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

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

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

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

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)

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

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

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

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

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

Temperature gradient 1040 K 1800 K at knot in the inner ring (2.5 arcmin from the central star) 900-1000 K at outer ring (Cox et al. 1995; O’dell et a. 2007) Temperature gradient 900K 1800 K 1080 K

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

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?

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)

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 20-30 km s-1?