1. 1 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Heterogeneous Interactions in the Interstellar Medium by Kristopher Yirak Advisor: Professor Adam Frank Computational Astrophysics Group Department of Physics & Astronomy School of Arts and Science University of Rochester, Rochester, NY Bausch & Lomb 372 August 10 th, 2010 by Kristopher Yirak Advisor: Professor Adam Frank Computational Astrophysics Group Department of Physics & Astronomy School of Arts and Science University of Rochester, Rochester, NY Bausch & Lomb 372 August 10 th, 2010 Background: HST image of a star-forming region in NGC3372, the Carina Nebula

2. 2 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Motivating my talk: astrophysics & numerics ● My work's application focuses on phenomena related to star formation. – In order to help you appreciate this environment and its beauty, I will introduce it. – All of my work relies on direct numerical simulations. ● In order to help you appreciate this, I will introduce numerical methods and will discuss my use of them in the AstroBEAR code. My work has consisted in equal parts of numerics and code development, and application of that code to astrophysical problems. ‡ ‡ – After the astrophysical introduction, and the discussion of numerics, we will then consider three applications revolving around star formation and related processes. Cunningham, A.J., PhD thesis, 2008

3. 3 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Astrophysical jets are widespread and important ● Astrophysical jets exist on a wide range of physical scales, from star-forming regions' Herbig-Haro (HH) objects to black hole-driven Active Galactic Nuclei (AGN) relativistic jets. HH-34MM87 jet

4. 4 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 HH objects play an important role in star-forming regions ● HH Objects were discovered independently in 1951 & 1952 by George Herbig and Guillermo Haro, respectively. ● From Haro 1952: they were interpreted as luminous nebulae perhaps associated with “faint, very blue, hot star[s].” Carroll, J., 2010 Now there are over 400 identified HH objects *; they are believed to play an important role in large-scale dynamics in molecular clouds. *Reipurth, 1999

5. 5 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 HH objects are interesting, important, and ideal for study ● HH objects are sequences of emission knots with aligned velocity vectors, typically culminating in a bow shock located 100s of AUs to parsecs or tens of parsecs from the originating YSO. ● The knots are more or less regularly spaced. The emission in H-α, [SII], etc. is assumed to come from shock heating. HH111 r~100 AU l~1 pc–10 pc (2e5 AU–2e6 AU)

6. 6 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 HH objects come from stars, from gas and dust ● HH objects are associated with Young Stellar Objects (YSOs). ● They are launched as a result of interplay between the forming star, disc of accreting material, and threaded magnetic fields. From Bachiller 1996 Ann. Rev.

7. 7 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 The equations describing fluid flow (named after Leonhard Euler) ● “Principes generaux du mouvement des fluides,” published in Mémoires de l'Academie des Sciences de Berlin in 1757 Conservation of momentum: (p: pressure) Conservation of energy: (E = kinetic + internal energy) Conservation of mass: (ρ: mass, v: velocity vector)

8. 8 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Computers are discrete, requiring discrete equations to solve at a finite number of points ● The equations are discretized by approximating derivatives, e.g. ● The equations are solved at discrete points in space. Cunningham, A.J., PhD thesis, 2008 u: fluid variable f(u): flux P: piecewise polynomial reconstruction

9. 9 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 The case for Adaptive Mesh Refinement (AMR) ● In 2D, doubling the resolution increases the computational time by a factor of 8*. In 3D, it is a factor of 16*. Simulations quickly become prohibitively large. ● AMR was long desired; the main stumbling block (pioneered by Berger & Oliger 1984) was the construction of conservative inter-level fluxes. * 1) Doubling resolution in dimension D results in 2 D more cells. 2) Half-cell-size reduces stable time step by half (v Δt/Δx≡C < 1/D!). ⇒ An overall slowdown of 2 D+1.

