fitting with upper limits, stars in accretion disks

We met today at Columbia for #AstroHackNY. Inspired by a problem from Ellie Schwab (CUNY), I spoke about the fitting of data in which you are presented with not just simple measurements, but some of the data are (only) upper limits. I gave a few strategies, from the life-hacking strategy of getting the data provider to replace the upper limits with forced measurements (who said measurements have to deviate significantly from zero to be useful?) to the ur-Bayesian strategy of including the missing data as (nuisance) parameters in the fit. After this, Alex Malz pointed me to the Kaplan–Meier estimator for survival analysis, and we figured out how we might convert the fitting problem into a survival-analysis analog.

After this, Nicholas Stone (Columbia) talked about the formation of stars (and thus binary stars, and thus black-hole binaries, and thus gravitational-wave events) in accretion disks. He has a whole theory of how to make binaries that are tight enough to lead to (relatively) prompt mergers. For me, the idea that you will have star formation in Q-unstable disks is a very good idea: In fact, this star formation ought to be self-regulating, because as stars form and heat up the disk, the disk becomes stable. Lots of predictions to be made here.

In between these things, and after, Adrian Price-Whelan and I discussed the visualization of the very faint, hard-to-see tidal stream he has found.


  1. DEar David, there is something I do not understand. Upper limits are measurements.... quite different from non detections. There is a lot of work in the literature about how to include upper limits in the analysis. What am I missing???