so, you are writing a review report?

I sometimes work long days, but I try not to fill my weekend with working. This weekend, however, I had promised myself that I would take the notes from the SDSS-V review I led in Denver and turn them into a draft report for the project. I can't believe it, but I succeeded!

Are you going to be on a review panel? I have advice (unsolicited advice, which I try not to give, but after this weekend, I can't help myself):

Make sure you do lots of writing while in session. If you just listen and talk for the period of the review, you leave the review with nothing written, and then you have to reconstruct it from memory and your notes. Instead, schedule executive-session writing time during the review and come away from the review with everyone's notes and comments compiled into one jointly editable document. I learned this from Mike Hauser (formerly STScI), who chaired the Spitzer Oversight Committee for many years.

Act fast. If you don't write your report immediately, you will never write it. So kill your procrastination and write the hell out of it immediately. And then your panel members will be so shocked at your turnaround time, they will be inspired to act fast themselves. They will take the draft you write fast and turn it into a final version.

Be helpful and constructive. Think carefully about and (more importantly) discuss with the team precisely what they want out of the report and what they can do. Make sure you are answering the questions they want answered, and that the answers you give can be implemented usefully and without huge burden. Report from reviews are about the future not the past.

I love the SDSS-V Project and Collaboration and I want both to succeed. I very much hope that what we have written will help them meet their goals.

Spitzer oversight

Today was the NASA Spitzer Science Center Oversight Committee meeting. As usual, the day was filled with insights about how you run a large integrated engineering and science operation. The project team particularly called out Lockheed Martin and the Deep Space Network (separately) for praise in how they have both supported the mission. One of the interesting stories of the day is how the mission depends on legacy hardware, including ground-based computers that are way out of date! The project has no programmers, so it has to keep its software running on late-1990s computer hardware!

Spitzer death; nearest neighbors

Today was spent at the Spitzer Science Center for the 39th meeting of the Oversight Committee, on which I have served since 2008. This meeting was just like every other: I learned a huge amount! This time about how the mission comes to a final end, with the exercise of various un-exercised mechanisms, and then the expenditure of all propellants and batteries. We discussed also the plans for the final proposal call, and the fitness of the observatory to observe way beyond its final day. On that latter note: We learned that NASA will transfer operations of Spitzer to a third party, for about a million USD per month. That's an interesting opportunity for someone. Or some consortium.

In unrelated news, Christina Eilers (MPIA) executed a very simple (but unprecedented) idea today: She asked what would happen with a data-driven model of stellar spectra (APOGEE data) if the model is simply nearest neighbor: That is, if each test-set object is given the labels of its nearest (in a chi-squared sense) training-set object. The answer is impressive: the nearest-neighbor method is only slightly worse than the quadratic data-driven model known as The Cannon. This all relates to the point that most machine-learning methods are—in some sense—nearest-neighbor methods!

music and stars

First thing, I met with Schiminovich (Columbia), Mohammed (Columbia), and Dun Wang (NYU) to discuss our GALEX imaging projects. We decided that it is time for us to produce titles, abstracts, outlines, and lists of figures for our next two papers. We also realized that we need to produce pretty-picture maps of the plane survey data, and compare it to Planck and GLIMPSE and other related projects.

I had a great lunch meeting with Brian McFee (NYU) to catch up on his research (on music!) and ask his advice on various time-domain projects I have in mind. He has new systems to recognize chords in music, and he claims higher performance than previous work. We discussed time-series methods, including auto-encoders and HMMs. As my loyal reader knows, I much prefer methods that deal with the data probabilistically; that is, not methods that always require complete data without missing information, and so on. McFee had various thoughts on how we might adapt methods that expect complete data for tasks that are given incomplete data, like tasks that involve Kepler light curves.

Spitzer Oversight, day 2

Today was the second day of the Spitzer Oversight Committee meeting. Far and away the highlight for me was a presentation by Sean Carey (IPAC) about the overall health of the spacecraft and the imaging instrument. He showed the photometric throughput of the system as a function of time, which has been amazingly constant (sub-percent level), and yet showing a consistent and repeatable trend (of less than one mmag per year, ish?). He showed the bad pixel count, which has risen linearly with time, but only to a few hundred (and many of those are nonetheless still calibrated and useful pixels). He showed the astrometric wobble and drifts, associated with spacecraft thermal events. These are substantial, but changing, as the spacecraft goes through more and more extreme solar-angle events to downlink its data to the Deep Space Network. Spitzer is in an Earth-trailing orbit, so as time goes on, it has to point at worse and worse Sun angles to send its data home.