10. 10 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Yirak, 2010

11. 11 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Considering algorithmic difficulty, is AMR really worth it? ● As long as the adaptive mesh is a small fraction of the entire domain, it is. However, once the adaptive mesh occupies much of the physical space. It is better to revert to a “fixed grid” calculation. In particular, if adaptive mesh covers entire domain, then the “waste” may be considerable. 2D2D }

12. 12 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Astrophysics with AMR: AstroBEAR ● AstroBEAR is the result of an active collaboration, with primary work undertaken by graduate students here at the UR. ● The code is “a parallelized astrophysics AMR code with capabilities of carrying out hydro- or magnetohydrodynamics (MHD) simulations in two or three dimensions.” ● The group recognizes that the variety of astrophysical problems requires flexibility in numerics. Hence, the code is modular, providing several integration scheme options. ● The code produces results: 30+ publications since ~2002. ● There exists a website & wiki for the code, with the latter being very important and novel in the community, serving both as living documentation and a repository of institutional memory.

13. 13 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49

14. 14 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49

15. 15 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Personal Highlights Timeline

16. 16 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Physical motivation for one code improvement: What to do when cooling clouds collapse? ● The physical process of optically-thin radiative cooling may allow shocked, dense clumps to collapse to the point where they become gravitationally unstable *. ● Such collapsing clumps may therefore be progenitors of localized star formation. ● Accurately capturing this evolution ** requires the inclusion of self- gravity, which is represented by a fundamentally different type of equation, * Characterized by the Jeans length: ** Accurate treatment imposes a Jeans-length-motivated constraint on the resolution, i.e. Truelove 1998

17. 17 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 HYPRE: what to do when cooling clouds collapse ● HYPRE is a library of linear system solvers written in C developed at LLNL for massively parallel applications. ● HYPRE has been implemented in the ● fixed-grid version of AstroBEAR. ● HYPRE is presently being implemented in the AMR version of AstroBEAR collaboratively with many members of the group working together. ● My poster outside of B&L 476 has more details.

18. 18 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Jets through debris ● Premise: The interstellar medium (ISM) is not smooth; smooth structures are susceptible to instabilities*. How is an astrophysical jet affected by this heterogeneity? ● Methodology: Does the propagation depend more on the number of clumps or their density? *Consider Rayleigh-Taylor instability: Yirak 2008 (unpublished) [Yirak et al., 2010]

19. 19 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 images & movies ● [movie] Velocity vectors indicate jet deflection.

20. 20 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 The clumps can divert and disrupt the jet Run A: jet-only Run B: light clumps Run C: heavier clumps Run D: few, heaviest clumps Run E: heaviest clumps Run F: many, heaviest clumps

21. 21 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 The crossing time relates to the dynamic filling fraction t end ∝ f d 2.02 N c : number of clumps A a : ambient area

22. 22 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Domain averages do not reproduce results well ● Comparison to average-domain calculation*: the closest agreement is the run with highest filling fraction. – Domain-averaged analysis is not a fruitful investigation tool. Run t end, sim t end, average rel. error A 162 201 24% B 165 207 25% C 202 249 23% D 180 345 92% E 277 421 52% F 554 529 5% *Cf. Poludnenko, 2002, § 3.3

23. 23 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Treating host as superposition fails, as well ● Can we treat the system as a superposition of single- clumps? – No. Based on a treatment of vorticity generation, the range of generated vorticity varies much less than would be expected. – The reason relates to the critical clump separation of Poludnenko (2002): the distribution of clumps falls into a regime where they are expected to influence each other's dynamics, so a superposition is not appropriate. Thus, we see that understanding the kinematics and morphology of such systems requires further investigation of systems of clumps along the lines here, as the system does not admit the assumptions of averages or superpositions.

24. 24 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 (Transition slide, for my eyes only) ● We have seen the effects that heterogeneity has externally. ● We used a pulsed jet, which is a common model. [show images of other models] ● [image of clumpy observation] What if we bring heterogeneity into the jet itself?

