Model fitting of high resolution x ray spectroscopy of the planetary nebula bd 30 3639
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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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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

Technion-Israel Institute of Technology, Israel


What are planetary nebulae pne

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


Various morphologies of pne

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


Stellar evolution along the hr diagram

Stellar evolution along the HR diagram

From Herwig

(2005, Annu. Rev. Astron. Astrophys.)


X ray emission from pne

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


The planetary nebula bd 30 3639

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)


Previous results from x ray ccd spectroscopy fitting models to bd 30 3639 spectra

Previous results from X-ray CCD spectroscopy: Fitting models to BD+30°3639 spectra

* NH constrained by AV for PSPC and SIS model fits


Chandra observation of bd 30 3639

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


Chandra observation of bd 30 36391

Chandra observation of BD+30°3639

We were granted 300ks observing time for Chandra Cycle 6.

Total: 298.1 5882


High resolution x ray spectroscopy of bd 30 3639

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


Extracted spectrum result from 5 split datasets

Extracted spectrum result from 5 split datasets


Model fitting result with aped

Model fitting result with APED

OVIII

NeIX

FeXVII

OVII

CVI


Model fitting result with aped1

Model fitting result with APED

CVI


Results

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)


The inner layers of a highly evolved star

The inner layers of a highly evolved star

AGB stars are carbon factories!

From Herwig

(2005, Ann. Rev. Astron. Astrophys.)


Interpretation

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


Summary

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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