!!!Worksheet 2 - Calibrating EIS data (eis_prep)

In general the user should calibrate EIS data before he/she attempts to look it. This is because EIS data are affected by warm pixels on the CCD which make it difficult to study the images. The EIS calibration routine is called 'eis_prep'.

For the present worksheets we will analyze a data-set taken on 2006 December 9 at 11:30. After the file has been downloaded (Worksheet 1), we set

IDL> filename=’eis_l0_20061209_113031.fits’

(if you have downloaded the file to a directory different to the current working directory you will need to add the full file path). The standard call to eis_prep is:

IDL> eis_prep, filename, /default, /save, /retain, /quiet

The /save keyword results in two files being created in the user's directory which have the names:

eis_l1_20061209_113031.fits\\
eis_er_20061209_113031.fits

TIP: it is a good idea to compress these files with gzip and move them to a directory called /level1.

The first file is the level-1 EIS FITS file containing calibrated intensity arrays. The second file is the error file which contains the corresponding 1-sigma intensity errors for the arrays stored in the level-1 file.

Full details of the various keyword inputs to eis_prep are given in EIS Note #1, where detailed descriptions of the various steps performed by eis_prep are given.

One featue of eis_prep is that bad pixels in the data are flagged as 'missing'. These bad pixels can be due to cosmic ray hits, saturated pixels, dust particles on the detector, hot pixels and warm pixels. The latter are by far the most numerous, and described in more detail in EIS Note #6. Bad pixels are flagged only in the error file and are assigned a value of -100. The bad pixels in the level-1 file are replaced by a value interpolated from neighbouring pixels. More details about the effect of missing data on EIS data analysis and interpolation methods are given in EIS Note #13.