KITP
catdynamics | March 13, 2009Theory grad students read this:
Rainer put up a summary of the numerical methods discussion for globular cluster modeling on the program wiki
if you are doing any sort of collisional dynamics, or numerical modeling of collisional self-gravitating systems, you might find this useful
There is also a nice summary of the different order post-Newtonian approximations here
and some random selected subset of references - for those discussions where a number of papers came up or were requested
Rainer also put up a summary of special purpose hardware status;
specifically the GRAPES and uses of…
catdynamics | March 12, 2009and we continue our lesson on extragalactic globulars, with a trifectaduet of talks and an emphasis on colour: red or blue, it is like South Central here sometimes
remember, red is metal rich or old
blue is metal poor or young...
except the reds are actually probably younger than the blues
so it is metal dominated, except for really young clusters
Steve first
then Jay
PS: our summary 20 minute talks have an interesting habit of actually lasting 60-90 minutes. I blame that rude chap in the front row who keeps interrupting the speakers with stoopid questions...
as usual the multimedia video…
catdynamics | March 12, 2009it is extragalactic day here at KITP
this could get exciting, if you like that sort of thing
unsolved problems in dynamical evolution, and why they are interesting...
for the five people who care.
This afternoon we tackle colour: red and blue, again...
All our data belongs to M87
'cause M87 has shitloads (technical term) of globulars.
Magic!
"Elowitz's Law: Sufficiently advanced image processing is not distinquishable from magic."
Yup, M87
SDSS image
What we know:
we ought to be able to calculate cluster mass loss rates, but we appear to be underestimating it by something like factor or…
catdynamics | March 11, 2009and we ponder the orbits of globulars, red and blue,
what does this tell us about where and when they formed
and where and when they get eaten
β(r) = 1 - σ2φ/&sigma22
- and be careful with your factors of 2 and φ here...
I just like this picture
ah, if we only knew that we would know something
in theory, we can look at the globular distribution - radial as we must, kinematic if we could
and hence infer whence they came at high z, given ΛCDM models
if we ignore the baryons, which i embarrassing, since globulars are baryonic and don't have much dark matter, at least not in the middle…
catdynamics | March 10, 2009we contemplate intermediate mass black holes and their possible presence in globular clusters
Eva gives us the summary:
Intermediate mass black holes, conventionally black holes with masses > 100 solar masses and less than about 10,000 solar masses, are interesting and useful beasties.
If any such things exist.
There are hints - superluminous x-ray sources in other galaxies in particular, and theoretical paths by which they could be made.
Several ways to make them suggest they ought to end up in the centers of globular clusters, and there have been repeated claims suggesting observational…
catdynamics | March 9, 2009new week, new topic - actually we'll be doing a lot of extragalactic globulars and the mass function of the clusters, but we start with Guido summarizing what we know about the stellar mass function within the clusters - including mass segregation and differential mass loss.
Wheee.
Sometime things are all topsy-turvy
as you know, Bob, stars come in a range of masses - going from about 0.1 solar masses (stars less massive than that are demoted to being non-stars, since they do not support thermonuclear fusion of hydrogen (1) in their cores on a sustained basis), up to somewhere around 100…
catdynamics | March 6, 2009ideally, globular clusters are tidally truncated
since real tidal fields are not spherically symmetric and static
we expect time varying aspherical stripping and shocking, and
with relaxation additional diffusion outside the tidal boundary
so... globular clusters should have tidal tails
we contemplate the difference between rJ and rt
How to steal a million stars: leverage of course.
first set up an investment institution, then securitize the stars, then convince your local Galactic Senate representative to repeal the archaean regulation of stellar securitization, then move to the SMC with…
catdynamics | March 5, 2009NASA's Science Mission Directorate produced a cross-discipline report on medium term needs for computational modeling capabilities; ie what serious iron NASA might want to get to play with
report is up here (pdf)
Panels from Earth System Modeling and Assimilation; Solid Earth and Natural Hazards; Astrophysics; Heliophysics; Planetary Science and Mission Engineering, considered current and near future needs and desire, scalability and both state of the art of the codes and development issues.
It is an interesting read, if you like that sort of thing.
Just for fun I did a keyword search:…
catdynamics | March 5, 2009is there, in fact, any system of globular clusters which actually traces the underlying stellar light across the underlying galaxy?
catdynamics | March 5, 2009we have our usual triplet of people talking about recent research on some theme
today we do first stars to first clusters
as usual these have video and podcasts for the hard core to enjoy
Matt on first stars - molecular association rates, accretion time scales onto protostars and reheating and shock dissociation of molecules, pre-enrichment and pop II.9 star formation
random recent reference
and Evan on Compact Stellar Clusters from galaxy outflows
random recent reference
oops coffee break, quick, before the String Theorists Eat All Our Cookies
and Loren on archaeology of merger remnants…
catdynamics | March 5, 2009we go back in time, to when the universe was young
and ponder when the globulars got made, how, why and why some are blue and some are red but very few are greenish
and we learn the globular cluster formation is not transitive
hah, and some people are impressed with mere non-commutation relations...
Jay is on deck, and he had drawn a lot of pictures.
