The ∼50 Myr Old TOI-942c is Likely on an Aligned, Coplanar Orbit and Losing Mass

Creators: Teng 滕, Huan-Yu 环宇^{1, 2}; Dai 戴, Fei 飞^{3, 4}; Howard, Andrew W.⁴; Isaacson, Howard^{5, 6}; Rubenzahl, Ryan A.⁴; Angelo, Isabel⁷; Polanski, Alex S.⁸

1. National Astronomical Observatories
2. Korea Astronomy and Space Science Institute
3. University of Hawaii at Manoa
4. California Institute of Technology
5. University of California, Berkeley
6. University of Southern Queensland
7. University of California, Los Angeles
8. University of Kansas

Abstract

We report the observation of the transiting planet TOI-942c, a Neptunian planet orbiting a young K-type star approximately 50 Myr years old. Using the Keck/High Resolution Echelle Spectrometer, we observed a partial transit of the planet and detected an associated radial velocity anomaly. By modeling the Rossiter–McLaughlin effect, we derived a sky-projected obliquity of |λ|=24_(−14)^(+14) degrees, indicating TOI-942c is in a prograde and likely aligned orbit. Upon incorporation of the star's inclination and the planet's orbital inclination, we determined a true obliquity for TOI-942c of ψ < 43° at 84% confidence, while dynamic analysis strongly suggests TOI-942c is aligned with stellar spin and coplanar with the inner planet. Furthermore, TOI-942c is also a suitable target for studying atmospheric loss of young Neptunian planets that are likely still contracting from the heat of formation. We observed a blueshifted excess absorption in the Hα line at 6564.7 Å, potentially indicating atmospheric loss due to photoevaporation. However, due to the lack of preingress data, additional observations are needed to confirm this measurement.

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

H.Y.T. appreciates the support by the EACOA/EAO Fellowship Program under the umbrella of the East Asia Core Observatories Association. This research is supported by the National Natural Science Foundation of China (NSFC) under grant No. 12073044 and U2031144. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. We thank the time assignment committees of the University of California, the California Institute of Technology, NASA, and the University of Hawai'i for supporting the TESS-Keck Survey with observing time at the W. M. Keck Observatory. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff for support of HIRES and remote observing. We recognize and acknowledge the cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are deeply grateful to have the opportunity to conduct observations from this mountain.

Facilities

- Keck:I, TESS - , Exoplanet Archive - .

Software References

Batman (L. Kreidberg 2015), Emcee (D. Foreman-Mackey et al. 2013), EXOFAST (J. Eastman et al. 2013), Isoclassify (D. Huber et al. 2017), lmfit (M. Newville et al. 2014), SpecMatch (E. A. Petigura 2015; S. W. Yee et al. 2017).

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