astro
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 3, 2009as you know, we're in the opening round of the decadal survey, prioritizing astronomy research and facilities for the next decade - I occasionally suspect all of astronomy has shut down while all of us either write or read white papers and policy documents on some subfield or another...
anyway, Julianne over at CV came up briefly for air to summarize what is going on
what she said.
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…
catdynamics | February 24, 2009What Julianne said.
It is not like going out into the Real World is a very promising career track right now.
catdynamics | February 24, 2009NASA's Orbiting Carbon Observatory had a launch failure.
Taurus launch out of Vandenberg last night, tried to stay up to see if I could see the launch - often possible from the area - but I crashed before scheduled launch time.
Apparently payload failed to separate after stage burnout and the whole lot crashed near one of the poles (south pole - thought that was what they said but wasn't sure till I saw the formal press release).
Total loss.
I guess we know what NASA's SMD will use their $400M stimulus for now - that should just about buy a replacement.
It is a bad loss, the OCO, or…
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…
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…