SEMI-EMPIRICAL MODELING OF THE PHOTOSPHERE, CHROMOPSHERE, TRANSITION REGION, AND CORONA OF THE M-DWARF HOST STAR GJ 832

Journal Article · Thu Oct 20 00:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/830/2/154· OSTI ID:22667295

Fontenla, J. M. ^[1]; Linsky, Jeffrey L. ^[2]; Witbrod, Jesse ^[3]; France, Kevin ^[4]; Buccino, A.; Mauas, Pablo; Vieytes, Mariela ^[5]

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1. NorthWest Research Associates, Boulder, CO 80301 (United States)
2. JILA, University of Colorado and NIST, Boulder, CO 80309-0440 (United States)
3. University of Colorado Boulder, CO 80309 (United States)
4. LASP, University of Colorado Boulder, CO 80309-0600 (United States)
5. Instituto de Astronomía y Física del Espacio (CONICET-UBA), C.C. 67, Sucursal 28, C1428EHA, Buenos Aires (Argentina)

Stellar radiation from X-rays to the visible provides the energy that controls the photochemistry and mass loss from exoplanet atmospheres. The important extreme ultraviolet (EUV) region (10–91.2 nm) is inaccessible and should be computed from a reliable stellar model. It is essential to understand the formation regions and physical processes responsible for the various stellar emission features to predict how the spectral energy distribution varies with age and activity levels. We compute a state-of-the-art semi-empirical atmospheric model and the emergent high-resolution synthetic spectrum of the moderately active M2 V star GJ 832 as the first of a series of models for stars with different activity levels. We construct a one-dimensional simple model for the physical structure of the star’s chromosphere, chromosphere-corona transition region, and corona using non-LTE radiative transfer techniques and many molecular lines. The synthesized spectrum for this model fits the continuum and lines across the UV-to-optical spectrum. Particular emphasis is given to the emission lines at wavelengths that are shorter than 300 nm observed with the Hubble Space Telescope , which have important effects on the photochemistry of the exoplanet atmospheres. The FUV line ratios indicate that the transition region of GJ 832 is more biased to hotter material than that of the quiet Sun. The excellent agreement of our computed EUV luminosity with that obtained by two other techniques indicates that our model predicts reliable EUV emission from GJ 832. We find that the unobserved EUV flux of GJ 832, which heats the outer atmospheres of exoplanets and drives their mass loss, is comparable to the active Sun.

• OSTI ID: 22667295
• Journal Information: Astrophysical Journal, Vol. 830, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CHROMOSPHERE
DWARF STARS
ENERGY SPECTRA
EXTREME ULTRAVIOLET RADIATION
LTE
LUMINOSITY
MASS TRANSFER
ONE-DIMENSIONAL CALCULATIONS
PHOTOSPHERE
PLANETS
RADIANT HEAT TRANSFER
RESOLUTION
SIMULATION
SPACE
STELLAR CORONAE
STELLAR RADIATION
STELLAR WINDS
WAVELENGTHS
X RADIATION