KITP
catdynamics | February 23, 2009In the Good Old Days, Globular Clusters were simple things: spherical, relaxed, coeval and homogenous.
Not so much anymore.The thorny issue of multiple populations keeps coming up at the workshop.
They're there, something is going on, but what, and how, and Y?
M13 embiggen
Guest author
Natalie Hinkel from ASU put some notes together from the sessions I missed earlier this month, and I post them below, with her permission, with light edits and addition of figures and links by me - any error is mine:
See, here is Good Old M54 (from Chaboyer) - simple.
Multiple Populations: A Summary
Looking…
catdynamics | February 23, 2009New week, and a new set of topics for us to contemplate.
This week we hear from the grad students, who will tell us what it is they have actually been doing all this time, scientifically...
Tom is here! For a flying visit.
We may go post-Newtonian, and we may meander back through stellar evolution for a bit.
So - where, cosmologically, and when, do globulars form?
Is the mass-metallicity relation for galaxies a clue? Should we look to dwarf galaxies with masses less than 1010 solar masses as cites for most or all of globular formation? How long can we delay globular formation?
How dense…
catdynamics | February 20, 2009I've never seen a green star
I hope to never see one
but I can tell you anyhow
I'd rather model it than observe it...
if you have a bunch of stars of some age, or range of ages, and composition
with the stars all different mass over some range of masses, and
maybe some binaries and peculiar stars and interacting stars, and
bit of dust, then
what colour are they?
In particular if you are looking at a big clump of stars from far away
the easy thing to do is to see the slightly fuzzy blob, plop some filters
on your aperture and measure the colour - the difference in brightness in a small number…
catdynamics | February 20, 2009Yesterday we talked about triples.
It is an interesting thing that as we seem to not find any binaries in clusters, we do find triples... hmm.
First Rosemary discussed stability of triples - dynamical stability of isolated triples to internal spontaneous ejection - looking at analytic criteria for overlapping resonances to second order in the disturbing function
then Ivanova and meself talked - first Ivanova skated through the theoretical zoo of dynamically formed triples, stable and not, finishing with a teaser about 4U1820-303, then I talked about The Triple.
PSR1620-26 in M4 - The Triple…
catdynamics | February 19, 2009While I was galavanting about the southland yesterday, the program moved on and
John compared N-body and Monte Carlo (video and podcast)
and Sverre and Rainer continued with the theme (video and podcast)
today we move onto triples
'cause you got to know that if two stars are good, three stars are more better...
theoretically a lot of stars are binaries, (cf Matthew's latest)
Hogeveen Monte Carlo'd observed binaries to try to invert the q distribution and concluded the secondary mass function is a steep function of q, suggesting a lot of unobserved low mass secondaries
someone needs to redo…
catdynamics | February 17, 2009long weekend over, and we're back at it.
today's topic is GRBs
and what, you might ask, do they have to do with clusters...?
Well, Bob, as you know, there are two types of gamma-ray bursters, or maybe three depending on how you counttype I and type II the long and the short
"Some say" that short gamma-ray bursts are, clearly, coalescing binary neutron stars, spiraling into contact through gravitational radiation emission.
This can, clearly, happen in globular clusters, as evidenced by PSR M15C, and taking a single data point, inverting the rate, and throwing in some theoretical…
catdynamics | February 12, 2009Latest on white dwarfs in globulars from Brad, John and Stefan.
White Dwarfs in Globular Clusters - Hansen - video and podcast
White Dwarfs in Globular Clusters - Fregeau and Rosswog - video and podcast
As we learned this morning, white dwarf cooling gives an absolute age indicator, essentially from ab initio physics calculations.
So you can independently measure cluster ages if you have very good photometry of very faint stars in very crowded regions. And we do.
cf NGC6397 - had a bit too much of M4 for now...
NB: white dwarf cooling age for NGC6397 is 11.5 Gyrs +/- 0.5
which is 1.2 Gy…
catdynamics | February 12, 2009All day discussion on white dwarfs today: cooling, kinematics, destruction etc
Starts off with Lars tutoring us in the morning...
Basics:
white dwarf origins - they are degenerate burnt out cores of low-to-medium mass main seqeunce stars
key issues still not fully resolved:
what is the relationship between the main sequence initial mass and the white dwarf final mass?
to what extent does it depend on main sequence composition?
binary companion? formation of He core white dwarfs due to envelope stripping - see white dwarfs with He cores and masses less than 0.48 solar mass, so no He core…
catdynamics | February 11, 2009Today we step back and Hans runs The Big Questions past us.
