The JWST overhead times are adopted by the Astronomer's Proposal Tool for each overhead activity.
The Astronomers Proposal Tool, APT, charges users time and overheads for their observing programs (see overview and summary). Instrument overheads are charged for operations performed during the use of each instrument. Approximate typical examples are given in Table 1; actual overheads will vary depending on observing parameters. Complete details are provided in Instrument Specific Overheads. Details for your observing program are available by exporting the times report from APT.
The JWST Astronomer's Proposal Tool and the model for calculating overheads is under development and subject to change. The following values are approximate guides of overheads in APT 25.4.
Table 1. Typical instrument overheads (in seconds) for common operations
|Onboard Script System (OSS) |
compilation (per exposure)
(full frame, single integration)
|69||74 (IRS2 readout)|
|Filter / grism change||110–190||200||84–140||50||N/A|
† Exposure Overhead is overhead charged ("Exp Ovhd" in the APT times report), not the exposure time itself.
‡ Visit Cleanup is charged in addition to the 282 seconds to acquire a guide star at the beginning of each visit.