ADASS, day 2

Some beautiful visualization talks were the highlight for me of day 2. I am suspicious about visualization for creating scientific results, although I think good visualization is essential in vetting data and procedures. In the former I think I differ from most of the ADASS crowd.

Speaking of which, we were strongly advised to interface Astrometry.net with World Wide Telescope (when Microsoft releases the product and an API) and the VirGO interface (which is built on Stellarium, a nice open-source planetarium). I hope we will do both in short order, along with Google Sky.


ADASS, day 1

I gave my talk at the ADASS meeting today. I was followed by Warren Hack (STScI), who demonstrated a nice, robust, hybrid scheme for aligning overlapping astronomical images precisely, even when those images contain very few (or no!) point sources, time-variable and moving sources, and cosmic rays. It could be a great back end for Astrometry.net.

Before Hack and me, there were talks about data preservation and archives, which emphasized the complexities and difficulties of preserving not just the data and meta data but an understanding of what it all means, which is currently preserved in people's heads. Bob Hanisch (STScI) gave a great talk about the VO which went beyond—and made specific—some ideas I have been floating around in one of my polemics, involving the relationships among data and code and the papers based on those data and that code. He agreed with me that incremental adoption of this kind of radical association will be fraught with cultural and political difficulties.


ADASS, day 0

Today was the reception and pre-meeting workshops for the annual ADASS meeting. The crowd is a good one because we can fully geek out and not feel like we are being too technical! I spent the day working on my viewgraphs for my presentation (on Astrometry.net, of course). At the reception I spent a lot of time talking with Emmanuel Bertin and the Terapix group. We have a lot in common. The Terapix group has an incredible track record of producing software that fills a need and works.



Two nice seminars today: The first was Jonathan Zrake (NYU) talking about Chandra observations of Farrar's putative UHECR source to identify possible interesting candidate objects. The second was Juna Kollmeier (OCIW) talking about using measurements of the IGM to constrain the feeding of galaxies with gas and thereby make the link between the simple physics of the early universe and the complex end processes of galaxy formation.


statistical weak lensing

Inspired by Sheldon's submission of this paper, I did literature research today on the use of statistical (averaged) weak lensing in constraining fundamental parameters of the dark sector. I decided that statistical weak lensing has shown us that dark matter halos exist around galaxies and groups and clusters with the masses, sizes, and radial profiles one would expect, at least on average. It is not a precise tool—because of the averaging—but it does bolster the dominant paradigm.


shift and add

I wrote the code to co-add small patches of SDSS data not at fixed position, but with a sliding coordinate system that moves linearly with time. This can be used to visually verify any proposed proper motion source.


faint-source proper motions

I returned to work on the faint-source proper motion project I started this summer at MPIA. Unfortunately, the fitting to real data is very fragile. There is quite a bit of work to do!


galaxy inclination effects

My research time this weekend was spent closely reading and commenting on Maller's draft of a paper about empirical determination of inclination corrections, or the effects of internal absorption in galaxies by dust that can be detected by observing similar galaxies at different inclinations to the line of sight. Maller's approach is unusual, because he simply tries to find the corrections such that the distribution of corrected galaxy properties (and more than just the spectrum can be affected) is independent of axis ratio (the observable most closely related to inclination).


missions accomplished

By the time Barron left today, we had accomplished all of our goals: We submitted the paper to AJ (it will appear as arXiv:0709.2358 on Monday; it is embargoed until then), we worked out some new computer-sciencey projects, and we worked out some new astronomy-ey projects. No time to celebrate, back to the grind!


density estimation

Barron and I played around with some ideas in two-dimensional density estimation with the idea being that we might be able to identify some of the spurious entries in the USNO-B Catalog that are not due to diffraction spikes and reflection halos. Barron coded up two ideas and both looked like they worked well. We aren't going to hold up our paper on USNO-B for this enhancement, but we might insert it into the Astrometry.net pipeline (which benefits enormously from a very clean USNO-B Catalog).


cleaning cleaning

Barron is in town and we worked on finishing up the USNO-B cleaning paper. We also had a phone conversation with Roweis, Lang, and Mierle about the long-term goals of astrometry.net and how the short-term activities might take us there.


Google (tm) Sky (tm)

I spent some time discussing the imaging in Google Sky with the Sky team and with Blanton and Sheldon, because the Sky team would like us to contribute some substantially-nicer SDSS imaging than they already have. I'm pleased—we do have the best images—but I don't relish the work it might involve. We have also been discussing connections between astrometry.net ans Sky. In the terrifying future, astrometry.net could drive traffic to Sky and Sky could allow browsing and visualization of astrometry.net's results. That would be fun.


nuclear astrophysics

Lars Bildsten (UCSB) was at NYU today, so much of the day was spent talking about nuclear astrophysics, including supernovae and the structure and cooling of white dwarfs. In his talk, Bildsten showed good empirical evidence that there are at least two different types of type Ia supernovae; this goes some way towards resolving a long-standing discrepancy between the observed Ia rate and iron abundance in galaxy clusters, and also the evolution in rate density as a function of redshift.


transparency of galaxy clusters

Moustakas and I sat down with Jo Bovy (NYU) to discuss his short-term project of measuring the transparency of galaxy clusters. We are interested in two things: (1) can we measure the amount of dust in the clusters, and does it make sense given the plasma temperature and the metallicity, and (2) can we rule out a class of naive axion models for the dark matter, which generically cause wavelength-dependent transparency variations in regions of high magnetic field? This all might sound crazy, but there hasn't been much work on the transparency of the Universe since the 80s, and the data have gotten much better. I expect us to put very strong limits and rule out some theories.

Or win the Nobel Prize!


psf-fitting in SDSS data

I spent a bit of time improving my treatment of the SDSS point-spread function in my project on faint-source proper motions. Because I am working at the faint, low signal-to-noise end, I don't need my PSF to be perfect. But I am making it less of a hack.



I spent some time researching the novelty of my faint-source proper motion work. The idea is so simple, I am sure it is not new. I couldn't find—even with help from the experts—any published work that measures proper motions below the individual-epoch detection limits. But I am not done: I only checked the stars literature and not the Solar System literature. It may be standard operating procedure for those looking for new Solar System objects.


dark-matter halos, conditions of use

I rearranged what I have written on dark-matter halos for Peebles's and my review of galaxies in CDM. I also worked on the conditions of use for the Astrometry.net data files (indices). These indices require conditions because they are built from data with conditions. Also we want to make sure that our code users play nice.