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.

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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.

Figure 1. Overview of JWST capabilities for time-series observations (TSOs)

Overview of TSO modes in JWST. This figure does not yet include TSO imaging with MIRI. (Image: N. Batalha)


TSO imaging modes 

Main articles: NIRCam Time-Series Imaging, MIRI Imaging
See also: MIRI Imaging TSOs

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

InstrumentMode

Wavelength range (µm)

Filter optionsSubarray optionsRead mode options
NIRCamtime-series imaging

short: 0.6–2.3
long: 2.4–5.0 
(simultaneous)

short: any filter, with/without weak lens WLP8
long: any filter


FULL
SUB400P
SUB160P
SUB64P

RAPID
BRIGHT1
BRIGHT2
SHALLOW2
SHALLOW4
MEDIUM2
MEDIUM8
DEEP2
DEEP8

MIRI (limited)time-series imaging5.625.5all standard imaging filters available (9)

SUB64
FULL
BRIGHTSKY
SUB128
SUB256

FAST



TSO spectroscopy modes

Main articles: NIRCam Grism Time Series, NIRISS Single Object Slitless Spectroscopy, NIRSpec Bright Object Time Series Observations, MIRI Low-Resolution Spectroscopy
See also: MIRI LRS TSOs

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

InstrumentModeWavelength range (µm)Disperser/Filter optionsSpectral resolving powerSubarray optionsRead mode options
NIRCamGrism time-series spectroscopy2.4–5.0short:
  • WLP8 + F182M
  • WLP8 + F187N
  • WLP8 + F210M
  • WLP8 + F212N
  • WLP4+CLEAR*

long:

GrismR plus a wide filter:

  • F277W
  • F322W2
  • F356W
  • F444W
1,500

FULL
2048 columns by 64, 128,
or 256 pixel rows

Read out through 4 outputs simulatenously
or via a single output

NIRISS

Single object slitless spectroscopy (SOSS)

0.62.8CLEAR, GR700XD700

SUBSTRIP256 (256 × 2048)
SUBSTRIP96 (96×2048)

NISRAPID

NIRSpec


Bright object time-series spectroscopy (BOTS)

  1. 0.7–1.27
  2. 0.97–1.89
  3. 1.66–3.17
  4. 2.87–5.27
  5. 0.7–1.27
  6. 0.97–1.89
  7. 1.66–3.17
  8. 2.87–5.27
  9. 0.6–5.3
  1. G140M/F070LP
  2. G140M/F100LP
  3. G235M/F170LP
  4. G395M/F290LP
  5. G140H/F070LP
  6. G140H/F100LP
  7. G235H/F170LP
  8. G395H/F290LP
  9. PRISM/CLEAR

combinations 14: 1,000

combinations 58: 2,700

combination 9: 100

SUB2048
SUB1024A
SUB1024B
SUB512
SUB512S

NRSRAPID
NRS

MIRISlitless low-resolution spectroscopy (LRS)512double prism (P750L)100SLITLESSPRISMFAST



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