The EUV spectrum of the Sun: SOHO CDS NIS radiances during solar cycle 23

Andretta, V.; Zanna, G. Del

doi:10.1051/0004-6361/201322841

Cited by 19 publications

(26 citation statements)

References 31 publications

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“…We measured average width values for histograms in He i and O v to be equal to 0.18 ± 0.01 and 0.22 ± 0.02 dex, respectively. The values reported in the study of Andretta & Del Zanna (2014) are 0.16 ± 0.015 dex for He i and 0.19 ± 0.02 dex for O v. The small difference might be due to the specific fitting approach applied by (Andretta & Del Zanna 2014), in which only the peak of the histograms, corresponding to the internetwork area, are fitted and the contribution of the brighter network is ignored.…”

Section: Discussionmentioning

confidence: 88%

“…The He i and Ca ii K results imply a certain level of decoupling between the chromospheric radiation and the photospheric field at least at very low level of activity. In a recent study by Andretta & Del Zanna (2014), the authors also analysed the radiance distribution over solar cycle 23 by investigating the full-disc and central meridian observations of the CDS studies USUN and SYNOP, respectively. They concluded that the quiet Sun radiance has undergone no significant changes during solar cycle 23, regardless of which spectral line is considered.…”

Section: Discussionmentioning

confidence: 99%

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Solar extreme ultraviolet variability of the quiet Sun

Shakeri¹,

Teriaca²,

Solanki³

2015

A&A

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The last solar minimum has been unusually quiet compared to the previous minima (since space-based radiometric measurements are available). The Sun's magnetic flux was substantially lower during this minimum. Some studies also show that the total solar irradiance during the minimum after cycle 23 may have dropped below the values known from the two minima prior to that. For chromospheric and coronal radiation, the situation is less clear-cut. The Sun's 10.7 cm flux shows a decrease of ∼4% during the solar minimum in 2008 compared to the previous minimum, but Ca ii K does not. Here we consider additional wavelengths in the extreme ultraviolet (EUV), specifically transitions of He i at 584.3 Å and O v at 629.7 Å, of which the CDS spectrometer aboard SOHO has been taking regular scans along the solar central meridian since 1996. We analysed this unique dataset to verify if and how the radiance distribution undergoes measurable variations between cycle minima. To achieve this aim we determined the radiance distribution of quiet areas around the Sun centre. Concentrating on the last two solar minima, we found out that there is very little variation in the radiance distribution of the chromospheric spectral line He i between these minima. The same analysis shows a modest, although significant, 4% variation in the radiance distribution of the TR spectral line O v. These results are comparable to those obtained by earlier studies employing other spectral features, and they confirm that chromospheric indices display a small variation, whereas in the transition region a more significant reduction of the brighter features is visible.

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Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Solar extreme ultraviolet variability of the quiet Sun

Shakeri¹,

Teriaca²,

Solanki³

2015

A&A

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“…To compare the EIS radiances with that of the resonance line, we have taken the quiet Sun irradiance measured by the prototype EVE (PEVE) instrument Woods et al 2009) and converted into a radiance, assuming a limbbrightening factor of 1.4, as done in Del Zanna (2013), based on the limb-brightening curves obtained from SOHO CDS described in Andretta & Del Zanna (2014). Despite the uncertainty in the conversion, there is good agreement (within 20%) between predicted and observed radiances, as shown in Fig.…”

Section: Comparison To Euv Observationsmentioning

confidence: 99%

Atomic data for astrophysics: Ni XI

Zanna¹,

Storey

Badnell

2014

A&A

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We present a new large-scale R-matrix scattering calculation for electron collisional excitation of Ni xi, carried out with the intermediate-coupling frame transformation method. The target includes all the main configurations up to n = 4, and is a significant improvement over earlier R-matrix (only three n = 3 configurations) and distorted-wave (DW) calculations. We find significant enhancements in the collision strengths of many of the strong transitions to the n = 3, 4 levels. They are due to the resonances that arise within the present large-scale target. This results in significant increases in the predicted intensities of the UV and visible forbidden lines within the 3s 2 3p 5 3d configuration, the strong EUV lines that result from the decays of the 3s 2 3p 5 3d levels to the ground state, and the decays from the n = 4 levels, which are visible in the soft X-rays. We find good agreement between predicted and observed line intensities in the EUV. With the present atomic data, lines from Ni xi can reliably be used for plasma diagnostics. We also revise some level energies and suggest a few new possible identifications.

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“…Paper III (Andretta & Del Zanna 2014) analysed in detail the radiances in the main lines. A new limb-brightening function was obtained and shown to be important for the characterisation of the solar radiances.…”

Section: Introductionmentioning

confidence: 99%

The EUV spectrum of the Sun: Irradiances during 1998–2014

Zanna

Andretta

2015

A&A

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We present calibrated EUV spectral irradiances obtained from observations with the Solar and Heliospheric Observatory (SOHO) Coronal Diagnostics Spectrometer (CDS) Normal Incidence Spectrometer (NIS) during the 1998-2014 period, which spans the cycle 23 maximum and minimum and the cycle 24 maximum. We revise the corrections for the burn-in of the strong lines and our previous long-term calibration of the NIS. We find no indications of further overall degradation of the instrument responsivities after 2010. We compare the CDS irradiances with those obtained by the prototype and flight instruments aboard the Solar Dynamics Observatory (SDO) Extreme ultraviolet Variability Experiment (EVE) and the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) Solar EUV Experiment (SEE) EUV Grating Spectrograph (EGS). We find overall excellent agreement (to within a relative 10-20%) with the EVE data (especially during 2010-2012), but point out inconsistencies in some of the prototype and flight EVE irradiances. There is overall agreement with some of the TIMED SEE EGS data. We confirm the small variations in the irradiances of low-temperature lines (except the helium lines) and show that the irradiances in the hot (2-3 MK) lines are significantly lower for the cycle 24 maximum compared to the previous one.

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The EUV spectrum of the Sun: SOHO CDS NIS radiances during solar cycle 23

Cited by 19 publications

References 31 publications

Solar extreme ultraviolet variability of the quiet Sun

Solar extreme ultraviolet variability of the quiet Sun

Atomic data for astrophysics: Ni XI

The EUV spectrum of the Sun: Irradiances during 1998–2014

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