JWST Time-Series Observations
JWST time-series observations provide a way to monitor time-variable phenomena, with observations optimised for detecting faint variations in flux over short or long timescales.
Time-series observations (TSO) are carried out to monitor astrophysical sources that are time-variable. A time-series observation is typically a long staring observation, optimised to detect and characterize faint temporal modulations in the source flux. Common examples are observations of stellar variability, eclipsing variables, brown dwarf variability, or exoplanet transits.
The lack of interference from Earth's atmosphere and the gravity-free environment make a large space-based observatory such as JWST particularly suitable for this type of observations. Such observations place specific requirements on the observatory and the instrumentation to ensure the highest possible level of stability over lengthy exposures; as well as on the data processing environment.
This article describes how TSOs are performed using JWST: the instrumentation and modes that are available, user tools to prepare TSO's, the data processing infrastructure, and some guidelines for preparing successful TSOs.
Time-series observation with JWST
A number of "special conditions" have been implemented for JWST that optimise the instrument setup and data processing for long-duration staring TSOs that require high stability:
- dithering is disabled
- target acquisition is enabled (mandatory for some modes)
- exposures can take longer than 10,000 s
- high gain antenna moves are allowed during the exposure
- data are processed via a dedicated, more minimal, pipeline branch (CALTSO3)
The TSO conditions are available to a number of modes across all 4 JWST instruments. Some of these have been designated as TSO-only modes, for others the user can choose to flag their observations as TSO via the Astronomer's Proposal Tool (APT).
Instrument modes for TSOs
Details about instrument modes available for TSOs are available in these articles:
- NIRISS Single-Object Slitless Spectroscopy (SOSS)
- NIRCam Time-Series Imaging
- NIRCam Grism Time Series
- NIRSpec Bright Object Time-Series Spectroscopy (BOTS)
- MIRI Imaging
- MIRI Low Resolution Spectroscopy (LRS)
The articles are dedicated instrument documentation pages for these modes, where the user can find detailed information on the instrument hardware and operations. Other modes can still be used to measure time series of sources, but the user should note that the conditions listed above will not be available. This section provides guidelines on the scientific applications of each TSO instrument/mode combination.
See the following article for guidelines and a roadmap for how to prepare your time series observations with JWST.
TSOs Example Science Programs
The following example science programs are available for time series observations.
- NIRCam Time-Series Imaging of HAT-P-18 b
- NIRCam Grism Time-Series Observations of GJ 436b
- NIRISS SOSS Time-Series Observations of HAT-P-1
- NIRSpec BOTS Observations of GJ 1214b