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About Meredith

My Science Talk NW presentation

Last week, I attended Science Talk Northwest in Portland and participated in their Science Communication Contest. Presentations had to fit within three minutes (with a 30 second grace period), you could not use any slides, and you could use a prop. The competition was specifically for “trainees,” who ranged from undergrads to postdocs.

I didn’t win, but I did make it into the Top 10! The winner and runner-up both did outstanding jobs and used props very creatively (did you know a super soaker is like a placenta, and that drumming can relate to personalized medicine?). I will have to think about how to incorporate props into future presentations about LSST and astronomy. I felt much more solid about this talk than previous three-minute slide-free talks I have given, however, because I began preparing it more than a couple days in advance and incorporated intentional gestures to help remind me what came next.

I was pleasantly surprised to find that, for me, gestures are the next best thing to having a slide or image as a visual memory cue. Deciding ahead of time what gestures to use was partially motivated by a workshop I attended on “The Performing Art of Science Presentation” by Nancy Houfek at the recent AAS meeting. I also appreciated the 30-second grace period, because it helped me be deliberate about my pacing and emphases. I was less likely to panic or speed up if I thought I was running behind.

Say… how is the whole I-work-for-LSST-at-UW-now-and-mostly-live-in-Seattle thing going? Very well, thank you! I only wish I could say the same for my country.

Without further ado, I present an approximate transcript of my #SciTalkNW three-minute talk. (I actually gave this talk twice: once in the initial round, and again in the final round, after some feedback from peers and experts.) When the conference organizers make a video available, I will update this post, and you can be amused at how my memory and the video differ.
UPDATE April 2017: link to my video, link to all the finalists’ videos

What’s your favorite picture of space? Maybe you think of one of those gorgeous Hubble pictures, like the Carina Nebula or the Pillars of Creation. Or maybe you have a memory of going outside at night, far from city lights, and looking up to see stars stretched across the sky.

All of these images have one thing in common: they’re static snapshots. They capture a single moment in time. But most things in space are dynamic and moving! While astronomers can learn a lot about our Universe from images like these, what we really need is a movie.

This is why a team of international scientists are building the Large Synoptic Survey Telescope, or LSST. It’s under construction right now on the top of a mountain in Chile. When completed, this telescope will have a main mirror that’s eight and a half meters across—that’s like 27 feet—and the largest camera ever built, the size of a small car. Inside the camera will be a detector with 3.2 gigapixels. That’s like several hundred iPhones in every snapshot.

When LSST comes online in 2022, it will begin mapping the entire southern sky. Every three nights, it will take one all-sky image. Then, over the course of a decade, it will stitch them together into the highest resolution movie of the night sky ever made. And, it’ll be in full color, because LSST will use six different color filters!

LSST is going to revolutionize pretty much every area of astrophysics. Everything from finding asteroids moving in our own Solar System, to observing stars explode as supernovae in distant galaxies.

But to do this, we recognize that the software is at least as important as the science. My team at the University of Washington is writing software to process the images that come from the LSST in real time. We’re talking 15 terabytes of data every night—that’s more than you can fit on your computer’s hard drive. And we have to process every image within 60 seconds of the shutter closing. Our software will take new images from the telescope, compare them to older images, and find anything that has changed. Those changes will then be broadcast in a public alert stream so that scientists can filter and search to find the targets they’re most interested in. All of our work is open and public, because we want scientists and folks like you to be able to use our tools.

So, in 2022, the movie begins! I am incredibly excited to share the ever-changing, dynamic cosmos with you. We’re going to find new kinds of variable and moving sources we didn’t even know to look for! Coming soon to a night sky near you: everyone’s new favorite space picture. LSST—it’s actually a movie.


Color is Weird

Yesterday on twitter, I ran across a perplexing image: yellow and magenta in a pair of windows that appeared to reflect blue and green, respectively, onto the sidewalk when illuminated by white light from the Sun.

What is going on?! I decided to put on my “I’m-an-astronomer-who-understands-light” cap and see if I could work it out. The rather circuitous tweet stream begins here, in which I made several errors: I tried to explain a complicated thing before I was fully awake, my brain kept switching key concepts like “absorb” vs. “reflect” and adding vs. subtracting colors of light, and I made a couple assumptions without explicitly stating them (spoiler: they turned out to be incorrect!).

