1. Lecture 9: Wind-Blown Bubbles September 21, 2011

2. Interstellar & Circumstellar Bubbles fast wind slow wind fast wind 1000 - 2000 km/s 10 - 50 km/s 2000 - 3000 km/s 10 -7 M  /yr 10 -4 M  /yr 10 -5 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.

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

4. Schematic Bubble Structure Weaver et al. 1977

5. 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

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

7. Copyright ©2002-2005 by Russell Croman The Bubble Nebula

8. N11B - Home of LH10

9. Naze, et al. 2001, AJ, 122, 921 Bubble Size ~ 15 pc Exp Vel ~ 15-20 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

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

11. 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

12. 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. 1998 Interstellar Bubbles - Naze et al. 2002

13. 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.

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

15. Circumstellar Bubble NGC 6888

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 Chandra X-ray Image of NGC 6888 R: H  G: [O III] B: X-ray Gruendl, Guerrero, Chu 2011, unpublished

17. S 308 - a WR Circumstellar Bubble Red: H  Green: [O III] Blue: X-ray

18. S 308 - a Detailed Look at Its Shell HD 50896 * R: H  G: [O III] B: X-ray Chu et al. 2003, ApJ, 599, 1189

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

20. 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

21. 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 NGC6164-5 may be detectable, but are not.

22. Hot Gas in the Orion Nebula T ~ 2  10 6 K Lx ~ 5.5  10 31 erg/s

23. 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

24. 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  10 6 100 10 31  10 32 WR 1-2  10 6 1 10 33  10 34 M17 7  10 6 0.3 10 33 Orion 2  10 6 0.2-0.5 5  10 31 (* Townsley et al. 2003; Guedel et al. 2007)

25. 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

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

27. UV Probes of the 10 5 K Gas C IV N V O VI  Å )  1548, 1550 1238, 1242 1031, 1037 Obs. HST STIS HST STIS FUSE I.P. (eV) 47.9 77.5 138.1 T (K) 1.0  10 5 1.8  10 5 3.0  10 5 T eff (K) >35,000 >75,000 >125,000

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

29. S 308 - ideal for conduction study HD 50896 * 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.

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

31. 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.

32. Pressure-driven bubble with heat conduction at interface Bubble dynamics does not match L x (obs) / L x (expected) = 10 -1 to 10 -3  Adjust fast wind - wind velocity - mass loss rate  Reduce heat conduction Dynamically mix nebular material (mass-loading)  

33. 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