On the Failure of Standard Emission Measure Analysis for Solar Extreme-Ultraviolet and Ultraviolet Irradiance Spectra

1995 ◽  
Vol 455 (1) ◽  
Author(s):  
P. G. Judge ◽  
T. N. Woods ◽  
P. Brekke ◽  
G. J. Rottman
Keyword(s):  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Measure Analysis ◽  
Ultraviolet Irradiance

Modeling solar extreme ultraviolet irradiance variability using emission measure distributions

1996 ◽  
Vol 23 (17) ◽  
pp. 2207-2210 ◽  
Author(s):  
H. P. Warren ◽  
J. T. Mariska ◽  
J. Lean ◽  
W. Marquette ◽  
A. Johannesson
Keyword(s):  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Ultraviolet Irradiance ◽  
Solar Extreme Ultraviolet Irradiance

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.

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 Anomalously low solar extreme-ultraviolet irradiance and thermospheric density during solar minimum

2010 ◽  
Vol 37 (16) ◽  
pp. n/a-n/a ◽  
Author(s):  
Stanley C. Solomon ◽  
Thomas N. Woods ◽  
Leonid V. Didkovsky ◽  
John T. Emmert ◽  
Liying Qian
Keyword(s):  
Solar Minimum ◽  
Extreme Ultraviolet ◽  
Ultraviolet Irradiance ◽  
Solar Extreme Ultraviolet Irradiance

UV Emitting Spicules

1980 ◽  
Vol 91 ◽  
pp. 199-201
Author(s):  
Giannina Poletto
Keyword(s):  
Coronal Hole ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Harvard College ◽  
Chromospheric Network ◽  
Harvard College Observatory ◽  
Ultraviolet Observations ◽  
Lower Limits

Extreme ultraviolet observations of the chromospheric network in a coronal hole obtained in 1973 by the Harvard College Observatory experiment aboard Skylab are analyzed. Upper and lower limits to the actual emission measure in UV spicules have been obtained, and the consistency of the derived values with the hypothesis that UV spicules are Hα spicules falling back after being heated is discussed.

scholarly journals Dissecting the EUV Spectrum of Capella

1996 ◽  
Vol 152 ◽  
pp. 105-112 ◽  
Author(s):  
Nancy S. Brickhouse
Keyword(s):  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Continuous Distribution ◽  
Line Emission ◽  
Local Maximum ◽  
Abundance Ratio ◽  
Emission Lines ◽  
Cool Star ◽  
The Individual ◽  
The Continuum

Extreme ultraviolet spectra of Capella, obtained at various orbital phases over the past two years by the EUVE satellite, show strong emission lines from a continuous distribution of temperatures (~ 105 − 107.3 K). In addition to the strong He II λ303.8, the spectra are dominated by emission lines of highly ionized iron. Strong lines of Fe IX, XV, XVI, and XVIII–XXIV are used to construct emission measure distributions for the individual pointings, which show several striking features, including a minimum near 106 K and a local maximum at 106.8 K. Furthermore, intensities of the highest temperature lines (Te > 107 K) show variations (factors of 2–3) at different orbital phases, while the lower temperature Fe lines show variations of about 30% or less. The low variability of most of the strong low temperature features motivates a detailed analysis of the summed spectrum. With ~ 280 ks of total exposure time, we have measured over 200 emission features with S/N ≥ 3.0 in the summed spectrum. We report here initial results from the analysis of this spectrum. We can now identify lines of Fe VIII and X–XIV, as well as a number of electron density and abundance diagnostic lines.We also report here the first direct measurement of the continuum flux around ~ 100 Å in a cool star atmosphere with EUVE. The continuum flux can be predicted from the emission measure model based on Fe line emission, and demonstrates that the Fe/H abundance ratio is close to the solar photospheric value.

scholarly journals EUVE Spectra of Coronae and Flares

1996 ◽  
Vol 152 ◽  
pp. 81-88 ◽  
Author(s):  
Carole Jordan
Keyword(s):  
Short Wavelength ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Wavelength Region ◽  
Late Type ◽  
Short Wavelength Region ◽  
Plane Parallel ◽  
Parallel Geometry ◽  
Measure Distribution

Following a summary of early solar EUV spectroscopy the spectra of some late-type stars obtained with the Extreme Ultraviolet Explorer (EUVE) are briefly surveyed. Some transitions which are not included in current emissivity codes but could lead to numerous weak lines, and an apparent continuum in the EUVE short wavelength region, are discussed. The importance of the geometry adopted when interpreting the emission measure distribution is stressed, since radial factors can lead to an apparent emission measure distribution gradient that is steeper than the value of 3/2 expected in plane parallel geometry.

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