ages and companions of stars

Anna Y. Q. Ho is in town to finish two—yes, two—papers on what can be learned about stellar properties from (relatively) low-resolution LAMOST spectroscopy. She has amazing results on ages and chemical abundances, which challenge long-held beliefs about what can be done at medium to low resolution. One of her two papers is about using C and N abundances to infer red-giant ages, as we did with APOGEE and The Cannon earlier. Ho and I met with Rix today to discuss error propagation from abundances to ages, and all the possible sources of scatter, including the unknown unknowns.

Adrian Price-Whelan started running our probabilistic inference of single-line spectroscopic binaries on the Troup et al sample. We had to complexify our noise model, since clearly there are variations larger than the error bars. We also had to reparameterize our binary-star parameters to a better set. In this process, we wanted to go from a phase angle to a time and back. Going from time to phase angle is a numerically stable mod() operation. Going from phase angle back to time can naively involve adding and subtracting huge numbers. We re-cast the function so no large subtractions ever happen. That was not totally trivial!

Late in the day, Melissa Ness and Jonathan Bird interviewed Price-Whelan about ideas potentially going into the nascent Disco proposal.

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