It is always good to think about the Big Picture.
The Big Questions
Most likely scenario for cluster formation:
a) compressed/triggered initial conditions: cloud collisions or intersecting shells, or
b) did globular clusters form as nuclei in dwarf galaxies that got accreted by our MW (dE,N hypothesis), or
c) scaled-up version of open cluster formation in mol. clouds? (Pudritz papers, Krumholz talk); the role of high pressure?
Relation of halo stars and globular cluster destruction ... (are Pop II stars dissolved globular clusters…
catdynamics | February 10, 2009today we start turning our minds back to techniques, before we start contemplating what to do about white dwarfs
Stephan tutors us on SPH.
Smooth Particle Hydrodynamics models fluid flow using a Lagrangian method - rather than constructing a grid, as in Eulerian techniques, SPH is not constrained by prior geometry.
Rather SPH samples the fluid flow with particles, which have a compact smoothing kernel to sample overlapping adjacent fluid elements.
The modern implementation of SPH as used in astrophysics goes back to the classic paper of Hernquist and Katz (1988), who combined the relatively…
catdynamics | February 10, 2009the other, other program running in parallel with the clusters09 program at KITP is "Low Dimensional Electron Systems", which seems intensely worried about the supply of pencils, or some such - at least graphene seems to be their buzzword du jour.
They, also, are having lots of talks, most all of which are also online video and podcast.
Monday they had their "Director's Seminar", to explain what the big deal is to the rest of us, and themselves:
Sankar Das Sarma "Low Dimensional Electron Systems: A Landscape of Graphene, Quantum Hall Effects, MOSFET, Luttinger Liquid, and Beyond"
most…
catdynamics | February 9, 2009Mark Krumholz's talk is here - video and podcast
Genevieve Permentier's talk is here - cluster formation, video and podcast.
catdynamics | February 6, 2009forming stars is easy, except for the details
Mark Krumholz is schooling us on the intricacies.
Awesome movies...
Binary star formation animation
Making a BIG star
Turbulence, dood - that one is just very pretty, nothing much to do with the talk.
catdynamics | February 6, 2009Yesterday, there was much talking about blue stragglers.
All preserved for posterity.
Francesco on Hubble observations of blue stragglers in galactic globulars - and VLT and GALEX too.
Barbara on more observations and modeling too.
Nathan on modeling and the mystery correlations in the amazing Nature paper too.
All with live high res video also.
This morning we move on to global properties of globulars and star formation processes.
Hm, globual is actually a potentially useful word, methinks.
catdynamics | February 5, 2009Blue straggler stars are, formally, main sequence stars that are too blue and bright on the colour-magnitude diagram - they are more massive than they ought to be given their age, is the other way of looking at it.
They are found in the field, and you might rightly ponder how we can tell, but in globular clusters there are lots, they really stick out, and they are rather fascinating.
And they make great Hubble Space Telescope targets, being rather blue, in crowded regions and teach you about physics, stellar processes etc.
Blue Straggler Stars (wiki):
Nice illustration of Blue Stragglers…
catdynamics | February 3, 2009What is string theory anyway?
Well, now you can find out.
Joe Polchinski at UCSB just gave the Director's Blackboard Seminar at KITP, and as usual it is webcast and podcast.
Go be inspired.
catdynamics | February 2, 2009Globular Clusters - what drives the evolution of the mass function?
Mark Gieles take is online here
Mike Fall's preceding talk on the subject is not available online. Should have been there...
catdynamics | January 30, 2009in which we contemplate a compact accretor and a low mass donor, in theory
if you have a compact object, like a neutron star or black holes, then the potential energy at the surface is very negative, so any mass that falls onto the compact object may release a large amount of energy per unit mass
since this large amount of energy may be radiated (must in the case of a neutron star) and the object is compact, the characteristic temperature of the object is high - so they are typically x-ray bright
however, it turns out to be surprisingly difficult to get a low mass star to be "in contact"…
catdynamics | January 29, 2009in which we ponder the globular cluster mass function and whether the current mass function really is lognormal and how this came about given that everybody but everybody believes the initial mass function must have been a power law...
wednesday afternoon was a good introduction and lively discussion of theoretical processes affecting globular cluster lifetimes and mass evolution - including some pdf of slides.
Just so we all remember what we are talking about: log-normalpower law
people in other fields might know these as Somebody's Law, but physical scientists do not deign to name the…
catdynamics | January 28, 2009I missed the session on tuesday of "Short Talks: Structure of GCs and Their Dynamics",
fortunately the audio and video feed is here for posterity
Fujii, Varri and Waters present.