TY - JOUR
T1 - Predicting the Extreme Ultraviolet Radiation Environment of Exoplanets around Low-mass Stars
T2 - The TRAPPIST-1 System
AU - Peacock, Sarah
AU - Barman, Travis
AU - Shkolnik, Evgenya L.
AU - Hauschildt, Peter H.
AU - Baron, E.
N1 - Funding Information:
We would like to thank B. Fuhrmeister, I. Short, and J. Aufdenberg for useful discussions. We also thank A. Schneider for providing GALEX photometry fluxes and D. Bardalez Gagliuffi for providing the TRAPPIST-1 SpeX spectrum. We gratefully acknowledge the helpful comments from the anonymous referee. This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program—Grant NNX15AQ94H. An allocation of computer time from the UA Research Computing High Performance Computing (HPC) at the University of Arizona is gratefully acknowledged. Resources supporting this work were also provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. This work was supported in part by DFG GrK 1351 and DFG projects HA 3457/20-1 and HA 3457/23-1. P.H.H. gratefully acknowledges the support of NVIDIA Corporation with the donation of a Quadro P6000 GPU used to support his research. A portion of the calculations presented here were performed at the Höchstleistungs Rechen-zentrum Nord (HLRN), and at the National Energy Research Supercomputer Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. We thank all these institutions for a generous allocation of computer time. E.B. acknowledges support from NASA Grant NNX17AG24G. E.S. appreciates support from the NASA Habitable Worlds grant NNX16AB62G.
Funding Information:
We would like to thank B. Fuhrmeister, I. Short, and J. Aufdenberg for useful discussions. We also thank A. Schneider for providing GALEX photometry fluxes and D. Bardalez Gagliuffi for providing the TRAPPIST-1 SpeX spectrum. We gratefully acknowledge the helpful comments from the anonymous referee. This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program - Grant NNX15AQ94H. An allocation of computer time from the UA Research Computing High Performance Computing (HPC) at the University of Arizona is gratefully acknowledged. Resources supporting this work were also provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. This work was supported in part by DFG GrK 1351 and DFG projects HA 3457/20-1 and HA 3457/23-1. P.H.H. gratefully acknowledges the support of NVIDIA Corporation with the donation of a Quadro P6000 GPU used to support his research. A portion of the calculations presented here were performed at the Höchstleistungs Rechenzentrum Nord (HLRN), and at the National Energy Research Supercomputer Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. We thank all these institutions for a generous allocation of computer time. E.B. acknowledges support from NASA Grant NNX17AG24G. E.S. appreciates support from the NASA Habitable Worlds grant NNX16AB62G.
Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved.
PY - 2019/2/1
Y1 - 2019/2/1
N2 - The high energy radiation environment around M dwarf stars strongly impacts the characteristics of close-in exoplanet atmospheres, but these wavelengths are difficult to observe due to geocoronal and interstellar contamination. On account of these observational restrictions, a stellar atmosphere model may be used to compute the stellar extreme ultraviolet (EUV; 100-912) spectrum. We construct semiempirical nonlocal thermodynamic equilibrium model spectra of the ultracool M8 star TRAPPIST-1 that span EUV to infrared wavelengths (100 -2.5 μm) using the atmosphere code PHOENIX. These upper atmosphere models contain prescriptions for the chromosphere and transition region and include newly added partial frequency redistribution capabilities. In the absence of broadband UV spectral observations, we constrain our models using Hubble Space Telescope Lyman α observations from TRAPPIST-1 and Galaxy Evolution Explorer UV photometric detections from a set of old M8 stars (>1 Gyr). We find that calibrating the models using both data sets separately yield similar far-ultraviolet and NUV fluxes, and EUV fluxes that range from (1.32-17.4) 10 -14 ergs s -1 cm -2 . The results from these models demonstrate that the EUV emission is very sensitive to the temperature structure in the transition region. Our lower activity models predict EUV fluxes similar to previously published estimates derived from semiempirical scaling relationships, while the highest activity model predicts EUV fluxes a factor of 10 higher. Results from this study support the idea that the TRAPPIST-1 habitable zone planets likely do not have much liquid water on their surfaces due to the elevated levels of high energy radiation emitted by the host star.
AB - The high energy radiation environment around M dwarf stars strongly impacts the characteristics of close-in exoplanet atmospheres, but these wavelengths are difficult to observe due to geocoronal and interstellar contamination. On account of these observational restrictions, a stellar atmosphere model may be used to compute the stellar extreme ultraviolet (EUV; 100-912) spectrum. We construct semiempirical nonlocal thermodynamic equilibrium model spectra of the ultracool M8 star TRAPPIST-1 that span EUV to infrared wavelengths (100 -2.5 μm) using the atmosphere code PHOENIX. These upper atmosphere models contain prescriptions for the chromosphere and transition region and include newly added partial frequency redistribution capabilities. In the absence of broadband UV spectral observations, we constrain our models using Hubble Space Telescope Lyman α observations from TRAPPIST-1 and Galaxy Evolution Explorer UV photometric detections from a set of old M8 stars (>1 Gyr). We find that calibrating the models using both data sets separately yield similar far-ultraviolet and NUV fluxes, and EUV fluxes that range from (1.32-17.4) 10 -14 ergs s -1 cm -2 . The results from these models demonstrate that the EUV emission is very sensitive to the temperature structure in the transition region. Our lower activity models predict EUV fluxes similar to previously published estimates derived from semiempirical scaling relationships, while the highest activity model predicts EUV fluxes a factor of 10 higher. Results from this study support the idea that the TRAPPIST-1 habitable zone planets likely do not have much liquid water on their surfaces due to the elevated levels of high energy radiation emitted by the host star.
KW - stars: activity
KW - stars: chromospheres
KW - stars: low-mass
KW - ultraviolet: stars
UR - http://www.scopus.com/inward/record.url?scp=85062011041&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85062011041&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/aaf891
DO - 10.3847/1538-4357/aaf891
M3 - Article
AN - SCOPUS:85062011041
SN - 0004-637X
VL - 871
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 235
ER -