Illustration of how colors of light add together. Source: Wikimedia commons

After much discussion on twitter, I concluded the paper posters in the window were reflecting their true colors (yellow and magenta) in all directions and leaving only their complementary light colors (blue and green) to reflect directly on the sidewalk. If you’re an astronomer, you might recognize this as analogous to Kirchhoff’s laws of spectroscopy: a nebula viewed from most lines of sight shows emission lines, but when it’s viewed in front of a bright object instead, you see absorption lines.

Yeah, that was wrong.

I took a closer look at the photo later that day, and realized the rectangles in the window were not posters at all, but looked more like transparent cellophane! That made things easier, I postulated:

Wrong again, though perhaps a bit closer.

The real explanation appeared today, when the original photographer returned to collect more data.




Trust me, you definitely want to play all those short videos (no sound required). The viewing angle changes everything! THAT’S SO COOL! Have you ever wondered why the cry of the scientist is “more data!”? It turns out that viewing something from more than one perspective can be very instructive, or should I say… illuminating? It’s enough to make this astronomer wish we had a way to fly halfway across the galaxy with a fleet of telescopes. Alas, space is way too big for that.

So there you have it: a learning experience, a more nuanced understanding of color, and a scientific quest all rolled into a handful of tweets.

Black Lives Matter

Together with colleagues from Astrobites, I am sharing a statement which appeared first on the Astronomy in Color blog and later on the Women in Astronomy blog. I have appended further thoughts inspired by the writings of Sarah Tuttle, Abigail Stevens, and Startorialist. Thank you all.

The recent extrajudicial killings of two Black men, Alton Sterling and Philando Castile, by the police have shocked, disturbed, and frightened many of us today. We express our unequivocal repulsion to these acts, which are just one manifestation of the underlying systemic racism in our country. These events affect our community directly. Many Black astronomers in this country, especially those in junior positions, are suffering at this moment. We encourage all of you to be mindful as you reach out to our fellow Black astronomers, and be present with them during these difficult times. The undersigned reaffirm our commitment to ensure the inclusion, support, and safety of every Black person in astronomy. Black lives matter!

To our present and future Black colleagues: your lives matter, and your contributions to science matter, too. We affirm that science does not happen in a societal vacuum. Science is done by human beings. We recognize that many forms of systemic racism take a real toll on you, and we know we cannot ignore this if we are serious about fostering an inclusive, equitable, and productive scientific community.

To everyone else: we need to stand in solidarity with our minoritized peers and colleagues, and with our Black colleagues in particular. The astronomical community is much more willing to discuss sexism than racism, and that is wrong. We live in a world where the inherent value of Black lives needs to be continually restated. White supremacy is what enables these extrajudicial murders by the police. White supremacy is what twists reality to tell you that Black Lives Matter is “political” and that science has no business acknowledging these atrocities. We disagree; inaction is not acceptable. There is humanity and there is racism. We hope you will join us in choosing humanity.

Dr. Meredith L. Rawls
Leonardo dos Santos
Ingrid Pelisoli
Kelly Malone
Evan Schneider
David Wilson
Susanna Kohler
Dr. Courtney D. Dressing

The above signatories are members of the Astrobites Collaboration ( This statement reflects our own personal views, and is not an official statement by Astrobites.

How to Make an Award-Winning Scientific Poster

  1. Decide with one month to spare that you will attend an overseas conference and frantically make travel arrangements.
  2. Email the incredibly responsive conference organizers because you’re not sure if you can give a talk or if you need to present a poster instead.
  3. Make a poster so great that you win the poster competition and get to give a last-minute talk the next morning as a result.

So that happened. You can watch my talk here.

The Cool Stars 19 conference was outstanding for many reasons, and winning the postdoc(!) poster competition was just one of them. Of course, the ability to make a good poster did not appear in my head out of nowhere! One set of great guidelines is here, and AstroBetter has compiled many handy resources about conference presentations (including posters) too.


Rather than rehash everything that has already been said about making effective posters (you did click on the links above, right?), here is an overview of how I approach poster design together with some tips to make your poster visually compelling.

