Movie Review - Fanboys

After four years of waiting, and being a complete n00b and missing it in theaters, I finally got to see Fanboys when Netflix sent it to me.

Quick review: It was funny. Not the funniest film I've seen, but I laughed. I think if you're not an immense Star Wars fan, this movie would have been pretty awful. There were so many little jokes that would go completely missed if you weren't intimately familiar with the Lucas films.

The plot was manageable even if somewhat predictable. The biggest surprise to me though, was the ending wasn't what I was expecting. The reason was that this Fanboys wasn't the first Fanboys with pretty much the exact same basis.

In 2003 a group of New Zealand film makers put together a short film called Fanboys about a group of friends that intended to steal a screener copy of Episode I before it was released in theaters. Hijinks ensued and it ended up that Lucas was aware of the plan and let them get away with a copy of the Star Wars Christmas Special as punishment. If you're not familiar with the Christmas Special, well, it's better that way. It featured Bea Arthur singing some crazy lyrics to the Star Wars theme and some campy story about Chewbacca having to get back to his family for “Life Day” (the Wookie knock off of Christmas). It was bad. Really bad. The only notable part of it was the first introduction of the bad ass bounty hunter Boba Fett who later appeared in Empire Strikes Back to capture Han, then fell into a Sarlaac in Return of the Jedi (yet lived according to the novels) and was later revealed to be a clone of Jango Fett in Attack of the Clones.

Anyway. That's how I was expecting the film to end. But it didn't. It ended as you'd expect if you were watching the movie with no prior knowledge of any of these things. The acting was pretty good from all the main actors. The Trekkies were pretty bad, but who cares? They're Trekkies. The cameos were awesome. And I swear Kristen Bell is stalking me. She's been in all sorts of cool stuff, from the Showtime adaptation of the musical version of Reefer Madness, to being a major character in the TV show Heroes, to a voice for the upcoming Astroboy movie, and apparently even a film adaptation of the classic mathy novella, Flatland. Either way, I can't get enough of her (or Felicia Day for that matter).

So should you run out and get the movie? If you've seen everything else for the summer and are feeling geeky, go for it. It has a few touching moments between a few laughs. It's short enough to hold your attention span. Seven stars out of ten.

Building a New Ladder

As I've discussed before, Cepheid variable stars are a fundamental method to the entire understanding of the scale of our universe. These standard candles were first used to conclusively demonstrate that fuzzy patches of light were entire “island universes” or, as we call them today, galaxies. From there, they've been used to calibrate most of the rest of our cosmic distance ladder.

So what would happen to our cosmic distance ladder if they'd never been discovered?

A paper in the June 1 ApJ is the third in a series that asks just this question. Sadly, only the first is available on the preprint server currently.

The first paper looks at how possible it is to rebuild the distance ladder without the use of Cepheids. As a replacement, they use the tip of the Red Giant Branch (RGB). As stars die, they expand. The larger surface area corresponds to a greater luminosity, but also means that the same energy is being spread out more, so the temperature drops. In more practical terms, this means that the star's position on the HR diagram moves up and to the right.

Overall, stars will max out at an absolute luminosity of about 10⁶ times the luminosity of the sun. If astronomers can isolate those stars, as with other distance indicators, they know how bright they should be, and then comparing them to how bright they are (and correcting for other dimming effects), they can then get a new distance estimate. Fortunately, the RGB tip method works very well because it's fairly insensitive to the chemical composition of the star (how much “metal” the star has).

This study used the RGB stars to calibrate the distance to 14 galaxies which was in turn used as a reformulation of the secondary distance indicator, the Tully-Fisher (TF) relation. Although there was some difference, it was very slight. In fact, it was very nearly within the error range (0.19 ± 0.13 mag).

Using this in turn, to recalculate the Hubble constant (which the inverse of gives the age of the universe) they got a value of 73 ± 5 km s^-1 Mpc^-1. This is amazingly close to the most recent calculation of 74.2 ± 3.6 km s^-1 Mpc^-1!

Since this paper was published in 2008 (before that most recent Hubble constant), the authors instead compared their value to that from Sakai et al. (2000) which gave a value of 67 ± 10 km s^-1 Mpc^-1.

In one case, a bit higher. In one a bit lower. In either case, a very consistent value! No matter how you approach it, the universe is 13 billion years old.

