Zwicky Transient Facility in 2018

December 2018 Newsletter

2018 saw the beginning of survey operations for the Zwicky Transient Facility (ZTF). ZTF is characterizing the Northern Hemisphere sky on timescales ranging from minutes to years. ZTF data will identify young supernovae, rare classes of explosive transients, variable stars, and solar system objects.

The Samuel Oschin 48″ telescope at Mt. Palomar, where the ZTF Survey takes place.
Credit to Palomar Observatories/Caltech

DIRAC researchers have been deeply involved in developing technical infrastructure for ZTF as well as leading science analyses.

A major achievement of the DIRAC team was deploying the public ZTF alert stream in June. DIRAC researchers Dr. Maria Patterson, Prof. Mario Juric, Prof. Eric Bellm, and Dr. Zach Golkhou adapted open-source tools from the commercial internet industry and applied them to the problem of streaming up to a million alerts each night in near real time to scientists around the world. Each alert provides an updated lightcurve for a time-variable object observed by ZTF, enabling researchers to identify objects of interest and trigger rapid followup observations. A corresponding public alert archive ( enables more leisurely study. The ZTF alert stream prefigures the larger stream expected by LSST, and DIRAC’s data engineering group is building and expanding on the alert stream tools to enable more sophisticated filtering, classification, and analysis.

In his role as ZTF Survey Scientist, Prof. Eric Bellm also spearheaded the development of the ZTF scheduler. This piece of software solves the complex problem of determining how to most effectively order the hundreds of observations ZTF obtains each night to maximize efficiency and scientific output. The ZTF scheduler has pioneered an innovative new scheduling algorithm based on Integer Linear Programming. A paper describing the algorithm as well as the ZTF surveys will soon be submitted to a special issue of the Publications of the Astronomical Society of the Pacific, where it will join other technical papers describing the ZTF camera, data system, alert system, and other components.

DIRAC researchers and students have been  pursuing a range of scientific investigations using the ZTF data. A highlight was the discovery of ZTF18abauprj, a young Type Ia supernova in NGC 6279 (Astronomer’s Telegram, No. 11721). Prof. Eric Bellm identified in it the ZTF alert stream while he was observing and was able to immediately obtain a spectrum. Graduate student Joachim Moeyens and Prof. Mario Juric are using ZTF data to test a new algorithm for discovering asteroids. Dr. Jim Davenport is searching for stellar flares in ZTF high-cadence data with undergraduate Courtney Klein and for SETI signatures as well. Prof. Eric Bellm is working with two undergraduates, Priscilla Dohrward and Rebecca Kyerr, to find compact binary candidates in the ZTF data. Dr. Daniela Huppenkothen, Leah Fulmer, and Zach Golkhou are working on large-scale classifications of ZTF objects.