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Spectroscopy for Hot Super-Earth Exoplanets
P. F. Bernath and M. DulickDepartment of Chemistry &
BiochemistryOld Dominion University, Norfolk, VA
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Exoplanets
E. Hand, 2011
Seager, 2013
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Transit: Dayside / Terminator
Day side
Night side
Terminator is the division between night and day
When the planet passes in front of the star, the atmosphere along the terminator can be studied. Different wavelengths make the planet appear different sizes.
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Transit spectroscopy
Brillance
Charbonneau et al., 2002; Vidal Madjar et al., 2003; 2004;Richardson et al., 2006
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Brillance
Transit spectroscopy
1
23Charbonneau et al., 2002;
Vidal Madjar et al., 2003; 2004; Richardson et al., 2006
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Transit Spectroscopy of the Exoplanet HD 189733b
Swain et al. Nature 452, 329 (2008).
Effective size of hot Jupiter
planet determines size of the
transit dips. Stronger
absorption gives bigger
dips.
CH4 opacity : HITRAN plus Nassar&Bernath
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Hot JupitersVenot et al., A chemical model for the atmosphere of hot Jupiters, A&A 546, A43 (2012)
HD 209458bHD 189733b
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Photochemical Model, HD 189733b
Pressure, mbar
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Super-Earths
From Schaefer et al., 2012
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Super-Earth Composition
At 100 bars for the bulk silicate Earth, from Schaefer et al., 2012 (thermodynamic equilibrium)
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CoRoT-7b Atmosphere (1800 K)
Earth continental crust
Bulk silicate Earth
Hot super-Earths: H2O, CO2, SO2, O2, HCl, HF, OH, SO, KCl, NaCl, KF, NaF, KOH, NaOH, etc.
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NaCl and KCl IR
EmissionSpectra
Ram et al., JMS 183, 360 (1997); New millimeter wave data so re-analysis is in progress; previous NaCl analysis is OK, but KCl has problems.
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Exoplanet RequirementsExoplanet Requirements
Line lists CO, H2O, CH4, NH3, CO2, HCN, OH, etc. (hot Jupiters) H2O, CO2, SO2, O2, HCl, HF, OH, SO, KCl, NaCl, KF, NaF, KOH,
NaOH, etc. (hot super-Earths) From Beer-Lambert law:
Need a lineshape function g(ν-ν10) (assumed to be Voigt, H2 pressure broadening estimated) and a line strength S’ given by (SI units, from Bernath, Spectra of Atoms and Molecules):
Therefore need a line position, ν10, partition function, QT (calculated), line intensity, SJ′J″ (or S′), and the lower state energy, Elow.
NlgSII 100 exp
kT
hν
kT
E
hcQε
SνπS low
T
JJ 10
0
102
exp1exp3
2
High spectral resolution at high temperatures
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Molecular OpacitiesCreate line list and then compute opacity tables (absorption cross-sections as a function of wavelength) suitable for a range of temperatures, pressures and compositions.
Line lists (ν10, S′, Elow) can be created by:1.Ab initio calculation. Solve the electronic Schrödinger equation (SE) to obtain potential energy and dipole surfaces, then vibration-rotation SE to obtain transitions energy levels (for transitions) and wavefunctions (for intensities).2.Experimental measurement.3.Combination of 1. and 2. (ab initio intensities particularly useful)
Ab initio calculations provide the large number transitions needed, but line position accuracy is too low. Experimental measurement has required accuracy, but not the millions of lines needed.
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Infrared Emission (+ Lamp for Absorption)
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CH4 Emission at 1000°C
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CH4 Lower State Energies
Dyad (ν4) region
Pentad (ν3) region
Octad (ν3+ ν4) region
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HITRAN lines and
Elow values (1000°C)
Observed lines and empirical Elow (1000°C)
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SO2 Absorption (1000°C)
Cold ends are a problem: new cell under construction.
ν1+ ν3 band
0.01 cm-1 resolution
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Acknowledgements• R. Hargreaves, G. Li, L. Michaud, M. Irfan,
C. Beale (York)