Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra

TL;DR

This paper introduces a novel method for extracting radial velocities from echelle spectra of rapidly rotating stars, enabling precise measurements despite broad spectral lines, with applications in binary detection and stellar kinematics.

Contribution

The authors develop a forward-modeling technique that simultaneously fits radial velocity shifts and blaze functions across all echelle orders for fast-rotating stars, improving measurement precision.

Findings

Achieved 0.5-2.0 km/s radial velocity precision per epoch.

Detected two new spectroscopic binaries and confirmed one known system.

Demonstrated the method's utility for binary detection and stellar studies.

Abstract

We present a technique to extract radial velocity measurements from echelle spectrograph observations of rapidly rotating stars ($V\sin{i} \gtrsim 50$ km s$^{-1}$). This type of measurement is difficult because the line widths of such stars are often comparable to the width of a single echelle order. To compensate for the scarcity of lines and Doppler information content, we have developed a process that forward-models the observations, fitting the radial velocity shift of the star for all echelle orders simultaneously with the echelle blaze function. We use our technique to extract radial velocity measurements from a sample of rapidly rotating A- and B-type stars used as calibrator stars observed by the California Planet Survey observations. We measure absolute radial velocities with a precision ranging from 0.5-2.0 km s$^{-1}$ per epoch for more than 100 A- and B-type stars. In our sample of 10 well-sampled stars with radial velocity scatter in excess of their measurement uncertainties, three of these are single-lined binaries with long observational baselines. From this subsample, we present detections of two previously unknown spectroscopic binaries and one known astrometric system. Our technique will be useful in measuring or placing upper limits on the masses of sub-stellar companions discovered by wide-field transit surveys, and conducting future spectroscopic binarity surveys and Galactic space-motion studies of massive and/or young, rapidly-rotating stars.