(PS: If anyone can get the next two articles in the series for me, I'd greatly appreciate it! DOI numbers are 10.1088/0004-637X/694/2/1331 and
10.1088/0004-637X/697/2/996.)

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Mould, J., & Sakai, S. (2008). The Extragalactic Distance Scale without Cepheids The Astrophysical Journal, 686 (2) DOI: 10.1086/592964

Gyrochronology

In case there was any confusion, we live in a dynamic universe. Stars are born. They die. Galaxies collide. Things happen.

In trying to put together a comprehensive picture of how this all happens, one of the things we need to know as astronomers, is in what order things happen. How has our universe evolved?

Knowing how to tell just how old objects in the universe are is a serious challenge. There's some tricks out there, like looking at the main sequence turn off for clusters, but for isolated stars, it's much more challenging. Stars that are still on the main sequence pretty much all look the same for a given mass. Although they cook up heavy elements in their cores, most of it will never reach the surface and even if it did, there would be no way to be certain that those heavy elements weren't present when the star formed.

For isolated stars, one of our best hopes is to look at how fast the star is spinning. As stars age, they radiate away energy in various manners, burning off the angular momentum with which they're born. So if stars of similar masses all started off with the same rotational speed, and spun down at the same rate, the amount by which they'd slowed down would tell us the age.

Sadly, nature's rarely so simple.

Dating stars from their spin can be done (known as gyrochronology) but it's a tricky business.

A paper in last month's ApJ discusses the problems and some of the solutions.

The idea is to calibrate the method by looking at the rotation period for stars for which we know the age. As I pointed out before, clusters offer this potential. Then, by plotting the period vs the age, we would hopefully be able to make some sort of relation.

This paper built on previous work which looked at clusters like the Pleiades, M34, NGC3532 and the Hyades. In specific, the authors added M35 to the list of clusters for which the periods were plotted.

As I hinted at before, things aren't quite so simple, mainly because there's other variables to consider. One of the ones you might expect is that the mass plays a factor. This study concentrated on “late” type stars; stars that are on the low end of the mass scale (G, K, and M spectral classes).

Another issue is that, even for a single cluster, there's apparently not just one sequence that stars for a given age, but two! Here's what I mean:From this picture, you can see that there's a line going diagonally from the lower left to the upper right, and one along the bottom. Incase you're unfamiliar with the terminology, the B-V (bottom axis) is the color. Bluer (hotter and more massive stars) are to the left. Cooler (less massive and redder) stars are to the right.

What this means, is that for stars of a given mass, you can have have two possible periods! Blah. Very blah.

The first question that should be asked from here is, "Why are there two sequences in the first place?"

The notion is that there's two different processes that are controlling how the star is spinning down at work. To understand one of them, let's consider a very simplistic model of stars:

Stars form as giant clouds of gas collapse. Since angular momentum is conserved the forming star spins up, faster towards the center (what will become the core). Once the star is formed, the core will be rotating faster than the surface. Since stars aren't solid, that means there's not a good way for the outer layers to steal the angular momenum from the core and for the rotational period of the core and the outside to even out. As such, the observed period of the star will be longer. The authors call this the "C sequence" for "convective". In this one, the core and shell are decoupled.

Quite often, however, this won't be the case. Stars will quite often have strong magnetic fields that act like anchors, and they drag the surface layers of the star along. This will speed up the outer layers and defines the second, faster sequence (the bottom one) which the authors call the "I sequence" for "interface".

Well, that's all well and good, but it still doesn't tell us anything about the age. At least, not until you start looking at the ratio of stars on each sequence vs cluster age. When that's plotted up, young clusters tend to have more stars that are on the C sequence with slow rotators. As you get to old clusters, more and more stars are on the I sequence (short periods). Obviously, stars will tend to switch from one to the other as the clusters age. The idea here is that the friction between the layers of the star will help create a dynamo and set up a magnetic field which will switch stars from the C to the I.

Regardless of what the processes are that govern the switch, the main thing is that it happens. And it works out that there's a fairly well defined way it changes from one to the other. The ratio of the number of stars on each sequence is directly correlated with the age!

So how well does it work? Using the data from M35 to help calibrate the method and then applying it to M35 gave the authors an age of 134 million years with about a 3% uncertainty. This isn't quite the 150 million year age given from the main sequence turn off, but it's still not a bad approximation.

