The Palomar Transient Factory photometric calibration

TL;DR

This paper details the photometric calibration process of the Palomar Transient Factory, establishing a reliable magnitude system for R and g bands with high precision and consistency across different observing conditions.

Contribution

It introduces a calibration method using SDSS standards, enabling accurate photometry and transformations for PTF data across various sky regions and conditions.

Findings

Achieved 0.02-0.04 mag precision in calibrated PTF data.

Calibrated data are consistent within ~0.02 mag across nights.

Provided transformation guides to SDSS and Johnson-Cousins systems.

Abstract

The Palomar Transient Factory (PTF) provides multiple epoch imaging for a large fraction of the sky. Here we describe the photometric calibration of the PTF data products that relates the PTF magnitudes to other mag systems. The calibration process utilizes SDSS r~16 mag point source objects as photometric standards. During photometric conditions, this allows us to solve for the extinction coefficients and color terms, and to estimate the camera illumination correction. This also enables the calibration of fields that are outside the SDSS footprint. We test the precision and repeatability of the PTF photometric calibration. Given that PTF is observing in a single filter each night, we define a PTF calibrated magnitude system for R-band and g-band. We show that, in this system, 59% (47%) of the photometrically calibrated PTF R-band (g-band) data achieve a photometric precision of 0.02-0.04 mag. Given the objects' color, the PTF magnitude system can be converted to other systems. A night-by-night comparison of the calibrated magnitudes of individual stars observed on multiple nights shows that they are consistent to a level of ~0.02 mag. Most of the data that were taken under non-photometric conditions can be calibrated relative to other epochs of the same sky footprint obtained during photometric conditions. We provide a guide describing the use of the PTF photometric calibration data products, as well as the transformations between the PTF magnitude system and the SDSS and Johnson-Cousins systems. (abridged).