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H 2 Excitation in The Dumbbell (M 27)

H 2 Excitation in The Dumbbell (M 27). Kevin France – CITA. Stephan McCandliss - JHU Roxana Lupu – JHU Eric Burgh – Wisconsin Paul Feldman – JHU Ken Sembach – STScI Jeff Kruk - JHU B-G Andersson – JHU. U of T G2000 March 14, 2007. H 2 in Planetary Nebula Shells.

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H 2 Excitation in The Dumbbell (M 27)

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  1. H2 Excitation in The Dumbbell (M 27) Kevin France – CITA Stephan McCandliss - JHU Roxana Lupu – JHU Eric Burgh – Wisconsin Paul Feldman – JHU Ken Sembach – STScI Jeff Kruk - JHU B-G Andersson – JHU U of T G2000 March 14, 2007 University of Toronto G2000 - March 14, 2007

  2. H2 in Planetary Nebula Shells • Bipolar morphology a “signpost” for an H2rich outflow • Surprising? • Molecules quickly destroyed in diffuse nebula • Requires a reservoir of H2 • Cometary Knots Zuckerman & Gatley 88 Kastner et al 96 Martin et al 98 H2 (1-0) S(1) 2.12 μm – APO 3.5m/NICFPS Lupu, McCandliss, and France – in prep University of Toronto G2000 - March 14, 2007

  3. H2 in Planetary Nebula Shells:Cometary Knots University of Toronto G2000 - March 14, 2007

  4. H2 in Planetary Nebula Shells:Cometary Knots • H2survives by self/dust-shielding from the intense EUV/FUV radiation field of the central star • H2knots interesting because: • Formation process (stellar evolution) • Enrichment of the ISM • Long-standing question about the excitation mechanism of the observed emission • Shocks? • Excitation by FUV photons? • Excitation by LyC/X-ray photons? Speck et al. 02 University of Toronto G2000 - March 14, 2007

  5. M 27 – nearby evolved PN • MCS = 0.56 M (progenitor = 3.4 ± 0.8 M) • 1.0 x 0.6 pc (@ ~420 pc) • TCS = 108,000 K • Age = 12,700 yrs • Bipolar -> H2 rich clumps • How to distinguish excitation between excitation processes? University of Toronto G2000 - March 14, 2007

  6. Far-UV Spectroscopic Diagnostics • NASA/JHU 36.136 UG • 40 cm SiC coated telescope feeding 400 mm diameter Rowland Circle spectrograph • Long-slit (12'' x 200''), far-UV (910-1370 Å, ~3 Å resolution) H2 Shaw et al. 05 H2 excitation by FUV (912 – 1110 Å) photons: Fluorescent cascade in VUV bandpass H2 excitation by collisional processes (such as shocks): Rovibrational excitation only, no VUV signature Payload Schematic University of Toronto G2000 - March 14, 2007

  7. Supporting UV Data: FUSE • FUSE covers 905 -1187 Å bandpass at medium resolution (R ~20,000) • Higher sensitivity than can be achieved with sounding rockets • FUSE wavelength calibration programs (high S/N spectra of the central star) + Cycle 5 GI program (nebular observations) Moos et al. 00 University of Toronto G2000 - March 14, 2007

  8. Supporting Data: Long-Slit Optical Spectroscopy APO • APO 3.5 m / DIS II • Long-Slit spectroscopic scans of M 27 • O.9” x 300”, 4000-7000 Å, 4 Å resolution • Nebular images in neutral and atomic lines • Nebular dust attenuation thought to be negligible • H/H, H/ H, H/ H ratio maps constrain dust attenuation and provide clues about LyC processes Lupu, McCandliss, and France–in prep University of Toronto G2000 - March 14, 2007

  9. Sounding Rocket Result:No detectable H2Fluorescence McCandliss, France, et al. 07 University of Toronto G2000 - March 14, 2007

  10. Sounding Rocket Result:No detectable H2Fluorescence McCandliss, France, et al. 07 “Traditional” UV fluorescence (912-1110 Å stellar continuum -> B-X & C-X) is NOT the dominant H2 excitation mechanism University of Toronto G2000 - March 14, 2007

  11. FUSE Result: HOT H2 and Ly pumped H2 Emission McCandliss, France, et al. 07 • HOT -> T(H2) ≥ 2000 K • HI Ly 1216Å coincident with transitions of HOTH2 (v, J) = (2,5) & (2,6) • How did the H2get HOT ? Lupu, France, McCandliss 06 Ly University of Toronto G2000 - March 14, 2007

  12. FUSE Result: HOT H2 and Ly pumped H2 Emission • HOT -> T(H2) ≥ 2000 K • How did the H2 get HOT ? • Shocks: McCandliss, France, et al. 07 • Shocks will be present if the high-ionization stellar wind interacts with the molecular knots • Timescale problems:  …  • COOL « SHOCK: the high temperature would be transient • and VION. FRONT « VSHOCK: the shock would have propagated along the knot (the observed H2 brightness profile would change) O’Dell et al 05 Lupu, France, McCandliss 06 • In M27, the high-ionization stellar wind is moving slower than the H2outflow University of Toronto G2000 - March 14, 2007 McCandliss, France, et al. 07

