A guide to accessing and analyzing EIS data#
This guide describes how to access, calibrate and derive scientific results from the EIS instrument on Hinode. For a description of EIS and its observing modes please consult the instrument paper, Culhane et al. (2007)
, and the MSSL Science Centre webpage.
Tutorial#
The sections below describe individual steps in going from finding data to deriving scientific results. For new users tutorials are provided that show how to process example data-sets and derive results.
Tutorial for narrow slit data (1", 2" slits)
Tutorial for slot data (40", 266" slits)
Searching and downloading EIS data#
There are several methods for searching and downloading EIS data and these are summarized below. Follow the links to find more details.
Hinode Science Data Centre Europe
Contains all of the Hinode data and has very flexible search tools.
MSSL Science Centre
EIS/XRT/SOT data all available. View thumbnails/movies for EIS data set; uses SQL for flexible searches.
Calibrating EIS data#
Calibration of EIS data is performed with a single IDL routine, EIS_PREP, which converts a level-0 FITS file (raw data) to a level-1 FITS file (calibrated data). Note that the data archives listed above do not distribute level-1 files, so the user needs to perform the calibration. It is highly recommended that the user perform calibration before browsing the data as detector artifacts called warm pixels make browsing the raw data difficult.
Detailed description of eis_prep processing steps
Taking a quick-look at your data#
For browsing a data-set there are several 'quicklook' tools available that can be accessed by first calling a single IDL widget called XFILES:
IDL> xfiles
The widget allows you to choose an EIS file by manually typing in the path to the EIS file. Make sure to change 'eis_l0_*' to 'eis_l1_*' in the 'Set search filter' box to look for level-1 files rather than level-0 files. After confirming your selection a new widget called XCONTROL pops up which allows the user to access the five quicklook tools:
Detector - displays detector images.
Browser - allows user to browse the 3D data cubes (wavelength-X-Y) obtained from narrow slit observations.
Spectroheliogram - for a specified line shows a solar-Y vs. wavelength plot for each exposure.
Whisker - for a specified line shows a solar-X vs. wavelength plot for each exposure.
Intensity map - for a specified line shows an intensity image.
EIS objects and structures#
After you have calibrated your data with eis_prep and had a quick-look at the contents you will be ready to do more detailed analysis from the IDL command line. There are two options:
- Read all EIS data into an IDL object
- Read an individual wavelength window into an IDL structure (EIS_GETWINDATA)
Many of the EIS analysis routines make use of the EIS_GETWINDATA structures, and so this is generally recommended.
Narrow slit data (1", 2" slits)#
The 1" and 2" slits return emission line spectra and a basic task for such data-sets is to fit Gaussians to the emission lines to return intensity, centroid and width information. Gaussian fitting routines available to EIS users are described below. Interpretation of centroids and widths is hampered by certain instrumental effects and these are dealt with in the sections below.
Gaussian fitting routines#
Intensity maps#
Velocity maps#
Line width maps#
Line ratio maps and density diagnostics#
Slot data (40", 266" slits)#
The EIS slots produce images rather than spectra, and the most common application will be to produce movies from the slot rasters in a range of emission lines. Diagnostics are possible with the slots, however, by taking ratios of images and temperature and density diagnostics are described below.
Making movies#
Temperature diagnostics#
Density diagnostics#
Pointing and co-alignment#
Most EIS users will be analyzing data-sets from multiple instruments and so it is necessary where an EIS raster is positioned relative to the other instruments. Usually the pointing information within an EIS file will not be good enough to accurately co-align data-sets and so cross-correlation will be necessary.
How to get the most accurate EIS coordinates#
EIS and IDL maps#
The set of IDL map software of D. Zarro is a popular means for handling solar image data. The situation is more complicated for EIS than imaging instruments as an image can be an intensity, velocity or line width map. EIS maps are generated from EIS data objects as follows (in the case of a velocity map from Fe XII 195.12):
IDL> obj=obj_new('eis_data', filename)
IDL> m=obj_new('eis_moment',obj,iwin=195.12)
IDL> mmap=m->mk_eis_map(195.12,/vel)
The output mmap is in the standard format accepted by the map software.
To generate an intensity map use keyword /int and for a line width map use /wid. When the 'eis_moment' object is created (step 2) a widget will pop up allowing you to define the spectral region containing the emission line. Moments are used to generate the velocity and line widths which ensures quick results. You can use Gaussian fitting by giving the additional keyword fit='gauss' in step 2 for the eis_moment call.