I immediately conclude that not everything to do with globulars is monotonic or even convex.
I also conclude Jay talks faster than I can type...
Bimodality
generally see blue metal poor clusters and red metal rich(er) clusters
usually (…
catdynamics | March 4, 2009we continue contemplation of stars going splat
there are blue stragglers in dwarf galaxies
they are presumably binaries merged through McCrea type I mass transfer
we're not sure exactly how that works in detail, but it must happen because we see it in progress - ie we see contact binaries on the main sequence which must eventually coalesce
if you look at the ratio of number of blue stragglers to some other stellar population, like horizontal branch stars, then the fraction of blue stragglers anti-correlates with the total luminosity of the parent dwarf galaxy
it is a weaker correlation then…
catdynamics | March 3, 2009ok, I am mightily puzzled by a technical issue and if anyone knows the answer authoritatively, then cough it up:
question is, does the radial non-adiabatic pulsation of δ Scu/SX Phæ stars really not depend on Y?
there are some theoretical papers in the literature, notably Templeton's thesis papers, which find that the period and period ratio in the δ Scu strip is not sensitive to the helium abundance
the pulsational analysis uses Guenther's solar code, combined with the Yale Rotating Evolution Code
now high Y, helium rich stars, are hotter and more luminous at fixed mass and age, but their…
catdynamics | March 3, 2009whee, we make stars go splat again!
what exactly does happen when stars collide,
just ordinary low mass main sequence stars
Glebbeek and Pols A&A 2008 - v 488 p 1007 and p 1017
BSE: binary stellar evolution code - Hurley et al 2002 from Tout et al 1997
- mass is wrong,
- lifetime is wrong,
- luminosity is wrong
If you are using the BSE prescription for merged stars.
Other than that it is pretty good...
We are adding two stars, M1 and M2 with M1+M2 < 2.5 solar masses
assume near parabolic collisions with velocities at infinity small compared to stellar surface escape velocities;…
catdynamics | March 2, 2009monday, again, already?
we get more fresh blood, and contemplate new topics
some interesting preprints out there on astro-ph:
the Bologna group has hi-res spectroscopy of old LMC clusters, and they see the dreaded Na-O anticorrelation there also! ref
Aargh, there is no escape...
the Sweigart and collaborators have an interesting letter doing combination log(g) and photometry of EHB stars in M3.
They say no helium enrichment ref
PS: hmmmmm - so, what happens if stars with higher Y lose more mass on the RGB?
Could there be a conspiracy to come out at near constant L?
Aargh!
Ok, that would…
catdynamics | February 27, 2009Ed continues, and does case A, B and C mass transfer.
Conservatively, mostly.
From an NWU crowd talk at CfA
For conservative mass transfer, mass and orbital angular momentum are conserved.
If you let mass leave the system, as it often does, and carry away some specific angular momentum, as it will, then things get more complicated.
So: M = M1 + M2 is constant
generally M1 >= M2
q = M2/M1
Jorb = M1M2 √ (G a/M1 M2) is constant
semi-major axis changes a/ai = (M01M02/M1M2)2
Since is is conservative, dM2/dt = - dM1/dt
and (1/a)da/dt = -2dM1/dt (1/M1 - 1/M2)
start mass…
catdynamics | February 27, 2009have you ever wondered what it is that graduate students do?
yeah, me too.
Well, know you can find out, from the horses' mouth
thursday afternoon was dedicated to a rapid fire "so, what have the graduate students been up to" as five of the students here at the program gave presentations on their research projects and what they've been up to in the last few weeks
good practise for them, and a learning experience all round
no pressure, just because about 87.3941% of their likely future employers were in the room, the atmosphere here is very collegial and laid back
Sourav on "Disturbed Blue…
catdynamics | February 27, 2009Is the title of the talk Juan Maldacena gave thursday morning.
I missed the live delivery, due to my deplorable inability to be in two different places at the same time, but, as always webcast video and podcast are here
Enjoy.
Ok, it is string theory, but Juan always gives good talks.
Or he did the other time I saw him give a talk.
catdynamics | February 26, 2009yesterday I missed the post-Newtonian discussion, which is a bummer, but I was busy explaining to a hoard of pre-Ks why Mars looked green...
so now we go back to blowing things up
yes, it turns out that not all whites are the same, and trying to project onto that shade of white which has just a tint of blue in it, is not the same as your eggwhite screen, when using an RGB projector.
I should have riffed on Kim Stanley Robinson, I guess, but I didn't.
Look!
Hubble Space Telescope! Astronauts! Rockets! Aliens!
Today, we return to massive binaries and long GRBs in particular, which lets me…
catdynamics | February 24, 2009our topic for today is to find the best paper on globulars published since the workshop started
sadly I'm only up to 2007 on astro-ph
My nomination of this paper failed to win the prize, due to the excessive integrity of the judge
PS: I WON!
WOO HOO!
Ok, it was the razzie.
But I like it.
The Munchkin, He Likes It!
we then somehow started discussing MOND and why measurements of accelerations in globular clusters all seem to give values of about 10-10...
bother
we then went on to discuss a Larson paper, no equations, no figures, lots of ideas
brilliant
seriously: no equations and no figures…