INVESTIGADORES
MAUAS Pablo Jacobo David
artículos
Título:
The Ultraviolet Radiation Environment around M dwarf Exoplanet Host Stars
Autor/es:
FRANCE, KEVIN; FRONING, CYNTHIA; LINSKY, JEFFREY; ROBERGE, AKI; STOCKE, JOHN; TIAN, FENG; BUSHINSKY, RACHEL; DÉSERT, JEAN-MICHEL; MAUAS, P. J. D.; VIEYTES, M. C.; WALKOWICZ, LUCIANNE
Revista:
ASTROPHYSICAL JOURNAL
Editorial:
IOP PUBLISHING LTD
Referencias:
Lugar: chicago; Año: 2013 vol. 763 p. 149 - 163
ISSN:
0004-637X
Resumen:
The spectral and temporal behavior of exoplanet host stars is a critical
input to models of the chemistry and evolution of planetary atmospheres.
Ultraviolet photons influence the atmospheric temperature profiles and
production of potential biomarkers on Earth-like planets around these
stars. At present, little observational or theoretical basis exists for
understanding the ultraviolet spectra of M dwarfs, despite their
critical importance to predicting and interpreting the spectra of
potentially habitable planets as they are obtained in the coming
decades. Using observations from the Hubble Space Telescope, we present
a study of the UV radiation fields around nearby M dwarf planet hosts
that covers both far-UV (FUV) and near-UV (NUV) wavelengths. The
combined FUV+NUV spectra are publicly available in machine-readable
format. We find that all six exoplanet host stars in our sample (GJ 581,
GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of
chromospheric and transition region UV emission. No "UV-quiet" M dwarfs
are observed. The bright stellar Lyα emission lines are
reconstructed, and we find that the Lyα line fluxes comprise
~37%-75% of the total 1150-3100 Å flux from most M dwarfs;
gsim103 times the solar value. We develop an empirical
scaling relation between Lyα and Mg II emission, to be used when
interstellar H I attenuation precludes the direct observation of
Lyα. The intrinsic unreddened flux ratio is F(Lyα)/F(Mg II)
= 10 ± 3. The F(FUV)/F(NUV) flux ratio, a driver for abiotic
production of the suggested biomarkers O2 and O3,
is shown to be ~0.5-3 for all M dwarfs in our sample, >103
times the solar ratio. For the four stars with moderate signal-to-noise
Cosmic Origins Spectrograph time-resolved spectra, we find UV emission
line variability with amplitudes of 50%-500% on
102-103 s timescales. This effect should be taken
into account in future UV transiting planet studies, including searches
for O3 on Earth-like planets. Finally, we observe relatively
bright H2 fluorescent emission from four of the M dwarf
exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). Additional
modeling work is needed to differentiate between a stellar photospheric
or possible exoplanetary origin for the hot (T(H2) ≈
2000-4000 K) molecular gas observed in these objects.
Based on observations made with the NASA/ESA Hubble Space Telescope,
obtained from the data archive at the Space Telescope Science Institute.
STScI is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555.