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Zwicky Transient Facility Science Requirements Document

Introduction

This document outlines the high-level science requirements of the Zwicky Transient Facility (ZTF), an optical time-domain survey to be based at Palomar Observatory. ZTF is the successor to the Palomar Transient Factory (PTF; 2009–2012) and Intermediate Palomar Transient Factory (iPTF; 2013–present) surveys. PTF and iPTF used a secondhand camera on the Palomar 48-inch Schmidt telescope to survey the sky for astronomical transients and variables. ZTF will instead use a purpose-built survey camera on the same telescope to achieve more than an order of magnitude improvement in survey speed relative to PTF.

Project Charter

The Zwicky Transient Facility collaboration shall construct an Observing System to be located on the Palomar 48-inch Schmidt Telescope and an associated Data System. These elements will be used to conduct a wide-area, high-cadence time-domain survey in order to discover rare and fast evolving explosive transients, large samples of photometrically variable objects, and solar system bodies.

Scope

This document outlines the primary science goals of the ZTF project and indicates where these goals lead to specific capability requirements for the ZTF Observing or Data Systems. Detailed discussion of the requirements flow-down and implementation is left to the various Instrument and subsystem Requirements Documents.

TODO: detailed list of CIN for cross-reference.

Definitions

 Can We use ‘can’ in statements of possibility and capability, whether material, physical, or causal; ‘can’ equates to ‘is able to’ May We use ‘may’ to indicate ‘is permitted to’; it does not represent uncertainty in a requirement (typically indicated through use of ‘TBD’) Shall We use ‘shall’; exclusively to indicate an instrument functional or performance requirement Should We use ‘should’ to indicate an instrument goal Will We use ‘will’ to indicate a statement of fact

Points of Contact

Eric Bellm, ZTF Project Scientist

Constraints and Assumptions

\label{sec:constraints}

ZTF will use the Palomar Samuel Oschin 48-inch Schmidt telescope (P48) to survey. While refurbishment of the P48 is within the ZTF project scope, use of the P48 imposes constraints on the ZTF survey.

Telescope

The Samuel Oschin Telescope provides a $$7^{\circ}\times 7^{\circ}$$ field at 67$${}^{\prime\prime}$$/mm, with some vignetting in the corners. It has a collecting aperture of 48-inches, operating at $$f$$/2.5. It was used with photographic plates from 1950-1957 for the first Palomar Sky Survey (POSS-I), and with enhanced Kodak emulsions and an achromatic doublet Schmidt corrector for the second Palomar Sky Survey (POSS-II) from the mid 1980’s to the late 1990’s. These survey plates were taken with an observer and the original telescope control system, installed in 1948.

In 2000 JPL upgraded the telescope via a contract with Vertex-RSI to provide an automated TCS, and equipped the telescope with a 50-Mpixel digital CCD camera consisting of three 4Kx4K Fairchild front illuminated detectors, each of which imaged 1.3 square degrees on the sky. This system was used until 2003 for the NASA-funded Near Earth Asteroid Tracking (NEAT) program, and successfully found many asteroids.

In 2003 Caltech entered into collaboration with JPL-NEAT and Yale University to further upgrade the detector to the QUEST camera of 160 Megapixels, consisting of 112 Sarnoff CCDs, imaging about 9 square degrees, although not all CCDs worked. The QUEST camera is novel in providing both point and shoot and driftscan capability. After a significant pipeline upgrade effort at JPL, the QUEST camera continued to find asteroids. Mike Brown used it to find several new solar system objects, including Sedna and Eris. It also found many Supernovae and was used to search for transient and variable objects.

In 2009 Caltech began the Palomar Transient Factory (PTF) survey, using the repurposed CFHT12k MOSAIC camera. The MOSAIC camera delivered more accurate photometry than the QUEST camera and enabled a significant survey for transients, variables, and asteroids.