Have you heard about how we’re finding tons of planets around other stars? It’s incredibly exciting—planets are everywhere! One way we find these exoplanets is by carefully staring at stars, using a telescope like Kepler, and wait to see if a planet passes in front and blocks a tiny percentage of starlight.
That’s not what my research is about, though. I study stars! I use many of the same techniques for exoplanets to detect stars orbiting other stars, and then I use the law of gravity to measure their properties. These sets of stellar dance partners are called binary stars. My research uses binaries and other kinds of varying stars as tools to learn more about how all stars live and evolve. Understanding the physics behind stellar variability can uncover many stellar secrets. Along the way, I share programs I write for my research so that others can use my methods without having to start from scratch. Below are brief overviews of some of the projects I’m currently working on.
Red Giant Asteroseismology and Eclipsing Binaries
Recently, astronomers have begun to study the interiors of stars by measuring starquakes. Many stars, including our Sun, vibrate due to convection in their upper layers. Much like you can learn about the interior structure of the Earth by studying earthquakes, we can learn a lot about the insides of stars by studying their oscillations. This is called asteroseismology. It’s especially useful for red giant stars, which are brighter and oscillate more slowly than Sun-like stars, so the vibrations are easier to see.
Colleagues at NMSU and I put these two things together: oscillating red giant stars in binary systems. While we generally know how to measure mass, radius, and other properties from binary stars, we are still learning how to do this accurately with asteroseismology. Because there are many more oscillating stars than easily-observed binary stars, the goal is to use well-understood binaries as a benchmark for measuring stellar properties with asteroseismology. Check out my post about one particularly interesting double red giant binary here. Once this project got underway, however, we discovered that many of the red giants in binary systems don’t oscillate at all! My dissertation and continuing research investigates why.
Characterizing Binaries in APOGEE and Kepler
Binary stars turn up in the darnedest places: when you’re trying to measure the chemistry and motion of a large number of stars throughout the Milky Way, some of them turn out to have consistently changing velocities. Those stars must be orbiting other stars! I am advising a team of students at NMSU and UW as they find binary stars that have been observed multiple times with the APOGEE Survey and have also been observed by the Kepler spacecraft. We are working to combine these observations to deduce these stars’ orbits and ultimately measure their masses and radii.
Software Development for LSST
More details coming soon!
- KIC 9246715: The Double Red Giant Eclipsing Binary With Odd Oscillations
M. L. Rawls, P. Gaulme, J. McKeever, J. Jackiewicz, J. A. Orosz, E. Corsaro, P. Beck, B. Mosser, D. W. Latham, & C. A. Latham
2016, The Astrophysical Journal, 818, 108
BONUS: blog post and AAS Nova Highlight
- Red Giants in Eclipsing Binary and Multiple-Star Systems: Modeling and Asteroseismic Analysis of 70 Candidates from Kepler Data
P. Gaulme, J. McKeever, M. L. Rawls, J. Jackiewicz, B. Mosser, & J. A. Guzik
2013, The Astrophysical Journal, 767, 82
- Refined Neutron Star Mass Determinations for Six Eclipsing X-Ray Pulsar Binaries
M. L. Rawls, J. A. Orosz, J. E. McClintock, M. A. P. Torres, C. D. Bailyn, & M. M. Buxton
2011, The Astrophysical Journal, 730, 25
What’s The Big Deal?
Since stars are the main source of light in the Universe, we use their light to learn about everything else: our Sun’s fate, distances to faraway exoplanets, our place in the Milky Way, the expansion rate of the Universe… you name it. If we don’t understand the basic physical properties of stars, then we don’t understand these things, either. And if that’s not good enough for you, consider that the iron in your blood and the calcium in your bones were forged deep in the heart of stars. (Every element heavier than Hydrogen, Helium and trace amounts of Lithium were created inside stars, in fact; the others were created shortly after the big bang.) The life story of stars is your story, too.