CDS Exercise #2

Title: Transition region intensities and velocities

Objective: To derive intensities and velocities from the transition region OV line.

Data: CDS synoptic raster from March 1998

Fits data file: s10693r02

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

Suggested menu:

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.

Calibrate the dataset using ergs/steradian as the output unit

Check the units by

Check which data window contains the OV line

Note that the OV data are in window number 3 and the window is 18 pixels wide and starts at detector pixel 989. Extract the OV data

Get a wavelength array to go with the OV spectrum

You should also investigate the routine gt_spectrum which can be used to extract a spectrum and wavelength array.

Average the spatial coordinates and plot the mean OV spectrum

Fit a single gaussian with linear background to the mean profile. Overplot the fit and print the fitted parameters

By creating a small IDL procedure, or on the command line, do the same fit for each pixel in the original OV data set and by saving the parameters create intensity, line-centroid and line-width maps. You may need to set a minimum intensity for the fit to avoid spurious fits. Eliminate any parameters that result from bad profile fits giving them a value that can be later specified as a 'missing' value.

The velocity map in particular will have systematic gradients both N/S and E/W owing to the tilt of the spectral line on the detector and the imaging of the scan mirror respectively. Derive corrections for these.

Translate the wavelength centroid map to a velocity map and look for any correlations between the map parameters.

Derive distributions for the map values. Investigate the shape of the intensity distribution.