The Danger Zone: Where the Buffalo Roam.
Defining a Molecular Cloud
I'm going to try to answer a few questions [this post is in-progress and will be updated]:
- Why are molecular clouds called molecular clouds?
- What distinguishes a molecular cloud from similar objects (e.g. cores, clumps, HII regions)?
- What do molecular clouds look like?
- How do astronomers look at molecular clouds?
- Why are astronomers look at molecular clouds (why are they interesting)?
- What do molecular clouds have to do with star formation and planet formation?
- How are molecular clouds involved in galactic evolution?
1. Molecular clouds are regions in space with densities high enough and temperatures low enough that molecules can form. The most common molecule is Hydrogen (H:sub:2), simply because hydrogen is the most common atom. The next most common is Carbon Monoxide, CO, that is ~104 times less common. It is the easiest to observe, though, because H2 can only emit light and energy in 'forbidden' transitions that don't happen very often. 2. Size, temperature, and composition all distinguish molecular clouds from other nebulae.
An H II region is very hot - in it, hydrogen atoms are ionized by radiation from a nearby O-type star. In regions hot enough to ionize hydrogen, all molecules are destroyed unless they have already collected into larger dust particles.
A core is a much denser bunch of gas than a molecular cloud. Cores are dense enough that their outsides shield their insides from the radiation of the rest of the universe and their insides cool to very low temperatures. At low temperatures, the pressure supporting the cloud against collapse is lower, and stars can form via gravitational collapse.
I don't really know what clumps are... they're supposed to be something intermediate between cores and clouds, but I don't know what their distinguishing features are.
3. It depends on what wavelength you're looking in. In the optical, where our eyes can see, they look dark - they're seen because they absorb light from behind them. In the infrared, the hot ones glow, but the cold ones are still invisible. If you go all the way to the millimeter, all molecular clouds glow, no matter how cold, but in order to see them there has to be a lot of material. I'll add some pictures here later. 4. Lots of ways. Optical telescopes aren't the best choice, though. With near-infrared images, we can detect molecular clouds by counting stars and noticing when there aren't as many in some regions. This technique is called "NICE" and works because there are so many stars in the sky and dust in molecular clouds includes some, but not all, of their light. In the far infrared, we can see hot dust glowing, but this is very difficult because our atmosphere is opaque in the infrared - it's like trying to look through a brick wall. We need telescopes in space to be able to see anything at these wavelengths. In the millimeter, there are some 'holes' in the atmospheric absorption, sort of like color filters, that we can see through to detect the coldest emission.
Delirium Nocturne
Delirium Tremens is a tasty beer itself, I think. I'm drinking Delirium Nocturne right now. It has a cool (opaque!) bottle, plus a pink elephant on the label. At 8.5% it's pretty strong, but very drinkable with no taste of alcohol. It's definitely my favorite Belgian brown now. It still has that wheat-soy-sauce taste to it, but very weakly. It poured with ridiculous head - I could not control it. Overall, great beer, worth the ridiculous price I paid for it, whatever that was.
Detexify!
for when you can't remember how to draw an angstrom: detexify .. image:: http://2.bp.blogspot.com/_lsgW26mWZnU/SydQdSeP5EI/AAAAAAAAFds/f8-29Qvef3E/s400/detexify.png
Do not install 10.5.5
Well, I didn't obey that excellent advice from Charles. I installed the 10.5.5 update. Now DS9 - in my opinion, one of the heartiest and most reliable programs I've dealt with in the astronomy world - won't work because TCL is broken. I doubt TUI or most of the other things I use will work either. That's a tragedy of significant proportions - I NEED ds9 to make my observing files! I can only pray that an update of TCL using port will work... if not I'm basically screwed.