The latter point is very interesting: Carey showed that the batteries are still just as good as new, but that the spacecraft draws 11 A (yes, 11 Amps at 300 Volts!) on average (don't ask why), and when it is in downlink to Earth, the solar panels are not getting enough insolation to cover it. This leads to non-trivial scheduling in which the spacecraft must point near-orthogonal to the Sun vector for a while (hours) after downlink. This complexity is handled without issues by the non-trivial scheduling systems, and the overall spacecraft health is excellent. The mission can run until March 2019, when it is cut off, both by funding and by these Sun-angle issues. Carey also showed the long-term performance of the solar panels. This also declines linearly with time, but is easily within spec to keep the mission running (barring any severe micrometeorite hit). Knock wood!

It has been a great two days, with an absolutely great team, working on an absolutely great mission.

Spitzer Oversight, day 1

Today was the first of two days at the Spitzer Science Center, where I am (for the 8th year in a row) helping to advise the Spitzer mission as part of the Spitzer Oversight Committee, chaired by Mike Hauser (STScI, retired). The mission is in its last years, funded to continue observing to March 2019, then closing out for a year-ish afterwards, with no opportunity for further extension. Its lifetime is not set by money alone, however: Geometric constraints on its downlink to the Deep Space Network and its power and insolation and thermal needs during that downlink take the spacecraft out of safe operating conditions in 2019.

One of the things that was discussed today was synergies with JWST and TESS. There will be more than a year in which TESS and Spitzer are simultaneously flying. This creates a lot of interesting opportunities. I made a mental note to discuss this with some of my more ambitious exoplanet people. The JWST Early Release Science call has been released, and the calibration and photometry things we have learned (over many years) in the Spitzer, Kepler, and SDSS contexts (and Euclid and LSST contexts) could form the basis of a great ERS proposal. Let's not wait for five to ten years to figure out how to do the best possible science with JWST! Again, if I am going to go there, I need to assemble the right team.

Before the start of the meeting, I had lunch with Kat Deck (Caltech). We had a wide-ranging conversation, which included exoplanets, proto-planetary disks, the theory of planet formation, and gravitational radiation backgrounds and sources. On the latter, I really have to get involved; there are so many simple questions at the intersection of theory and data analysis.

stars

As always, MPIA Milky Way group meeting was a pleasure today, featuring short discussions led by Nicholas Martin (Strasbourg), Adrian Price-Whelan, and Andy Casey. Casey showed his developments on The Cannon and applications to new surveys. Price-Whelan spoke about our ability to see possible warps (coherent responses) in the Milky Way disk from interactions with satellites. Martin showed amazing color-magnitude diagrams of stars in Andromeda satellite galaxies. So. Much. Detail.

Chaos reigned around me. Jonathan Bird and Melissa Ness worked on the Disco concept. Anna Y. Q. Ho, working on a suggestion from Casey, found Li lines in (a rare subsample of) LAMOST giants, leading to a whole new insta-project on Li. Price-Whelan figured out multiple methods for initializing and running MCMC on our single-line binary stars, initializing from either the prior or from literature orbits. It looks like many (or maybe all) of the APOGEE variable-velocity stars have multiple qualitatively different but nonetheless plausible orbital solutions. Casey and I conceived of a totally new way to build The Cannon as a local model for every test-step object; a non-parametric Cannon if you wish? I spoke with Jeroen Bouwman (MPIA) about his (very promising) work using Dun Wang's Causal Pixel Model to fit the Spitzer data on transit spectroscopy for a hot Jupiter.

clusters, telescopes, and pixel models

In the morning, Melissa Ness showed me very strong evidence that not all open clusters are mono-abundance! This is surprising, and violates my expectations based on recent work by Jo Bovy. It doesn't literally conflict with his results, because the clusters in which we find this are not the clusters he looked at, and the elements we find it in are exposed only subtly in the data. Now we have yet another paper to write this summer!

