavy Elements ◽  
Volume Filling ◽  
Dominant Component ◽  
Weak Component ◽  
Cool Stars ◽  
Spurious Result

We discuss the coronal spectra of a sample of cool stars observed with the spectrometers of the Extreme Ultraviolet Explorer (EUVE). The emission measure distributions show (a) a relatively weak component between 0.1 MK and 1 MK, (b) a dominant component somewhere between 2 MK and 10 MK, and (c) in all cases but one a component in the formal solution at temperatures exceeding ≈ 20 MK. Where this hot tail is not associated with a real hot component, it is a spurious result reflecting a lowered line-to-continuum ratio, which, for instance, may be the result of a low abundance of heavy elements or of resonant scattering in some of the strongest coronal lines. We suggest that in Procyon’s corona photons in the strongest lines formed around a few million Kelvin undergo resonant scattering in a circumstellar medium, possibly a stellar wind. The flare spectrum of AU Mic suggests that resonant scattering may also occur in dense, hot flare plasmas. The electron densities of the 5–15 MK component are some three orders of magnitude higher than typical of the solar-like component around 2 MK; the volume filling factors of the hot components are therefore expected to be relatively small.

scholarly journals Calculation of the Temperature Structure of an Optically Thin Plasma From its Emission Line Spectrum

1977 ◽  
Vol 43 ◽  
pp. 42-42
Author(s):  
K.D. Evans ◽  
J.P. Pye ◽  
R.J. Hutcheon
Keyword(s):  
Emission Measure ◽  
Temperature Structure ◽  
Differential Emission Measure ◽  
X Ray ◽  
Measure Function ◽  
Fundamental Significance ◽  
Early Results ◽  
Emission Line Spectrum ◽  
Thin Plasma

Knowledge of the (differential) emission measure function (with temperature), Y(Te), is likely to be of fundamental significance in attempts to understand the behaviour of any optically thin plasma - and this is certainly true of present studies of the solar atmosphere. In this latter case the gross temperature structure of material below 106K has been deduced from uv line measurements since the early 1960's and, since 1968, similar analyses of the material above 106K have been made using emission lines at x-ray wavelengths. In this latter case the validity, and even desirability, of published results has recently been quite strongly challenged. Comment is made upon those criticisms of early results and upon their relevance to present day analyses. In this paper the crucial value of fine temperature resolution in the determination of the emission measure function of this coronal material is argued.

scholarly journals Spectroscopic EUVE Observations of the Active Star AB Doradus

1996 ◽  
Vol 152 ◽  
pp. 159-164
Author(s):  
Slavek M. Rucinski ◽  
Rolf Mewe ◽  
Jelle S. Kaastra ◽  
Osmi Vilhu ◽  
Stephen M. White
Keyword(s):  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Continuum Emission ◽  
Temperature Structure ◽  
Differential Emission Measure ◽  
High Temperature Component ◽  
Late Type Star ◽  
Measure Analysis ◽  
Temperature Component ◽  
Dem Analysis

We present observations of the pre-Main Sequence, rapidly-rotating (0.515 day) late-type star, AB Doradus (HD 36705), made by the Extreme Ultraviolet Explorer (EUVE) satellite. A high-quality spectrum was accumulated between November 4-11, 1993, with an effective exposure time of about 40 hours. The data constrain the coronal temperature structure between several 104 K up to roughly 2 × 107 K through a differential emission measure analysis using an optically-thin plasma model. The resulting differential emission measure (DEM) distribution shows: a) dominant emission from plasma between about 2 × 106 K and 2 × 107 K, b) very little emission from plasma between 105 K and 2 × 106 K, and c) emission from plasma below about 105 K. If solar photospheric abundances are assumed, then the formal DEM solution also requires the presence of a strong high-temperature component (above about 3 × 107 K) in order to fit the strong continuum emission below about 150 Å; however, we believe that this component of the solution is not physical. The DEM analysis gives a best-fit value for the interstellar hydrogen column density of NH = (2.4 ± 0.5) × 1018 cm−2.

The Interpretation of Solar Spectral Intensities

1988 ◽  
Vol 102 ◽  
pp. 329
Author(s):  
R.W.P. McWhirter
Keyword(s):  
Emission Measure ◽  
Physical Nature ◽  
Atomic Data ◽  
The Sun ◽  
Atomic Properties ◽  
Outer Atmosphere ◽  
Spectral Intensities ◽  
Thin Plasma ◽  
Number Of Authors

The intensity of a specrtal line from an optically thin plasma such as the outer atmosphere of the sun depends on both the atomic properties of the atomic ion responsible for the line and the physical nature of the plasma. In this paper we discuss the various ways in which the measured spectral intensities from the sun are used to discover something about the nature of the sun’s atmosphere. The technique has been referred to as the emission measure method. It has important limitations in terms of the accuracy of the specrtal data as well as the atomic data. We discuss some of these and suggest methods by which they may be assessed. The technique is illustrated by application to real observations from a number of authors.

scholarly journals ON THE ACCURACY OF THE DIFFERENTIAL EMISSION MEASURE DIAGNOSTICS OF SOLAR PLASMAS. APPLICATION TO SDO /AIA. II. MULTITHERMAL PLASMAS

2012 ◽  
Vol 203 (2) ◽  
pp. 26 ◽  
Author(s):  
C. Guennou ◽  
F. Auchère ◽  
E. Soubrié ◽  
K. Bocchialini ◽  
S. Parenti ◽  
...  
Keyword(s):  
Emission Measure ◽  
Differential Emission Measure ◽  
Solar Plasmas

Analysis of the differential emission measure distributions for solar flares observed by RESIK

2018 ◽  
Vol 179 ◽  
pp. 545-552
Author(s):  
A. Kepa ◽  
B. Sylwester ◽  
J. Sylwester ◽  
M. Gryciuk ◽  
M. Siarkowski
Keyword(s):  
Solar Flares ◽  
Emission Measure ◽  
Differential Emission Measure

scholarly journals Energetics of Hi-C EUV brightenings

2018 ◽  
Vol 615 ◽  
pp. A47 ◽  
Author(s):  
Srividya Subramanian ◽  
Vinay L. Kashyap ◽  
Durgesh Tripathi ◽  
Maria S. Madjarska ◽  
John G. Doyle
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Extreme Ultraviolet ◽  
Thermal Structure ◽  
Emission Measure ◽  
Light Curves ◽  
Solar Dynamics Observatory ◽  
Differential Emission Measure ◽  
Dominant Mechanism ◽  
Solar Dynamics

We study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings within a system of fan loops observed in the active region AR 11520. These brightenings were simultaneously observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA 193 Å light curves. The energetics of these brightenings were studied using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range log T(K) = 6.2−6.6 with radiative energies ≈1024−25 ergs and densities approximately equal to a few times 109 cm−3. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation.

scholarly journals The Slowly Varying Corona. I. Daily Differential Emission Measure Distributions Derived from EVE Spectra

2017 ◽  
Vol 844 (2) ◽  
pp. 163 ◽  
Author(s):  
S. J. Schonfeld ◽  
S. M. White ◽  
R. A. Hock-Mysliwiec ◽  
R. T. J. McAteer
Keyword(s):  
Emission Measure ◽  
Differential Emission Measure
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