ds9 commands to test distortion mapping
trying to figure out whether I'm screwing something up in the distortion map phase... the -scale limits command here is new and useful
ds9 testfields_*pix5*_map0.fits -cmap sls -scale limits 0 .005 -zoom 4 -match frames wcs -match scales -match colorbars &ds9 testfields_*pix15*_map0.fits -cmap sls -scale limits 0 .003 -zoom 4 -match frames wcs -match scales -match colorbars &ds9 testfields_*pix10*_map0.fits -cmap sls -scale limits 0 .004 -zoom 4 -match frames wcs -match scales -match colorbars &
DS9 - crosshairs on command line
ds9 pmm*_map0.fits -zscale -match scales -zoom 4 -match frames wcs -crosshair 17:33:02.7 -13:04:49.5 wcs fk5 -lock crosshairs wcs & ds9 pmp*_map0.fits -zscale -match scales -zoom 4 -match frames wcs -crosshair 17:33:02.7 -13:04:49.5 wcs fk5 -lock crosshairs wcs & ds9 mpp*_map0.fits -zscale -match scales -zoom 4 -match frames wcs -crosshair 17:33:02.7 -13:04:49.5 wcs fk5 -lock crosshairs wcs & ds9 mpm*_map0.fits -zscale -match scales -zoom 4 -match frames wcs -crosshair 17:33:02.7 -13:04:49.5 wcs fk5 -lock crosshairs wcs & DS9's crosshairs are extremely useful for checking on WCS coordinate matching, especially when they can be set precisely using the command line. I don't know how to set the coordinates exactly interactively... that may come later.
DS9 gaussian fitting
One thing DS9 desperately needs is an interactive gaussian fitter. I have NOT implemented one yet, but it is high on my to do list. Has anyone else (googlers?) tried or succeeded in implementing such a thing? Ideally, something with NO dependencies: if I write one, it will require python, numpy, and probably pyds9 - ick. Straight-up TCL would be very much preferable.
Dying Dock
My dock keeps dying. Repeatedly. Over and over. Only solution so far: ps -vax | grep -E "Dock|PID"kill -HUP PIDkill -s SIGCHLD PID And similarly for problems with Chrome + /usr/sbin/mDNSResponder. They tend to go bad together.... no clues yet from the system logs. Ironically, the crash reporter seems to fail the most often...
Electron-Cyclotron Masers from planets around White Dwarves
I believe two departures from the stated topic become a rule rather than an exception. OK, so this is now a blog about generally interesting astronomical topics. Today's topic is planets around white dwarves. First, why do we care? Well, everyone wants to find more planets, and in this case we'd be seeing planets that survived the deaths of their host stars. When a main sequence star like the sun reaches a certain age (around 10 billion years old for the sun), it expands and cools, becoming a red giant. At this point, depending on a number of factors including the mass of the star, it can engulf the planets around it. If this happens, the planets experience a drag force (think "wind resistance") as they move through the star's atmosphere and they spiral in to the center, where they burn up and are destroyed.
However, if the star is just the right size and the planet is in just the right place, something more interesting may happen. The Red Giant phase lasts for a few hundred million years, after which it undergoes an Asymptotic Giant Branch (AGB) phase where it alternately grows and shrinks. During this phase, it will temporarily engulf a planet, but not for long enough to destroy it - just long enough to move it inwards a little bit. Of course, conditions on the planet won't be very pleasant during this period.
As shown in the animation, the AGB phase leads into the formation of a planetary nebula with a white dwarf at the center. If things went right, a planet could end up close to the white dwarf after the tumultuous period just described. This is an exciting proposition because it opens the possibility that we could detect the planet interacting with the White Dwarf's magnetic field. You may recall hearing that the Earth has an iron core, which is why it has a magnetic field surrounding it. A similar planet orbiting a white dwarf would generate currents, and the electrons would then flow onto the poles of the white dwarf and show up as hot spots, like on Jupiter.
The hot spots would be impossible to spot by normal methods, but on either side of the hot spots there are big lobes where the electrons will emit radio light, which is detectable by the best radio arrays on the ground (e.g. the Very Large Array and LOFAR).
Why should we care? Well, besides just detecting the presence of a planet, we would be able to tell something about the conductivity of its core, which is very difficult in any other situation. We might also be able to say whether the planet has a magnetosphere and therefore was Earth-like. Finally, we could say something definitive about the eventual fate of the Earth... in about 4.5 billion years. This post was based on papers by Andrew Willes and Kinwah Wu in 2004 and 2005.
