astro
catdynamics | March 22, 2009ever wondered what age the universe is at redshift 6.7?
or how many nanoJanskys there are coming in the R band from a 23rd magnitude star?
well, a couple of web based calculators will tell you, rapidly and precisely
in cosmology, it is easy to get a crude estimate of time lapsed since the Big Bang, given the measured redshift, by assuming a pseudo-Euclidean universe, but often the precise time actually matters.
But, for a ΛCDM cosmology, the redshift-age formula is messy
Fortunately, Ned Wrigh at UCLAt has a handy dandy web Cosmology Calculator, which will give you the answer at the press…
catdynamics | March 20, 2009I am in an all day meeting with bio/geo types, as one does, and as I sit here a random thought struck me, since us astronomers will insist on asteroids as the universal explanation for all things
we have a nice medium sized impact structure in Chesapeake Bay,
the ripples seem to have come as far as Pennsylvania, possibly responsible for the rather bothersome acid rock that almost ruined our most recent local attempts to stimulate through the I-99 construction
anyway, the Chesapeake Bay impact structure is about 35 Myrs old.
In fact, at a glance from an outsider, it seems to coincide within…
catdynamics | March 19, 2009
Bit behind with KITP program events, mostly due to my deplorable inability to be in two or more places at the same time.
Bit on multiple populations, and then gravitational radiation sources.
Franca d'Antona's talk on multiple stellar populations is here - thought we knew simple main sequence stars?
Hah!
Worried?
You ought to be...
I'll be getting back to multiple populations and why some of us are worried later.
Richard on gravitational waves here follow by Ilya here
Another topic due to get heated.
More on that next week.
catdynamics | March 19, 2009Nice article over at Universe Today on
The Sun As A White Dwarf Star and why it might become a DAZ.
Good stuff.
Even though I say it meself.
catdynamics | March 17, 2009stars do turn, sometimes fast enough to be noticeably flattened
this may have consequences
Like So
there are two issues related to stellar rotation contemplated this morning:
Altair
now, way flatter than that...
self-enrichment - back to the good old O/Na anti-correlation
evidence for H burning at high T
trick is not so much to burn the H, but to get the ashes out...
can do that either with AGB stars, yes, it is the dreaded "third dredge up", or just boring old hot bottom burning... ok, don't ever google that.
AGB dredge up (from Eskridge's online lecture notes at MNSU)
anyway, to get…
catdynamics | March 16, 2009I think, that every large spectroscopic bucket telescope really ought to have a colocated wide field imaging telescope
like a 4m spotter telescope
seriously
catdynamics | March 16, 2009lovely day, here at the beach
we have a busy week, the start of a busy month
we'll be doing multiple populations in depth, again,
and yet more on IMBH
this morning we contemplate, via Mario, whether globulars occupy a fundamental plane like galaxies, maybe even the same plane
log(Re) = 1.24 log(σ) + 0.33 SBe - 8.895 (for galaxies)
refs Djorgovski 1995 and Pasquato & Bertin 2008
1.24? 1.24!
Observers are soooooooo silly sometimes.
Clearly it must be 5/4 and 1/3
I mean 31/25 is just a silly number.
There is still a fundamental plane though P&B have somewhat different slope and a zero…
catdynamics | March 13, 2009"Astronomers are just as dumb as economists"
are not!
poopyhead!
and, anyway, at least we know how to spell asteroid... nah, nah.
from Economists Aren't More Stupid than Other Scientists
- wait: "Other Scientists"...?
Tee hee.
h/t CR
Oh, if we're going to be all serious and shit:
asteroids really truly do exist
we know asteroids hit in the past (cf The Moon)
we have seen significant planetesimal impacts in the current epoch (cf SL-9 on Jupiter)
we know asteroids will hit in the future
- aside: I spent an enjoyable dinner with an economist considering his rational estimate…
catdynamics | March 13, 2009Fermi Gamma-ray Telescope has results.
We hear about them.
why, yes, that really was 47 Tuc
"Discovery of γ-ray sources from the globular cluster 47 Tuc" or something similar, in preparation, at a glossy journal near you soon
in the mean time, browse the LAT bright source catalog (for high galactic latitude - none has dared descend into the plane yet...)
this will really screw up starry eyed particle (astro)physicists who were desperately hoping to find cold dark matter annihilation radiation from substructure in the halo
hah!
we temporarily ignore gamma-ray bursts...
we will return to your…
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, 2009Fermi gamma ray telescope has released the all sky image.
Some interesting stuff...
click for big, zoomable
yup, that's 47 Tuc down there at the bottom.
More on that tomorrow, I expect.
Fermi press relase
catdynamics | March 12, 2009yes, the Photomixers are back!
"...get your motor running
head up Mauna Kea
looking for some spectra..."
"..fire all your lasers at once
and explode into space..."
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 12, 2009we are currently at a solar minimum, and the next cycle is starting,
but the numbers are down and the
Sun is unusually quiet
Like so:
yup, still no spots
Ok, should we be worried?
Is this the start of a new Maunder Minimum?
Will the Thames freeze?
Will there be knee deep snow in New England before Thanksgiving?
Will annoying climate skeptics chuckle and gloat?
Well, no, not yet:
though if by this time next year there are still no spots, we might start to think...
One should note that solar radiance and activity is independent of atmospheric IR opacity - it is perfectly possible for cyclic…
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 10, 2009There have been several interesting candidates for binary supermassive black holes found recently.
New data suggests one of the recently announced candidates is probably not a binary.
A recent press release from NOAO suggested that SDSS J153636.22+044127.0 might be a close binary supermassive black hole. (Nature paper here, subscription required).
The object was picked from the Sload Digital Sky Survey catalog of active galactic nuclei based on its extreme spectral properties.
click to embiggen
The observation was of a double peaked broad emission line spectrum, and Todd and Tod suggested…
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…