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Last modified: 14 June 2013

URL: http://cxc.harvard.edu/iris/bugs/index.html

Iris Bugs & Caveats

The following is a list of known limitations of the Iris software. If you encounter a software bug or analysis caveat that is not listed here, please report it to the VAO Helpdesk.

For troubleshooting the Iris installation, see the Troubleshooting page.

Multiple Users

Iris cannot currently be launched by multiple users on the same system.

Screen size and resolution

Some of the Iris windows will not be fully rendered on systems with a very low screen size or screen resolution, in particular netbooks.

Fitting Data with Custom Models

o When a spectral model component is deleted from the Custom Model Manager, the Sherpa model expression being used for fitting, shown in the Fitting Tool window, is not automatically updated; it needs to be edited manually by the user.

o In the Iris 2.0 version of sherpa_samp, custom template models cannot be mixed with other Sherpa model components. E.g., the model cannot be a template model multiplied by a power-law, or combined with any other component. The template model can only be used on its own.

o When fitting with a template model, the search method is automatically switched to a grid search over the templates included in the model. Interpolation between templates is not supported in the Sherpa 4.5 functionality which provides the fitting support for Iris v2.0.

o All custom table and template data files must be in ASCII format. Table and template models do not read from FITS files in Iris 2.0.

o The data contained in custom table and template models must have the same units that Iris uses internally for modeling and fitting. The x-axis units must be in Angstroms, and the y-axis units must be in erg/s/cm2/Angstrom. (These units match the internal units used for fitting in the original Specview, and which are still used in the Iris components derived from Specview. These components prepare data and model for fitting with Sherpa.)

o Iris fits in photon-flux density (photons/sec/cm^2/angstrom) and the best-fit parameters values will always be in terms of Angstroms, regardless of the user-defined unit settings.



o If one has the Model Window (the one with the list of models) and the Fit Window (the one with the optimization and statistics drop-down menu) both opened, some changes in the Model window (e.g. Thaw all, Freeze all) will not affect the Fit Window. The fit will be performed with an out-of-date model. If you have to change the model, it is preferable to close the Fit Window and open it again by clicking on "Fit" in the Model window.

Science Tools


o Integration Too few points in the region of interest of the Integrated SED will result in NaNs. In order to obtain good results you need to have a "good" density of points in the interval over which you are integrating. I am not sure I can define "good". However, problems arise when one interpolates a whole SED with more than 1.5k bins: with too many points the SED Viewer chokes.


Accessing Metadata

o The single-point metadata display first tab (marked "Point metadata" when one rightclicks on a plotted point and get a tree representation) seems to be broken and might be removed in the next release

o The Segment metadata table, both in single-point mode (right click on point) and entire SED mode (Metadata button) also uses some column names taken from that same old Spectrum Data Model. Column names in all-capitals are in fact FITS keywords that are associated to the corresponding utypes in that old Spectrum Data Model. Not all utypes have an associated FITS keyword, so in those cases, the software that builds the table uses as column name the 'name' of the corresponding field in the matadata structure. That may lead to entire sets of metadata to be ignored because these names may not be unique to each type. An example is the column named "Unit" in NED SEDs. There is a field named "Unit" in the Characterization.FluxAxis" element, and another field with same name in the Characterization.SpectralAxis" element. And likely in other places as well. There is no way for the table-building software to tell apart one from the other, once they are taken out of context (that is, striped out from the fully qualified type). Thus the software currently is retaining the last one it finds when traversing the metadata tree. For the interim solution I put in this release for the missing characterization entries, I used in the characterization spatial and time axis columns the fully qualified utype as column name. That is not very practical for the user (the strings are too long), but ensures unambiguous names, and also ensures that every utype gets its own column.

o Handling of other elements in the same table, such as SpectralAxis and FluxAxis, is still done by the old FITS/element name mapping.

Missing error bars

o Spectral coordinate errors are ignored if present in the input SED data. This means that errors on the X axis are not displayed nor taken into account for modeling.

Unexpected changes to data display

o Model components which are deleted in the Fit -> Component window, are not removed automatically from the model expression.

o In the window(s) that give individual access to spectral model parameters (double click on a row with a spectral component in the list displayed by the Fitting Tool), the Apply button is used just to apply changes in the Fit check box. Any other change, achieved by typing a value in a numeric or text field, is immediately applied as soon as the Return/Enter key, or the Tab key, are pressed. The change is also applied if, right after typing the new value, the mouse cursor is clicked on another field.

o When the user deletes a model component in the model editor window, Iris automatically renames and renumbers the remaining model components. This may oblige the user to then rewrite the model expression. For example, if the user creates the models:

and defines the model expression as "c2+c3", then the model that is fit to the data is a broken power-law plus a log-parabola model. If the user deletes the power-law component c1, then the remaining models are automatically renamed:
The model expression, however, remains "c2+c3" now a log-parabola model plus a model component that does not exist. The user must rewrite the model expression as "c1+c2" before proceeding with the fit.

Last modified: 14 June 2013
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