Precision Doppler spectroscopy serves as an important tool for Radial Velocity (RV) measurements by observing Doppler shift in the stellar spectrum, which are used for various applications. Passively stabilized Fabry-Perot (FP) etalon based wavelength calibration is one of the techniques used for Doppler spectroscopy. The FP is kept in a pressure and temperature-stabilized environment for it to produce equispaced transmission lines. Since the FP is stable and the line shape is invariant across wavelength pass band, they can be used to determine the spectrograph’s instrumental artifacts and hence analyze spectrograph performance. Knowledge of instrument effects also helps in better prediction of the wavelength calibration model for the spectrograph. We have tested a passively stabilized FP on Vainu Bappu Telescope (VBT) Echelle spectrograph and Hanle Echelle spectrograph (HESP) and observed field curvature and distortion in both. We are analyzing the artifacts introduced and correcting for the same using image processing methods to compensate for the same in wavelength calibration model developed for the FP-based calibrator.
Precision Doppler spectroscopy serves as an important tool for Radial Velocity (RV) observations of stars. High precision spectroscopy is bound by two major challenges, first being the instrument instability which is mainly caused by temperature and pressure variations and second, the limitations imposed by traditional wavelength calibration methods. In this work we report our progress on the development of a passively stabilized Fabry-Perot (FP) calibrator. We have designed and built an air-spaced etalon with 30 GHz free spectral range for accurately tracking the short-term drift of our high resolution (R = 60,000) Echelle spectrograph on Himalayan Chandra Telescope (HCT), Hanle. Instrument is built using off-the-shelf components, with the required temperature and pressure stability being achieved in initial test runs. For transporting light in and out of the vacuum system without incurring losses at fiber interconnects, we have used a simple way to insert a FC/APC connectorized fiber into the flange. We also present the results of transmission spectra of the FP taken with high resolution Fourier Transform Spectrometer.
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