Electron Densities and Alkali Atoms in Exoplanet Atmospheres

Lavvas, P.; Koskinen, Tommi; Yelle, R. V.

doi:10.1088/0004-637x/796/1/15

Cited by 71 publications

(105 citation statements)

References 98 publications

(155 reference statements)

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“…Detailed theoretical models of planetary atmospheres demonstrate that photochemistry cannot explain such different ratios, and drastic changes to atmospheric temperature profiles or clouds are not supported by the data (e.g., Lavvas et al 2014). It is suggested that disk evolution might change the Na/K abundance ratios of the gas that giant planets accrete during formation.…”

Section: Introductionmentioning

confidence: 97%

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

Pascucci

Edwards

Rigliaco

et al. 2015

ApJ

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We present a detailed analysis of narrow Na I and K I absorption resonance lines toward nearly 40 T Tauri stars in Taurus with the goal of clarifying their origin. The Na I λ5889.95 line is detected toward all but one source, while the weaker K I λ7698.96 line is detected in about two-thirds of the sample. The similarity in their peak centroids and the significant positive correlation between their equivalent widths demonstrate that these transitions trace the same atomic gas. The absorption lines are present toward both disk and diskless young stellar objects, which excludes cold gas within the circumstellar disk as the absorbing material. A comparison of Na I and CO detections and peak centroids demonstrates that the atomic gasand molecular gas are not co-located, the atomic gas being more extended than the molecular gas. The width of the atomic lines corroborates this finding and points to atomic gas about an order of magnitude warmer than the molecular gas. The distribution of Na I radial velocities shows a clear spatial gradient along the length of the Taurus molecular cloud filaments. This suggests that absorption is associated with the Taurus molecular cloud. Assuming that the gradient is due to cloud rotation, the rotation of the atomic gas is consistent with differential galactic rotation, whereas the rotation of the molecular gas, although with the same rotation axis, is retrograde. Our analysis shows that narrow Na I and K I absorption resonance lines are useful tracers of the atomic envelope of molecular clouds. In line with recent findings from giant molecular clouds, our results demonstrate that the velocity fields of the atomic and molecular gas are misaligned. The angular momentum of a molecular cloud is not simply inherited from the rotating Galactic disk from which it formed but may be redistributed by cloud-cloud interactions.

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Section: Introductionmentioning

confidence: 97%

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

Pascucci

Edwards

Rigliaco

et al. 2015

ApJ

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“…The atmosphere of HD 209458b has been modeled in order to compare to the observed H Lyα, O, Si III , and Na I lines (Fortney et al 2003;Koskinen et al 2013a,b;Lavvas et al 2014). For the purpose of studying the Lyα emission spectrum, Menager et al (2013) calculated the Lyα resonant scattering process in the atmosphere of HD 209458b, based on the atmospheric structure model in Koskinen et al (2013a), and HD 189733b based on an unpublished model (Koskinen et al 2011).…”

Section: Introductionmentioning

confidence: 99%

“…If only photoelectric heating and line cooling from hydrogen were included, the atmosphere would be hotter by 2000 − 3000 K (Christie et al 2013), giving transit depths far too large in comparison to observations. Furthermore, several studies (García Muñoz 2007;Koskinen et al 2013a;Lavvas et al 2014) suggested that the transition from atomic to molecule hydrogen occurs at pressures P 10 µbar. These studies included detailed heating and cooling physics in the molecular layer.…”

Section: Introductionmentioning

confidence: 99%

A Model of the Hα and Na Transmission Spectrum of HD 189733b

Huang

Arras

Christie

et al. 2017

ApJ

101

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This paper presents a detailed hydrostatic model of the upper atmosphere of HD 189733b, with the goal of constraining its temperature, particle densities, and radiation field over the pressure range 10 −4 −10 µbar, where the observed Hα transmission spectrum is produced. The atomic hydrogen level population is computed including both collisional and radiative transition rates. The Lyα resonant scattering is computed using a Monte-Carlo simulation. The model transmission spectra are in broad agreement with the data. Excitation of the H(2 ) population is mainly by Lyα radiative excitation due to the large Lyα intensity. The density of H(2 ) is nearly flat over two decades in pressure, and is optically thick to Hα. Additional models computed for a range of the stellar Lyman continuum (LyC) flux suggest that the variability in Hα transit depth may be due to the variability in the stellar LyC. Since metal lines provide the dominant cooling of this part of the atmosphere, the atmosphere structure is sensitive to the density of species such as Mg and Na which may themselves be constrained by observations. Since the Hα and Na D lines have comparable absorption depths, we argue that the center of the Na D lines are also formed in the atomic layer where the Hα line is formed.

