alphas, robots, u-band

In an absolutely excellent Stars and Exoplanets Meeting, Rodrigo Luger (Flatiron) had everyone in the room (and that's more than 30 people) say what they plan to get done this summer!

Following that, Melissa Ness (Columbia) talked about the different alpha elements and alpha enhancement: Are all alpha elements enhanced the same way? Apparently models of type-Ia supernovae say that different alpha elements should form in different parts of the supernova, so it is worth looking to see if there are abundance differences in different alphas. The generic expectation is that there should be a trend with Z. She has some promising results from APOGEE spectra.

Mike Blanton (NYU) talked about how we figure out how to perform a set of multi-epoch, multi-fiber spectroscopic surveys in SDSS-V. He has a product called Robostrategy which tries to figure out whether a set of targets (with various requirements on signal-to-noise and repeat visits and cadence and so on) is possible to observe with the two observatories we have, in a realistic set of exposures. That's a really non-trivial problem! And yet it appears that Blanton may have working code. I'm impressed, because integer programming is hard.

And Shuang Liang (Stony Brook) showed us that it is possible to calibrate u-band observations using the main-sequence turn-off, as long as you account for the differences between the disk and the halo. He has developed empirical approaches, and he has good evidence that his calibration based on the MSTO is better than other more traditional methods!

#mwmw, day 1

Today was the first day of the Milky Way Mapper Workshop, at the Max Planck for Solar System Research in Goettingen. The meeting is about points of target selection, operations, commissioning, and planning. I am very excited about Milky Way Mapper, which is part of the SDSS-V family of projects; it will take infrared and optical spectra of millions of stars. From my perspective a few important things happened at the meeting (note the subjectivity and unfairness of this; it is not a summary):

MWM will operate in a robotic mode, with robotic fiber positioners. This permits us to observe enormous numbers of stars, but it means that our default calibration strategy of arcs and flats between exposures that we have used in SDSS through SDSS-IV will not be tenable. That's good! Because it causes us to do some commissioning work at the start where we quantitatively analyze the calibration strategy.

We discussed principles underlying target-selection in our various target categories. Hans-Walter Rix (MPIA) and I intend to write a general paper for the astrophysics community about this question, because there are some hard-won lessons from previous projects and things we and others have done wrong. I will say more about this in future blog posts as I try to write some of it up, but the extremely important underlying principle is the likelihood principle: If information comes through the likelihood function, then you have to select your targets such that, at the end of the day, you can write down a computationally tractable likelihood function for the parameters of interest. That's perhaps a Duh! point, but I'd like to point out that many of the complex, multi-stage projects (like RV surveys, or time-domain follow-up spectroscopic projects) fail to meet this requirement! More on this over the next weeks.

I learned a few crazy simple things today. One is that SDSS-IV APOGEE is taking multiple hot-star standards per plate! That means that the survey has, through its calibration work, created a huge time-domain survey of hot stars over a huge part of the sky. That's pretty important for science. And at this point, they have not been fully exploited as a scientific project. It's many thousands of stars!

Another crazy thing is that the SDSS projects have obtained enormous numbers of white-dwarf spectra, sometimes deliberately and sometimes by accident. These cover large parts of the white-dwarf sequence in ESA Gaia data, and this sequence contains lots of informative and intriguing structure. That suggests an interesting Gaia Sprint project.

Trojans, Oort Cloud, greedy algorithm paradox

Early in the day, undergraduate Mitchell Karmen (NYU) blew me away by showing a possible Trojan satellite hiding in the Kepler false-positive bin. It probably has some other explanation, but damn it's exciting! I discussed this with Rodrigo Luger (Flatiron) who dampened my excitement (for good reasons).

At stars meeting, Michele Bannister (Belfast) spoke about ways in which we might use the properties of the outer Solar System (and especially the things past the Kuiper Belt and including the Oort Cloud) to constrain the birth environment and subsequent dynamical environment of the Sun at formation. It appears that these structures could be created early and are strongly modified by nearby stars and close passages. One implication is that different stars should have very different Oort Clouds. That's a great prediction; now how to test it?