Meanwhile, there's still a few niggling bits to clear up. The big one is what's with the stars that aren't in either sequence? There's a lot of stars that fall somewhere in between. The authors predict that these stars are likely close binaries that have slowed without the benefit of magnetic fields, but rather, through tidal locking. At least one of the dozen or so stars caught in between is known to be a binary star with a period of 10.33 days. This orbital period is strikingly similar to the 10.13 rotational period which lends support to this prediction. Additionally, 3 of the other stars in the gap are photometric binaries (in otherwords, their brightness changes in a manner consistent with what's expected for a binary system).

So overall, this method looks like it works pretty well. Undoubtedly, more clusters will be added and the relation further refined. Obviously, isolated stars can't take advantage of this method either, since it requires a ratio of many coevolutionary stars. But that's a challenge that will have to be met in another paper.

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Meibom, S., Mathieu, R., & Stassun, K. (2009). STELLAR ROTATION IN M35: MASS-PERIOD RELATIONS, SPIN-DOWN RATES, AND GYROCHRONOLOGY The Astrophysical Journal, 695 (1), 679-694 DOI: 10.1088/0004-637X/695/1/679

Scientia Pro Publica #4

My post on the cosmic distance ladder was submitted and selected for the blog carnival Scientia Pro Publica. If you're interested in other sciency things, head over and check it out.

In the mean time, I'm slogging through some new (and very long) journal articles I'll post on once I finish them.

Egads! What's 'appened to that galaxy?

It's going backwards!

Well, part of it at least.

A paper from last month's ApJ takes a look at two galaxies (NGC 2551 and NGC 5631) that are a bit... odd. Namely, part of the disk of the galaxy rotates one way, part of it rotates the other.

Both of these galaxies are classified as spiral galaxies, but only just. SIMBAD (an astronomical database) lists NGC 5631 as an S0/Sa galaxy which means it barely shows any spiral structure. Meanwhile, NGC 2551 is just a generic S, so very little spiral structure at all.

One of the things I found interesting about this paper is that just reading the galaxy designations in the abstract, I suspected these galaxies were not particularly nearby (since if they were, I'd probably have heard of them before). Thus, since they're likely too far away to resolve individual stars, how do they separate the rotational velocities of the stars from that of the gas?

The answer is to look for properties that are different between the two. The two are largely composed of the same elements, but they exhibit different properties due to the difference in pressures and temperatures. Low density gasses like gas exhibit emission line spectra while stars which are at high density have absorption spectra. (I talk more about these here if you need a refresher).

By picking out lines of each that would be prominent (the NII line for gas and the K1III and K3III lines for stars), it was possible to separate the radial velocities of each of the components.

So what's up with the backwards gas? Or is it the stars that are backwards?

The best answer is that gas rich satellite galaxies, like our own Magellanic clouds were cannibalized by these galaxies. Statistically, these types of mergers were calculated to happen fairly often and be present in 8-12% of spiral galaxies. But is that just jumping the gun and assigning a probable causation to this?

Not at all. In at least the case of NGC 5631, there was also a prominent dust ring associated with the gas that is inclined 35º to the plane of the galaxy! (I've talked about similar phenomena in our own galaxy here.)

Oh, and this group also gets cool points for using a telescoped name SAURON.

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Sil'chenko, O., Moiseev, A., & Afanasiev, V. (2009). TWO MORE DISK GALAXIES WITH GLOBAL GAS COUNTERROTATION The Astrophysical Journal, 694 (2), 1550-1558 DOI: 10.1088/0004-637X/694/2/1550

Why did no one tell me?

Fanboys was released? How did this sneak in under my Nerd-dar?

Dear Kansas Republicans,

What are you smoking? May I have some?

I read a while ago that there was a cut of 3% across the board to help balance the budget. Could be worse.

Then I read that this is hitting education in Kansas on top of a cut of already 7%. Uh, not cool.

Then I read that the budget defect is $328 million and you're wanting to solve over half of that by cutting education?

I guess this is a pretty clear sign of where your priorities lie.

So if you'll excuse me, I have some more resumes to send to schools in Missouri, since they seem to actually respect education over there.

Bye Venomfang!

Looks like VenomfangX is gone again. His youtube channel has been deleted, his videos are gone, and even his website is taken down.

