The Impact of Stellar Surface Magnetoconvection and Oscillations on the Detection of Temperate, Earth-Mass Planets Around Sun-Like Stars

Abstract

Detecting and confirming terrestrial planets is incredibly difficult due to their tiny size and mass relative to Sun-like host stars. However, recent instrumental advancements are making the detection of Earth-like exoplanets technologically feasible. For example, Kepler and TESS photometric precision means we can identify Earth-sized candidates (and PLATO in the future will add many long-period candidates to the list), while spectrographs such as ESPRESSO and EXPRES (with an aimed radial velocity precision [RV] near 10 cm s −1 ) mean we will soon reach the instrumental precision required to confirm Earth-mass planets in the habitable zones of Sun-like stars. However, many astrophysical phenomena on the surfaces of these host stars can imprint signatures on the stellar absorption lines used to detect the Doppler wobble induced by planetary companions. The result is stellar-induced spurious RV shifts that can mask or mimic planet signals. This review provides a brief overview of how stellar surface magnetoconvection and oscillations can impact low-mass planet confirmation and the best-tested strategies to overcome this astrophysical noise. These noise reduction strategies originate from a combination of empirical motivation and a theoretical understanding of the underlying physics. The most recent predications indicate that stellar oscillations for Sun-like stars may be averaged out with tailored exposure times, while granulation may need to be disentangled by inspecting its imprint on the stellar line profile shapes. Overall, the literature suggests that Earth-analog detection should be possible, with the correct observing strategy and sufficient data collection.

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

“…Dumusque et al 2011;Cegla et al 2013Cegla et al , 2015Cegla et al , 2018Cegla et al , 2019Meunier et al 2015;Sulis et al 2016Sulis et al , 2017aChaplin et al 2019) for the Sun and other stars. More details can be found in the review by Cegla (2019). The impact of granulation on the use of standard statistical tools has been pointed out by Sulis et al (2017b), who proposed a new method (based on periodogram standardisation) to improve these tools, so far for a solar type star.…”

Spatially resolved spectroscopy across stellar surfaces. V. Observational prospects: Toward Earth-like exoplanet detection

“…Although the tiny amplitude induced by the Earth on the Sun amounts at most to only 0.1 m s −1 (e.g., Hall et al 2018), instrument precisions are now beginning to reach these levels (Blackman et al 2020;Brewer et al 2020;Cale et al 2019;Gilbert et al 2018;Langellier et al 2020;Lo Curto et al 2012;Metcalf et al 2019;Pepe et al 2014;Petersburg et al 2020;Probst et al 2020;Robertson et al 2019;Roy et al 2016;Strassmeier et al 2018a;Suárez Mascareño et al 2020;Wilken et al 2012;Zhao et al 2021) and they are design criteria for future instruments (Halverson et al 2016;Pasquini et al 2010;Plavchan et al 2019;Zerbi et al 2014). The main limitations are no longer technical but lie in understanding the complexities of atmospheric dynamics and spectral line formation, manifest both as a jitter of the apparent radial velocity and as a flicker in photometric brightness (Cegla 2019;Fischer et al 2016).…”

The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities

“…Solar-type stars will also exhibit granulation patterns, which arise from convection in the outer layers of the star (Dravins 1982;Lanza et al 2019;Kjeldsen & Bedding 1995;Lindegren & Dravins 2003;Nordlund et al 2009;Dumusque et al 2011b;Cegla et al 2018;Cegla 2019). Upflows in the middle of granulation cells appear blueshifted while the downflows in the narrow, dimmer edge regions appear redshifted.…”