esc-etc: Exposure Time Calculator for the Lazuli ESC

Schmidt Observatory System

esc-etc is the exposure time calculator (ETC) for the ExtraSolar Camera (ESC), the coronagraphic instrument on Lazuli, the Schmidt Observatory System’s space telescope. You describe a host star, a planet and the sky background, pick a filter and a coronagraph setting, and it returns the signal-to-noise ratio for a given integration time, the integration time that reaches a target signal-to-noise, and the longest frame the detector can take before the brightest pixel saturates. Each result can also be drawn with one method call.

A hosted web version of the ETC is available at simulators.schmidtobservatorysystem.org/esc.

Note

New here? Read Installation, then Quick start. If coronagraph vocabulary (dark hole, raw contrast, post-processing gain) is new to you, the primer at the top of Coronagraph and contrast defines the terms the rest of this site uses.

What it models

  • A calculation is built from four objects, a Telescope, a Sensor, a Scene (host star, planet, zodiacal and exozodiacal light) and a Coronagraph, combined into one Simulation.

  • The noise budget counts photon noise from the planet, the sky backgrounds and the residual starlight (speckles), dark current, read noise per frame, and a systematic floor from the speckles that post-processing does not remove. That floor gives every configuration a maximum reachable signal-to-noise.

  • The coronagraph is described by its raw dark-hole contrast, an assumed post-processing gain, the planet separation and a throughput curve for the focal-plane mask. Reference-star subtraction can be switched on.

  • filter="F630N", or any of the twelve ESC filters, uses that filter’s measured end-to-end throughput, at end of life or at beginning of life.

  • Photometry is done in a chosen aperture: the resolution element by default, or an optimal, box or matched aperture, each with its own encircled energy.

  • Integration time can be solved for a target signal-to-noise, and every frame time is checked against saturation.

  • sim.plot() draws a six-panel overview. The simulation, sensor, scene and coronagraph have plot_*(ax=None) methods for the count-rate budget, SNR against time (with parameter sweeps), the mask throughput, the bandpass, the aperture footprint and the scene spectra.

Where the instrument comes from

The telescope and instrument properties (mirrors, coatings, filters, detector tables) come from configuration files for the Lazuli 3 m telescope and the ESC, maintained by the University of Arizona Space Astrophysics Laboratory (UASAL). A snapshot of those files ships inside esc_etc, so nothing else is installed. Configuration and filters lists what is in the snapshot and how to point the ETC at your own instrument.

Contents

Getting started

User guide

Tutorials

Reference

Indices and tables