Lecture 9: Wind-Blown Bubbles September 21, 2011

Interstellar & Circumstellar Bubbles fast wind slow wind fast wind km/s km/s km/s M  /yr M  /yr M  /yr    interstellar circumstellar circumstellar bubble nebula bubble O star  LBV  WR (60 M  ) O star  RSG  WR (35 M  ) Low-mass   RG, AGB  planetary neb.

Interstellar Bubble Castor, McCray, Weaver 1975, ApJL Weaver et al. 1977, ApJ

Schematic Bubble Structure Weaver et al. 1977

Variations of Bubble Models Superbubble Model - intermittent SNe averaged over time ~ stellar wind - blown out of galactic plane (Mac Low & McCray 1998) - blown in magnetized medium (Tomisaka 1992) - hot interior enriched with O and Fe (Silich et al. 2001) Circumstellar Bubble Model - ambient medium with density  r -2 - wind velocity and mass loss rate are functions of time - hydrodynamic model (Garcia-Segura et al. 1996) - radiative hydrodynamic model (Freyer et al. 2006) - mass -loading by evaporation/ablation (Pittard et al. 2001) Planetary Nebula model - similar to circumstellar bubbles - stellar radiation is a strong function of time - Schoenberner, Steffen, Warmuth 2006

I. Dense Swept-up Shell - Why aren’t there more interstellar bubbles?

Copyright © by Russell Croman The Bubble Nebula

N11B - Home of LH10

Naze, et al. 2001, AJ, 122, 921 Bubble Size ~ 15 pc Exp Vel ~ km/s Ionized shell (H II) - sound vel ~ 10 km/s - no strong shocks - no large density jump - no limb-brightening Neutral shell (H I) - sound vel ~ 1 km/s - large density jump - limb-brightening - frequently seen

I. Dense Swept-up Shell - Why aren’t there more interstellar bubbles? - clumpy / inhomogeneous ambient ISM Orion Nebula N44F

I. Dense Swept-up Shell - Why aren’t there more interstellar bubbles? - clumpy / inhomogeneous ambient ISM - clumpy circumstellar bubble RCW58 O  RSG  WR LBV Garcia-Segura, Langer, Mac Low 1996 RSG wind Inside an Interstellar Bubble

I. Dense Swept-up Shell - Why aren’t there more interstellar bubbles? - clumpy / inhomogeneous ambient ISM - clumpy circumstellar bubble - observed bubble dynamics does not match that expected from bubble models; e.g., observed kinetic energy is too low Superbubbles - Oey 1996; Kim et al Interstellar Bubbles - Naze et al. 2002

I. Dense Swept-up Shell - Why aren’t there more interstellar bubbles? - clumpy / inhomogeneous ambient ISM - clumpy circumstellar bubble - observed bubble dynamics does not match that expected from bubble models; e.g., observed kinetic energy is too low There are problems. Remember the clumps.

II. Hot Bubble Interior - X-ray emission from bubble interior

Circumstellar Bubble NGC 6888

Chandra X-ray Image of NGC 6888 R: H  G: [O III] B: X-ray Gruendl, Guerrero, Chu 2011, unpublished

S a WR Circumstellar Bubble Red: H  Green: [O III] Blue: X-ray

S a Detailed Look at Its Shell HD * R: H  G: [O III] B: X-ray Chu et al. 2003, ApJ, 599, 1189

[O III] [N II] HH HH X-ray emission starts here  RSG wind

II. Hot Bubble Interior - X-ray emission from bubble interior - Why aren’t more bubbles detected in X-rays? NGC 6888 (Chandra) S 308 (XMM) 1  10 6 K2-3  10 6 K

II. Hot Bubble Interior - X-ray emission from bubble interior - Why aren’t more bubbles detected in X-rays? If T ~ 1  10 6 K, interstellar absorption killls the others. If T ~ 2-3  10 6 K, RCW58 and NGC may be detectable, but are not.

Hot Gas in the Orion Nebula T ~ 2  10 6 K Lx ~ 5.5  erg/s

Hot Gas in the Omega Superbubble Two young superbubbles are detected in X-rays by Chandra: Omega and (Rosette) ROSAT - Dunne et al. 2003, ApJ, 590, 306 Chandra - Townsley et al. 2003, ApJ, 593, 874

X-ray Observations of Bubbles Detection of hot gas associated with fast winds - 10 PNe, 2 WR bubbles, 2 superbubbles* Properties of the hot gas: T e [10 6 K ] N e [cm -3 ] L X [erg/s] PN 1-3   WR 1-2   M17 7  Orion 2   (* Townsley et al. 2003; Guedel et al. 2007)

II. Hot Bubble Interior - X-ray emission from bubble interior is soft - ISM absorbs soft X-ray emission - X-ray emission depends on: wind properties concentration of massive stars clumpy structure of the ambient medium magnetic fields

III. Conduction Layer - Probe the thermal conduction layer High ions produced by thermal collisions O VI N V C IV Si IV

UV Probes of the 10 5 K Gas C IV N V O VI  Å )  1548, , , 1037 Obs. HST STIS HST STIS FUSE I.P. (eV) T (K) 1.0    10 5 T eff (K) >35,000 >75,000 >125,000

Interface of the WR Bubble S308 C IV Boroson et al. 1997, ApJ, 478, 638 N V S II

S ideal for conduction study HD * R: H  G: [O III] B: X-ray Boroson et al. (1997) detected N V absorption from the conduction layer. HST STIS observation of N V and C VI emission was scheduled, but STIS died. FUSE observations of O VI were awarded, and it died, too. Spitzer can observe Ne V, but it ran out cryogen.

FUSE Observations of NGC 6543 Gruendl, Chu, Guerrero 2004, ApJL

III. Conduction Layer - Probe the thermal conduction layer High ions produced by thermal collisions - NGC 6543: given the boundary conditions of hot interior and warm shell, thermal conduction appears to be consistent, but does not explain the low X-ray luminosity.

Pressure-driven bubble with heat conduction at interface Bubble dynamics does not match L x (obs) / L x (expected) = to  Adjust fast wind - wind velocity - mass loss rate  Reduce heat conduction Dynamically mix nebular material (mass-loading)  

What Next? Swept-up Shell Reasonably well understood Interface (conduction) layer Spatially-resolved high-dispersion UV spectra are needed Hot interior Spatially-resolved high-resolution X-ray spectra are needed