Sherpa "Watch Out" Page

This page lists noteworthy items and issues about the Sherpa 4.1 release. For the full list of known issues please review the:

• Sherpa bug list
• Sherpa Frequently Asked Questions page

Running Sherpa

IPython Packaged with CIAO OTS

CIAO includes IPython in the CIAO OTS directory which is used by Sherpa and ChIPS to provide command-line user interfaces. These programs create an IPython profile in the directory $HOME/.ipython-ciao.

If IPython users want any personal customizations to be available when running CIAO, they will have to copy them from $HOME/.ipython to $HOME/.ipython-ciao.

User Python modules must not have the same name as CIAO/Sherpa modules.

When loading a module in Python, Python first looks in the current working directory for this module, then in the directories listed in the PYTHONPATH environment variable. Therefore, if you have a script named 'sherpa.py' in your current working directory, for example, Sherpa will fail to load because the script ./sherpa.py is loaded, not the code in the module ${ASCDS_INSTALL}/lib/python2.5/site-packages/sherpa. Please ensure that the names of your Python scripts do not exactly match those of Python modules packaged with CIAO.

General

'atten' model parameter values are erroneously returned in energy units

Currently, the Sherpa atten (S-Lang or Python help) model erroneously returns model parameter values in energy units, as the internal grid of this model is defined in Angstroms. To use this model in wavelength analysis, see the atten bug page for a workaround.

Model evaluation is always based on an energy grid

When Sherpa 4.1 evaluates a model for an input PHA data set, model parameter values are always returned in units of keV (energy). Model parameters are computed using an energy grid, regardless of whether the set_analysis("wavelength") (S-Lang or Python help) command has been issued. See the bug page for set_analysis for a workaround.

Data Caveats

Spectral analyses of ACIS data with a limited pulse-height range

Before fitting ACIS data sets with restricted pulse-height ranges, please read the CIAO caveat "Spectral analyses of ACIS data with a limited pulse-height range."

A complete list of caveats for Chandra data is available on the CIAO Data Caveats webpage.