The EUV spectrum of the Sun: SOHO CDS NIS irradiances from 1998 until 2010

Zanna, G. Del; Andretta, V.

doi:10.1051/0004-6361/201016106

Cited by 27 publications

(25 citation statements)

References 40 publications

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“…As discussed in Del ; Del Zanna & Andretta (2011), there is now good evidence that the basal quiet Sun irradiances in lines formed at or below 1 MK are relatively unchanged across solar cycles. Also, that irradiances during solar minimum conditions are similar for different cycles.…”

Section: Previous Observations and Line Identificationsmentioning

confidence: 90%

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Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines

Zanna¹

2012

A&A

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A collection of the best solar and laboratory spectra in the soft X-rays is used here to perform a preliminary benchmark in this wavelength region, by comparing observed vs. predicted wavelengths and calibrated solar irradiances. The benchmark focuses on the Fe ix -Fe xiv ions, for which we have recently calculated the relevant atomic data, however a few other ions have also been benchmarked. The iron ions are dominating the soft X-rays, however a large fraction of the strongest soft X-ray lines due to n = 4 → n = 3 transitions were previously unidentified. The strongest transitions are all identified here, in particular the decays from the core-excited levels (3s 3p l 4s, l = 5,4,3,2,1 for Fe x, Fe xi, Fe xii, Fe xiii, and Fe xiv respectively) which are the strongest soft X-ray transitions from these ions. Many new identifications are proposed, some only tentatively. Good agreement in terms of solar irradiances between the soft-Xray and EUV (n = 3 → n = 3) transitions is found, confirming the reliability of the new large-scale calculations. Some of the new atomic data and identifications are particularly important for the Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 Å band.

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Section: Previous Observations and Line Identificationsmentioning

confidence: 90%

“…The F10.7 radio flux on that day was only 69. Indeed during the previous extended minimum the solar corona was very quiet (Del Zanna & Andretta 2011). One drawback of the EVE spectra is the low spectral resolution (about 1 Å), hence the majority of the lines are blended.…”

Section: Previous Observations and Line Identificationsmentioning

confidence: 99%

Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines

Zanna¹

2012

A&A

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“…The SERTS-97 observation at pointing 1 showed variations of He ii intensities in "quiet region" from 4500 to 12000 erg s −1 cm −2 sr −1 over the 353 slit. Del Zanna & Andretta (2011) showed that the He ii irradiance measured during this solar minimum (2006)(2007)(2008) is about a factor of 1.3 smaller than that measured in 1998 at the beginning of the last solar cycle. The dispersion of He ii intensities shown in Table 5 suggests that one should be cautious about using the quiet-Sun He ii line as a standard light source.…”

Section: Discussionmentioning

confidence: 99%

“…Note that the old measurements include the blending emission from Si xi line, but the blending typically contributes less than 10% of the total intensity of these two lines in the quiet Sun, so it cannot explain the big difference from the EUNIS-07 measurement. Based on the longterm monitoring of CDS NIS irradiances from 1998 to 2010, Del Zanna & Andretta (2011) suggested that the Skylab values of the He ii 304 Å line in the quiet Sun were overestimated, as were those measured by SERTS-89, SERTS-91, SERTS-93, and SERTS-95, whose absolute radiometric calibrations were based on the Skylab measurements. The large difference between the SERTS-97 and EUNIS-07 measurements, which were both based on the direct laboratory-calibration, suggests that the large dispersion of measurements from different instruments may be partially ascribed to true variations depending on observed locations (if the average is limited in a small FOV) and on observing times (e.g., different phases of a solar cycle, or different solar cycles).…”

Section: Discussionmentioning

confidence: 99%

UNDERFLIGHT CALIBRATION OF SOHO /CDS AND HINODE /EIS WITH EUNIS-07

Wang¹,

Thomas²,

Brosius³

et al. 2011

ApJS

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Flights of Goddard Space Flight Center's Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket in 2006 and 2007 provided updated radiometric calibrations for Solar and Heliospheric Observatory/Coronal Diagnostic Spectrometer (SOHO/CDS) and Hinode/Extreme Ultraviolet Imaging Spectrometer (Hinode/EIS). EUNIS carried two independent imaging spectrographs covering wavebands of 300-370 Å in first order and 170-205 Å in second order. After each flight, end-to-end radiometric calibrations of the rocket payload were carried out in the same facility used for pre-launch calibrations of CDS and EIS. During the 2007 flight, EUNIS, SOHO/CDS, and Hinode/EIS observed the same solar locations, allowing the EUNIS calibrations to be directly applied to both CDS and EIS. The measured CDS NIS 1 line intensities calibrated with the standard (version 4) responsivities with the standard long-term corrections are found to be too low by a factor of 1.5 due to the decrease in responsivity. The EIS calibration update is performed in two ways. One uses the direct calibration transfer of the calibrated EUNIS-07 short wavelength (SW) channel. The other uses the insensitive line pairs, in which one member was observed by the EUNIS-07 long wavelength (LW) channel and the other by EIS in either the LW or SW waveband. Measurements from both methods are in good agreement, and confirm (within the measurement uncertainties) the EIS responsivity measured directly before the instrument's launch. The measurements also suggest that the EIS responsivity decreased by a factor of about 1.2 after the first year of operation (although the size of the measurement uncertainties is comparable to this decrease). The shape of the EIS SW response curve obtained by EUNIS-07 is consistent with the one measured in laboratory prior to launch. The absolute value of the quiet-Sun He ii 304 Å intensity measured by EUNIS-07 is consistent with the radiance measured by CDS NIS in quiet regions near the disk center and the solar minimum irradiance recently obtained by CDS NIS and the Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment.

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“…Peres et al (2000) studied the long-term variation of the soft X-ray flux measured by Yohkoh/SXT (Tsuneta et al, 1991) and found that the emission measure of the whole Sun changes by orders of magnitude between the solar activity maximum and the minimum. The irradiances of EUV coronal emission lines exhibit a large variation in sync with the solar cycle, with larger amplitude at the higher temperatures (Del Zanna and Andretta, 2011). Since the coronal irradiance is thought to be a measure of the magnetic activity of the whole corona, it is important to understand what features on the Sun cause the irradiance variation.…”

Section: Introductionmentioning

confidence: 99%

Long-Term Variation of the Corona in Quiet Regions

Kamio

Mariska

2012

Sol Phys

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Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun center from the end of 2006 to early 2011, we studied the longterm evolution of the quiet corona. The light curves of the higher temperature emission lines exhibit larger variations in sync with the solar activity cycle while the cooler lines show reduced modulation. Our study shows that the high temperature component of the corona changes in quiet regions, even though the coronal electron density remains almost constant there. The results suggest that heat input to the quiet corona varies with the solar activity cycle.

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The EUV spectrum of the Sun: SOHO CDS NIS irradiances from 1998 until 2010

Cited by 27 publications

References 40 publications

Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines

Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines

UNDERFLIGHT CALIBRATION OF SOHO /CDS AND HINODE /EIS WITH EUNIS-07

Long-Term Variation of the Corona in Quiet Regions

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