At lunch, Joe Hennawi (MPIA) interviewed me about the argument (often given by the builders of small telescope projects) that the surface-brightness sensitivity of a small telescope is just as good as that of a large telescope, provided that the detectors and f-ratios are similar. I have always been suspicious of this argument, and Hennawi shares my suspicion. We discussed the simplifications in the argument and planned to write out a well-posed data analysis question and answer it. A project for the garden.

Late in the day, Jeroen Bouwman (MPIA) showed me the results of running a CPM-like (modeling data with data) model on some Spitzer spectroscopy of a star through a planet transit, as we had discussed a few days ago. It looks like it does almost as well as a full calibration of the data. In precision, not accuracy though: There are some things that the data-driven model erases. This is the problem in general with data-driven models: When you go data-driven, you lose some aspects of interpretability.

chemistry projects, deployable space telescopes

In a research-packed day, Anna Ho, Melissa Ness, and I met with Kevin Schlaufman (OCIW) to discuss what we should do with tens of thousands of stars, each of which has a dozen or more abundances measured with good precision. He had a million things to suggest! He said that there are physics-of-type-Ia-supernovae questions that could be answered with the distribution of Mn relative to Fe at low metallicity. He said that the Ni to Fe ratio might also tell us things about the deflagration-to-detonation transition. He said that we might look at the relationships between abundances and velocity differences (induced by, say, binary stars) to see if we can say something about chemical abundances and binarity. He also pointed out that there are other low-hanging fruits in the APOGEE data. So. Many. Projects. It was a great conversation and possibly the start of something.

In the late afternoon, Marcia Rieke (Arizona) gave the Astronomy Colloquium, about JWST. It was the first-ever Neugebauer memorial lecture (named after Gerry Neugebauer, one of my PhD advisors); she concentrated on engineering issues, and particularly those that flowed from Spitzer Space Telescope. The crowd was all interested in the deployment, since it is so insane. After the talk I interviewed Fiona Harrison (Caltech) about NuSTAR, which successfully deployed an immense boom to position its grazing-incidence optics.

cryo-EM calculus, NASA

I started reading this classic (and pay-walled) paper by Sigworth on cryo-EM imaging reconstruction. It contains an error in elementary probability (one I warn against in my probability calculus tutorial): It marginalizes out the angle variables using the likelihood or posterior on angles where it should use the prior. However, the paper is filled with good ideas and is strongly related to what I hope to do in this area. Indeed, all the opportunity is in incremental improvements, I suspect, not (probably) fundamentals. The paper also contains some nice toy problems!

In the afternoon and into the evening, I participated in the Spitzer Oversight Committee meeting (from my sick bed and by telecon). The big issue is the upcoming Senior Review; the project needs to figure out how many more years to ask for, at what budget, and for what reason. These are hard questions, even though the project has been incredibly productive in its latter years (and more productive per dollar every year).

proposals

I spent the day at the Spitzer Science Center participating in a review of preparations for Spitzer's proposal to the NASA Senior Review, which is empowered to continue or terminate the ongoing missions. I also wrote text for the NSF proposal being submitted by Geha, Johnston, and me.

Dobbs-Dixon

Ian Dobbs-Dixon (UW) gave a very nice informal talk at the blackboard today about planet migration and planetary atmospheres, prompted by questions out of the blue from various CCPP members (including myself). He placed exoplanet science in the realm of applied physics, which is a reasonable place, although I have been thinking that the subject also has some possible connections to very fundamental physics questions: In some sense it could eventually lead to understandings about the origin of life, which remains one of the great gaps in human knowledge. Dobbs-Dixon described asymmetries in hot Jupiters that could be created by the anisotropic insolation plus rotation; in principle the secondary eclipses measured by Spitzer (or something next-generation) might get asymmetric, especially at wavelengths where there is strong absorption by atmospheric elements. It's a small effect, but exoplanet science is the science of small effects; indeed that's why I am getting interested.

parameterizing exoplanets

Foreman-Mackey and I had a long conversation about parameterizing exoplanet models for transit lightcurves (and also radial-velocity measurements, direct-detection experiments, and astrometric data). The issue is that there are multiple angles—between the orbital plane and the plane normal to the line of sight, between the line of sight and the perihelion direction, and between the perihelion and both the ascending node and the fiducial time (zero of time). These angles are all differently degenerate for different kinds of data, and a well-measured angle can be hidden if you parameterize it such that the well-measured angle appears as a difference or sum of parameters. We also pair-coded some improvements to his transit-fitting code. The fits—to Kepler and Spitzer data—are sweet. Because his code is flexible, he can learn the limb darkening along with all the orbit and transit parameters.

