High-Resolution Transmission Spectroscopy: Conclusion and Acknowledgement

Table of Links

• Abstract & Introduction
• Observation
• Data Reduction and Processing
• Model Spectra
• Cross-Correlation Method
• Results
• Clouds and Hazes
• Implications for JWST
• Conclusion and Acknowledgement
• Appendix & References

9. CONCLUSION

In this study, we searched for the atmosphere of the 1.3 R⊕ exoplanet GJ 486b using high-resolution transmission spectroscopy. Our resultant atmospheric constraints additionally offer an improved understanding of the possible atmospheres for terrestrial planets orbiting M-dwarf stars.

We observed three transits of GJ 486b with the spectrographs IRD, IGRINS, and SPIRou, and searched for absorption by its atmosphere with the high-resolution cross-correlation method. We searched for C2H2, CH4, CO, CO2, FeH, H2O, HCN, H2S, K, Na, NH3, PH3, SiO, TiO, and VO, but did not detect any robust atmospheric signals. Our best potential detection was H2O at the 3σ level, seen only in the IGRINS data set. However, this potential signal is likely an artifact of imperfectly removed H2O lines in the stellar spectrum. We suggest that it may be possible to improve the suppression of these stellar lines by using 3D models of stellar convection, as shown by Chiavassa & Brogi (2019).

Nevertheless, we derived informative upper limits on the abundances of many chemical species by performing signal injection and recovery tests. Our recovery tests allow us to rule out a clear H2/He-dominated atmosphere with solar molecular abundances to a confidence of >5σ, while also ruling out a clear 100% water atmosphere to a confidence of 3σ. Since a water-dominated atmosphere is often considered to be the most likely possibility for 3 M⊕ planets like GJ 486b (e.g., Ortenzi et al. 2020), our results could have important implications for planetary interior models.

We also investigated the implications of our findings for the upcoming JWST transit observations of GJ 486b. We found that these observations will be especially sensitive to the presence of CO2, but with weaker sensitivity to H2O, highlighting the complementary capabilities of high-resolution and JWST observations.

In summary, our results indicate that GJ 486b does not possess a cloud-free H/He-dominated atmosphere that has solar abundances. However, it may possess a secondary atmosphere with high mean molecular weight or a H2/He-dominated atmosphere with clouds. Our findings provide further evidence suggesting that terrestrial planets orbiting M-dwarf stars experience significant atmospheric loss.

ACKNOWLEDGMENTS

We thank the anonymous reviewer for constructive comments. We are also grateful to Hajime Kawahara for helpful suggestions.

This research is based [in part] on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawaii.

This work used the Immersion Grating Infrared Spectrometer (IGRINS) that was developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the Mt. Cuba Astronomical Foundation, of the US National Science Foundation under grants AST-1229522 and AST-1702267, of the McDonald Observatory of the University of Texas at Austin, of the Korean GMT Project of KASI, and of the Gemini Observatory.

Based on observations obtained at the international Gemini Observatory, a program of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), the National Research Council (Canada), Agencia Nacional de Investigaci´on y Desarrollo (Chile), Ministerio de Ciencia, Tecnolog´ıa e Innovaci´on (Argentina), Minist´erio da Ciˆencia, Tecnologia, Inova¸c˜oes e Comunica¸c˜oes (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea).

Based on observations obtained at the CanadaFrance-Hawaii Telescope (CFHT), which is operated from the summit of Maunakea by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. The observations at the Canada-France-Hawaii Telescope were performed with care and respect from the summit of Maunakea which is a significant cultural and historic site.

Based on observations obtained with SPIRou, an international project led by Institut de Recherche en Astrophysique et Plan´etologie, Toulouse, France.

This research has made use of the Extrasolar Planet Encyclopaedia, NASA’s Astrophysics Data System Bibliographic Services, and 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.

M.T. is supported by JSPS KAKENHI grant Nos. 18H05442, 15H02063, and 22000005. S. K. N. is supported by JSPS KAKENHI grant No. 22K14092.

J.D.T’s support for this work was provided by NASA through the NASA Hubble Fellowship grant #HSTHF2-51495.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5- 26555.

Facilities: 8.2 m Subaru telescope (IRD), 8.1 m Gemini-South telescope (IGRINS), 3.6 m Canada France Hawai’i Telescope (SPIRou)

Software: Astropy (Astropy Collaboration et al. 2013, 2018); SciPy (Virtanen et al. 2020); NumPy (Harris et al. 2020); petitRADTRANS (Molli`ere et al. 2019); SpectRes (Carnall 2017).