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http://hdl.handle.net/20.500.12386/29070
Titolo: | The high-energy radiation environment of the habitable-zone super-Earth LHS 1140b | Autori: | Spinelli, R. BORSA, Francesco GHIRLANDA, Giancarlo GHISELLINI, Gabriele CAMPANA, Sergio Haardt, F. PORETTI, Ennio |
Data pubblicazione: | 2019 | Rivista: | ASTRONOMY & ASTROPHYSICS | Numero: | 627 | Da pagina:: | A144 | Abstract: | Context. In the last few years many exoplanets in the habitable zone (HZ) of M-dwarfs have been discovered, but the X-ray/UV activity of cool stars is very different from that of our Sun. The high-energy radiation environment influences the habitability, plays a crucial role for abiogenesis, and impacts the chemistry and evolution of planetary atmospheres. LHS 1140b is one of the most interesting exoplanets discovered. It is a super-Earth-size planet orbiting in the HZ of LHS 1140, an M4.5 dwarf at 15 parsecs. <BR /> Aims: In this work, we present the results of the analysis of a Swift X-ray/UV observing campaign. We characterize for the first time the X-ray/UV radiation environment of LHS 1140b. <BR /> Methods: We measure the variability of the near ultraviolet (NUV) flux and estimate the far ultraviolet (FUV) flux with a correlation between FUV<SUB>1344-1786Å</SUB> and NUV<SUB>1771-2831Å</SUB> flux obtained using the sample of low-mass stars in the GALEX archive. We highlight the presence of a dominating X-ray source close to the J2000 coordinates of LHS 1140, characterize its spectrum, and derive an X-ray flux upper limit for LHS 1140. We find that this contaminant source could have influenced the previously estimated spectral energy distribution. <BR /> Results: No significant variation of the NUV<SUB>1771-2831Å</SUB> flux of LHS 1140 is found over 3 months, and we do not observe any flare during the 38 ks on the target. LHS 1140 is in the 25th percentile of least variable M4-M5 dwarfs of the GALEX sample. Analyzing the UV flux experienced by the HZ planet LHS 1140b, we find that outside the atmosphere it receives a NUV<SUB>1771-2831Å</SUB> flux <2% with respect to that of the present-day Earth, while the FUV<SUB>1344-1786Å</SUB>/NUV<SUB>1771-2831Å</SUB> ratio is 100-200 times higher. This represents a lower limit to the true FUV/NUV ratio since the FUV<SUB>1344-1786Å</SUB> band does not include Lyman-alpha, which dominates the FUV output of low-mass stars. This is a warning for future searches for biomarkers, which must take into account this high ratio. <BR /> Conclusions: The relatively low level and stability of UV flux experienced by LHS 1140b should be favorable for its present-day habitability. | URI: | http://hdl.handle.net/20.500.12386/29070 | URL: | https://www.aanda.org/articles/aa/full_html/2019/07/aa35636-19/aa35636-19.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201935636 | Bibcode ADS: | 2019A&A...627A.144S | Fulltext: | open |
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