  • Re-read the abstract you submitted to the conference weeks ago. Is it overly ambitious? Totally off-base? No matter. Your poster is an opportunity to communicate what you’ve done as of TODAY. Hundreds of people will glance at your poster, but only a few will skim your abstract.
  • With the above in mind, copy just the title and author list from your abstract submission (or craft a condensed version if necessary) and forget about the rest of it. Do not copy and paste your abstract anywhere. You will be staring at a giant blank canvas; it will be tempting. Just say no.
  • Use whatever software you are most comfortable with to make your poster. This could be Illustrator, Keynote, Powerpoint, Word, whatever. Does your software let you make a large page size, insert text boxes, images, and shapes, adjust fonts and colors, and precisely drag stuff around? Yes? Good.
  • Follow the conference’s rules for poster size. Sometimes you have a choice between portrait and landscape, and sometimes you don’t. You can make a good poster in virtually any aspect ratio, so pick something within the limit and stick with it. (US-based pro tip: 36 x 48″ is a standard size at FedEx Office and very similar to A0; having one dimension be 36″ also makes printing on fabric easier.)
  • Boil your message down to two main points, and be able to say each point in one tweetable sentence or less. Then divide your poster into three chunks: the first portion is reserved for big-picture motivation and context, and each of your main points gets another third. Use distilled versions of these points as headers for each chunk instead of meaningless words like “Introduction” and “Conclusions.”
  • The focus of each chunk must be figures. Let the figures speak for themselves. For example, you do not need to write “y generally increases with x over the full range of the dataset.” Instead, use clear axis labels that communicate why the correlation is important.
  • Write bullets and single-sentence captions, not paragraphs. Write only the most essential words to explain each figure, and no more. Notice there are no end-of-sentence periods on my poster, because each thought stands alone.
  • Avoid acronyms and jargon. Yes, knowing your audience is critical, but mostly, your audience is tired. Write what you mean, not what your sub-discipline’s jargon-and-acronym-machine expects you to say. If you must use acronyms, define them near the very start of your poster’s first chunk.
  • There is no ultimate poster font size law… but yours is too small because you’re trying to cram in too many words! My default was 52 pt (with some figure labels necessarily a bit smaller). Sans-serif fonts are easier to read than serif fonts.
  • Pick a simple, colorblind-friendly color scheme and stick with it. This means your plots, your text, and anything that goes on your poster should ideally coordinate. If you’re not sure what to choose, consider the colors in the figures you plan to include, and/or consider the color palette for the conference itself. Dark text on a light background is easier to read than the opposite.
  • Don’t be afraid to overhaul your figures. Crop out extraneous axes and tiny labels. Make custom legends. Annotate plots to drive home key messages. Present one illustrative example instead of seventeen nearly-identical panels.
  • Advertise your papers, and give credit where credit is due. Essentially everything on my poster is from my own work or my credited coauthors’ work, so there are very few formal citations. If you borrow any plots or images, be sure to cite the original source. However, a poster is not a literature review; if people are truly interested in your full set of citations, they can read your papers.
  • Take your time and be picky. Ensure elements line up within and between chunks, use the exact same colors and fonts throughout, and get several sets of eyes to proofread.

Remember: the whole reason you travel to conferences is to talk to people about your research. Sometimes you will be standing near your poster and sometimes not. Do you know what I did with all the words I wanted to put on my poster but didn’t? I used them in conversations, and they appear or will appear in papers. So yes, your poster must stand alone, but it shouldn’t have to tell the full story.

Finally, consider how you usually feel during a conference. Mentally sharp? Plenty of free time? Excited to carefully read each poster twice? Of course not. Everyone is exhausted and overwhelmed. That’s really what these tips are dancing around. Could your sleep-deprived officemate distill the essence of your poster after staring at it for 20 seconds? And do those 20 seconds make them care about your results? If not, you still have some work to do.

Dr. Rawls

My PhD defense took place in Las Cruces on April 8, and was successful! If you’re interested, you can watch my presentation and/or view my slides. However, please be aware the intended audience for this talk is fellow astronomers, not the general public.


I’ve spent the last week or so revising my dissertation, and I’m happy to report it passed the graduate school’s format review today. Once the final copies are printed (yes, multiple copies; yes, printed) and accepted, I will add it to the Astronomy Thesis Collection online and write a post summarizing the main results. I’ll be back in New Mexico in May to celebrate graduation with my family, and I intend to consume even more burritos before embarking on a road trip north.


