nam and ukstp 11 april 2003 sensitivity differences in pre-loss and post-recovery nis/cds spectrum...

NAM and UKSTP11 April 2003

Sensitivity Differences in Sensitivity Differences in Pre-Loss and Post-Recovery Pre-Loss and Post-Recovery

NIS/CDS SpectrumNIS/CDS SpectrumBy Steven Chapman

Centre for AstrophysicsUniversity of Central Lancashire


ContentsContents• Background on the side effects of the recovery of

SoHO concerning CDS/NIS

• The Synoptic data

• Determining the modal low-emission intensity and showing the variation

• Aligning the pre-loss and post-recovery low-emission intensities

• Conclusion

• Aligning higher intensities


Background…Background…

• My main area of work has been studying the variation of the coronal hole area over cycle 23, with the CDS/NIS synoptic study. This will be combined with magnetic flux data to show how the open flux varies.

• This has involved contouring low-emission regions, but to do this you need a cut-off level between the low-emission region and the quiet sun.


What Changed After the Recovery?What Changed After the Recovery?

• The spectral line profiles of the NIS-1 and NIS-2 had acquired substantial wings on either side of the line.

• The sensitivity of the NIS-1 instrument has been noticeably reduced. NIS-2 sensitivity appears to be unaffected.

• CDS Software Note 53


Pre-Loss and Post-Recovery Line Pre-Loss and Post-Recovery Line profiles of Mg IX and Mg VII (NIS-1)profiles of Mg IX and Mg VII (NIS-1)


Synoptic DataSynoptic Data• SoHO CDS Synoptic data is a long, near continuous

data set.

• This is ideal to study changes in the behaviour of the CDS/NIS instrument

• Covers 5 lines in EUV wavelengths – He I, Fe XVI, Mg IX, Mg X (added in May 1998) and O V.

• The meridian of the Sun is covered by 9 rasters.

• Each raster is a cube of data. A 2D image where each pixel is made up of a spectrum of the mentioned lines.


22 May 1998 - EIT 195Å Full Disk of the Sun, 22 May 1998 - EIT 195Å Full Disk of the Sun, with CDS synoptic pointings of all nine with CDS synoptic pointings of all nine

rasters overlaidrasters overlaid


22 May 1998 Mg IX Meridian Strip22 May 1998 Mg IX Meridian Strip

Intensity Contoured Low-Emission

Extracted Low-Emission


Finding the Modal Low-Emission Finding the Modal Low-Emission IntensityIntensity

Histograms of all the masked pixels intensities are created. The peak shows the most common low-emission intensity for each masked image.


Variation of the Modal Low-Emission Variation of the Modal Low-Emission Intensity, UncorrectedIntensity, Uncorrected


Aligning the Post-Recovery Low-Emission Aligning the Post-Recovery Low-Emission Intensities, Correction = 1.45Intensities, Correction = 1.45


ConclusionConclusion

• The sensitivity of the NIS1 instrument has been affected by the temporary loss of SoHO.

• The post-recovery low-emission intensities need a correction factor of ~1.8 to align it with the pre-loss.

• This investigation has only been done with ~300 days of data. Work is currently being done in studying all of the CDS synoptic data, to determine an acceptable low-emission correction factor for post-recovery NIS-1 data.


Preliminary Investigation into Preliminary Investigation into Other Intensity LevelsOther Intensity Levels

• Early results in aligning post-recovery to pre-loss intensity levels shows that a non-constant correction factor is needed.

• Masked images have been created with a Mg X image using the following intensity level bands. These have been overlaid with the corresponding Mg IX image and then the pre and post intensity levels have been aligned.

0.0 0.07 (Coronal Hole)0.07 0.40.5 0.6 (Quiet Sun)0.7 0.80.8 ∞ (Active Region)

(intensity units – photons-events/sec/pixel)


A Non-Constant Correction FactorA Non-Constant Correction Factor

nam and ukstp 11 april 2003 sensitivity differences in pre-loss and post-recovery nis/cds spectrum...

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