Simulations for Planning Next-Generation Exoplanet Radial Velocity Surveys

Abstract

Future direct imaging missions such as HabEx and LUVOIR aim to catalog and characterize Earth-mass analogs around nearby stars. The exoplanet yield of these missions will be dependent on the frequency of Earth-like planets, and potentially the a priori knowledge of which stars specifically host suitable planetary systems. Ground or space based radial velocity surveys can potentially perform the pre-selection of targets and assist in the optimization of observation times, as opposed to an uninformed direct imaging survey. In this paper, we present our framework for simulating future radial velocity surveys of nearby stars in support of direct imaging missions. We generate lists of exposure times, observation time-series, and radial velocity time-series given a direct imaging target list. We generate simulated surveys for a proposed set of telescopes and precise radial velocity spectrographs spanning a set of plausible global-network architectures that may be considered for next generation extremely precise radial velocity surveys. We also develop figures of merit for observation frequency and planet detection sensitivity, and compare these across architectures. From these, we draw conclusions, given our stated assumptions and caveats, to optimize the yield of future radial velocity surveys in support of direct imaging missions. We find that all of our considered surveys obtain sufficient numbers of precise observations to meet the minimum theoretical white noise detection sensitivity for Earth-mass habitable zone planets, with margin to explore systematic effects due to stellar activity and correlated noise.

Impact of Correlated Noise on the Mass Precision of Earth-analog Planets in Radial Velocity Surveys

“…In this work, we build on the results of Newman et al (2022) by including a more realistic model for correlated noise due to stellar activity, granulation, and oscillation in the calculation of planet-mass precision. We choose GP noise models for each of the three key mechanisms responsible for stellar variability, following the prescription of activity in Gilbertson et al (2020b) and the model for oscillations and granulation in Pereira et al (2019).…”

“…An advantage of the noise models in this work is that we scale granulations and oscillations based on stellar properties and use the GP formulation of these signals to construct the covariance matrix for a simulated set of observations, rather than assuming independent observations. In Section 2 we summarize the simulated EPRV surveys from Newman et al (2022). In Section 3 we describe the GP covariance kernels used in this work, which are necessary for the calculation of the mass precision outlined in Section 4.…”

“…With this idea in mind, the NASA/NSF EPRV Working Group was established to study the feasibility of a large-scale RV survey to detect and precisely measure the masses of Earthanalogs in support of future direct imaging missions, such as LUVOIR or HabEx (Newman et al 2022). One focus of the working group was to explore the specific design of such a survey, including telescope size, longitudinal coverage, and instrument capabilities, decisions that affect not only the science results of the mission but also the required cost to build and operate.…”

“…One focus of the working group was to explore the specific design of such a survey, including telescope size, longitudinal coverage, and instrument capabilities, decisions that affect not only the science results of the mission but also the required cost to build and operate. To fully explore the impact of these decisions on the scientific goals to measure precise masses, Newman et al (2022) investigated 10 "architectures"-defined to encompass all decisions about telescope size, observing plan, instrument, longitudinal coverage, etc.-and simulated a 10 yr survey of ∼100 nearby stars that are likely targets for future direct imaging missions. The promising results of these simulations found that multiple architectures could measure the masses of HZ Earth-analogs to better than 10%, under optimistic assumptions for the mitigation of stellar variability.…”

“…The survey simulations carried out for the EPRV working group simulation (Newman et al 2022) were made under optimistic assumptions, assuming that each RV measurement has uncertainty dominated by photon noise and/or instrumental precision and that the measurement noise for each observation is independent and uncorrelated. The most straightforward interpretation of the results is that it assesses how RV surveys would perform if surveying stars with no intrinsic stellar variability (and any instrumental noise is uncorrelated).…”