AstroNote 2024-172

Since 2023 December, the Zwicky Transient Facility (ZTF) has been conducting monthly experimental surveys, each lasting three consecutive nights, to explore unique survey cadences, exposure times, and synergies with other facilities to accomplish specific science objectives (see astronotes Ho et al., 2024-135 and Ahumada et al., 2023-349). These experiments are conducted as public surveys, allowing all transient alerts to be released in real-time. Light curves can also be generated in near real-time using the Infrared Processing and Analysis Center (IPAC) forced photometry service. Standard ZTF light curves and catalogs are also made available during ZTF public data releases.

The next ZTF experiment, similar to another ZTF experiment conducted UT 2024 January 8-10, will focus on the galactic plane, assessing stellar variability in dense galactic plane regions on timescales that span a few minutes up to the full duration of a night, which is about 6.2 hours at Palomar Observatory in early July. This experiment will start UT 2024-07-01 at 04:43:34 and end UT 2024-07-03 at 11:00:31. Each night, we will pick one galactic plane field and observe it continuously in the ZTF r-band with 30-s exposure times, providing full-night light curves for millions of sources with an effective cadence of 42-s including readout times. We will observe a different field each night to increase the number of observed sources.

Exact field selections will not be made until day-of for each experiment night. This is so we can attempt concurrent observations of Sloan Digital Sky Survey (SDSS-V) BOSS spectroscopic targets. The SDSS-V schedules are the most reliable day-of, so each morning we plan to check the SDSS-V schedules and make a final ZTF field selection. The chosen fields, their central RA and Dec coordinates, and the precise observing window times will be made publicly available each morning on the ZTF experiment website before the observations take place.

While we do not have exact field selections now, below are the criteria currently constraining our field selection:

• Galactic latitude |b|<20 deg
• Observable at airmass <2 for >6 hr each experiment night between 18-deg twilight
• More than 50 Pan-STARRS1 r-band sources per square arcminute

These criteria limit our options to just 18 ZTF primary-grid fields during our 3-night experiment, with the following ZTF field IDs: 435, 436, 486, 487, 488, 538, 539, 540, 541, 589, 590, 591, 592, 639, 640, 686, 687, 768. We will choose among these fields each night after looking at the SDSS-V Apache Point and Las Campanas Observatory schedules, prioritizing fields that cover the most SDSS-V targets/epochs. The ztffields python package can be used to quickly visualize ZTF field locations and view field metadata like central RA and Dec. A flat file containing all ZTF field coordinates can also be found on this ztffields github page.

ZTF is supported by the National Science Foundation under Grants No. AST-1440341 and AST-2034437 and a collaboration including current partners Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley, the University of Wisconsin at Milwaukee, University of Warwick, Ruhr University, Cornell University, Northwestern University and Drexel University.