Best and Brightest EMP Stars

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Today we (Schlaufman and I) posted our latest paper on extremely metal-poor (EMP) stars to the arXiv.

Extremely metal-poor stars are interesting because they uniquely inform us to the early chemical state of the universe, amongst other things (metal-free stellar populations, supernova, etc). Unfortunately EMP stars are extremely rare and usually intrinsically faint. In fact, progress on identifying and characterising EMP stars is limited because of how faint these stars typically are.

To address this, Schlaufman and I have developed a novel selection technique that identifies intrinsically luminous EMP stars using only infrared all-sky photometry. There is good astrophysical basis for our selection, which we have iterated upon with a data-driven apparoch. Our selection is as efficient as existing techniques but the candidates we identify are typically 3 magnitudes (x1000 times) brighter than other groups. That means it takes ~15 minutes to get good (high-resolution, high S/N) spectra for these stars, instead of the ~4 hours that would be required for targets identified by other methods.

Using only infrared photometry has a number of advantages over existing selection techniques. Unlike objective prism surveys, our selection works well in crowded fields. Additionally, the effects of dust is ~50 times less in infrared photometry than the optical. That means our approach is uniquely suited to places with high extinction (e.g., the bulge, where most Population III stars are expected to reside). And since our input photometry covers the entire sky we can focus on the Northern hemisphere, where there has been relatively little work on searching for extremely metal-poor stars.

Now that we have proved our selection we are increasing our rate of follow-up: next semester we are submitting proposals for telescope time on five different telescopes (between 2.5m-8m) to exploit our novel technique. Hopefully the telescope time allocation committees will take note of our quick turn-around in this paper: most of our 506 stars were only observed 11 weeks ago! And a lot of that time was spent with Schlaufman and me debating as to who would lead the first paper. We were both arguing for the other to lead.

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