On Writing a Thesis

If you spend any time around graduate students, you know the culmination of years of work toward a degree ultimately comes down to pouring the essence of that work into a giant written document very few will ever read: a thesis. Also known as a dissertation. (Due to my US-centric perspective, I treat the two as synonyms in this post.)

As it happens, I finished a full draft of my thesis yesterday. It has been a stressful, exhausting, anxiety-riddled few… weeks? months? Yeah. The “fun” isn’t over yet because there are certainly revisions in my future, not to mention the actual thesis defense, which will consist of a public talk followed by an indefinite period of conversation/questions/snake fights with my committee behind closed doors.

So that’ll be great.

But my goal today is to give future-thesis-writers a window into what my process looks like, and share the tools I used to make it slightly less painful than it could have been.

My thesis contains five chapters and three appendices in about 200 pages and roughly 25,000 words. (The word count is imprecise and rounded down because a thesis has lots of words that aren’t exactly part of the main text.) As I understand it, this is a reasonably typical length for astronomy, but I honestly don’t care, because I think I said everything I needed to say.

I have three pieces of unsolicited advice, which boil down to: know how you work, get tools you’ll use, and what I’ll call “think globally, write locally.” Let’s go.

Know how you work

Maybe you’re one of those people who likes to wake up early, gets important work done before the rest of the world is awake, has completed all your thesis research well in advance of when you’d like to defend, and has published four papers along the way. In that case, I say congratu-effing-lations, you have this in the bag.

For the rest of us, it’s time to take stock of how you work. Think about the last time you were really “in the zone” and got a lot of work done solo. Where were you? What was the environment like? What time of day was it? Did you have a certain beverage, view, or music at hand? Figure out what works best for you and structure your life around it. Maybe that means you need to unplug the internet, build a playlist, budget for daily coffeeshop purchases, work in pomodoros, disable email notifications, or embrace the popcorn workstation. Maybe it means you need to block out writing hours on your calendar, get a transit pass, find a standing desk, set weekly deadlines, or pull all-nighters every Tuesday. It doesn’t have to make logical sense and it doesn’t have to be a lifelong commitment; it just has to work for you for now.

If you’re having a hard time remembering the last time you felt highly productive working alone, or the specific circumstances, don’t despair. It’s never too late to try new productivity techniques. We’re all making this up as we go!

Get tools you’ll use

Writing a thesis is more than just opening a blank document and dumping your brain into it. There’s formatting and references and figures and tables and… so many pieces that somehow have to come together. Thankfully you are not the first person in the history of humanity to tackle these problems, and lots of tools exist to help. Good tools are easy to use and lighten your cognitive load so you can focus on the content of your thesis rather than the mechanics of writing it. But not every tool works for everyone, and sometimes you have to be patient with yourself and your computer while you try and discard one after another. After much trial and error, here are some of my favorites.

OmniFocus: The powerful to-do list app that basically changed my life. This is a place to write down action items for everything in your life, from errands to work to any random task or idea you need to get out of your brain. The degree to which I use OmniFocus to its full potential varies, but whenever I need to get something done I take the time to break it up into small, manageable pieces here. You can use it to set deadlines, start-later deferral dates, color categorizations, location- or person-based contexts, and so much more. OmniFocus is not free, it is only for Mac/iOS, and it syncs seamlessly between them. If you are thinking of trying just one of the tools listed here, it is the one I recommend most highly.

TeXShop, ShareLaTeX, and a LaTeX class file: If you want to write a thesis, you’re probably going to need some LaTeX. My editor of choice is TeXShop, which is free and lets you place writing (editor) and viewing (PDF) windows side by side. If installing LaTeX gives you trouble, I recommend ShareLaTeX, which is also free, works in any browser, and syncs with Dropbox (see below). You’ll also need a class file with various packages to tell LaTeX how you want your thesis formatted. Many departments and universities have official or unofficial class files that adhere to formatting guidelines. Ask around to see what older students or recent graduates from your department have used. In my case, NMSU graduate Jeff Coughlin created aastex-thesis (based on AASTeX v5) and a set of well-documented sample files that compile into a pretend thesis—about exowhales, no less!

