2023-09-25 ミシガン大学
◆研究者は、星が観測に与える影響に焦点を当て、星からの干渉を考慮する必要性を強調しました。TRAPPIST-1は小さく冷たい太陽よりも40光年遠くにあり、2017年に7つの地球サイズの太陽系外惑星が発見され、地球外の生息環境を見つける可能性が高まりました。
◆この研究は、TRAPPIST-1 bの特性に関する重要な洞察を提供し、将来の観測プログラムに貢献するもので、太陽系外の惑星の大気とその生息可能性に関する幅広い理解に寄与します。
＜関連情報＞
- https://news.umich.edu/jwsts-first-spectrum-of-a-trappist-1-planet/
- https://iopscience.iop.org/article/10.3847/2041-8213/acf7c4
JWST/NIRISSによるTRAPPIST-1 bの大気探査：透過スペクトルにおける恒星の強い汚染の証拠 Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra
Olivia Lim, Björn Benneke, René Doyon, Ryan J. MacDonald, Caroline Piaulet, Étienne Artigau, Louis-Philippe Coulombe, Michael Radica, Alexandrine L’Heureux, Loïc Albert, Benjamin V. Rackham, Julien de Wit, Salma Salhi, Pierre-Alexis Roy, Laura Flagg, Marylou Fournier-Tondreau, Jake Taylor, Neil J. Cook, David Lafrenière, Nicolas B. Cowan, Lisa Kaltenegger, Jason F. Rowe, Néstor Espinoza, Lisa Dang, and Antoine Darveau-Bernier
The Astrophysical Journal Letters Published:2023 September 22
DOI:10.3847/2041-8213/acf7c4
Abstract
TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth atmospheric studies. Each TRAPPIST-1 planet has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with JWST/MIRI are consistent with little to no atmosphere given the lack of heat redistribution. Here we present the first transmission spectra of TRAPPIST-1 b obtained with JWST/NIRISS over two visits. The two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. The transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. Fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free, hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. We find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). Without affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. This need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler TRAPPIST-1 planets for which transmission spectroscopy is currently the most efficient technique.
