Overview of Time-Series Observation (TSO) Modes
Time-series observations can be taken with all four of JWST's instruments using specific imaging and spectroscopic modes.
JWST has four instruments on board, three covering the near-infrared part of the spectrum, and one for the mid-infrared regime. Each instrument has at least one TSO-specific mode of observation, offering the user a range of capabilities for such observations. This article describes the basic parameters for these dedicated TSO modes.
As a reminder, the following conditions are enabled for a TSO:
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)
A schematic overview of the available modes is shown in Figure 1.
TSO imaging modes
For time-series imaging, the only dedicated, fully-supported mode is in NIRCam, which offers simultaneous imaging in the short and long wavelength channels with a range of broad-, medium- and narrowband filters in each channel. In the short wavelength channel, the user can, in addition, select the weak lens WLP8 to increase the dynamic range. Four different array readout configurations are allowed with all of NIRCam's detector read modes. Time-series imaging is also possible with MIRI, though not with full support for all capabilities. Full details on MIRI TSO imaging capabilities and limitations can be found in the MIRI-Specific TSO Strategies article, in this section, and the MIRI TSO Imaging article in the MIRI documentation.
Links are provided below to further documentation articles on these modes and capabilities.
Table 1. TSO imaging is available in NIRCam; limited support for MIRI TSO imaging
Wavelength range (µm)
|Filter options||Subarray options||Read mode options|
short: any filter, with/without weak lens WLP8
|MIRI (limited)||time-series imaging||5.6–25.5||all standard imaging filters available (9)|
TSO spectroscopy modes
For time-series spectroscopy, the near-IR instruments offer three different types of spectroscopic observations. These modes are optimized for stability over long observations, throughput, and dynamic range. In the mid-IR, MIRI provides low-resolution slitless spectroscopy to 12 µm. The table below gives an overview of the available modes.
Table 2. TSO spectroscopy modes
|Instrument||Mode||Wavelength range (µm)||Disperser/Filter options||Spectral resolving power||Subarray options||Read mode options|
|NIRCam||Grism time-series spectroscopy||2.4–5.0||short:|
GrismR plus a wide filter:
Read out through 4 outputs simulatenously
SUBSTRIP256 (256 × 2048)
combinations 1–4: 1,000
combinations 5–8: 2,700
combination 9: 100
|MIRI||Slitless low-resolution spectroscopy (LRS)||5–12||double prism (P750L)||100||SLITLESSPRISM||FAST|