Apparently, there's been claims that he's received "death threats" from "Muslims". He's posted some pretty condemning things in regards to Muslims before, so it wouldn't completely surprise me, but if he really were going to let that cause him to wet his pants, why not just take those down and leave up all his Creationism nonsense?

Safe to say, I'm highly skeptical. My personal thought when I heard this, is that VFX is doing what he tends to do a lot: Play games to try to garner emotional sympathy. If you watched his video in response to one of his followers going and committing the murder/suicide earlier last month, he has his little "crying moment" at the beginning and intentionally chooses not to edit it out. Why? Because it makes him look sympathetic and plays the pity card. Sadly, that's the best he has to offer.

Meanwhile, his website tells a different story:

This site has been taken offline by the parents of VenomFangX, they don't support/share his views and apologize if he has offended anyone.

Oops. Guess mommy and daddy didn't like having a little liar in the family pushing it all over the internet.

Is he really gone though? Who knows. After all, he pulled disappearing act last year too.

Another Rung on the Ladder

One of the most fundamental problems in all of astronomy is to determine the distance to objects. To be able to do this, astronomers have developed what's known as the cosmic distance ladder. The base is built with extremely reliable methods, like parallax, which is then used to calibrate distance indicators for objects further away, which are then used to calibrate even further objects, etc....

In this ladder, one of the most helpful and commonly used types of distance measurement is based on a type of star known as Cepheid Variables. These stars are stars towards the end of their lives, off the main sequence, in what's known as the instability strip. Because of their unstable nature, they change their brightness in a regular way. In particular, the average brightness is directly related to the amount of time it takes to make one full cycle (the period) by the equation

M_V = -1.34 – 2.85 logP.
Thus, by observing a Cepheid type variable's period, we can determine the overall brightness, which we can then compare to how bright it actually looks to determine distance via the distance modulus.

As with all things, there is some inherent error in this equation. It's well established that the amount of heavy elements in a star (the “metals”) will change the overall brightness. As a result, it's suggested that Cepheids in the Large Magellanic Cloud are about 0.4 magnitudes fainter than stars with metallicities similar to the sun (Sekiguchi & Fukugita). Additionally, the calibration of the equation I listed also has general error associated with it as well, but in general it's nothing too outstanding. In general, Cepheids are a wonderfully reliable distance indicator that works over a large range of distances.

However, there's a limit. The problem is that this type of variation only occurs with the more massive stars. Since more massive stars burn through their lives faster, Cepheids are relatively speaking, young. As a result, they tend to be concentrated in clusters since they have not yet had time to disperse. The problem then becomes that, eventually, you simply can't reliably resolve the star you want and be certain you're not getting light contamination from other stars of a similar brightness contaminating your data. Due to this Cepheids only end up being useful to a distance of about 25-30 million parsecs.

A recent paper in the Astrophysical Journal provides a potentially new way to extend that distance to as much as 100 million parsecs (Bird, Stanek, Prieto)! Their trick is to use Cepheids that aren't the prototypical variety. Normal Cepehids are considered to have periods of about 3 days to about 100. But the ones looked at in this study exist at the upper edge of that limit and well beyond, going from 80 days to as much as 210 for the 18 stars they analyzed. They call these stars, “Ultra Long Period” (ULP) Cepheids.

The advantage to these stars is that they're about 2.5 magnitudes brighter than their classical companions (remember that the magnitude system is a logarithmic scale so that's actually about 23 times as bright!). This means that (1) we can see them further away and (2) it's less likely that there will be stars of a similar brightness to contaminate the field. Sounds like it solves all our problems, right?

As of yet, I'd still be somewhat skeptical to fully rely on this system. The issue is that, although promising, the statistical certainty just isn't there yet. The authors of this new paper looked for a new period-luminosity relation in three different filter systems. In all three, the root mean squared values (in essence, the amount of uncertainty) was at least twice as high as it was for classical Cepheids. While twice the error can be dealt with and doesn't ruin the science done with such a method (assuming that the error is properly figured in), it does not yet match the statistical certainty of other available methods available up to 100 million parsecs (namely the use of Type Ia supernovae).

But could it get there?

