Echelle Spectra

This Chapter provides the basic information necessary to understand the echelle  package implemented in MIDAS. It includes the description of the reduction method and the system implementation, without reference to a particular instrument. A detailed description of the operation and relevant parameters for the different instruments supported are described in the corresponding Appendix . Tutorial examples are available in the system (command TUTORIAL/ECHELLE) and are also included in the Appendix so that users without previous experience in MIDAS could become familiar with the calibration procedures.

The package follows a very flexible scheme, where most of the reduction steps include several algorithms which can be dynamically chosen and some of the steps can be executed optionally. Experienced users could modify the scheme to adapt it to their data configuration. The methods described here are generally sufficient to cover a wide range of echelle formats. The ESO instruments supported by the package are CASPEC (Cassegrain Echelle Spectrograph), EFOSC(1+2), ECHELLEC, and EMMI.

The package provides a set of about 30 first-level basic commands to perform the reduction, most of them having the qualifier ECHELLE. These commands are structured in five main MIDAS procedures to perform complete steps of reduction. In Section we describe the algorithms used in the echelle reduction, i.e. the algorithms to find the position of the echelle orders, order extraction procedures, wavelength calibration and instrument response correction. In Section we include a brief outline of the different data formats involved in the reduction and a summary of the commands. Finally, the session parameters are detailed in Section

Note This chapter only provides a synopsis of the commands needed for the reduction of echelle spectra. It is important to realise that it can neither substitute the HELP information available for each command nor be exhaustive, especially not with regard to the usage of general utilities such as the MIDAS Table System, the AGL Graphics package, etc. Reduction steps which are not specific to echelle spectra are described in more detail in Chapter . The Appendix provides a practical approach to echelle reduction.

• Echelle Reduction Method
  • Input Data and Preprocessing
  • Retrieving demonstration and calibration data
  • General Description
• Order Definition
• Removal of particle hits
• Background Definition
  • Bivariate polynomial interpolation
  • Smoothing spline interpolation
  • Background estimate by filtering
  • Sky background definition
• Order Extraction
• Wavelength Calibration
  • General Description
  • The Echelle Relation
  • Estimating the angle of rotation
  • Identification loop
  • Resampling and checking the results
• Flat Field Correction
• Instrument Response Correction
  • Using a Standard Star
  • Fitting the Blaze Function
• Order Merging
• Implementation
  • The Session Manager
  • Image Formats
  • Table Formats
  • MIDAS Commands
• Session Parameters