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Title: Modelling high resolution Echelle spectrographs for calibrations: Hanle Echelle spectrograph, a case study
Authors: Anantha, Ch
Jones, D
Sivarani, T
Keywords: Astronomical spectrographs;Calibration;Instrument modeling;Physical model based calibrations
Issue Date: Jun-2015
Publisher: Springer
Citation: Experimental Astronomy, Vol. 39, No. 2, pp. 423-443
Abstract: We present a modelling scheme that predicts the centroids of spectral line features for a high resolution Echelle spectrograph to a high accuracy. Towards this, a computing scheme is used, whereby any astronomical spectrograph can be modelled and controlled without recourse to a ray tracing program. The computations are based on paraxial ray trace and exact corrections added for certain surface types and Buchdahl aberration coefficients for complex modules. The resultant chain of paraxial ray traces and corrections for all relevant components is used to calculate the location of any spectral line on the detector under all normal operating conditions with a high degree of certainty. This will allow a semi-autonomous control using simple in-house, programming modules. The scheme is simple enough to be implemented even in a spreadsheet or in any scripting language. Such a model along with an optimization routine can represent the real time behaviour of the instrument. We present here a case study for Hanle Echelle Spectrograph. We show that our results match well with a popular commercial ray tracing software. The model is further optimized using Thorium Argon calibration lamp exposures taken during the preliminary alignment of the instrument. The model predictions matched the calibration frames at a level of 0.08 pixel. Monte Carlo simulations were performed to show the photon noise effect on the model predictions.
Description: Restricted Access
The original publication is available at
ISSN: 0922-6435
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Appears in Collections:Publications based on data from IAO, Hanle
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