OrCAS: Origins, Compositions, and Atmospheres of Sub-neptunes. I. Survey Definition

TL;DR

OrCAS is a survey aimed at understanding the origins, compositions, and atmospheres of sub-Neptunes by selecting suitable targets for atmospheric characterization through radial velocity and transit observations.

Contribution

This paper introduces the OrCAS survey, including its target selection metric, data analysis methods, and its role in expanding the sample of well-characterized sub-Neptunes.

Findings

Targeting 26 systems with transiting sub-Neptunes.

Performed light-curve fits and statistical validation.

Established a framework for future atmospheric studies.

Abstract

Sub-Neptunes - volatile-rich exoplanets smaller than Neptune - are intrinsically the most common type of planet known. However, the formation and nature of these objects, as well as the distinctions between sub-classes (if any), remain unclear. Two powerful tools to tease out the secrets of these worlds are measurements of (i) atmospheric composition and structure revealed by transit and/or eclipse spectroscopy, and (ii) mass, radius, and density revealed by transit photometry and Doppler spectroscopy. Here we present OrCAS, a survey to better elucidate the origins, compositions, and atmospheres of sub-Neptunes. This radial velocity survey uses a repeatable, quantifiable metric to select targets suitable for subsequent transmission spectroscopy and address key science themes about the atmospheric & internal compositions and architectures of these systems. Our survey targets 26 systems with transiting sub-Neptune planet candidates, with the overarching goal of increasing the sample of such planets suitable for subsequent atmospheric characterization. This paper lays out our survey's science goals, defines our target prioritization metric, and performs light-curve fits and statistical validation using existing TESS photometry and ground-based follow-up observations. Our survey serves to continue expanding the sample of small exoplanets with well-measured properties orbiting nearby bright stars, ensuring fruitful studies of these systems for many years to come.