25. 25 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Reexamining the pulsed jet: what models exist? t v ● Emission comes from ejecta ● steady jet ● KH instabilities HD – pros: direct from theory; cons: incorrect knot spacing ● KH instabilities MHD – pros: (same) but w/ correct knot spacing; cons: requires B field ● current-driven instabilities – pros: (same); cons: requires B field (toroidal) ● variable jet ● shock-steepening, “internal working surfaces” – pros: leading explanation, can extrapolate 'velocity histories,' explain origin of shocks; cons: no obvious explanation for sub radial or non axial structure ● “interstellar bullet” – pros: freedom to place bullets as you wish; cons: bullets break up ● Emission comes from ambient ● “shocked cloudlet” – pros: same as with bullets; cons: reverse-facing bow shock [Yirak et al. (2009); Yirak et al., in prep]

26. 26 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 The pulsed jet cannot reproduce all observed features ● YSO jets for example feature sub-radial structure (off-axis knots; “spur” shocks). HH11 1

27. 27 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 What if the pulsed jet successes come from it being a limiting case of a more general model: the “clumped” jet? ● Treat the jet beam as a stream in which individual spherical “clumps” are located. ● The clumps have a range of densities ρ (ρ C >ρ J ), velocities with respect to the beam Δv, sizes r (r C <r J ), and radial locations within the beam. ● This allows a parameter space to be explored, which may recover a range of reminiscent morphologies. = ?

28. 28 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Example 1: If Δv is large, the clumps may disrupt the beam

29. 29 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Example 2: When the jet beam is removed, the clump-clump interactions are (even more) important

30. 30 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 A natural corollary: the evolution of radiatively cooling shocked clumps ● In the adiabatic limit, shocked clumps have been extensively studied (Stone, Norman 1992; Klein et al. 1994; Shin et al. 2008; many, many others). ● Less extensive when radiative cooling is included (Mellema et al. 2002; Fragile et al. 2004; Orlando et al. 2008). adiabatic cooling [Yirak et al. 2010, accepted last Friday by the ApJ]

31. 31 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Cooling can have a significant effect on the shocked clump evolution ● The removal of thermal support potentially allows total collapse down to grid scales, instead of the collapse/re expansion/mixing that is observed in adiabatic simulations. ● These results first reported in Mellema et al. 2002. Fragile et al. 2004 extended that work and saw similar behavior. initial cloud boundary

32. 32 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Why: cooling reduces the size of interaction regions in multiple-shock systems ● Cooling reduces shock speeds (via effectively lowering γ). ● For clumps, this implies smaller bow shock stand-off distances, as well as longer cloud-crushing times (t CC ). ● The limiting case is isothermal ( v PS = v S for M ≫ 1) (e.g., Dyson & Williams 1980). ● The effect is determined by the ratio of cloud radius to cooling length, χ COOL ≡ r C /L COOL. For numerics, this implies a limiting resolution, below which important physics will not be fully resolved. ● Convergence studies of adiabatic clumps propose 100-200 cells/r C is sufficient to resolve hydrodynamics. ● No convergence study of cooling clumps previously in the literature. ⇒

33. 33 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 A convergence study from L COOL /Δx ≪ 1, to L COOL /Δx ~ 16 at bow shock illustrates the importance of resolving the cooling length ● 2.5D simulations w/ cooling. ● Global evolution depends on the Reynolds number because of KH and RT growth at the clump's leading edge (contact discontinuity). ● KH and RT growth times decrease with cooling, due to larger velocity shear & density stratification at the contact. ● Measuring convergence using time evolution of global quantities is accordingly restricted to earlier in the simulation. ● This implies a (higher) resolution requirement than for adiabatic clumps (100-200 cells/r C ) dependent on χ COOL. ● The problem is ideal for investigation with explicit viscosity (e.g. Pittard et al. 2009).

