Transcript OSU-68th Federman.ppt

Revised Term Values for the A – X (v′=09, v′′=0) Bands in 13C16O from HighResolution Spectra Acquired at the SOLEIL
Synchrotron
L. Gavilan, J.L. Lemaire, M. Eidelsberg, (Obs. de Paris), S.R.
Federman (U. of Toledo), G. Stark (Wellesley), A.N. Heays
(Wellesley/Leiden), J.-H. Fillion (UMPC), J.R. Lyons
(UCLA), and N. de Oliveira (SOLEIL)
This research was supported by grants from NASA and CNRS-PCMI program
Outline
Background
CO Photochemistry
Results from SOLEIL
Summary
Background
• CO observed in many astronomical environments
– Diffuse and dark, molecular interstellar clouds
– Circumstellar shells of asymptotic giant branch stars and planetary
nebulae
– Circumstellar disks around newly formed stars
– Comets and planetary atmospheres
• Experimental data for photochemical models
– Electronic transitions (ultraviolet)
– Oscillator strengths
– Predissociation rates
Photochemistry of Interstellar CO
Processes affecting mix of isotopologues
• Isotope Charge Exchange – favors 13C16O
– It has lower zero-point energy
– 13C+ + 12C16O → 12C+ + 13C16O – ΔE (ΔE/k ≈ 35 K)
• Selective Isotopic Photodissociation – favors more
abundant isotopic variant
– Dissociation occurs through line absorption at far UV wavelengths
– More abundant variant has lines that are more optically thick,
shielding itself from further dissociation
Photochemistry of Interstellar CO
• Accurate column densities needed
– A – X (4th positive) system of (ν′,0) bands in 12C16O now have
well-determined (self-consistent) f-values via electron scattering
(Chan et al. 1993), laser absorption (Stark et al. 1998), and
synchrotron absorption (Eidelsberg et al. 1999)
– Agreement between astronomical f-values (e.g., Sheffer et al.
2002) and theoretical values (Eidelsberg & Rostas 2003) for
triplet-singlet transitions (a′ – X, d – X, and e – X) is now excellent
for 12C16O, better than 1 σ in most instances
• Do the same values apply to 13C16O?
SOLEIL Experiments
• DESIRS beamline with a VUV FTS at SOLEIL Synchrotron
SOLEIL Experiments
• The FTS (de Oliveira et al. 2009, Rev. Sci. Instru., 80, 043101;
de Oliveira et al. 2011, Nature Photonics, 5, 149)
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Resolving power as high as 1,000,000
Based on wave front division instead of amplitude division
Relies on modified bimirror configuration requiring only flat mirrors
Path difference scanning through translation of one reflector
Results from SOLEIL
Results from SOLEIL
Results from SOLEIL
Results from SOLEIL
+ Predicted by Hakalla et al. 2012 at J′ = ±1
* Previously seen in Kępa et al. 2003
** Previously seen in Kępa et al. 2011
Summary
• SOLEIL FTS extends VUV measurements to higher J′ for
most bands and lower J′ for v′ = 0
• Confirm previously assigned perturbations, but now seen in
greater detail
• Evidence for new perturbations seen
• Next steps
– Extract f-values for A – X bands in 13C16O
– Extract f-values for triplet-singlet bands for comparison with results
for 12C16O (Eidelsberg and Rostas 2003)
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