RV Measurements of Directly Imaged Brown Dwarf GQ Lup B to Search for Exosatellites

Creators: Horstman, Katelyn¹; Ruffio, Jean-Baptiste¹; Batygin, Konstantin¹; Mawet, Dimitri^{1, 2}; Baker, Ashley¹; Hsu, Chih-Chun³; Wang 王, Jason J. 劲飞¹; Wang 王, Ji 吉⁴; Blunt, Sarah³; Xuan, Jerry W.¹; Xin, Yinzi¹; Liberman, Joshua⁵; Agrawal, Shubh^{1, 6}; Konopacky, Quinn M.⁷; Blake, Geoffrey A.¹; Do Ó, Clarissa R.⁷; Bartos, Randall²; Bond, Charlotte Z.⁸; Calvin, Benjamin^{1, 9}; Cetre, Sylvain¹⁰; Delorme, Jacques-Robert^{1, 10}; Doppmann, Greg¹⁰; Echeverri, Daniel¹; Finnerty, Luke⁹; Fitzgerald, Michael P.⁹; Jovanovic, Nemanja¹; López, Ronald⁹; Martin, Emily C.¹¹; Morris, Evan¹¹; Pezzato, Jacklyn¹; Ruane, Garreth^{1, 2}; Sappey, Ben⁷; Schofield, Tobias¹; Skemer, Andrew¹¹; Venenciano, Taylor¹²; Wallace, J. Kent²; Wallack, Nicole L.¹; Wizinowich, Peter¹⁰

1. California Institute of Technology
2. Jet Propulsion Lab
3. Northwestern University
4. The Ohio State University
5. University of Arizona
6. University of Pennsylvania
7. University of California, San Diego
8. UK Astronomy Technology Centre
9. University of California, Los Angeles
10. W.M. Keck Observatory
11. University of California, Santa Cruz
12. Pomona College

Abstract

GQ Lup B is one of the few substellar companions with a detected cicumplanetary disk (CPD). Observations of the CPD suggest the presence of a cavity, possibly formed by an exosatellite. Using the Keck Planet Imager and Characterizer (KPIC), a high-contrast imaging suite that feeds a high-resolution spectrograph (1.9–2.5 µm, R∼35,000), we present the first dedicated radial velocity (RV) observations around a high-contrast, directly imaged substellar companion, GQ Lup B, to search for exosatellites. Over 11 epochs, we find a best and median RV error of 400–1000 m s⁻¹, most likely limited by systematic fringing in the spectra due to transmissive optics within KPIC. With this RV precision, KPIC is sensitive to exomoons 0.6%–2.8% the mass of GQ Lup B (∼30 M_(Jup)) at separations between the Roche limit and 65 R_(Jup), or the extent of the cavity inferred within the CPD detected around GQ Lup B. Using simulations of HISPEC, a high resolution infrared spectrograph planned to debut at W.M. Keck Observatory in 2026, we estimate future exomoon sensitivity to increase by over an order of magnitude, providing sensitivity to less massive satellites potentially formed within the CPD itself. Additionally, we run simulations to estimate the amount of material that different masses of satellites could clear in a CPD to create the observed cavity. We find satellite-to-planet mass ratios of q > 2 × 10⁻⁴ can create observable cavities and report a maximum cavity size of ∼51 R_(Jup) carved from a satellite.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

K.H. is supported by the National Science Foundation Graduate Research Fellowship Program under grant No. 2139433.

J.X. is supported by the NASA Future Investigators in NASA Earth and Space Science and Technology (FINESST) award #80NSSC23K1434.

Funding for KPIC has been provided by the California Institute of Technology, the Jet Propulsion Laboratory, the Heising-Simons Foundation (grants #2015-129, #2017-318, #2019-1312, #2023-4598), the Simons Foundation, and the NSF under grant AST-1611623.

The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We also wish to recognize the very important cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. K.H. wishes to acknowledge her settler status on the ancestral lands of the Gabrielino/Tongva people and recognizes that the astronomical observations in this paper were possible because of the dispossession of Maunakea from the Kanāka Maoli.

Facilities

Facility: Keck II (KPIC) - .

Software References

Software: Astropy²³(Astropy Collaboration et al. 2013, 2018, 2022), Matplotlib²⁴(J. D. Hunter 2007), PSIsim,²⁵RVSearch²⁶(L. J. Rosenthal et al. 2021), KPIC Data Reduction Pipeline²⁷(J.-R. Delorme et al. 2021), BREADS²⁸(J.-B. Ruffio et al. 2021; S. Agrawal 2022).

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