34. 34 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 The results extend to 3D (at 192/r C ) 3D 2.5D

35. 35 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 ● Simulation slated to run on 1,024 processors on Bluegene/P system at the Center for Research Computing at UR. ● Same physical parameters as Fragile et al. 2004, but with much higher resolution, so that L COOL /Δx ~ 1. ● Cf. Klein Woods 1998: Nonlinear Thin Shell Instability requires higher resolution in cooling & isothermal 200 cells/r C 3,016 cells/r C initial cloud boundary Keeping χ COOL in mind, it will be interesting to revisit previous cooling clump results initial cloud boundary Yirak 2010 (unpublished)

36. 36 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 In conclusion, The parallel, AMR, HD/MHD code AstroBEAR benefits from ongoing development aimed at improving both its algorithms and its capabilities. My own contributions to the code base have been consistent and important. Jets propagating into debris fields can be deflected and disrupted if the mass and distribution of the clumps are large. Instantiating clumps in the jets themselves provides a natural mechanism for reproducing the complex morphology observed in HH objects. Finally, numerical study of the fundamental problem of cooling shocked clumps requires careful evaluation of numerical resolution. Either criteria based on the cooling length itself, or other careful arguments, should be adopted.

37. 37 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Ongoing and future work ● Debris fields: 3D + B fields; multiclumps paper ● Clumped jet: B fields again (cf. magnetized single-clumps), chemical compositions, emission characteristics ● Cooling and clumps: Current cooling regime study; clump-clump collisions; lab astro clumps ● AstroBEAR: HYPRE, parallel, NewNewAMR, bluegene Artist's depiction of AstroBEAR with graduate student.

38. 38 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Timeline: looking to the future Los Alamos National Lab, postdoc with Melissa Douglas in laboratory astrophysics

39. 39 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Laboratory experiments: an exciting testbed for astrophysics In the lab a supersonic, radiatively cooling jet surrounded by a magnetized cavity is produced using a wire-array z-pinch assembly. After its launching, the jet goes unstable, resulting in a collection of discrete denser regions, all of which continue to propagate in the jet direction. After emerging from the cavity, however, the transported magnetic field is expected to diffuse on a timescale comparable to the jet dynamical timescale (Ciardi et al. 2007). Nonetheless, the jet remains collimated. Ciardi et al. 2007

40. 40 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Thank you. ● Thanks to past and present group members: ● PI: Adam Frank ● Alexei Poludnenko (Naval Lab) ● Andrew Cunningham (LLNL) ● Brandon Shroyer ● Christina Haig (UNC) ● Ed Schroeder (LLE) ● Jonathan Carroll ● Martin Huarte-Espinosa ● Matt Noyes ● Peggy Varniere (U. Paris 7) ● Sean Tanny (Rice U.) ● Shule Li ● Tim Dennis ● Thanks to Spitzer, NSF, STSci, and the University of Rochester Laboratory for Laser Energetics (LLE) who have provided me with a Frank J. Horton Fellowship (2004-). ● Special final thanks to Barbara Warren (Graduate Program Coordinator). She is the tireless mother to all us grad students, especially when our real moms live far, far away. Thank you for all your work, Barb. ● Thanks to friends and family (some of whom might be sitting next to you right now)!

41. 41 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Extra Slides

42. 42 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Observations lead to a variety of interpretation ● First models of the bow shocks were ballistic: either a stationary clump overrun by a wind, or a clump moving into ambient material. ● The aligned knots in HH objects leads to a YSO “jet” model, in which material flows from a launching engine. ● Jet models include a range of tweaks: precession, varying opening angle, pulsation, velocity profile, etc. ● Pulsed jets are a popularly used model. sin t r v t