Dropbox: You probably don’t back up your work as often as you should, and even if you do, it’s probably not every time you hit “save.” I initially uploaded my thesis files to ShareLaTeX, linked that to Dropbox, and then did most of my writing in TexShop. So long as I was online, the latest versions of all my thesis files were automatically synced with the cloud. This offered peace of mind, because if my computer spontaneously self-destructed, I could have continued working with ShareLaTeX on any computer with internet access.

TextWrangler: My go-to text editor. You can use alt/option-click to select a rectangular block of text (a column), it has brilliant find-and-replace, and it lets you remotely edit files over ssh. I use this for everything, including python programming, formatting LaTeX tables, and keeping a BibTeX bibliography file up to date. TextWrangler is free and for Mac only.

Papers: The absolute last thing I want to actively think about is how to cite a paper or format my bibliography. BibTeX handles some of this, but it can’t help me find the paper I’m looking for or open several in tabs for me to continually reference. Papers lets you save PDFs in a special folder, automatically organizes that folder and imports information about that paper, and makes it easy to copy a BibTeX record into your bibliography file. From there, you can customize a natbib keyword, run a series of LaTeX-BibTeX-LaTeX-LaTeX commands in TeXShop, and carry on writing. Papers also syncs between devices (Mac/Windows/iOS) so you can read papers on the go. It’s not free, but they offer student pricing and it is well worth the investment.

SnagIt: This is just a fancy screenshot program. I use it to grab a figure from a paper, save it in the “figures” subdirectory of my main thesis directory, and add it to my thesis. It’s not free, but there are many other perfectly good screenshot options out there.

Evernote: My research notebook. My workflow is essentially paperless, so anything I need to jot down goes here. I write a brief summary of what I did each day for my own personal reference. Quick calculations, the location of important files, and notes taken during meetings all land in Evernote. It’s free and syncs between all my devices which makes it a handy reference during meetings and conferences.

RescueTime: A neat little free app that runs in the background on my computer and tracks how much time I spend using different applications. It keeps you honest and lets you compare hours spent on different tasks from week to week.

focus@will: Various types of music and ambient sounds that help get you in the flow of working. I use this when I just can’t concentrate and/or when I want music but don’t want to spend time deciding what to listen to. It’s a subscription service with a free trial period. [post edited to add this one]

Slack: Did I mention I’ve been finishing my PhD remotely over the last year? This means my collaborators are never “just down the hall,” and Slack bridges that gap for free. I’ve become at least as good of a communicator from afar than I ever was when I could theoretically walk to a colleague’s office. For example, during a virtual meeting, everyone can easily share plots and other files in real time.

“Think globally, write locally”

One of the most challenging parts of a thesis is figuring out just how to pitch your epic, unprecedented contribution to the field. There’s no getting around it: this is important, and part of the game is convincing others your results matter. But if you don’t have it figured out yet, there’s no reason you can’t start writing your thesis anyway. I essentially arrived at my conclusions as I was writing, for two reasons: the final numbers pertaining to my stars weren’t ready until days before my draft was due, and the process of writing about those numbers helped me clarify the story they could tell.

I can’t work if things aren’t organized, so the first thing I did after I had a set of mostly-empty LaTeX files in place was come up with chapter and section titles. I decided, quite arbitrarily, that I was going to have four chapters: Introduction, That Paper I Just Published, and Applying Stuff I Did In That Paper To Similar Situations (split into two logical halves), and three appendices. Then I created sections, and subsections, and even a few sub-subsections. Once all this was written down, I had a clearer idea of what my thesis looked like globally. Then I could pick a smaller “local” section I was ready to work on and get a finite piece of thesis done in one writing session.

That’s not to say the chapters and sections couldn’t change! They most certainly could, and did; for instance, at the eleventh hour, it was decided I would write a fifth chapter entitled Larger Context And Summary Of This Entire Damn Thing. More or less. But by that point, it was clear I had some things left to say which did not fit in the other four chapters, and adjusting course made sense.

