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Stars Collide……

Stars Collide……. An overview of the advancements in modelling of stellar collisions, filtered through the biases of Alison Sills MODEST-6, Northwestern, August 2005. …..and then what?. What can you get?. Table stolen from talks by Charles Bailyn, 1995-2000. Added a new kind of star.

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Stars Collide……

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  1. Stars Collide…… An overview of the advancements in modelling of stellar collisions, filtered through the biases of Alison Sills MODEST-6, Northwestern, August 2005 …..and then what?

  2. What can you get? Table stolen from talks by Charles Bailyn, 1995-2000

  3. Added a new kind of star Simulations done by Laycock & Sills 2005

  4. Everything you wanted to know about MS-MS collisions Freitag & Benz 2005 • Most masses • Most velocities • Most impact parameters • SPH simulations with ~few thousand particles • Results: mass loss, energy loss, deflection angle, angular momentum loss, merger or disruption

  5. 74.2 M2 in M Vrel dmin 0.1 Freitag & Benz 2005 0.1 M1 in M 74.2

  6. What happens after the collision? • We already knew that MS-MS collision products retain chemical info about parents, are puffed up and take a ~ thermal time to settle to main sequence (e.g. Sills et al. 1997, 2001) • Evolution after the collision is like truncated main sequence evolution, and otherwise normal • Angular momentum problem solvable with disks and/or winds (Sills, Adams & Davies 2005)

  7. What happens with populations of collisions? • M67 from Hurley et al: very nice fit to data; no blue stragglers from single-single collision • (Ultra-)simple cluster models + (slightly more) detailed collision models  distributions of blue stragglers in CMD (yes, I’ve been presenting these for a long time, but they’re still really interesting and they still tell us something)

  8. Core: 0 – 23” Mass function x = -8 Formation time: 7 Gyr ago to now KS test: 93% young, massive ! Mid: 23 – 130” Mass function x = -3 Formation time: 7 – 0.6 Gyr ago KS test: 44% older, less massive ? 47 Tuc data from Ferraro et al & Piotto et al HST + ground-based Outside: 130 – 1200” Mass function x = 1.35 Formation time: 7 – 1.2 Gyr ago KS test: 35% Monkman & Sills 2006 old, light ??

  9. Beyond Blue Stragglers • Stripping of giants (Adams, Davies & Sills 2004) – not the dominant way of getting rid of bright giants • Increased interest in mergers/collisions in context of massive star formation (Bally & Zinnecker 0502485, Bonnell & Bate 0506689) • Runaway collisions  IMBH (SM & SPZ, MF & FR) – depends on knowing radii of products after collision (Fregeau et al 2004, see Marc’s talk) • Ultra-compact X-Ray Binaries (see Jamie’s talk)

  10. The Story So Far • We basically understand blue stragglers if they are collision products (and perhaps some of them are….) • We can model and evolve collisions of non-main sequence stars, and we will if you make us • But we’d rather be modeling binary mergers (if we could only figure out how)

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