Appendix J: Glossary

*Component*- A part of a model.*Additive*- A component which produces a theoretical spectrum.*Multiplicative*- A component which produces multiplicative factors to apply to the current theoretical spectrum.*Convolution*- A component which modifies the current theoretical spectrum*Mixing*- If there are multiple datasets with separately calculated theoretical models this component modifies all of them simultaneously.

*Datagroup*- A set of observed spectra which will all be fit using the same model and parameter values.*Dataset*- The observed spectrum and its associated information.*Fit statistic*- The statistic used to determine the best fit value. The options are based on maximizing the likelihood.*Model*- The parameterized theoretical model for the source spectrum. There is a default unnamed model but additional named models can be defined.*Plotgroup*- A set of spectra which are summed together for plotting purposes only.*Response Model*- A model which modifies the response. At the moment this is limited to the gain.*Source*- In some observations several objects can contribute to the same spectrum. In this case XSPEC refers to them as different sources and each source can have its own model and response.*Table Model*- A model component stored as a FITS file containing model spectra tabulated on a grid of parameter values.*Test Statistic*- The statistic to provide the goodness-of-fit criterion after the parameters have been optimized based on the fit statistic