Mike Blanton (NYU) showed some very cool results from the work being done on SDSS-V robot fiber positioners. As you might guess, the positioning of fibers on a focal plane by robot arms that can collide is an intractable problem in general—it's like traveling salesman. But you might also know that most NP problems are pretty well-served by sensible greedy algorithms. That is, you can usually do something akin to the simplest thing and still succeed most of the time.

Blanton showed the interesting thing (worked out by Conor Sayres at UW) that if they do a greedy algorithm to take the robot arms from the "home" state to the configuration they want, it is very slow and hard, and it still fails in many cases. But if they do the exact same greedy algorithm the other way—that is, to take the arms from the configuration they want back to the home state—it works fine! So they do that and then run the result backwards!

Crazy talk. And cool. And worthy of a lot more thought. And something about entropy? After all, the home state is like a crystal.

fiber robots; gravitational waves

At lunch, Mike Blanton (NYU) and I discussed operational matters for SDSS-V. One thing we discussed was how to have different cadences for different types of stars, when we have a huge field of view and finite target densities for each stellar type. His view is that we should re-formulate the question in terms of sky patches, and set cadences for particular sky patches, and then observe the stars inside those patches as makes sense given the patch cadences. We also asked how to formulate this problem in terms of a scalar objective function or cost function, which is essential if we are going to let loose with optimizers.

The other thing we talked about is positioning a dense set of fibers. There are configurational constraints on the path that the fiber robots can take if they are going to avoid collisions and conflicts. Can we resolve these? And what engineering literature do we look to for the best or standard solutions to problems of this type. I am sure there is a huge literature, because it connects to all sorts of things like milling machines and warehousing and things like that. But I need keywords. I promised to deliver some to the SDSS-V Collaboration.

At the end of the day, Vicky Kalogera (Northwestern) gave a great talk about gravitational wave observing. Her group has been essential in converting the theory of gravitational-wave sources into practical schemes for performing principled probabilistic inferences on the data. She said, in her talk, that in the process she has become an observer, but she only observes in the gravitational-wave sector! And it is really true: She referred consistently in her talk to astronomers as “electromagnetic observers”. I love that! But really, the LIGO results are incredible, and Kalogera deserves a lot of credit for them.

Gaia, asteroseismology, robots

In our panic about upcoming Gaia DR2, Adrian Price-Whelan and I have established a weekly workshop on Wednesdays, in which we discuss, hack, and parallel-work on Gaia projects in the library at the Flatiron CCA. In our first meeting we just said what we wanted to do, jointly edited a big shared google doc, and then started working. At each workshop meeting, we will spend some time talking and some time working. My plan is to do data-driven photometric parallaxes, and maybe infer some dust.

At the Stars Group Meeting, Stephen Feeney (Flatiron) talked about asteroseismology, where we are trying to get the seismic parameters without ever taking a Fourier Transform. Some of the crowd (Cantiello in particular) suggested that we have started on stars that are too hard; we should choose super-easy, super-bright, super-standard stars to start. Others in the crowd (Hawkins in particular) pointed out that we could be using asteroseismic H-R diagram priors on our inference. Why not be physically motivated? Duh.

At the end of Group Meeting, Kevin Schawinski (ETH) said a few words about auto-encoders. We discussed imposing more causal structure on them, and seeing what happens. He is going down this path. We also veered off into networks-of-autonomous-robots territory for LSST follow-up, keying off remarks from Or Graur (CfA) about time-domain and spectroscopic surveys. Building robots that know about scientific costs and utility is an incredibly promising direction, but hard.

after-Sloan-4 proposal writing, day 1

Today was the first day of the AS-4 (After-Sloan-4) proposal-writing workshop, in which we started a sprint towards a large proposal for the Sloan Foundation. Very intelligently, Juna Kollmeier (OCIW) and Hans-Walter Rix (MPIA) started the meeting by having every participant give a long introduction, in which they not only said who they are and what they are interested in, but they also said what they thought the biggest challenges are in making this project happen. This took several hours, and got a lot of the big issues onto the table.