43. 43 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 How I Spent My Summer ● numerous additions to in-house post-processing suite (2006-) ● wrote most of original documentation (6/06), recently updated and improved by KY, EK, MN ● created original code API on wiki (4/07), heavily updated by BS ● linsolve integrated (4/07; 4/08) ● numerous updates/bugfixes to integration schemes and general codebase (2007-) ● improved parallelization (2008-), including – 2/08: first investigation of scalability – 3/09: improvements reduced TGHOST from 17% to 7% ● constant diffusion RT (9/08ish) ● introduce HYPRE (1/09-), ongoing multi-developer project ● built ability to view compile-time information via command-line arguments (2/09-4/09) ● “elliptic” variables, allow glimpse into proc IDs, etc. (4/09) ● NewAMR with J (5/09) ● coded ability to keep track of parallel execution, revealed previously unknown bottlenecks (5/09) ● with J, created dynamic domain decomposition (8/09) ● fixed-grid HYPRE + s.g. (8/09) ● conversion to namelists for better forward/backward compatible IO (9/09) ● improved real-time code execution reporting (10/09) ● bg/p compatible (4/10) ● continued documentation (6/10-) ● Talks: – JETSET, 1/07 (Turin, Italy) – JETSET, 1/08 (Galway, Ireland) – Qualifying Examination, 9/08 – Kingston Meeting, 10/09 (Halifax, Nova Scotia) – Papers: ● 1. Submit: 4/07, accepted: 9/07 ● 2. Submit: 5/08, accepted: 1/09 ● 3. Submit: 3/10, accepted: 8/10 – Problem modules: ● cj, pulsed, nopulse ● plugshock ● rt, rt betti, rt diffusion, rt multimode ● sg, bonnor-ebert ● template (shocked clump) ● others

44. 44 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Temperature profiles: bow shock

45. 45 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Temperature profiles: transmitted shock

46. 46 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Temperature profiles: transmitted shock (Fragile 2004 parameters)

47. 47 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Temperature profiles: transmitted shock (Fragile 2004 parameters)

48. 48 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 At the highest resolution, 1,536 cells per clump radius, complex evolution is observed Yirak et al. 2010, accepted ApJ

49. More of NGC3372 (because it's pretty) ●a●a

50. 50 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Using a pulsed jet, a series of sine modes is invoked to explain knot spacing ? Raga et al., 2002, A&A, 395, 647 Raga et al. define a “dynamical time” which they in turn use to ascribe a 2-mode launching profile to the object: x Pat Hartigan's webpage

51. 51 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 Doppler shifts, proper motions Emission lines Emission line ratios parallel to shocks (Hartigan 2007) Direct observation Emission line ratios source

52. 52 / 40 AstroBEAR wiki: http://clover.pas.rochester.edu/trac/astrobear My webpage: http://www.pas.rochester.edu/~yirak 04:49 References ● Carroll, J., Frank, A., & Blackman, E., 2010, submitted to ApJ ● Dyson, J. & Wiliams, D. 1980, The Physics of the Interstellar Medium, Taylor & Francis ● Fragile, C.P., Murray, S.D., Anninos, P., & van Breugel, W. 2004, ApJ, 604, 74 ● Klein, R.I., McKee C.F., & Colella, P. 1994, ApJ, 420, 213 ● Klein, R.I., & Woods, D.T. 1998, ApJ, 497, 777 ● Mellema, G., Kurk, J.D., & Rottgering, H.J.A. 2002, A&A, 395, L13 ● Orlando, S., Peres, G., Reale, F., Bocchino, F., Rosner, R., Plewa, T., & Siegel, A. 2008, A&A, 444, 505 ● Pittard, J.M., Falle, S.A.E.G., Hartquist, T.W., & Dyson, J.E. 2009, MNRAS, 394, 1351 ● Shin, M.S., Stone, J.M., & Snyder, G.F. 2008, ApJ, 680, 336 ● Stone, J.M. & Norman, M.L. 1992, ApJ, 612, 319 ● Yirak, K., Frank, A., Cunningham, A., & Mitran, S. 2009, 695, 999