a sandbox for Milky Way dynamics

Today I met with Micah Oeur (Merced) and Juan Guerra (Yale) to discuss the project they are doing as part of the Flatiron summer school on stellar dynamics. Their project is to make a sandbox for testing different methods for inferring force laws (or gravitational potentials or mass distributions) from stellar kinematic data. We are starting by building very simple potentials (like literally simple one-d potentials like the simple harmonic oscillator) and very simple distribution functions (like isothermal) and seeing how the different methods (virial, Jeans, Schwarzschild, and torus imaging) work. The medium-term goal is to figure out how these methods are sensitive to their assumptions, and robust to data that violate those assumptions. Also some information theory!

asteroseismology model; organizing a workshop

This week is a sprint week for Ana Bonaca (Harvard) and me to work on our asteroseismology likelihood and search, for (possibly even ground-based) irregularly spaced data and heterogenous data. We figured out what we need for inputs to this likelihood function: We need empirical relationships between the nu-max parameter and other aspects of the power spectrum, like the mean heights of the mode peaks, and the width of the mode forest or comb. It seemed daunting at first, but awesomely a lot of what we need is in the Basu & Chaplin book. Most of our current technical struggles relate to the problem that the likelihood function is amazingly, amazingly featured. It's almost adversarial!

Late in the day, Tyler Pritchard (NYU) and I met socially distanced in a park to make final plans for a working meeting on time-domain astrophysics for NYC. The plan is to start to build a community around Vera Rubin LSST (which I just learn got backronymed) that is centered here in New York, and possibly build and operate a real-time event broker. But in this first meeting we want people to really discuss ideas and get something started: How to design online meetings to involve discussions and idea generation? We are learning a lot from our friends at TESS dot science online and AstroHackWeek 2020, both of which worked out new ways to have scientists who aren't physically in the same space—and maybe don't know one another all that well yet—do novel work together.

#AAS235, day 4 and #hackaas

Today was Hack Together Day #hackaas at #AAS235. We computed that this is the eighth winter AAS meeting to have a hack day, making it (AAS Hack Together Day) one of my scientific accomplishments of the decade. At the hack day, the main thing I did was hack on hack day, working with Jim Davenport (UW) to brainstorm things we can do to keep the event fresh, and keep us experimenting with it. I also had a great conversation with Brigitta Sipocz, Geert Barentsen, and others about ways we can use our hacking and design thinking to support a reduction in CO₂ emissions by astronomers and academics in general. Related to my conversations of yesterday.

But many great things happened in the Hack Together Day. Too many to list here. Look at the wrap-up slides to get a sense of the range and depth of the projects. So many people learned a lot and did a lot. I'm proud, which is a sin, apparently.

#hackAAS at #aas233

Today was the AAS Hack Together Day, sponsored by the National Science Foundation and by the Moore Foundation, both of which have been very supportive of the research I have done, and both of which are thinking outside the box about how we raise the next generation of scientists! We had a huge group and lots happened. If you want to get a sense of the range and scope of the projects, look at these telegraphic wrap-up slides, which (as always) only paint a partial picture!

We were very fortunate to have Huppenkothen (UW) in the room, and in (literally) five minutes before we started, she put together these slides about hack days. I love that! I think Huppenkothen is the world ambassador and chief philosopher of hacking.

I worked on two hacks. Well really one. The one I didn't really work on was to launch a Mastodon instance. Mastodon is the open-source alternative to Twitter(tm) and has nice features like content warnings (on which you can filter) and community-governable rules and restrictions. I thought it might be fun to try to compete with the big players in social! Although I didn't work on it at all, Dino Bektešević (UW) took over the project and (with a lot of hacking) got it up and running on an AWS instance. It took some hacking because (like many open-source projects) the documentation and tutorials were out of date and filled with version (and other) inconsistencies. But Bektešević (and I by extension) learned a lot!

The hack I actually did (a very tiny, tiny bit of) work on was to write a stellar-binaries-themed science white paper for the Decadal Survey. Katie Breivik (CITA) and Adrian Price-Whelan (Princeton) are leading it. Get in touch with us if you want to help! The point is: Binary stars are a critical part of every science theme for the next decade.

#DSESummit2018, day 3

In one of today's lightning talks, Chris Holdgraf (Berkeley) showed us JupyterHub and related projects, which are methods for distributing data, software, and compute to students (or members of a group) so they can transparently use a non-trivial data-science environment, through any kind of client. It is beautiful stuff, but also very interesting in its origins: It grows out of the undergraduate class Data 8 at Berkeley, which is an innovative project to teach the fundamentals of data science to all Berkeley undergrads, independent of their backgrounds. And much later, over drinks, Holdgraf explained to me lots of chaos-monkey-ish and sensible things they do at Berkeley to make sure that their code is truly and absolutely platform-neutral and vendor-independent. The intellectual content of these projects is truly impressive.

In the afternoon, I got some quality time in with Sarah Stone (UW) on our commitments to produce final products for this project around spaces. We discussed the role of ethnography, architects, and data scientists in figuring out what is and isn't working in our spaces. We also discussed what kinds of products we want to produce.

The last event of the day included a great plenary by Huppenkothen (UW) about the AstroHackWeek and related projects. She emphasized its interdisciplinarity, its values of experimentation, and above all, its commitment to broadening the fields of study and being welcoming to all. It was inspiring and enjoyable. I am extremely proud to have been a part of these projects.

optimization is the worst

After the incredibly valuable Milky Way Group Meeting discussion of the spectrophotometric parallaxes, Eilers (MPIA) and I simplified our model, re-factored the code, and re-ran. And, despite the fact that the new model is provably better than the old model, everything failed. The reason is: Our objective isn't convex. Not only that, but there is an enormously high-dimensional degenerate bad optimum that is hard to avoid. That sent us back to the books: Optimization is hard!

The trick we settled on (and you are allowed to do many, many tricks here) is to take the very highest signal-to-noise stars (in terms of Gaia parallax) to optimize an initialization and then do our final optimization with all stars, but starting off from that initialization. That is, we burn in to the optimum using the best stars first. It's a hack but it worked, and now the better model is performing the way it should be. That's good! Because it is discouraging when you refactor your code and everything goes worse.

A MPIA Galaxy Coffee, Wolfgang Brandner (MPIA) described the new GRAVITY results on the perihelion passage of S2 at the Galactic Center. The perihelion passage shows gravitational and transverse-Doppler redshifts and puts an amazingly strong constraint on the geometry and kinematics of the Galactic Center.

resonances!

[No posts for a while: I was on a short break.]

A huge highlight today was in parallel-working meeting, where Elisabeth Andersson (NYU) got her code working to plot Kepler light curves folded on various periods. In particular, periods that are integer ratios of known exoplanet periods. We are going to search for resonant signals. And warning: We are even going to look for 1:1 resonances, which might have escaped detection previously! We did various hacks to flatten the heck out of the light curves, which we might come to regret if we don't come back to them.