JWST Time-Series Observations
JWST time-series observations provide a way to monitor time variable phenomena, with observations optimized 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, optimized 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 TSOs, the data processing infrastructure, and some guidelines for preparing successful TSOs.
Time-series observation with JWST
Several steps have been implemented to optimize JWST's instrument setup and data processing to provide the highly stable conditions needed for long duration staring at TSOs:
- 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 pipeline branch (CALTSO3); every integration is treated as an individual observation.
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 modes, a user can choose to flag observations as TSO via the Astronomer's Proposal Tool (APT).
Typical noise sources that affect the (spectro-) photometric precision in TSOs are described in this dedicated article.
Instrument modes for TSOs
Details about TSO-specific instrument modes 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 TSOs
- MIRI Low Resolution Spectroscopy (LRS)
- MIRI Medium Resolution Spectroscopy (MRS)
These articles are dedicated instrument documentation pages for these modes, with detailed information on the instrument hardware and operations. Other modes may be used to measure time series of sources, but 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 WASP-79b