  13. FUSE Result: HOT H2 and Ly pumped H2 Emission • HOT -> T(H2) ≥ 2000 K • How did the H2 get HOT ? • Shocks: McCandliss, France, et al. 07 • Shocks will be present if the high-ionization stellar wind interacts with the molecular knots • Timescale problems:  …  • COOL « SHOCK : the high temperature would be transient • and VION. FRONT « VSHOCK : the shock would have propagated along the knot (the observed H2 brightness profile would change) (Most Likely) Not Shocks Lupu, France, McCandliss 06 • In M27, the high-ionization stellar wind is moving slower than the H2 outflow University of Toronto G2000 - March 14, 2007

  14. FUSE Result: HOT H2 and Ly pumped H2 Emission • How did the H2get HOT ? • LyC Radiation: • (Helix Nebula) Only LyC (~100 ≤  ≤ 911.7 Å) flux from star has the energy budget to produce observed IR flux (compared to X-rays and 912-1100 Å continuum) Lupu, France, McCandliss 06 O’Dell et al. 07 • H2 heating: • LyC + H -> p+ + e- • p+ + e- + advected(H2) -> H2* (HOT H2) • (also dissociation by reactions with O+ ) University of Toronto G2000 - March 14, 2007

  15. FUSE Result: HOT H2 and Ly pumped H2 Emission • When exposed to < 911.7 Å, new paths for H2 ionization & dissociation become available • Two main routes: • H2(X 1+g) + LyC -> • H(1s) + H(nl) … pre/direct-dissociation • H2+(X 2+g) + e- … photoionization • And following the photoionization channel, dissociative recombination • H2+ (X 2+g) + e- -> H(1s) + H(nl) • How did the H2get HOT ? • LyC Radiation: Lupu, France, McCandliss 06 University of Toronto G2000 - March 14, 2007 McCandliss, France, et al. 07

  16. Enhanced Nebular H/H: H2 Dissociation by LyC Photons • Laboratory studies* suggest that the most energetically favorable: • B, B’, C -> H(1s) + H(2l) [844.8 Å] • D, B’’ -> H(1s) + H(3l) [748.5 Å] • H2+  -> H2+ + e- [803.7 Å] McCandliss, France, et al. 07 • We expect enhanced Ly (H(2l)), Ly (H(3l)) and H (H(3l))emission due to LyC irradiation of H2 • Thus, enhanced H/H relative to 2.86 (recombination rate) H HeII H H H Lupu, McCandliss, and France–in prep University of Toronto G2000 - March 14, 2007 *needs astrophysical model

  17. Enhanced Nebular H/H: H2 Dissociation by LyC Photons • Laboratory studies* suggest that the most energetically favorable: • B, B’, C -> H(1s) + H(2l) [844.8 Å] • D, B’’ -> H(1s) + H(3l) [748.5 Å] • H2+  -> H2+ + e- [803.7 Å] • We expect enhanced Ly (H(2l)), Ly (H(3l)) and H (H(3l))emission due to LyC irradiation of H2 • Thus, enhanced H/H relative to 2.86 (recombination rate) H/H H/H McCandliss, France, et al. 07 H/H University of Toronto G2000 - March 14, 2007

  18. LyC Illumination of Cometary Knots in PNe:H/H & HOT H2 & Ly Fluorescence University of Toronto G2000 - March 14, 2007

  19. LyC Illumination of Cometary Knots in PNe:HOT H2 & Ly Fluorescence&H/H University of Toronto G2000 - March 14, 2007

  20. Conclusions • Cometary knots in PN are a source for molecular enrichment of the ISM, and challenge models of the AGB->PN transition • The H2 excitation mechanism in these knots has been the subject of debate • Shocks and FUV (912-1110 Å) have been ruled out as the dominant processes in PNe knots • Surface illumination by LyC (100-912 Å) radiation can explain the heating of the H2, the IR H2brightness, Ly pumped H2 emission in the far-UV bandpass, and enhanced H/H ratios in the absence of dust • Additional Reading: www.cita.utoronto.ca/~france/ • astro-ph/0602547 – Lupu, France, and McCandliss • astro-ph/0701439 – McCandliss, France, Lupu et al. • astro-ph/0701636 – O’Dell, Henney, and Ferland University of Toronto G2000 - March 14, 2007

  21. Central Star Extinction • Data=Orange • Red Curve is model attenuated by E(B-V) = 0.05 • Observed H/H: E(B-V)~0.10 University of Toronto G2000 - March 14, 2007

  22. H2 Dissociation via LyC D, B’’ -> H(1s) + H(3l) [748.5 Å] Ly (H(3l)) & H (H(3l)) H2+  -> H2+ + e- [803.7 Å] B, B’, C -> H(1s) + H(2l) [844.8 Å] Ly (H(2l)), University of Toronto G2000 - March 14, 2007

  23. (N27, NGC6853, The Dumbbell) Other PNe? (NGC 3132, The Eight Burst) (M57, NGC6720, The Ring) (NGC7293, The Helix) University of Toronto G2000 - March 14, 2007 Lupu, France, McCandliss 06

  24. Comparison with Spitzer Observations of The Helix University of Toronto G2000 - March 14, 2007

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