Exoplanets & Exomoons

Detecting Exomoons From Radial Velocity Measurements Of Self-luminous Planets: Application To Observations Of HR 7672 B And Future Prospects

By Keith Cowing
Status Report
February 26, 2023
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Detecting Exomoons From Radial Velocity Measurements Of Self-luminous Planets: Application To Observations Of HR 7672 B And Future Prospects
Exomoon detection limits around HR 7672 B with the Keck Planet Imager and Characterizer (KPIC) using the open-source python module RVsearch (Rosenthal et al. 2021). (Left) Periodogram of the RV times series shown in Figure 2 expressed a ∆BIC comparing a model with and a model without a planet. The empirical detection threshold is indicated in the legend. (Right) Exomoon completeness derived from injection and recovery tests. The periodogram and the completeness are shown for two cases: the single full night of observations on 07/04/2022 and all the available data including three additional epochs with 1-2 hours of data each. The variable conditions on 07/04/2022 led to HR 7672 B to not be detected during portions of the night, or in the RV precision to get significantly worse. By simulating RV time series, we estimate that the lost data only affected the final sensitivity by 20%. — astro-ph.EP

The detection of satellites around extrasolar planets, so called exomoons, remains a largely unexplored territory.

In this work, we study the potential of detecting these elusive objects from radial velocity monitoring of self-luminous directly imaged planets. This technique is now possible thanks to the development of dedicated instruments combining the power of high-resolution spectroscopy and high-contrast imaging.

First, we demonstrate a sensitivity to satellites with a mass ratio of 1-4% at separations similar to the Galilean moons from observations of a brown-dwarf companion (HR 7672 B; Kmag=13; 0.7″ separation) with the Keck Planet Imager and Characterizer (KPIC; R~35,000 in K band) at the W. M. Keck Observatory.

Current instrumentation is therefore already sensitive to large unresolved satellites that could be forming from gravitational instability akin to binary star formation. Using end-to-end simulations, we then estimate that future instruments such as MODHIS, planned for the Thirty Meter Telescope, should be sensitive to satellites with mass ratios of ~1e-4. Such small moons would likely form in a circumplanetary disk similar to the Jovian satellites in the solar system.

Looking for the Rossiter-McLaughlin effect could also be an interesting pathway to detecting the smallest moons on short orbital periods. Future exomoon discoveries will allow precise mass measurements of the substellar companions that they orbit and provide key insight into the formation of exoplanets. They would also help constrain the population of habitable Earth-sized moons orbiting gas giants in the habitable zone of their stars.

Jean-Baptiste Ruffio, Katelyn Horstman, Dimitri Mawet, Lee J. Rosenthal, Konstantin Batygin, Jason J. Wang, Maxwell Millar-Blanchaer, Ji Wang, Benjamin J. Fulton, Quinn M. Konopacky, Shubh Agrawal, Lea A. Hirsch, Andrew W. Howard, Sarah Blunt, Eric Nielsen, Ashley Baker, Randall Bartos, Charlotte Z. Bond, Benjamin Calvin, Sylvain Cetre, Jacques-Robert Delorme, Greg Doppmann, Daniel Echeverri, Luke Finnerty, Michael P. Fitzgerald, Nemanja Jovanovic, Ronald López, Emily C. Martin, Evan Morris, Jacklyn Pezzato, Garreth Ruane, Ben Sappey, Tobias Schofield, Andrew Skemer, Taylor Venenciano, J. Kent Wallace, Nicole L. Wallack, Peter Wizinowich, Jerry W. Xuan

Comments: Accepted to AJ (Jan 10, 2023)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2301.04206 [astro-ph.EP] (or arXiv:2301.04206v1 [astro-ph.EP] for this version)
Submission history
From: Jean-Baptiste Ruffio
[v1] Tue, 10 Jan 2023 20:59:21 UTC (1,183 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