With tools in place to handle formatting, citations, figures and tables, colleague communication, a to-do list with bite-sized pieces, and an outline as a jumping-off point, all that was left was the writing. I know enough about how I work to block off large chunks of time in the afternoon and evening during the last few weeks, which culminated in one final writing push from 10pm-5am on Sunday night. It sucked, but it worked. At least, I think it did. My committee will have the final say on that in the next couple of weeks.

Not my favorite way to spend Easter weekend, but I think the bunny had it worse.

My Next Adventure

Earlier this year, I remarked that I had no idea what my next step was going to be career-wise. I am thrilled to report that uncertainty is history! This September, I will begin working as a postdoctoral research associate in the Large Synoptic Survey Telescope (LSST) Data Management team at the University of Washington in Seattle.

That is a lot of words. What do they all mean?!

The LSST is a ginormous 8.4-meter telescope currently under construction in Chile. Beginning around 2020, it will image the entire visible sky every few nights for a decade. LSST’s camera takes 3200 megapixel images, which means it will amass 15 Terabytes of data every night. This is a whole new level of “I have more data than I know what to do with” for astronomers, and we are really excited about it.

There are several teams around the country working on various aspects of LSST, and the Data Management folks are primarily writing software to automatically process raw images and turn them into useful databases for the community. As a member of the UW team, I will spend about 80% of my time on LSST projects and 20% of my time on independent research. Some of that 20% will be related to my present work on red giant binaries, but I’m also excited to begin new collaborations.

And yes, this means I am moving to Seattle! But, not immediately. I’m still working hard to finish my PhD, and I plan to work remotely part of the time for the first several months of my new position. In general, I have a lengthy list of more pressing concerns to attend to before I think very hard about relocating.

For example, I am flying to Florida in less than three hours to catch a week-long ride on a Nerd Boat in the Caribbean, and then I have four weeks to finish my dissertation draft.

Catch you on the other side!

The Double Red Giant With Odd Oscillations

My latest paper was accepted for publication on December 31, announced on the astro-ph preprint arXiv on January 5, and will appear soon in The Astrophysical Journal [UPDATE Feb 11! Rawls et al. 2016, ApJ, 818, 108]. It was written online using Authorea. I also wrote several programs in python to analyze data for this paper.

Picture two nearly-identical stars orbiting each other. Something like this:

An approximation of the double red giant binary KIC 9246715, created using an eclipsing binary simulator. In reality, the two stars are separated by more than 200 times our Sun’s radius, but this simulator maxes out at 60. One orbit takes 170 days rather than the 26 illustrated here. The brightness, or flux, dips when one star passes in front of the other. The eclipses are not evenly spaced in time because the orbit is eccentric.

Even though they usually appear as a single dot of light, binary stars are one of the best tools astronomers have to measure stellar properties. Thanks to the math behind gravity, we can weigh pairs of stars using the relationship between how long an orbit takes and how far apart the things are doing the orbiting. Weighing stars accurately is important because a star’s mass seals its fate. So if every star in the night sky had a secret companion star (or exoplanet!), we could wrap this up pretty neatly and move on to deeper questions about stars’ lives.

Unfortunately, only about half of stars have orbiting companions, and many of those aren’t observable because they don’t happen to be edge-on like the case shown above. This is where starquakes come in.

Weighing stars from the inside out

Some stars, including our own Sun, ring like bells. Pressure waves are excited by convection inside stars, and the waves bounce around at resonant frequencies just enough to make them pulse, or oscillate. Because an oscillating star is changing brightness ever-so-slightly, we can use regular observations of brightness versus time (from Kepler, in my case) to pull out the frequencies of oscillation. Heavy stars oscillate differently from lighter ones, and big stars oscillate differently from smaller ones. Voila—a new technique for weighing stars that doesn’t require anything in orbit!

Of course, the story doesn’t end there. While the study of starquakes (more formally known as asteroseismology) is a powerful way to characterize many stars quickly, it remains relatively untested. We don’t know how accurate of a scale we’re using when we whip out asteroseismology to weigh stars. To address this, my colleagues and I identified about twenty binary systems containing red giants. That’s the kind of star our Sun will become when it runs out of fuel in billions of years. Red giants are convenient targets for asteroseismology because they are bright and oscillate slowly. Both properties make them easier to observe than Sun-like stars. And since our red giant stars all live in binaries, we should be able to weigh them in two independent ways and compare the results.

