分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The nearby bright M-dwarf star L~98-59 has three terrestrial-sized planets. One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres. Here we report the study of the atmospheres of L~98-59~c and L~98-59~d using the near-infrared spectral data from the G141 grism of HST/WFC3. We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of $\sim$ 3~sigma for both planets. Thus they may have a primary hydrogen-dominated atmosphere with an opaque cloud layer, or have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere, or have no atmosphere at all. We cannot distinguish between these scenarios for the two planets using the current HST data. Future observations with JWST would be capable of confirming the existence of atmospheres around L~98-59~c and d and determining their compositions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The nearby bright M-dwarf star L~98-59 has three terrestrial-sized planets. One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres. Here we report the study of the atmospheres of L~98-59~c and L~98-59~d using the near-infrared spectral data from the G141 grism of HST/WFC3. We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of $\sim$ 3~sigma for both planets. Thus they may have a primary hydrogen-dominated atmosphere with an opaque cloud layer, or have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere, or have no atmosphere at all. We cannot distinguish between these scenarios for the two planets using the current HST data. Future observations with JWST would be capable of confirming the existence of atmospheres around L~98-59~c and d and determining their compositions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We are using archived data from HST of transiting exoplanet L~98-59~b to place constraints on its potentially hot atmosphere. We analyze the data from five transit visits and extract the final combined transmission spectrum using Iraclis. Then we use the inverse atmospheric retrieval code TauREx to analyze the combined transmission spectrum. There is a weak absorption feature near 1.40~$\mu m$ and 1.55~$\mu m$ in the transmission spectrum, which can be modeled by a cloudy atmosphere with abundant HCN. However, the unrealistically high abundance of HCN derived cannot be explained by any equilibrium chemical model with reasonable assumptions. Thus, the likeliest scenario is that L~98-59~b has a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a thin atmosphere with high mean molecular weight, an atmosphere with an opaque aerosol layer, or no atmosphere, and it is very unlikely for L~98-59~b to have a clear hydrogen-dominated primary atmosphere. Due to the narrow wavelength coverage and low spectral resolution of HST/WFC3 G141 grism observation, we cannot tell these different scenarios apart. Our simulation shows future higher precision measurements over wider wavelengths from the James Webb Space Telescope (JWST) can be used to better characterize the planetary atmosphere of L~98-59~b.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We are using archived data from HST of transiting exoplanet L~98-59~b to place constraints on its potentially hot atmosphere. We analyze the data from five transit visits and extract the final combined transmission spectrum using Iraclis. Then we use the inverse atmospheric retrieval code TauREx to analyze the combined transmission spectrum. There is a weak absorption feature near 1.40~$\mu m$ and 1.55~$\mu m$ in the transmission spectrum, which can be modeled by a cloudy atmosphere with abundant HCN. However, the unrealistically high abundance of HCN derived cannot be explained by any equilibrium chemical model with reasonable assumptions. Thus, the likeliest scenario is that L~98-59~b has a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a thin atmosphere with high mean molecular weight, an atmosphere with an opaque aerosol layer, or no atmosphere, and it is very unlikely for L~98-59~b to have a clear hydrogen-dominated primary atmosphere. Due to the narrow wavelength coverage and low spectral resolution of HST/WFC3 G141 grism observation, we cannot tell these different scenarios apart. Our simulation shows future higher precision measurements over wider wavelengths from the James Webb Space Telescope (JWST) can be used to better characterize the planetary atmosphere of L~98-59~b.
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