Last modified: December 2020

AHELP for CIAO 4.13


Context: concept


Chandra Interactive Analysis of Observations


The remarkable science capabilities of the Chandra X-ray Observatory demanded new, flexible, multi-dimensional, software to analyze the data it returned. The result is CIAO - the Chandra Interactive Analysis of Observations - a system that has proven itself useful for the analysis of data from other, non-X-ray missions, because of the mission independence that is the basis of the CIAO design. This document provides an introduction to the CIAO software; more information is available from the CIAO website and via CIAO's command-line help system, ahelp (see "ahelp ahelp").

Introduction to CIAO Tools

CIAO is a data analysis system written for the needs of users of the Chandra X-ray Observatory. Because Chandra is the first mission with 4-dimensional data (2 spatial, time, energy) in which each dimension has many independent elements, CIAO was built to handle N-dimensional data without concern about which particular axes were being analyzed. Also, apart from a few Chandra instrument tools, CIAO is mission independent.

In order to allow users of Chandra data to use pre-existing tools, all CIAO tools read and write several formats, including FITS tables (which includes event files), ASCII formats, and FITS images.

CIAO also needed to be able to filter down and project the 4-D Chandra event data to managable sizes and convenient arrays. This has to be done flexibly, so we have built all CIAO tools to take a `filtering and binning' specification on the command line, making use of a general purpose `regions' syntax. See "ahelp dm" for information on the Data Model that makes all this possible.

Since Chandra data can be sliced and diced in so many ways, and because the Chandra calibration is spatially and energy dependent, we needed to keep track of just how the data had been filtered and binned, which we do in a `data subspace'. The tools keep track of this subspace automatically and allow users to review previous data processing. See "ahelp subspace".

The CIAO design allows close interconnection of tools. For example, the output of any of the source DETECT programs can be fed into dmextract to create a summed spectrum which can then be fit in Sherpa.

Modeling and Fitting

The modeling and fitting tool Sherpa is central to the CIAO system. Sherpa performs forward fitting of models to data in N-dimensions. Refer to "ahelp sherpa" and the Sherpa website for complete details.

Altogether CIAO is a powerful system for the analysis of all types of data.

Further information:

Changes in CIAO 4.13

Removal of peg and taskmonitor

The peg and taskmonitor Graphical User Interface tools have been removed in CIAO 4.13. The "Analysis Menu" has been removed from the prism GUI tool.

DS9 and prism-like capabilities

DS9 version 8.2, included in CIAO 4.13, contains a number of improvements to its support for ploting data, including a new "Prism" mode which can be selected either from the File/Prism... menu item or by starting DS9 with the -prism flag:

unix% ds9 -prism

or, to load a specific file (in this case "tbl.fits"),

unix% ds9 -prism tbl.fits

See Also

coords, level, pileup, times
autoname, ciao-install, ciaorc, history, parameter, stack, subspace
dm, dmascii, dmbinning, dmfiltering, dmmasks, dmopt, dmregions