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.

novelty

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.

scripting web bots

I spent the day working on scripting a web bot to run a bunch of the "lost" SDSS images mentioned yesterday through our web service.

recovering lost SDSS data

One of the things we like to brag about with astrometry.net is that it can be used to recover data that have been lost or badly archived (that is, have been tagged with incorrect meta-data). We recovered SDSS run 2301, which is an engineering run of no particular import except that the astrometry for the run was never correctly determined (probably because the telescope was confused about where it was pointed at the start of the run). Today, some SDSS collaborators contacted me about SDSS run 6895, which goes through globular cluster M71. I spent the few research minutes I got today trying to massage the data into astrometry.net.

Note added next morning: When I got the first field of the SDSS data into JPEG form and got it into the system, it solved fast, and our system even said that the field contains M71.

Red stars are our object-detections and green stars are in the USNO-B. M71 is in the upper right corner.

results section of USNO-B paper

My loyal readers may have noticed that I have spent most of the last month writing rather than doing. It is annoying, but it ain't science if it ain't published! I finished a first draft of the results section of the USNO-B Catalog cleaning paper, making a complete first draft of the whole paper for the first time. Barron will visit in September for us to finish and submit it!

tarball

We are so close to having our Astrometry.net alpha code on the web as a tarball plus associated binary files. I spent a little time today testing the compilation and running of the tarball in preparation for making a tutorial.

test-driven halo measurements

I encouraged Zolotov to go with a test-driven development style in her work on the shape of the Milky Way and simulated galaxy stellar halos. When it is important to be not wrong, test-driven is very good. I have learned this the hard way!

statistics and language

At group meeting, Eyal Kazin (NYU) told us about measurements of the redshift-space, projected two-dimensional, and comoving-space correlation functions of LRGs in the current SDSS sample. He has a beautiful detection of the baryon acoustic feature even in the projected function! This means that it has great signal-to-noise in the overall data. After Kazin, I spoke about my statistical work on proper motions.

In the afternoon, much work was done (largely by email) on the language and writing of the USNO-B cleaning paper among Lang, Barron, and me. We made good progress on language and presentation issues.

submitted!

I finished the Masjedi, Hogg, and Blanton paper on the accretion rate for luminous red galaxies and submitted it to the Astrophysical Journal. It has a nice punchline: The accretion rate, even when integrating over a factor of 50 in merger mass ratios, is less than a few percent per Gyr, substantially lower than that predicted in CDM simulations, and much lower than many morphological measures of the merger or accretion rate. It will appear tomorrow as arXiv:0708.3240.

galaxy merging

With funding proposals and the beginning of term looming, I didn't get much time for research yesterday and today, but what I got was spent working through the literature on galaxy merging for the LRG accretion rate paper, which is so close to being done!

papers

I worked on the LRG accretion rate and USNO-B cleaning papers today.