CDS Exercise #1

Title: Densities in an Active Region Loop

Objective: By using line ratios derive the density in different locations of an AR loop

Data: CDS full spectrum raster taken on 28-Apr-96. Fits data file: s765r00

Note: information on all the routines used can be obtained from the on-line help procedures.

Read the data into a CDS data structure

To allow the software to recognise missing data, set a flag. Remember it is still necessary on some general routines to include the missing value explicitly.

Remove cosmic ray events (this step may be omitted if it takes too long).

Note: If this cosmic ray cleaning process or the next calibration process takes too long on your current setup, an already cleaned and calibrated dataset can be restored from an IDL saveset, ie.

will make the dataset 'data' available within your IDL session.

This dataset consists of 10 exposures stepped in solar-x. For each exposure the complete NIS1 and NIS2 spectra have been recorded. Each consists of 1024 pixels in the wavelength dimension. You can explore the data structure with the quicklook program

Although some analysis can be done within that program, for the purpose of this exercise exit dsp_menu and proceed to calibrate the dataset using ergs/ster/sec/cm ² as the output unit and check the units are as required.

To view any solar structures present in the field of view create a 2-d spatial image by integrating over a wavelength range. eg use wavelength limits applicable to the SiX 347A line.

and display the image

Adjust the plot window and/or the data plotted so you can determine which pixels contribute to a bright feature. eg

From this display determine which pixels in the original image you want to integrate to obtain an average spectrum for the feature. Extract the NIS1 spectral bands from the original data

Pick out the relevant pixels (choose your own!) and average them into one spectrum and check its size

Create a wavelength array to go with the NIS1 spectrum

Read the documentation on the routine ezmgn, particularly in regard to the use of the cursor. Derive an intensity for the SiX 347.4 Å line (you will need to select a restricted wavelength range and fit more than one profile owing to the line blending). Line profiles of CDS data taken before the temporary loss of SOHO in June 1998 are well fitted by a simple Gaussian.

Rerun for the SiX 356.0 A line (wavelength range 354, 358) and record the derived intensity.

The intensity ratio of the two SiX lines as a function of density can be determined using the chianti_ne program.

Select the element, ion and wavelength range (340 Å to 360 Å). Calculate the line intensities in the wavelength range and select the contributing SiX lines from the list shown (Hint: this should be line 0 and lines 5 & 6) and calculate the ratio versus density plot using the "Plot ratio" button.

Determine the density given by your analysis results. Repeat for other areas of the raster.