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Stars and the Exolab on PhD Comics!

Like most former and current grad students, I'm a huge fan of PhD comics. I'm also a fan of the artist behind PhD Comics, Jorge Cham, in particular his online shows on scientific topics such as dark matter, the Higgs boson and Open Access publishing. When I first watched Dark Matters, my immediate thought was "Wow, this is an amazing teaching tool. I wonder if Jorge would like to do one on exoplanets."

So, even though I had never met him, I nervously typed out an email, proof-read it, reread it, and finally hit send. Lo and behold, I managed to set up a lunch meeting with Jorge and we talked about academia, comics, teaching, and my research. He agreed that it would be fun to do a video on Exoplanets and we scheduled a date to record the audio last Summer. I also applied for and received funding from the Caltech Innovation in Education fund to contract Jorge's expertise for the whole endeavor.

Jorge and I decided to do things a bit differently than his past animated pieces. First, instead of interviewing a single scientist, he would capture the highly interactive nature of my group by gathering several scientists and having us all talk with him. So I convened a meeting in my office with my two then-first-year students Melodie Kao and Ben Montet, and one of the postdocs in my group, Jon Swift.
The second difference would be the use of full color, which as you'll see was a necessary touch given the topic of our discussion.

We recorded about 5 hours of audio (!), which included a large amount of information about stars. Our detour into stellar astronomy was no accident: in order to understand planets, one must understand the physical characteristics of stars that they orbit. Consider how the three smallest planets detected to date were uncovered by learning more about their host star. When we were done, it was clear that we not only had material for an animated piece on exoplanets, but we also had great material for stars.

The 5-hour interview was whittled down to 8 minutes and 21 seconds, and Jorge applied his magical touch to create this amazing video. After the video, I show some actual stellar spectra. Jorge and I hope that after watching this piece that you have a better appreciation for how fundamental stars are, and how astronomers can use stellar spectra to learn about our Galaxy, our Sun and ourselves as humans comprised of elements heavier than hydrogen and helium!

Bonus material:

Here are some actual stellar spectra from stars hotter and cooler than the Sun. For the aficionados among my readers, you'll note that these aren't *real* spectra, but instead model spectra (Oops! I was wrong about this. See this correction.). There are no instruments that can provide this sort of wavelength coverage in a single shot. Also, it would be exceedingly difficult to get a spectrum of an M6 dwarf of this quality even if such an instrument existed, because those tiny stars are so faint.
The spectrum shown above is that of an A0V star, which has a temperature of approximately 10,000 K (where K = Kelvin; 280 K is approximately room temperature) and a mass of about twice the Sun's. Many of the stars you see in the night sky are A-type stars, but this is because they're so bright, not because they're common. In fact, of the 100 nearest stars to the Sun, only two are A stars. Famous A-type stars include Sirius, Vega and Fomalhaut.
 This spectrum is an F0 dwarf, which has a temperature of roughly 8000 K, a bit hotter than the Sun, 30% higher mass, and very different in appearance and behavior. A star like this and the A0 star above will tend to be a very rapid rotator, lack magnetic activity and the associated spots, plage and flares common to less massive stars because they lack convective envelopes. Most naked-eye stars are F dwarfs.
 Here's a spectrum of a G2V dwarf, just like our Sun (.
 Here's a K dwarf, with a temperature of roughly 5000 K and a mass of 70% of the Sun's.
 Here's an "early" M dwarf (M1V). Note the dramatic shift in the peak of the spectrum, indicating a much cooler star (Temperature = 3700 K) and about half the mass of the Sun. These stars are the most numerous stars in the Solar Neighborhood: M dwarfs make up about 7 out of every 10 stars in the Galaxy! All of those spikes and wiggles are real features due to the more complex nature of molecular absorption lines, as opposed to the atomic lines seen in hotter stars.

Here's one of the most diminutive stars at the "bottom of the main sequence." This is an M6 dwarf with roughly 10% the mass and radius of the Sun, or about the size of Jupiter! Any less mass and it would be able to fuse hydrogen to support itself and it would instead be a brown dwarf, destined to radiate its birth heat until it fades into the thermal background of the Galaxy. Instead, a star like this one will be the last hydrogen-fusing stars in the Galaxy, with a lifetime of roughly 10,000 times longer than the Sun's 10 billion-year lifespan!


mama mia said…
So Joni Mitchell wasn't too far off when she described us as "stardust"?

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