Finding Fingerprints XDAP 16|11|2004

FINDING FINGERPRINTSProbing the interaction between

comets and the solar wind

Dennis Bodewits

Xander Tielens, Ronnie Hoekstra

KVI Atomic Physics

Zernikelaan 25, 9747 AA Groningen

Finding Fingerprints XDAP 16|11|2004

Cometary X-Ray emission

Features:

•Bright in 0.2-1000eV

•Line emission

•Variable

•Common property of (nearby) comets

Charge Exchange

Finding Fingerprints XDAP 16|11|2004

Interaction between comet and wind

•10 km Nucleus•103 km Contact surface•106 km Bowshock•108 km Tails

Oq+

photon

O(q-1)+

Finding Fingerprints XDAP 16|11|2004

Slow<400 km/s

Fast1000 km/s

Solar Wind

• Northern Light!!

• Per cm3: - 9 protons- 10 elektronen- 0.5 He2+

- few Oq+,Cq+,Nq+,…

• Windtypes

• Variability!

Finding Fingerprints XDAP 16|11|2004

Fingerprints of Charge Exchange

Photon(s)

Aq+ + B A(q-1)+(nl) + B+

Encke 2003

McNaught-Hartley

1999 S4 Linear

• Quasi resonant

• Excited state

• Molecules?

• Multiple EC?

Finding Fingerprints XDAP 16|11|2004

Photon emission spectroscopy

gas jet

nozzle

Ions from ECRIS

Faraday cup

spectrometer

Photon(s)

Aq+ + B A(q-1)+(nl) + B+

Finding Fingerprints XDAP 16|11|2004

Solar wind helium - experimental results

velocity (km/s)

0 250 500 750 1000 125010-2

10-1

100

101

102

line

ratio

H2O

H2

CO

He He+

Electron capture strongly depends on collision partner and velocity

Finding Fingerprints XDAP 16|11|2004

Sun

yR r

x

observer

Interaction model

atoms

Gas Production Q, Heliocentric Distance, Scale Lengths

molecules

1. Comet atmosphere

2. Charge state dist.

3. Image & spectrum

Finding Fingerprints XDAP 16|11|2004

Charge state distribution

Big comet•Cross section

•Density distribution

O8+

O7+

O6+

O8+

O7+What collisions? Depends on properties of wind AND comet

Small comet

O6+

Finding Fingerprints XDAP 16|11|2004

1027 10291028 1030

Model results I: X-Ray morphology

small big

Finding Fingerprints XDAP 16|11|2004

Model results II – synthetic spectra

Combination of composition + comet + cross sections

Aq+ + molecules?? Multiple electron capture??

Experiments!!!

200 300 400 500 600 700 800 900 10000

1

2

3

4

5

6

7

8

9

10x 10

23

Wavelength (eV)

Inte

nsity (

ph

oto

ns/s

/eV

)

Encke spectra due to fast SW Oq+, Cq+ and Nq+

OVIII np - 1s

OV

III 2

p -

1s

OVII np - 1s O

VII 2

p -

1s, O

VII [2s-1

s]

CV

I np

- 1

s

CV

I 2p

- 1

s, [2

s-1

s]

CV

np -

1s

NV

I 2-1

,[2

-1]

OVIIIOVIICVICVNVIINVIsum

Finding Fingerprints XDAP 16|11|2004

Example: CXO observations Comet Encke

• Collisionally thin coma • close to the sun• fast wind O8+

C6+ O7+

C5+

Finding Fingerprints XDAP 16|11|2004

velocity (km/s)

0 250 500 750 1000 125010-2

10-1

100

101

102

line

ra

tio

Summary

Spectra and morphology in x-ray and FUV depend on solar wind AND comet characteristics

Charge exchange emission strongly depends on collision partner and velocity

Provides excellent diagnostic tool, but….• need of laboratory data!• need of spatially resolved high res. spectra!

200 300 400 500 600 700 800 900 10000

1

2

3

4

5

6

7

8

9

10x 10

23

Wavelength (eV)

Inte

nsity

(ph

oto

ns/s

/eV

)

Encke spectra due to fast SW Oq+, Cq+ and Nq+

OVIII np - 1s

OV

III 2

p -

1s

OVII np - 1s

OV

II 2p

- 1

s, O

VII

[2s-

1s]

CV

I np

- 1

s

CV

I 2p

- 1

s, [2

s-1

s]

CV

np

- 1s

NV

I 2-1

,[2-1

]

OVIIIOVIICVICVNVIINVIsum

Finding Fingerprints XDAP 16|11|2004

Thank you!

http://www.kvi.nl/~atf