Spectral Calibration of VERVE

Abstract

With the exception of the transit method employed by the Kepler Space Telescope, the radial velocity (RV)technique has proven to be the most fruitful exoplanet detection method to date. High precision measurements with state-of-the-art equipment have achieved RV precision on the order of 0.5 m s^(−1). Given that Earth's induced RV on the sun is on the order of 10 cm s^(−1), this regime represents the next milestone on the path to finding Earth-like planets orbiting distant stars. We describe the Vacuum Extreme Radial Velocity Experiment (VERVE), a single mode fiber-fed high-resolution echelle spectrometer which integrates interferometry with spectroscopy with the aim of achieving RV precision at the 10 cm s^(−1) level, on par with the ESPRESSO spectrograph (Pepe et al., 2014 [1]). The addition of interferometry relaxes the spectral calibration requirement by several orders of magnitude. We detail the spectral calibration of VERVE, including the development of a precise forward model and a data reduction pipeline to facilitate spectral extraction. We examine the model's agreement with the spectra of various calibration sources and present the results of spectral extractions performed on 635 nm and 780 nm laser sources to demonstrate VERVE's spectroscopic capabilities. We note the 10 cm s^(−1) RV precision threshold for detecting Earth-like planets, and show that the ~ 2 pixel agreement we achieve is consistent with this requirement. We briefly introduce results pertaining to interferometry and conclude by describing the future stages of testing to prepare VERVE for novel RV measurements.

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