1. Catching Some Sun Catching Some Sun the interaction between comets and the solar wind Dennis Bodewits Zoltàn Juhàsz, Xander Tielens*, Reinhard Morgenstern, Ronnie Hoekstra Atomic Physics Groningen, NL * Kapteyn Astronomical Institute, Groningen University, Groningen, NL

2. Catching Some Sun Amazing!! X-Ray and FUV emission due to electron capture from cometary neutrals by solar wind HCI Outline: Intro: Comets, Solar Wind Atomic Physics Model: Solar wind Helium Conclusion How can you use the X-Ray/FUV emission to study the interaction between comets and the solar wind?

3. Catching Some Sun Comets & the Solar Wind Nucleus produces water at ca. 3000 kg/s Gas is photo-ionized and/or -dissociated 10 protons, 10 electrons, 5% He 2+ cm -3, some O q+,C q+,N q+,Ne q+ … Origin determines composition and velocity Slow <400 km/s Fast 1000 km/s

4. Catching Some Sun The process: Charge Exchange Electron is captured into excited state (nl) Over-the-Barrier Model: resonant electron capture, n depends on q and I b and v Cross sections: total, state selective iontargetiontargetQuasi molecule photon

5. Catching Some Sun Experiment: AGORA Wide velocity range ECRIS allows for different projectiles : He q+, O q+, N q+, … Different target gases possible : H, H 2, CO,..? Perfect for the comet-solar wind system!

6. Catching Some Sun Single electron capture 30.4 nm He + emission He 2+ + CO  He + !! 30.4 nm !! Total – Ishii, Rudd (1s) – Kearns (2p) - KVI

7. Catching Some Sun Double electron capture He 2+ + CO  He 58.4 nm He emission !! 58.4 nm !! Total (Rudd, Cadez) (2p) - KVI

8. Catching Some Sun Observations vs. Experiments Line ratio indicates solar wind velocity EUVE observations of Hale-Bopp and Hyakutake CO H2H2 He + + X  He(1s2p) And by He q+ + H Problem: contamination of ratio by He 2+ He + He 30.4 nm 58.4 nm

9. Catching Some Sun Cometary model: –Gas production rate Q –Distance to Sun D –CO abundance Comet-Solar Wind Helium Model atomsmolecules He 2+ He + He

10. Catching Some Sun Results: Giotto probe Halley: Distance to Sun = 1 A.U. Q = 6*10 29 s -1 contains 10% CO Solar wind v = 300 km/s

11. Catching Some Sun Model parameters Solar Wind velocity: 50 km/s - 1100 km/s Gas production rate Q: 10 27 -10 31 molecules/s Distance to Sun: 0.5 – 3 A.U. Composition: 0-100 % CO The 30.4/58.4 ratio is a good velocity probe Intensity 30.4 nm (Arb. Units) Intensity 58.4 nm (Arb. Units) Hale-Bopp 425 km/s; Hyakutake 220 km/s D v CO v Q Line ratio

12. Catching Some Sun Conclusions & Outlook Helium line ratio is a powerful probe for solar wind velocity Helium line intensities  cometary environment First investigation of FUV/X-ray; line ratios in HCI even more promising but data needed. State selective cross section experiments are crucial for the interpretation of cometary FUV/X-Ray spectra How can you use the X-Ray/FUV emission to study the interaction between comets and the solar wind?

13. Catching Some Sun Thank you!