Accurate Group Delay Measurement for Radial Velocity Instruments Using the Dispersed Fixed Delay Interferometer Method

TL;DR

This paper presents two methods for accurately measuring and calibrating the group delay in dispersed fixed-delay interferometers, enhancing the precision of radial velocity measurements for exoplanet detection.

Contribution

It introduces and compares two effective methods for group delay measurement and calibration in DFDI instruments, improving their precision and reliability.

Findings

Both methods achieve adequate precision for current RV measurements.

The methods enable submeter-precision Doppler measurements.

They serve as standard procedures for PV-scale calibration.

Abstract

The dispersed fixed-delay Intereferometer (DFDI) method is attractive for its low cost, compact size, and multiobject capability in precision radial-velocity (RV) measurements. The phase shift of fringes of stellar absorption lines is measured and then converted to an RV shift via an important parameter, phase-to-velocity scale (PV scale), determined by the group delay (GD) of a fixed-delay interferometer. Two methods of GD measurement using a DFDI Doppler instrument are presented in this article: (1) GD measurement using white-light combs gen- erated by the fixed-delay interferometer and (2) GD calibration using an RV reference star. These two methods provide adequate precision of GD measurement and calibration, given the current RV precision achieved by a DFDI Doppler instrument. They can potentially be used to measure GD of an fixed-delay interferometer for submeter- precision Doppler measurement with a DFDI instrument. Advantages and limitations of each method are discussed in detail. The two methods can serve as standard procedures of PV-scale calibration for DFDI instruments and cross- checks for each other.