For me, the highlights of the day were presentations by Rick Pogge (OSU) and Niv Drory (Texas) about the hardware work that needs to happen. Pogge talked about the fiber positioning system, that will include robots, and a corrector, and a [censored] of a lot of sophisticated software (yes, I love this). It will reconfigure fast, to permit millions (something like 25 million) exposures (in five years) with short exposure times. Pogge really convinced me of the feasibility of what we are planning on doing, and delivered a realistic (but aggressive) timeline and budget.

Drory talked about the Local Volume Mapper, which mates a fiber-based IFU to a range of telescopes with different focal lengths (but same f-ratio) to make 3-d data cubes at different scales for different objects and different scientific objectives. It is truly a genius idea (in part because it is so simple). He showed us that they are really, really good at making close-packed fiber bundles, something they learned how to do with MaNGA.

It was a great day of serious argument, brutally honest discussion of trade-offs, and task lists for a hard proposal-writing job ahead.

after SDSS-IV; red-clump stars

At Stars group meeting, Juna Kollmeier (OCIW) spoke about the plans for the successor project to SDSS-IV. It will be an all-sky spectroscopic survey, with 15 million spectroscopic visits, on 5-ish million targets. The cadence and plan are made possible by advances in robot fiber positioning, and The Cannon, which permits inferences about stars that scale well with decreasing signal-to-noise ratio. The survey will use the 2.5-m SDSS telescope in the North, and the 2.5-m du Pont in the South. Science goals include galactic archaeology, stellar systems (binaries, triples, and so on), evolved stars, origins of the elements, TESS scientific support and follow-up, and time-domain events. The audience had many questions about operations and goals, including the maturity of the science plan. The short story is that partners who buy in to the survey now will have a lot of influence over the targeting and scientific program.

Keith Hawkins (Columbia) showed his red-clump-star models built on TGAS and 2MASS and WISE and GALEX data. He finds an intrinsic scatter of about 0.17 magnitude (RMS) in many bands, and, when the scatter is larger, there are color trends that could be calibrated out. He also, incidentally, infers a dust reddening for every star. One nice result is that he finds a huge dependence of the GALEX photometry on metallicity, which has lots of possible scientific applications. The crowd discussed the extent to which theoretical ideas support the standard-ness of RC stars.

MaxEnt2013, day 4

In the time around sessions, and on the conference hike (with kangaroos), I had many conversations with Marcus Frean (Wellington) about a generalization of his source finding system. He finds sources in data by looking for anomalies in the "pixel histogram"; his model has no knowledge of astronomy (or anything else) on the inside. We discussed several generalizations in which the model would learn—as it saw more and more data—what kinds of properties that astronomical data have. The idea is that the system should learn that the anomalies (sources) fall into different categories, learn the process that generates each of those categories, and instantiate new categories as required by the data. A system like this would be like a simulation of a hypothesis-generating astronomer! It also would be extremely useful running on any operating astronomical survey; "eyes on the data" are always valuable and usually very expensive. As my reader knows, I think that eyes on the data is the most valuable contribution of massive citizen science projects like the Zooniverse; awesome if we could add some robots into the mix!

At the end of the day (Australian time), during the MaxEnt2013 conference dinner, Gaia launched! It looks right now like the launch was successful. This is potentially the beginning of a new era in observational astrophysics. Congratulations to everyone involved.

dotastro, day 3

The third and last day of dotastronomy 5 started with reports of the outcome of the Hack Day. Various extremely impressive hacks happened, way too many to mention, but including a very impressive video about planet naming, by Deacon and Angus and others, an automated astronomer-career mapping app by Foreman-Mackey and others, a XBox-Kinect doppler-shift app by Lynn that got everyone in the room dancing and spinning more than once, and (near and dear to my heart) improved functionality for the Zoonibot by Barentsen and Simmons and others. That latter hack is an extension of the the bot that got started by Beaumont and Price-Whelan (at, I am proud to say, my suggestion) at dotastronomy 4.

