1. Infrared integral field spectroscopic observations of globules (cometary knots) in the Helix Nebula (NGC 7293)
Mikako Matsuura
National Astronomical Observatory of Japan
University College of London
A.K. Speck, M.D. Smith, A.A. Zijlstra, K.T.E. Lowe, S. Viti,
M. Redman, C.J. Wareing, E. Lagadec

2. Contents Introduction Observations & Analysis Discussion
H2 excitation mechanism
Shaping of the knot

3. Introduction Globules or (cometary) knots
Smallest scale structures observed in PNe (1-2 arcsec at ~219pc in the Helix)
~20,000 knots in the Helix (Meixner et al. 2005)
Commonly found in nearby PNe
Brightest parts of PNe; understanding physics in knots might help to understand physics in PNe
Formation mechanisms of knots
Radiation: sunny side at the tip + tail (e.g. Speck et al. 2002)
Instability of winds (e.g. Dyson et al. 2006)
H2 excitations
Photon dominated region (PDR)
Shocks

4. Contents Introduction Observations & Analysis Discussion
H2 excitation mechanism
Shaping of the knot

5. Observations Target: a knot in the Helix Nebula Observations
Target knot K1
AO guide star
Observations
Target: a knot in the Helix Nebula
219 pc (Harris et al. 2007)
Observations
8.2-meter Very Large Telescope (VLT)
Spectrograph for INtegral Field Observations (SINFONI)
Adaptive Optics (AO) guided by a nearby star
125x250 mas2 (pixel size limited spatial resolution): re-sampled to 125x125 mas2
50x100 mas2 : re-sampled to 50x50 mas2
K-band grating (R~4490)

6. Integral field spectrograph SINFONI
2.12 m image
Image + spectrum at each pixel
Spectral variation within a knot

7. Shape of the knot Tadpole shape Narrower tail Matsuura et al.
Narrower tail than the head
Narrower tail
Matsuura et al.
Submitted to MNRAS

8. Spectra Up to 12 H2 lines (9 in this figure) No Br
Spectra at brightest point of the knot

9. H2 excitation temperature
Rotational temperature
Vibrational temperature
Uniform excitation temperature within the knot

10. H2 excitation temperature
Level population diagram
LTE
Excitation temperature of 1800K

11. Temperature gradient 1040 K
1800 K at knot in the inner ring (2.5 arcmin from the central star)
K at outer ring (Cox et al. 1995; O’dell et a. 2007)
Temperature gradient
900K
1800 K
1080 K

12. Contents Introduction Observations & Analysis Discussion
H2 excitation mechanism
Shaping of the knot

13. H2 excitation mechanism
H2 line
Line Ratio
Obs
ShockModel
1.958 m v=1-0 S(3)
220 91
2.034 m v=1-0 S(2) 36
2.073 m v=2-1 S(3) 4
2.128 m v=1-0 S(1)
100
2.154 m v=2-1 S(2) 3
2.224 m v=1-0 S(0) 22
2.248 m v=2-1 S(1) 9
2.408 m v=1-0 Q(1) 99 75
2.413 m v=1-0 Q(2) 29 24
2.424 m v=1-0 Q(3) 70
2.438 m v=1-0 Q(4) 30 20
C-type shock
Relatively well reproduced line ratio at wind velocity 27 km s-1 (Kaufman & Neufeld 1996)
Observed velocity is ~10 km s-1
PDR model
72 Solar luminosity at 219 pc
UV strength G0=8
Only 100 K
Observed 1800 K
Shock H2 excitation at the knot K1?

14. Density
Shaping
Among existing models, wind instability models by Pittard et al (2005) & Dyson et al. (2006) can reproduce the shape well
Wind + grain
Wind velocity of 22 km s-1 required (faster than observed velocities; Meaburn et al. 2005; 10 km s-1)
Wind instability model
(J-type shock; Pittard et al. 2005)
Density
Dyson et al. (2006)

15. Conclusions
Among existing models, shock can produce the shape and H2 line ratio of the knot K1 well.
Stellar wind is important at the inner ring of the Helix?
Wind velocity at knot K1 is km s-1?