At applied-math-meets-astronomy group meeting, we discussed various things, including using classification within a sampler to split the parameter space (in which there is a multi-modal likelihood function or posterior PDF) into a set of unimodal sub-models. On this subject, it is great to have Muandet visiting from MPI-IS; he is an expert on support vector machines and their extensions. Another thing that we discussed is the possibility in the Goodman & Weare stretch move underlying emcee and Hou's code, we might be able to improve the acceptance rate by changing the proposal distribution in the one-dimensional walker-mixing direction. That is super cool and something to work on at sleep time.

Spitzer precision

I spent the day at the Spitzer Science Center, where I continue to serve on the Spitzer Oversight Committee. Perhaps it isn't research but I sure do learn a lot at these meetings. Among the many remarkable things I learned is that in the Warm Mission, the Spitzer IRAC instrument continues to get more precise with time. This is unusual for an aging, distant space observatory! The reason is that exoplanet observers are feeding systematic noise information back to the instrument team, who are working to implement hardware, software, and observation-planning changes. Right now the instrument is working at tens-of-micromagnitudes precision (parts in 10⁵), which has permitted it to measure transits of Earth-sized exoplanets.

Over dinner, we discussed my long-term fantasy of hijacking a decommissioned satellite (any satellites coming to end-of-life in the next few years?) and setting it up as an autonomous, intelligent observer, saving on operations and telemetry by having it phone home only when it has something interesting to say.

software instrumentation

In an action-packed day, I had several conversations about software as instrumentation. The first was with Rob Simcoe (MIT), after his excellent talk about his FIRE spectrograph: I asked him what aspects of the design were driven by the desire to make data reduction simpler. He claimed none, though I didn't entirely believe him. My point is that instruments should be designed to preserve or transmit information and we shouldn't be afraid to write complicated software. So making the scattered light low is good, because scattered light reduces signal-to-noise, but making the traces straight is bad, because that can be handled in software. Simcoe said that all significant costs were of the first kind and not the second. The second conversation about software was with J. D. Smith (Toledo) on the bus, who is responsible for some of the most important Spitzer-related projects. He, like me, would like to see changes in which there are ways to reward and recognize astronomers for the infrastructure they create.

The day also included work on binary black holes, M31 dust, and M31 proper motion.

Dr Ronin Wu

Wu successfully defended her PhD today. Well, actually, she defended half of it yesterday, but for scheduling reasons we had to finish today. She presented the molecular hydrogen mass function as her principal result, and all the Spitzer data on which it is based. She has the largest uniform sample of Spitzer spectroscopy in existence. She is off to start a postdoc working with Herschel data this month.

Spitzer oversight

I spent yesterday and today on Spitzer Space Telescope oversight activities, which are not research according to The Rules (or at least I think they aren't). My only scientific activities were reading Wu's thesis, talking with Tsalmantza about binary quasars and the like, and discussing the stellar IMF with Lang.

Spitzer and exoplanets

I spent a big chunk of the day working on the Spitzer Oversight Committee, which is helping the Spitzer Science Center react to funding realities and the slow shut-down of an incredibly productive and successful but finite observatory mission. We spent some time in the meeting talking about Spitzer's capabilities for (and successes in) exoplanet science, and the possibility of encouraging that even more in the future. This post bends the rules but oddly I truly find the work I do on this committee to be of great intellectual interest.

thesis abstract, metals

On a very short day (it is spring break here and beautiful weather) I spoke with Wu about her thesis abstract (due this week) and Zolotov about the first draft of her paper on stellar metallicities in galaxy formation models. Not a huge research day.

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!