Among the talks, one of the highlights for me was Trouille (Adler) talking about the Galaxy Zoo Quench project, in which Zooites are taking the project from soup to nuts, including writing the paper. She spent a time in her talk on the problem of getting the participants to boldly play with the data as professional scientists might. It is a rich and deep piece of public outreach; it takes self-selected people through the full scientific process. Another highlight was Microsoft's Tony Hey talking about open access, open data, open science, libraries, and the fourth paradigm. Very inspiring stuff.

Related to that, there was great unconference action in a session on open or low-page-charge publishing models, led by Lynn (Adler) and Lintott (Oxford), in which Simpson (Oxford; and our fearless dotastronomy leader) got emotional (in all the right ways) about how crazy it is that the professional societies and individual scientists have signed away their right to their own work that they researched, wrote, reviewed, and edited for the literature. Testify!

I ran a short unconference session on combining noisy information coming from Zoo participants (or equivalent) in citizen-science and croud-sourcing situations. A good discussion of many issues came up, including about the graphical model that represents our assumptions about what is going on in the projects, about active learning and adaptive methods, and about exposing the internal data in real time so that external (third-party) systems can participate in the adaptive decision-making. I also advocated for boosting-like methods, based on the idea that there might be classifiers (people) with non-trivial and covariant residual (error) properties.

It has been a great meeting; Rob Simpson (Oxford) and Gus Muench (Harvard) deserve huge thanks for organizing and running it.

data science; autonomous robots

The morning was spent with various NYU luminaries preparing for a proposal (or really a design process leading up to a proposal) to the Moore and Sloan Foundations relating to "data science". The most interesting aspects of the question are that no two people agree on what data science is, and even for any component of data science, no two people agree on what the big issues are that need addressing. So that is the beginning of an interesting set of conversations.

At lunch, Foreman-Mackey and I met up with Schiminovich to discuss a proposal that Schiminovich wants to put in to NASA about autonomous platforms that will make space missions and suborbital projects cheaper, faster, and easier to deploy. The idea is for the platform to be able to make scientific decisions and re-scopes in real time, in reaction to changing conditions. Could be fun! Of course I argued that we should take an economic model, with utilities specified in dollars. And I need more projects to be doing, because I just don't have enough irons in the fire! (Note ironic tone.)

writing, robots

On the subway up to an undisclosed location in the West 70s, I wrote text for my Atlas of Galaxies. At the location, Schiminovich and I discussed next steps in the GALEX Photon Catalog project. We also discussed a proposal that Schiminovich is writing for a balloon-borne instrument that deals with variable conditions by making non-trivial decisions in real time in response to real-time measurements of transparency, sky brightness, and field-of-view (which can be hard to control on balloons). Obviously, a custom-built on-board lightweight implementation of Astrometry.net would be useful!

automating high-resolution spectroscopy

I spent a great day at Utah, in the care of Adam Bolton. I gave my talk in the morning and then talked with the graduate students. In the afternoon, I visited two large group meetings, one the combined groups of Bolton and Kyle Dawson, the other the group of Inese Ivans. A lot of things were discussed in both meetings. In the Bolton–Dawson meeting, among other things, we discussed what to do with objects that have uncertain redshifts or redshifts based on a single emission line (which will be a problem for SDSS-IV). In the Ivans meeting, we discussed a wide range of problems related to high-resolution spectroscopy. Ivans and her group is finding that it is very hard to automate certain parts of spectroscopic analysis of stars. We discussed how these might be robustly automated. One problem—which also exists in cosmological projects that take spectra of quasar absorption lines—is to find the continuum relative to which absorption lines are measured. We came up with some ideas and I volunteered to work as a consultant in the future.

