Primary Velocity and Orbital Phase Effects on Planetary Detectability from Small Epoch Number Data Sets

TL;DR

This study investigates how the timing of observations affects the ability to detect exoplanets using high-resolution spectroscopy, finding that observing when the star's velocity is near zero enhances detection success.

Contribution

It demonstrates that selecting observation epochs with near-zero stellar velocity significantly improves planetary detection in few-epoch spectroscopic data sets.

Findings

Epochs with near-zero primary velocity increase detection significance.

Careful planning of observation timing reduces structured noise.

Targeting specific velocities enhances planetary signal detection.

Abstract

Cross correlation analyses of high resolution spectroscopic data have recently shown great success in directly detecting planetary signals and enabling the characterization of their atmospheres. One such technique aims to observe a system at multiple epochs and combine the measured planetary radial velocities from each epoch into a measurement of the planetary Keplerian orbital velocity $K_p$, constituting a direct detection of the planetary signal. Recent work has shown that in few-epoch ($\sim$5) data sets, unintended structure can arise at a high level, obscuring the planetary detection. In this work, we look to simulations to examine whether there are ways to reduce this structured noise in few-epoch data sets by careful planning of observations. The choice of observation date allows observers to select the primary (stellar) velocity - through a set systemic velocity and chosen barycentric velocity - and the planetary orbital phase, and so we focus on the effects of these two parameters. We find that epochs taken when the primary velocity is near zero, and the stellar lines remain relatively fixed to the telluric rest-frame, greatly reduce the level of structured noise and allow for much stronger planetary detections, on average more than twice the significance of detections made with epochs using randomly selected primary velocities. Following these results, we recommend that observers looking to build up high-resolution multi-epoch data sets target nights when their system has a near-zero primary velocity.