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Issue 7: 15th October 2002
Latest News

Welcome to the CDS Newsletter. The goal of this Newsletter is to inform the CDS user community of
  • current CDS science topics
  • developments in CDS data analysis
  • instrumental matters
  • operational issues
We invite your contributions on CDS-related matters: data analysis, science results, instrument calibration, software and questions on these topics. Your responses will influence the content of future issues. Please send newsletter inputs and correspondence to the editor,

This Month's Topics:

CDS Meeting

A CDS Users Meeting will be held in Dublin on 10 and 11 April 2003, in conjunction with the National Astronomy Meeting/UK Solar Physics Meeting, 7-11 April 2003.

CDS Meeting Schedule:

Thursday, 10 April, 16:00 - 17:30 CDS Science Session

Friday, 11 April, 9:00 - 10:30, 11:00 - 12:30, 14:00- 15:30, three CDS Users sessions.

The 'CDS Science' session on Thursday will contain science talks presenting results obtained from CDS data. These presentations will be in a usual conference format. During Friday sessions we will discuss issues related to data analysis and the instrument, with full participation from the audience. More details on the CDS Meeting programme will be sent later.

Information about the NAM/UKSP Meeting is available at:

Please mark the CDS Meeting in your calendars. We look forward to seeing you in Dublin.
- Andrzej Fludra & Peter Young

MEDOC Campaign

Medoc Campaign #10 will take place 21 Oct - 03 Nov. CDS will support several observing programmes, listed on the SOHO monthly calendar at:

EGSO Update

The EGSO (European Grid of Solar Observations) project is progressing well with various technical surveys and requirements reports being produced. Public documents can be seen on the Wiki website to which visitors may also register and contribute:
Dave Pike


Version 4.0 of the CHIANTI database for astrophysical spectroscopy has been released. The main new features included in this version are the inclusion of proton excitation rates and photoexcitation. In addition there are a number of updated ions and improvements to both the database and the software.

A paper describing the new contents of CHIANTI Version 4.0 will appear soon in The Astrophysical Journal Supplement Series (Young et al., 2002) and a preprint is available at
The CHIANTI package is distributed in two ways, as a stand-alone package and through SolarSoft. The CHIANTI package, and information on how to install it, can be found at our web sites:
- Peter Young

A wavelet analysis of quasi-periodic variability across a solar coronal hole region

M. S. Marsh, R. W. Walsh and B. J. I. Bromage, 2002, A&A 393, 649

High time resolution (~13 s cadence) Solar and Heliospheric Observatory (SOHO) Coronal Diagnostic Spectrometer (CDS) Grazing Incidence Spectrometer (GIS) time series data is analysed for evidence of quasi-periodic variability in the solar corona. The observations are obtained from a GIS study of a coronal hole boundary region taken in October 1997. A wavelet analysis is applied to EUV emission lines covering a temperature range of log Te=5.3-6.1 K. Wavelet analysis allows the frequency and temporal information of any periods present within the data to be analysed. Statistically significant periods are found within the range 100-900 s and 1500 s. Observations of short wavepackets with periods of the order 50-100 s with durations of 2-5 cycles are reported. Observations of a decay in the driving period over time are also described.

Coronal Polarization Measurements with CDS - by Roger J. Thomas

As mentioned in an earlier newsletter ( issue 3), an attempt was made to validate our understanding of basic emission mechanisms in the solar corona during a special SOHO roll maneuver last year, by making use of the polarization sensitivity of CDS. Preliminary analyses of these observations show that the expected EUV polarization signatures are indeed seen in coronal emission of low temperature lines above the limb, at the expected locations and with the proper sign. But the observed strength of these signals is much higher than expected, and on the verge of what seems physically possible. A similar result was obtained from the 1997 SOHO roll, although at the time there was concern that the very high intensity modulations observed may have been due to time-variability instead of due to polarization effects. The 2001 data do not allow that interpretation, so something very peculiar may actually be going on in the solar corona.

Figure 1 - Intensity gradients above the limb (click on Figure for better resolution)

Figure 1 shows intensity gradients up to 220 arcsec above the limb measured before, during, and after the roll maneuver. Since the entire sequence took nearly two and a half days to complete, observations were made at the north solar pole to minimize effects of temporal variations. In all cases, the pre- and post-roll curves are nearly identical, confirming this lack of variability. The first three lines shown, He I 584A, O IV 555A, and O V 630A, are all formed at temperatures below logT = 5.4. All three have a break in their exponential intensity falloff at about 20-30 arcsec above the limb, indicative of a change between emission dominated by collisional excitation (with an Ne^2 dependence) to radiation from resonance scattering (which varies as Ne to the first power). This latter radiation should be linearly polarized in the plane parallel to the limb because of the asymmetric illumination field incident on the scattering ions. And because the CDS normal-incidence spectrometer is fed by sectors of a telescope with two grazing-incidence reflections, its response should then decrease at the 90-degree roll position for such polarized light, which is exactly what is observed.

This intensity modulation can not be due to some internal instrumental effect, because the other three lines plotted in Figure 1, Mg IX 368A, and Mg X 610 & 625A, show no such strong variation with roll angle, though their wavelengths are interspersed with the others. However, these latter three lines are all formed at temperature above logT = 6.0 with much larger density scale-heights, and so are expected to be collisionally dominated and thus un-polarized over the full range of coronal heights measured, again exactly matching what we see.

Figure 2 - Polarisation above the limb (click on Figure for better resolution)

Thus, these detections of the expected intensity gradients and polarization signatures ought to provide a unique and compelling confirmation of the two principal emission mechanisms thought to operate in the solar corona. The problem is that the measured intensity modulations are far too large to be explained by simple models, which predict response variations near 10% as a function of roll angle from heights at which resonance scattering dominates. Figure 2 shows that the measured responses for the three low-temperature lines were modulated by up to 80% or so, implying a source polarization near 100%. This is very difficult to understand, yet seems to confirm similar results from the 1997 SOHO roll maneuver. The sun apparently still has some surprises for those who dare explore her secrets.

GIS Slit Anomaly

We have finally been able to complete tests on the slit rastering problem and we are fairly confident that we can soon start to permit the use of GIS studies that do slit rastering. However we will be restricting the range of slit movements and this will apply to all slit numbers used by the GIS. Once we have decided on the useable range and looked into any impact on the raster definitions we will make a further announcement.
We are starting now a short evaluation period using the GIS SPECT_1 study; this should be finished by mid-November and hopefully slit rastering studies can be included in the science plan from then.
- Jeff Payne

CDS-SOFT Mailing List Archive

Ron Yurow has been working on a new interface to the CDS-SOFT list archive and this is now available online via the CDS web site:
The pages are still under development, but you are now able to access all mailings to the CDS-SOFT list and the old, discontinued CDS-DATA list.

From the CDS Operations Management Team in the Space Science & Technology Department at CCLRC Rutherford Appleton Laboratory
Site maintained by John Rainnie.
Last revised on Tuesday (22/Jan/2019) at 15:07.