galaxy and star images, job ad

I met with Ekta Patel to discuss progress on sample selection and context information for the Sloan Atlas of Galaxies. I am past due on various deadlines on that project! I met with Kilian Walsh (NYU) who is going to do some trial projects this summer with me, relating to Astrometry.net and automated astrophysics data analysis in input data. Our hope is to facilitate making discoveries in data input to the system on the Web. Schiminovich came down for a few hours and found that WISE photometry does a good job of ruling out the possibility that any of our GALEX-discovered white-dwarf transits is caused by a planet (rather than a low-mass star). The jury is still out, I hope, but we also have much more to discover. Foreman-Mackey and I ran on the challenge that Federica Bianco gave us, but we didn't find the elusive third star that we are supposed to find. But then I started to get suspicious that it even exists.

In related news, a group that includes Rob Fergus and me has funding to hire a postdoc. The successful applicant will have experience in advanced probabilistic inference and also sophisticated astronomical image modeling, calibration, or measurement. If that sounds like you and you are interested in doing more of that kind of stuff, send me email.

everything except the task at hand

Once again, Schiminovich and I were at our undisclosed location to work on GALEX time-domain projects. Instead we had a wide-ranging conversation about upcoming projects. We discussed the GALEX photon list project, and the kinds of things we will be able to do with a trillion time-tagged photons. We discussed joint NYU-Columbia advanced astrophysics lab courses that would have the students building and operating autonomous telescope hardware on NYC roofs. That project could beautifully combine teaching and research. We discussed what Popper calls verisimilitude: Are our well established models of the physical world literally true? Uh oh, weren't we supposed to be writing a paper? We discussed dispersed integral-field spectroscopy but also spatially dispersed to drop the background levels.

In the airport (on my way to Lund, Sweden) I had conversations with Foreman-Mackey about the arXiv and Lang about jobs.

spectral modeling

In the morning I spoke with Tsalmantza about our spectral modeling project, which we are using to find gravitational lenses, black-hole binaries, and quasar redshifts. Well, we aren't, but we hope to be. We have a smoothing or softening parameter—a continuous model-complexity parameter—and Tsalmantza proposed a simple cross-validation test to set it. In the afternoon I tried to start writing words about the project.

pixel modeling and giving up

I spent the day talking with Bolton and Lang (and, variously, Blanton and Bovy) about modeling images and spectra. We principally debated what advantages you will or could get in data analysis by building good models of the raw data at the pixel level. We all have intuitions that it will be good, but we have few concrete examples. We assigned Bovy one task along these lines: Show that the SDSS astrometry of point sources could or would be much better if we re-centroid using a PSF fit rather than the (approximate) thing done by the pipelines at present.

In the afternoon, I made the difficult decision to drop my robotic telescope proposal for NYU Abu Dhabi and the NYU Global Campus. This is a great project, which we might resurrect, but I am feeling stretched too far and I need more time to understand my research program in the post-Roweis period. Argh.

introductions

I spent a great lunch and early afternoon with Maurizio Porfiri (NYU Poly), who is a mechanical engineer and applied mathematician working on dynamical networks of independent agents like fish. He has some sweet experiments in which his lab watches fish schooling, works out the schooling rules, and then inserts a robotic fish and uses the robotic fish to take control of the school and drive it around! I discussed with him the possible relevance of his work to our ideas about building a collaboration between NYU, NYU Poly, NYU Abu Dhabi, and NYU Global that will create and run a global network of autonomous telescopes.

In the late afternoon, a group of high school students came from NEST high school in Manhattan to NYU to present original research they have done with the Spitzer Space Telescope on the AGN NGC 4051. They got time from the director's discretionary time and they have done a huge amount of work with the data and come to some interesting conclusions about the structure of the dust torus. Nice work!