Solar-like oscillations make a comb-shaped pattern at different resonant frequencies. The central location of the spikes and their spacing in frequency tell us about a star’s average surface gravity and density, respectively. Red is oscillations from the double red giant binary in my paper. Gray is oscillations of a single red giant star with similar properties, plotted upside-down for reference. Figure 7 from Rawls et al.

The case of the missing oscillations

In my paper, I present a case study of two red giant stars in an eclipsing binary. From binary modeling, I show that the stars are both a little more than two times as massive as the Sun, and over eight times as large. However, I am surprised to only find a single signature of starquakes in the observations. Two similar but not-quite-identical stars should, in principle, both oscillate. The oscillation modes, pictured above, are broader and weaker than expected, too. The same physical process could be fully stopping oscillations in one star and only partially suppressing them in the other.

By harnessing many observations (both images and spectra) and modeling techniques, I thoroughly characterize both stars and investigate why only one of them appears to oscillate. I measure each star’s mass, size, temperature, chemical composition, level of magnetic activity, and tidal force strength, among other things. Then I bring in asteroseismology to see if I can tell which star is oscillating and if its story checks out.

By simultaneously modeling different observations of this double red giant binary, I can map the geometry of its orbit in space and measure each star’s mass and size. I do this by fitting a model (black) to observations (red and yellow). The top panel shows radial velocities, or how fast each star is moving toward/away from us, and the other panels show a light curve, or brightness versus time, with two eclipses (the bottom is a zoomed view of each eclipse). The x-axis is in units of how long one orbit takes, which is about 170 days for this binary. Figure 6 from Rawls et al.
Stars emit different amounts of light (flux) at different colors (wavelengths), but the light from a binary contains overlapping information about both stars. As the stars orbit, characteristic dips in flux shift to higher or lower wavelengths depending on how fast they are moving. To create one representative spectrum for each star as shown here (red and yellow), I used a physical model of the stars’ orbit to remove the velocity offset from each observation and then combined them. This process is called disentangling. An example of a single observation containing light from both stars (before disentangling) is plotted in black. Figure 5 from Rawls et al.

As it turns out, the two stars in this binary are similar enough that it’s impossible to say for sure which one the oscillations belong to. Recent work has shown that magnetic fields may suppress oscillations in stars, however, so I strongly suspect the oscillating star is the less magnetically active of the pair. There may be a weak second set of oscillations, but the signal is very noisy and doesn’t appear quite where it should. Either way, the single mass and radius derived from asteroseismology is consistent with that of both stars from binary modeling.

Fraternal twins: born together, but not identical

Because oscillations bounce around inside stars, they carry information about how stellar interiors are structured. Stars of different ages have very different things happening inside: younger red giants are still fueled by hydrogen, while older ones are fueled by helium. The oscillating star in this binary appears to be in an advanced helium-burning stage of its life called the horizontal branch or secondary red clump. I verify this with stellar evolution modeling, and confirm that the two stars most likely were born, grew up, and evolved together. They are about 940 million years old.

The next step is to do a similar analysis for the other red giant binaries my team identified. We are working on two fronts: comparing masses and radii from binary modeling and asteroseismology, and using those results to investigate why about a third of red giants don’t show any oscillation behavior. Our work has important implications for understanding the composition of our Milky Way galaxy, because bright red giants are often surveyed to better understand our galaxy’s history and structure. It’s important to get their stories right.

Astrobites Emeritus

After writing monthly posts at Astrobites for two years, I have officially retired from the “regular rotation.” This comes as Astrobites welcomes a new cohort of authors and I refocus my writing energies toward more pressing matters (you know, like my dissertation and job applications). I will still serve as an editor, mentor, and occasional website wrestler, and I am proud to be one of four Astrobites Correspondents at next week’s American Astronomical Society (AAS) meeting near Orlando, Florida.

Things have been quiet here at AstronoMerrdiff while I’m in thesis mode. I’ll be presenting a portion of my dissertation research at AAS on Jan 5, which just happens to coincide with the arXiv announcement date of my latest accepted journal paper! This is a large chunk of my thesis and I’m thrilled how it finally came together (all 20 pages, 12 figures, and 4 tables of it). Look for an Astrobites-esque summary here in the coming weeks.

