Measuring Stellar Radial Velocities with a Dispersed Fixed-Delay Interferometer

TL;DR

This paper demonstrates that a dispersed fixed-delay interferometer can measure stellar barycentric radial velocities with high precision, enabling large-scale surveys for exoplanets and stellar kinematics using modest spectral resolution.

Contribution

It introduces a method using a Michelson interferometer coupled with a spectrograph for precise radial velocity measurements at R ~ 5100, suitable for multi-object surveys.

Findings

Achieved radial velocity precision of 0.047 km/s with iodine calibration.

Demonstrated the feasibility of multi-object radial velocity measurements (~500 stars/night).

Enabled large-scale stellar kinematic surveys for galactic studies.

Abstract

We demonstrate the ability to measure precise stellar barycentric radial velocities with the dispersed fixed-delay interferometer technique using the Exoplanet Tracker (ET), an instrument primarily designed for precision differential Doppler velocity measurements using this technique. Our barycentric radial velocities, derived from observations taken at the KPNO 2.1 meter telescope, differ from those of Nidever et al. by 0.047 km/s (rms) when simultaneous iodine calibration is used, and by 0.120 km/s (rms) without simultaneous iodine calibration. Our results effectively show that a Michelson interferometer coupled to a spectrograph allows precise measurements of barycentric radial velocities even at a modest spectral resolution of R ~ 5100. A multi-object version of the ET instrument capable of observing ~500 stars per night is being used at the Sloan 2.5 m telescope at Apache Point Observatory for the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS), a wide-field radial velocity survey for extrasolar planets around TYCHO-2 stars in the magnitude range 7.6<V<12. In addition to precise differential velocities, this survey will also yield precise barycentric radial velocities for many thousands of stars using the data analysis techniques reported here. Such a large kinematic survey at high velocity precision will be useful in identifying the signature of accretion events in the Milky Way and understanding local stellar kinematics in addition to discovering exoplanets, brown dwarfs and spectroscopic binaries.