J/ApJ/759/141 Emission measures in solar active regions (Warren+, 2012)
A systematic survey of high-temperature emission in solar active regions.
Warren H.P., Winebarger A.R., Brooks D.H.
<Astrophys. J., 759, 141 (2012)>
=2012ApJ...759..141W 2012ApJ...759..141W
ADC_Keywords: Sun
Keywords: Sun: corona
Abstract:
The recent analysis of observations taken with the EUV Imaging
Spectrometer and X-Ray Telescope instruments on Hinode suggests that
well-constrained measurements of the temperature distribution in solar
active regions can finally be made. Such measurements are critical for
constraining theories of coronal heating. Past analysis, however, has
suffered from limited sample sizes and large uncertainties at
temperatures between 5 and 10MK. Here we present a systematic study of
the differential emission measure distribution in 15 active region
cores. We focus on measurements in the "inter-moss" region, that is,
the region between the loop footpoints, where the observations are
easier to interpret. To reduce the uncertainties at the highest
temperatures we present a new method for isolating the Fe XVIII
emission in the AIA/SDO 94Å channel. The resulting differential
emission measure distributions confirm our previous analysis showing
that the temperature distribution in an active region core is often
strongly peaked near 4MK. We characterize the properties of the
emission distribution as a function of the total unsigned magnetic
flux. We find that the amount of high-temperature emission in the
active region core is correlated with the total unsigned magnetic
flux, while the emission at lower temperatures, in contrast, is
inversely related. These results provide compelling evidence that
high-temperature active region emission is often close to equilibrium,
although weaker active regions may be dominated by evolving million
degree loops in the core.
Description:
EIS (EUV Imaging Spectrometer) is a high spatial and spectral
resolution imaging spectrometer. EIS observes two wavelength ranges,
171-212Å and 245-291Å, with a spectral resolution of about
22mÅ and a spatial resolution of about 1"/pixel. Solar images can
be made by stepping the slit over a region of the Sun and taking an
exposure at each position.
We have designed several EIS observing sequences that contain all of
the emission lines needed to compute emission measure (EM)
distributions. Of particular importance is the observation of emission
lines from CaXIV to CaXVII, which constrains the analysis at
temperatures above 3MK. For each observation we determined the NOAA
coordinates for the active region of interest at the mid-point of the
EIS raster.
AIA (Atmospheric Imaging Assembly) is a set of multi-layer telescopes
capable of imaging the Sun at high spatial resolution (0.6"/pixel) and
high cadence (typically 12s). Images are available at 94, 131, 171,
193, 211, 304, and 335Å.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2a.dat 49 336 Differential Emission Measure Model from EIS
(EUV Imaging Spectrometer) instrument
table2b.dat 37 16 Differential Emission Measure Model from AIA
(Atmospheric Imaging Assembly) instrument
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See also:
J/A+A/555/A123 : 3D-MHD model of a solar active region corona (Bourdin+, 2013)
J/A+A/552/A114 : Sun chromospheric CaII-HK emission (Shapiro+, 2013)
J/ApJ/752/126 : Modeling the magnetic field in the corona (Yamamoto+, 2012)
J/ApJS/181/351 : Solar flux model in 30-1300nm wavelength range (Killen+, 2009)
J/A+A/432/1063 : Analysis of inner solar corona in EUV (Lanzafame+, 2005)
Byte-by-byte Description of file: table2a.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Reg [1/16] Active region (G1)
4- 10 A7 --- Line Line identifier
12- 18 F7.3 0.1nm lambda [180/285] Line wavelength (Å)
20- 27 F8.2 mW/m2/sr OInt [7.9/12734] Observed intensity (1)
29- 35 F7.2 mW/m2/sr e_OInt [1.7/2802] Error in OInt (1)
37- 44 F8.2 mW/m2/sr DInt [6.6/19162] Differential emission measure
intensity (1)
46- 49 F4.2 --- O/D(Int) [0.6/2.9] Ratio of OInt to DInt
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Note (1): EIS line intensities are in units of erg/cm2/s/sr.
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Byte-by-byte Description of file: table2b.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Reg [1/16] Active region (G1)
5- 6 I2 0.1nm lambda [94] Wavelength identifier (in Å)
8- 15 F8.2 --- OInt [2.1/102] Observed intensity (1)
17- 23 F7.2 --- e_OInt [0.4/21] Error in OInt (1)
25- 32 F8.2 --- DInt [2.8/116] Differential emission measure
intensity (1)
34- 37 F4.2 --- O/D(Int) [0.6/1.3] Ratio of OInt to DInt
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Note (1): AIA intensities are in units of DN/s/pixel.
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Global note:
Note (G1): Active region cores in table 1 are defined as:
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Reg NOAA Date Xcen Ycen AM φM Ihot
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1 1082 2010 Jun 19 01:57:44 -306.4 439.3 2.87(19) 4.08(21) 1.36(04)
2 1158 2011 Feb 12 15:32:13 -248.4 -211.8 3.04(19) 4.22(21) 1.88(04)
3 1082 2010 Jun 21 01:46:37 162.9 405.2 3.29(19) 4.72(21) 1.05(04)
4 1259 2011 Jul 25 09:36:09 224.7 323.4 3.98(19) 5.68(21) 7.81(03)
5 1150 2011 Jan 31 11:25:19 -470.9 -250.6 5.17(19) 7.50(21) 1.47(05)
6 1147 2011 Jan 21 14:10:50 26.6 476.5 6.49(19) 1.02(22) 2.28(05)
7 1243 2011 Jul 2 03:38:08 -299.0 216.6 6.79(19) 1.09(22) 6.18(04)
8 1089 2010 Jul 23 15:03:07 -363.4 -453.6 6.96(19) 1.12(22) 1.84(05)
9 1109 2010 Sep 29 23:51:36 361.5 261.5 7.19(19) 1.16(22) 1.50(05)
10 1193 2011 Apr 19 13:32:20 36.3 363.5 7.94(19) 1.35(22) 2.50(05)
11 1190 2011 Apr 11 12:00:42 -492.6 281.0 8.61(19) 1.37(22) 1.11(05)
12 1271 2011 Aug 21 12:25:42 -50.8 150.8 9.59(19) 1.57(22) 1.47(05)
13 1190 2011 Apr 15 01:17:19 218.1 304.4 1.04(20) 1.78(22) 5.22(05)
14 1339 2011 Nov 8 19:14:27 88.1 258.4 1.41(20) 2.60(22) 6.08(05)
15 1339 2011 Nov 10 11:33:19 406.0 266.8 1.48(20) 2.73(22) 9.75(05)
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Xcen and Ycen are the NOAA active region coordinates differentially rotated
to the mid-point of the EIS raster. AM is the total area occupied by pixels
between 50 and 500G in cm2. φM is the total unsigned magnetic flux in
Mx. Ihot is the total AIA FeXVIII intensity in the field of view in DN/s.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Jul-2014