I’ll be in Las Cruces to touch base with colleagues in early February. That same month, I will lead an astronomy-themed retreat weekend at Ghost Ranch (join me!), and take a much-needed vacation with JoCo and friends. My thesis defense is scheduled for April 8, and I’ve got loads of research and writing to wrap up between now and then.

This is the time in a PhD career when everybody loves to ask, “what’s next?” For now, I don’t have an answer. I’ve applied for a few Seattle-based postdoc positions, and am keeping my eyes open for other astronomy jobs of interest. I have two other potential career trajectories up my sleeve: education/outreach and data science. (I’m also applying to be an Astronaut, but I think the likelihood of that is even lower than landing a position in academia!)

As usual, PhD Comics nails it.

Setting overly-apt PhD Comics aside… certainly writing and online communication will play a role in my career wherever I wind up. I’m thrilled to have contributed so much to Astrobites and thankful for the friends I’ve made there. In this present moment, I recognize how incredibly lucky I am to get paid (a little) to do what I love (a lot) while living where I want (the Pacific Northwest). These early months of 2016 will be one heck of a ride. I’m hanging on tight; the Universe awaits.

Mapping Car2Go Portland

As a relatively new resident of Portland, Oregon who doesn’t own a car, I’ve become quite reliant on walking, public transit, and a nifty service called Car2Go (plus the occasional Uber or Lyft). Car2Go is a pretty neat on-the-spot car rental service that I first joined while visiting San Diego a few years ago.

Basically, there are a bunch of 2-seater Smart Cars all around a city, and anyone with a membership can walk up to one and rent it for $0.41/minute. You can park it anywhere on the street in that city’s “home area” when you’re done, and if there’s a meter, you don’t have to feed it. There’s a one-time $35 signup fee and a free smartphone app that shows you where cars are in real time. It’s a pretty awesome deal.

(I could go into more detail about the service, like how you can reserve a car for up to 30 min ahead of time if you want, and how one time it said there was a car and there wasn’t and I was sad, and how parking rules vary a bit from city to city, and even how they have not-unreasonable-but-pricey maximum rates for hourly and daily rentals… but you get the idea.)

The branch of Car2Go in Portland announced today that it was “updating” its home area—that’s the area where you can find cars to rent and end your rental—so I went to take a look.

Here’s the present Home Area.


And here is the new Home area, effective August 24, 2015.


I was initially annoyed, because this interfered with my brilliant plan to take Car2Go to within a couple blocks of symphony rehearsals in East Portland this fall. But then I thought a bit more, after realizing that my home and most places I frequent are still well within the new Home Area. I wondered who will actually be most affected by this change. So I pulled up the trusty Racial Dot Map and sketched the old (red) and new (green) Car2Go borders on top of it.


I learned three things during this exercise. 1) Manually drawing a bunch of lines on a screenshot is probably not the most efficient way to compare map data, 2) The old Car2Go map is much better drawn to scale than the new one, and 3) Asians, Hispanics, and Blacks will disproportionately be excluded from Car2Go beginning August 24. I took a quick look at a map of Portland income and earnings too, and was unsurprised to see that the areas cut appear to be overall poorer than the areas retained. And for reference, here is a cool map of the “Transit Oriented Development” score throughout Portland. (Note this map is significantly more zoomed-out than all the others here. Source here.) The areas excluded are much less well-served by public transit than the areas retained. Intentionally or not, Car2Go has chosen to offer the convenience of renting a car on the spot predominantly to white, wealthy people who already live near public transit.

About the change, Car2Go has this to say:

Based on careful evaluation of member feedback and historical data, we have determined that members are not able to experience the true benefits of car2go as the Home Area size results in vehicles sitting in areas, where they are idle four times as long as our vehicles in high demand areas. By updating the Home Area, we are confident that members will be now able to find a vehicle in the areas that they frequent most.

Of course, Car2Go can do whatever they want. But I wish they had dug a little deeper into their ridership data. I would love to see them market their service specifically to areas underserved by public transit and to individuals and families who might not otherwise have the privilege of a private vehicle. With an effort like that, Car2Go could make a real difference in the cities they serve rather than just giving lazy, wealthy white folks (like me) an excuse not to take the bus.