# Frequency-comb-calibrated Laser Heterodyne Radiometry for Precision Radial Velocity Measurements

## TL;DR

A new method using laser heterodyne radiometry and frequency comb calibration enables precise solar radial velocity measurements with high accuracy and stability.

## Contribution

A novel approach combining laser heterodyne radiometry with frequency comb calibration achieves sub-meter-per-second radial velocity precision.

## Key findings

- The system achieves high spectral resolution (∼800,000) and signal-to-noise ratio (∼2600).
- Sub-meter-per-second radial velocity precision is achieved over single-day measurements.
- The method demonstrates long-term stability suitable for studying stellar variability.

## Abstract

Disk-integrated observations of the Sun provide a unique vantage point to explore
stellar activity and its effect on measured radial velocities. Here we report a
new approach for disk-integrated solar spectroscopy and evaluate its
capabilities for solar radial velocity measurements. Our approach is based on a
near-infrared laser heterodyne radiometer (LHR) combined with an optical
frequency comb calibration, and we show that this combination enables precision,
disk-integrated solar spectroscopy with high spectral resolution (∼800,000),
high signal-to-noise ratio (∼2600), and absolute frequency accuracy. We use the
comb-calibrated LHR to record spectra of the solar Fe i 1565 nm
transition over a 6-week period. We show that our measurements reach
sub-meter-per-second radial velocity precision over a single day, and we use
daily measurements of the absolute line center to assess the long-term stability
of the comb-calibrated LHR approach. We use this long-duration data set to
quantify the principal uncertainty sources that impact the measured radial
velocities, and we discuss future modifications that can further improve this
approach in studies of stellar variability and its impact on radial velocity
measurements.