The authors suggest (and I'm prone to agree) that their uncertainty is not too much higher than that of the Type Ia supernovae. But to get the certainty of the supernovae method as low as it is, significant effort has been invested in beating down the statistical errors. If a larger survey was conducted and the baseline was expanded it's entirely possible that the errors for this ULP Cepheid method would decrease as well. It's not a guarantee, of course. It's entirely possible that in expanding the sample size may begin to reveal other variables they had not yet considered, but it's a good possibility.

So in the end, this paper is giving us the very real possibility of adding a new rung to our cosmic distance ladder. Each step makes us more certain of where we fit in our universe.

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Sekiguchi, M.; Fukugita, M. (1998). Metallicity dependence of the Cepheid calibration The Observatory, 118, 73-77

Bird, J., Stanek, K., & Prieto, J. (2009). USING ULTRA LONG PERIOD CEPHEIDS TO EXTEND THE COSMIC DISTANCE LADDER TO 100 Mpc AND BEYOND The Astrophysical Journal, 695 (2), 874-882 DOI: 10.1088/0004-637X/695/2/874

Knowing Our Cosmic Sperm Donor

In perusing the recent articles in the ApJ, one of the ones that caught my eye this week was one entitled, “²⁶Al and the Formation of the Solar System from a Molecular Cloud Contaminated by Wolf Rayet Winds”. Quite the mouthful to be sure, but it's an interesting paper.

The idea is that a number of unstable elements (specifically ²⁶Al) are present in the oldest of meteoritic materials in higher concentrations than would be expected if our solar system had simply formed from the gravitational collapse of the local interstellar cloud. Their presence indicates that some sort of event happened near our solar system which injected these elements as the cloud underwent its collapse.

In general, heavy elements like aluminum are cooked up in stars. In fact, the ratios of elements observed in these remnants suggest it wasn't just any star, but a massive star. But once those elements are cooked up, the next trick is transporting them to our fledgling solar system. But how?

One obvious answer is to blow up the star that's making the elements in a supernova and spread them all over the place. Another possibility was that the elements were blown here in a gentler manner from a type of star known as a Wolf Rayet star. These stars are massive stars that are so hot, they blow off their outer layers.

The trick is to determine which of these possibilities was the real deal. Again, the ratios tend to rule out supernovae as a possibility due to the fact that such an occurrence “invariably over-predict the abundance of ⁵³Mn”. To get the right abundances, the scenario that fit was that a nearby cluster of stars released the necessary elements as our solar system was forming, but while it was still dispersed enough to be vapor.

This paper really highlights one of the things I really love about astronomy and science in general; Small details, like the overabundances of rare materials in this case, can give hints at very grand questions, like where we came from. I find it amazing that we are capable of determining what our fore bearers must have been like even though they are no longer around just by looking at that which we carry inside our own solar systems and bodies.

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Gaidos, E., Krot, A., Williams, J., & Raymond, S. (2009).
Al AND THE FORMATION OF THE SOLAR SYSTEM FROM A MOLECULAR CLOUD CONTAMINATED BY WOLF-RAYET WINDS
The Astrophysical Journal, 696 (2), 1854-1863 DOI: 10.1088/0004-637X/696/2/1854

On the other foot

In America, we frequently hear that this country "is a Christian Nation". While I disagree in some senses, this is in many ways very true; The majority of the nation is composed of Christians, and despite laws against it, Christian morality works its ways into our politics, schools, and just about everything else. Those of us that aren't Christians, or are but are the wrong kind of Christians constantly have an uphill battle to make sure that our rights aren't trodden upon. It would be wonderful for atheists as a minority, if we got the theocrats out of power and had a secular government.

So wouldn't it be strange for Christians to be the persecuted minority praying for a secular government?

Turns out, it's happening in India. The plight there seems worse than minorities have in the US, but it's a good reminder of what happens to minorities under sectarian governments. So while Christians have it good here, they should keep in mind just what it would be like if that shoe was on the other foot.

Sadly, experience has told me that those that most desperately need to keep this perspective are completely blind to it.

Pareidolia: n + 18

Apparently fried junk food must be among the favorite foods for divine beings. Of all the pareidolia cases I see, it seems there's an unusually large number from diners. Either that, or people working at such places are credulous twits. And yet again, a fuzzy figure has shown up on a griddle.

Phenomenon

Made by a friend for an Astronomy project. Too epic not to share.