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“…Interestingly, χ 2 m (r g = 0) ∼ χ 2 m (r g = 0.1) < χ 2 m (r g = 0.2) < χ 2 m (r g = 0.3), and thus better fits are obtained when the prescribed cloud rests above a poorly reflecting gas atmosphere. Provided that alkalis dominate the gas-phase absorption, this might be consistent with a cloud that lies at pressures less than 10 −4 bar for which the neutral-to-ion alkali transition likely occurs in the atmospheres of close-in giant planets (37).…”

Section: Phase Curve Interpretationmentioning

confidence: 61%

Probing exoplanet clouds with optical phase curves

Muñoz

Isaak

2015

Proc. Natl. Acad. Sci. U.S.A.

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Kepler-7b is to date the only exoplanet for which clouds have been inferred from the optical phase curve-from visible-wavelength whole-disk brightness measurements as a function of orbital phase. Added to this, the fact that the phase curve appears dominated by reflected starlight makes this close-in giant planet a unique study case. Here we investigate the information on coverage and optical properties of the planet clouds contained in the measured phase curve. We generate cloud maps of Kepler-7b and use a multiple-scattering approach to create synthetic phase curves, thus connecting postulated clouds with measurements. We show that optical phase curves can help constrain the composition and size of the cloud particles. Indeed, model fitting for Kepler-7b requires poorly absorbing particles that scatter with low-to-moderate anisotropic efficiency, conclusions consistent with condensates of silicates, perovskite, and silica of submicron radii. We also show that we are limited in our ability to pin down the extent and location of the clouds. These considerations are relevant to the interpretation of optical phase curves with general circulation models. Finally, we estimate that the spherical albedo of Kepler-7b over the Kepler passband is in the range 0.4-0.5.close-in giant | exoplanets | atmospheric characterization | clouds | optical phase curves P hase curves provide unique insight into the atmosphere of a planet, a fact well known and tested in solar system exploration (1-3). Disentangling the information encoded in a phase curve is a complex process however, and interpretations can be faced with degeneracies. The potential of phase curves to characterize exoplanet atmospheres, particularly in combination with other techniques, is tantalizing. Phase curves observed over all orbital phases (OPs) are available for a few close-in planets in the optical (passband central wavelengths λ < 0.8 μm) (4-15) and the infrared (1 μm ≤ λ ≤ 24 μm) (16-19). At infrared wavelengths the measured flux from hot planets is typically dominated by thermal emission. In the optical, both thermal emission and reflected starlight contribute, with the relative size of the contributions dependent on the measurement wavelength as well as on the temperature of the atmosphere and the occurrence of condensates (20-25).Kepler-7b (26) is one of the ∼1,000 planets discovered by the Kepler mission. Its inferred mass M p (= 0.44 M J ; J for Jupiter) and radius R p (= 1.61 R J ) result in an unusually low bulk density (0.14 g·cm −3 ) that is inconsistent with current models of giant planet interiors (27, 28). Kepler-7b orbits a quiet G-type star of effective temperature T ⋆ = 5,933 K every 4.89 d (orbital distance a = 0.062 astronomical units) (6, 7), and tidal forces have likely synchronized its orbit and spin motions. Taken together these set a planet equilibrium temperature T eq ≤ 1,935 K.Kepler photometry (0.4-0.9 μm) of the star-planet system has enabled the optical study of 10,14). The inferred geometric albedo, A g = 0. 25-0.38 (4, 6, 7, 10...

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Electron Densities and Alkali Atoms in Exoplanet Atmospheres

Cited by 71 publications

References 98 publications

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

A Model of the Hα and Na Transmission Spectrum of HD 189733b

Probing exoplanet clouds with optical phase curves

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