Spectroscopy for Hot Super-Earth Exoplanets

P. F. Bernath and M. DulickDepartment of Chemistry &

BiochemistryOld Dominion University, Norfolk, VA

Exoplanets

E. Hand, 2011

Seager, 2013

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.

Transit spectroscopy

Brillance

Charbonneau et al., 2002; Vidal Madjar et al., 2003; 2004;Richardson et al., 2006

Brillance

Transit spectroscopy

1

23Charbonneau et al., 2002;

Vidal Madjar et al., 2003; 2004; Richardson et al., 2006

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

Hot JupitersVenot et al., A chemical model for the atmosphere of hot Jupiters, A&A 546, A43 (2012)

HD 209458bHD 189733b

Photochemical Model, HD 189733b

Pressure, mbar

Super-Earths

From Schaefer et al., 2012

Super-Earth Composition

At 100 bars for the bulk silicate Earth, from Schaefer et al., 2012 (thermodynamic equilibrium)

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.

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.

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

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.

Infrared Emission (+ Lamp for Absorption)

CH4 Emission at 1000°C

CH4 Lower State Energies

Dyad (ν4) region

Pentad (ν3) region

Octad (ν3+ ν4) region

HITRAN lines and

Elow values (1000°C)

Observed lines and empirical Elow (1000°C)

SO2 Absorption (1000°C)

Cold ends are a problem: new cell under construction.

ν1+ ν3 band

0.01 cm-1 resolution

Acknowledgements• R. Hargreaves, G. Li, L. Michaud, M. Irfan,

C. Beale (York)