New spectrograph data pipeline yields high quality results
6 January 2014
Integral field spectroscopy provides a remarkable observational window into the most complex astrophysical objects. By obtaining spectra at multiple contiguous positions, the spatially resolved structure of star-formation and chemical enrichment can be revealed for complex systems such as galaxies and gaseous nebulae. The Wide Field Spectrograph (WiFeS) on the Australian National University (ANU) 2.3m telescope is one of the world's most sensitive integral field spectrographs and the workhorse for many Australian spectroscopic efforts including supernova classification, exoplanet characterisation, stellar structure measurements, and galaxy emission line mapping. A paper led by CAASTRO researcher Michael Childress (ANU) presents a new data reduction pipeline PyWiFeS which enables rapid and scriptable data reduction for WiFeS.
WiFeS "slices" a 25"x38" field of view into 25 1"-wide "slitlets" by means of a fanned segmented mirror. Light in each slitlet is dispersed in the same manner as a longslit spectrograph, but ultimately yields a data volume 25 times that of a standard longslit spectrograph. Calibrating this volume of data is a challenging task, but one well suited to recursive software techniques such as PyWiFeS that accomplishes end-to-end processing of WiFeS data with minimal user interaction by utilising an abstract metadata format and a carefully constructed data reduction script.
PyWiFeS also marks the implementation of several new innovative data processing routines which provide optimal data quality. These include scattered light corrections for flat-field calibrations, a WiFeS-tailored implementation of Laplacian kernel cosmic ray rejection, and a global detector wavelength solution based on an optical model of the instrument. The research team around Mike Childress made sure that PyWiFeS can be easily scripted to facilitate rapid data reduction, and the ANU supernova group, for instance, use it to classify and process new supernova data in under one minute from completion of detector readout.
by M. Childress
Data from a WiFeS observation of SN 2012ec in the nearby galaxy NGC 1084. The top left panel shows the full red camera data, illustrating the multiple slitlet configuration. The lower panel shows a zoom of the SN 2012ec trace in one slitlet, along with neighbouring emission lines from the SN host galaxy. The top right panel shows an image of the final data cube generated by summing the 3-dimensional data along the wavelength direction.
M. J. Childress, F. P. A. Vogt, J. Nielsen, R. G. Sharp in Astrophysics & Space Science (2014) "PyWiFeS: a rapid data reduction pipeline for the Wide Field Spectrograph (WiFeS)"