interstellar bands; PSF dictionaries

Gail Zasowski (JHU) gave an absolutely great talk today, about diffuse interstellar bands in the APOGEE spectra and their possible use as tools for mapping the interstellar medium and measuring the kinematics of the Milky Way. Her talk also made it very clear what a huge advance APOGEE is over previous surveys: There are APOGEE stars in the mid-plane of the disk on the other side of the bulge! She showed lots of beautiful data and some results that just scratch the surface of what can be learned about the interstellar medium with stellar spectra.

In CampHogg group meeting in the morning, we realized we can reformulate Vakili's work on the point-spread function in SDSS and LSST so that he never has to interpolate the data (to, for example, centroid the stars properly). We can always shift the models, never the data. We also realized that we don't need to build a PCA or KL basis for the PSF representation; we can use a dictionary and learn the dictionary elements along with the PSF. This is an exciting realization; it almost ensures that we have to beat the existing methods for accuracy and flexibility. Also interesting: The linear algebra we wrote down permits us to make use of "convolutional methods" and also permits us to represent the PSF at pixel resolutions higher than the data (super-resolution).

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