Catching Some Sun

Catching Some Sunthe interaction between comets and the solar wind

Dennis BodewitsZoltàn Juhàsz, Xander Tielens*,

Reinhard Morgenstern, Ronnie Hoekstra

Atomic Physics Groningen, NL

* Kapteyn Astronomical Institute,

Groningen University, Groningen, NL

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?

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% He2+ cm-3, some Oq+,Cq+,Nq+,Neq+…

• Origin determines composition and velocity

Slow<400 km/s

Fast1000 km/s

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 Ib and v

• Cross sections: total, state selective

ion target ion targetQuasi molecule

photon

Catching Some Sun

Experiment: AGORA

• Wide velocity range• ECRIS allows for different projectiles: Heq+, Oq+, Nq+, …

• Different target gases possible: H, H2, CO, ..?

Perfect for the comet-solar wind system!

Catching Some Sun

Single electron capture

30.4 nm

He+ emission

He2+ + CO He+

!! 30.4 nm !!

Energy (keV/amu)

0.01 0.1 1 10

(

10-1

6 c

m2 )

0.01

0.1

1

10

Total – Ishii, Rudd(1s) – Kearns

(2p) - KVI

Catching Some Sun

Double electron captureHe2+ + CO He

58.4 nm

He emission

!! 58.4 nm !!

Energy (keV/amu)

0.01 0.10 1.00 10.00

0.1

1

10

(

10-1

6 cm

2 )

Total (Rudd, Cadez)

(2p) - KVI

Catching Some Sun

Observations vs. Experiments

•Line ratio indicates solar wind velocity•EUVE observations of Hale-Bopp and Hyakutake

CO

H2

He+ + X He(1s2p)

And by

Heq+ + H

Problem: contamination of ratio by

He2+

He+

He

30.4 nm

58.4 nm

Catching Some Sun

• Cometary model:– Gas production rate Q– Distance to Sun D– CO abundance

Comet-Solar Wind Helium Model

atoms molecules

He2+

He+He

Catching Some Sun

Results: Giotto probe

Halley:

Distance to Sun = 1 A.U.Q = 6*1029 s-1 contains 10% CO

Solar wind v = 300 km/sDistance to the Nucleus (km)

1e+41e+51e+6

He

+/(

He+

+ H

e2

+)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Catching Some Sun

Model parameters

•Solar Wind velocity: 50 km/s - 1100 km/s

•Gas production rate Q: 1027-1031 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)

Inte

nsi

ty 5

8.4

nm

(A

rb. U

nit

s)

Hale-Bopp 425 km/s; Hyakutake 220 km/s

Dv

COv

Q

Line ratio

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?

Catching Some Sun

Thank you!