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Model fitting of high-resolution X-ray Spectroscopy of the Planetary Nebula BD+30◦3639

Model fitting of high-resolution X-ray Spectroscopy of the Planetary Nebula BD+30◦3639. Young Sam Yu, Joel Kastner Rochester Institute of Technology, USA John Houck Massachusetts Institute of Technology, USA Ehud Behar, Raanan Nordon, Noam Soker

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Model fitting of high-resolution X-ray Spectroscopy of the Planetary Nebula BD+30◦3639

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  1. Model fitting of high-resolution X-ray Spectroscopy of the Planetary Nebula BD+30◦3639 Young Sam Yu, Joel Kastner Rochester Institute of Technology, USA John Houck Massachusetts Institute of Technology, USA Ehud Behar, Raanan Nordon, Noam Soker Technion-Israel Institute of Technology, Israel

  2. What are planetary nebulae (PNe)? • Last stages of evolution for stars of initial mass(1-8M⊙) • Unveiled central star has terminated its asymptotic giant branch (AGB) evolution • Ejected AGB envelope is ionized by central stellar UV radiation and has yet to disperse entirely • The remnant carbon-oxygen core will become a white dwarf

  3. Various morphologies of PNe Optical images in red/green (mostly from HST) X-ray images in blue (XMM & Chandra) X-ray/visual image overlays by M. Guerrero Montage by B. Balick

  4. Stellar evolution along the HR diagram From Herwig (2005, Annu. Rev. Astron. Astrophys.)

  5. X-ray emission from PNe • Photoionized gas in PNe is far too cool to emit X-rays • The central stars are at best source of very soft X-rays • Theorists have long predicted “X-ray emitting gas (hot bubble) comes from wind interactions” Possible scenarios: - Shocked fast wind (~700-2000 km/s) from central star rams into the ejected red giant envelope that is coasting outward at ~10km/s - Collimated fast winds or jets blown in conjunction with the companion to the central star (e.g. NGC 7027) => X-ray observations are essential to verify & distinguish scenarios

  6. The planetary nebula BD+30°3639 Basic data: Distance from Earth : 1.2 kpc Dimensions: 4 X 5’’ (~0.02 pc) Dynamical age : less than 1000yr Central Star: Carbon-rich Wolf-Rayet type Temp : 30,000K Mass loss rate : ~10-6 Msolar/ yr Wind speed: ~700 km/s Top left : Optical (HST WFPC2 in [S III] at 9532A) (Arnaud et al. 1996) Top right : infrared (Gemini at 2.2 microns (K band) ) Bottom left : Chandra Image (ACIS-S3) Bottom right : Chandra spectrum (ACIS- S3) (Kastner et al. 2000)

  7. Previous results from X-ray CCD spectroscopy: Fitting models to BD+30°3639 spectra * NH constrained by AV for PSPC and SIS model fits

  8. Chandra observation of BD+30°3639 • BD+30°3639 is the best target for getting high resolution X-ray grating spectroscopy due to its large X-ray flux at Earth. We decided to use LETG/ACIS-S combination (rather than HETG/ACIS-S) after conducting MARX simulations

  9. Chandra observation of BD+30°3639 We were granted 300ks observing time for Chandra Cycle 6. Total: 298.1 5882

  10. High resolution X-ray spectroscopy of BD+30°3639

  11. Extracted spectrum result from 5 split datasets

  12. Model fitting result with APED OVIII NeIX FeXVII OVII CVI

  13. Model fitting result with APED CVI

  14. Results • Temperature of shocked plasma: T ~ 2.25x106 K • Hydrogen column density : log NH(cm-2) = 21.4 • Plasma abundances, relative to solar: • C/O ~ 49.3 (yes, C is very overabundant!) • Ne/O ~ 4.5 (yes, Ne is overabundant) • Fe/O ~ 0.3 (yes, Fe is quite depleted!) • N/O ~ 0.3 (yes, N is quite depleted)

  15. The inner layers of a highly evolved star AGB stars are carbon factories! From Herwig (2005, Ann. Rev. Astron. Astrophys.)

  16. Interpretation • X-ray temperature (Tx) • lower than expected from a simple adiabatic shock model (700 km/s wind should produce a few x 10 million degree plasma) • Possible scenarios • Heat conduction moderates Tx • Shocked wind presently seen in X-rays was ejected at earlier epoch, when the “fast wind” was slower (~400km/s) • C/O overabundance • He shell burning and subsequent dredge-up (AGB “third dredge-up”) brings intershell products (C, s-process elements) to the surface • Ne/O over abundance • α capture process(α : He) • 14N + α -> 18O(Burnt in He shell burning) -> 22Ne 18F • Fe/O, N/O depletion • s-process within pulse-driven convection zone(PDCZ) ), associated He shell burning • 22Ne is neutron source in s-process and make Fe depletion => non-solar composition of shocked gas originated from intershell region of AGB star

  17. Summary • Chandra provides unique means for studying origin of X-ray-emitting gas in Planetary nebulae • Sharply non-solar composition of shocked gas originated from intershell region of AGB star • Our preliminary results can provide strong constraints on shock and AGB interior models • To further understand morphologies and density structures of X-ray-emitting plasmas in PNe, we need to develop 3D volumetric model based on these results

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