Changes between Version 44 and Version 45 of u/EricasLibrary

Timestamp:

03/11/13 12:08:17 (12 years ago)

Author:

Erica Kaminski

Comment:

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u/EricasLibrary

@@ -185 +185 @@
   The paper then begins to set up its motivation - namely that research on flat topped isothermal spheres have begun to be pursued, such as F&C. They say F&C gets more accurate results, but that the collapse is triggered artificially. They plan to take the studies further on non-singular spheres, but by initiating collapse in a more physically relevant way (increasing Pext as suggested by Myers et al). They claim that most of the observational constraints (such as decreasing accretion rate, velocity fields, initial condition) are recovered by this model (although in my opinion - they also seem to have been recovered in F&C model too... so maybe they find MORE accurate lifetimes for their collapsing BE spheres). I find it interesting that they do not call the sphere a Bonnor Ebert sphere, but rather an isothermal sphere... is there any significance to this?
 
-  In their results section they present very weak quantitative results/explanations/insight of their plots. Their different runs are broken down into the rate of compression, in how much time (measured in units of sound crossing time -- ostensibly in terms of the BE sphere) does the Pext double. They initiate the collapse of the critical BE sphere by increasing Pext (by any amount would increase Pext beyond Pcrit as the sphere is already critical), but then they continue to increase Pext throughout the course of the simulation (this potentially is similar to what we did in practice by just allowing the simulation to evolve "naturally" with no forced increase in Pext, simply Pext at the sphere's outer edge increased naturally by the infall of material onto that outer edge).
+  In their results section they present very weak quantitative results/explanations/insight of their plots. Their different runs are broken down into the rate of compression, in how much time (measured in units of sound crossing time -- ostensibly in terms of the BE sphere) does the Pext double. They initiate the collapse of the critical BE sphere by increasing Pext (by any amount would increase Pext beyond Pcrit as the sphere is already critical), but then they continue to increase Pext throughout the course of the simulation (this potentially is similar to what we did in practice by just allowing the simulation to evolve "naturally" with no forced increase in Pext, simply Pext at the sphere's outer edge increased naturally by the infall of material onto that outer edge). In the first couple of cases they show, compression is slow. In the first 3 panels of Fig. 1, a sink has not yet formed, and so they identify this phase as the pre-stellar (aka the pre-protostellar) phase. It appears to me that they get a nice outside in flow beginning to develop in these plots, although the radius of the BE sphere is unclear. No compression wave seems evident in these plots, but instead, it seems to be a re-equilibration of matter in terms of the language I use in my paper. This could be due to early subsonic adjustment of the material into a modified BE profile that exceeds the critical mass, and hence collapses in the canonical fashion. They use no such language, and make no such identification which is curious. They describe this, as well as all other cases, as being a compression wave solution. This might make sense if you follow Whitworth language that all collapse problems are due to compression waves, but some of the waves have 0 amplitude..? This case looks most like some of our lighter ambient runs, where the Pext increases very slowly due to a slow accumulation of matter.. In the next 2 panes of the plot, a central sink has formed that accretes matter in a free-fall manner (vrad~r^1/2) that they say moves outward in time. I can't tell from this plot that this type of flow is moving outward in time.  
 
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