Model fitting of high-resolution X-ray Spectroscopy of the

Planetary Nebula BD+30◦3639

Young Sam Yu, Joel KastnerRochester Institute of Technology, USA

John HouckMassachusetts Institute of Technology, USA

Ehud Behar, Raanan Nordon, Noam SokerTechnion-Israel Institute of Technology, Israel

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

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

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

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

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)

Basic data:

Distance from Earth : 1.2 kpcDimensions: 4 X 5’’ (~0.02 pc)Dynamical age : less than 1000yr

Central Star: Carbon-rich Wolf-Rayet typeTemp : 30,000KMass loss rate : ~10-6 Msolar/ yrWind speed: ~700 km/s

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

* NH constrained by AV for PSPC and SIS model fits

telescope (instrument)

NH (1021 cm-2)

TX (106 K) abundances reference

ROSAT (PSPC) 1.4* 2.5 …Kreysing et al

(1992)

ASCA (SIS) 1.2* 3.0C greatly enhanced;

N, Ne enhanced;

Fe depleted

Arnaud et al. (1996)

Chandra (ACIS) 1.0 2.7C, Ne enhanced;

Fe depletedKastner et al.

(2000)

Chandra (ACIS) 2.5 2.1C, Ne greatly enhanced;

N, O enhanced;

Fe depleted

Maness et al. (2003)

Chandra (ACIS)

SUZAKU

2.0

2.1

2.4

2.2

No useful constraints!

C, N, Ne greatly enhanced;

Fe depleted

Georgiev et al. (2006)

Murashima et al.

(2006)

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°3639

Observation ID

Date Instrument Exp (ks)

1st order counts

5409

7278

Feb. 13. 2006

Mar. 22. 2006

LETG/ACIS-S

LETG/ACIS-S

85.4

61.8

1742

1231

5410

8495

8498

Dec. 21. 2006

Dec. 22. 2006

Dec. 24. 2006

LETG/ACIS-S

LETG/ACIS-S

LETG/ACIS-S

53.9

77.1

19.9

1043

1480

386

Total: 298.1 5882

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

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

Extracted spectrum result from 5 split datasets

Model fitting result with APED

NeIX FeXVII OVIII OVII CVI

Model fitting result with APED

CVI

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

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

AGB stars are carbon factories!

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

• 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