NIRSpec BOTS Calibration Status

Tthe overall calibration status and estimated accuracy of NIRSpec bright-object time series (BOTS) observations are described in this article; please also see the article on known issues affecting NIRSpec BOTS data.

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Photometric calibration


The results on photometric calibration for FS also apply to the BOTS mode when considering the net extracted absolute, as opposed to relative, spectra.



For bright stars (K mag ~ 7.7 to 9.5) it has been demonstrated that observations with G395H can measure broadband transit depth variations to an accuracy of 50 to 60 ppm. Similar behavior is expected for other modes.

Typical drifts in the measured count rate are between 30 to 140 ppm/hour for NRS1 and 10 to 40 ppm/hour for NRS2, with the drift rate declining over the course of multi-day observations.

Stability of the trace location on the detector is typically between 1/300th and 1/1000th of a pixel.

See Espinoza et al. 2023 , Mikal-Evans et al. 2023, Lustig-Yaeger et al. 2023.

For more information, see NIRSpec Time Series Observations Pipeline Caveats.


Espinoza, N., et al. 2023, PASP, 135 018002
Spectroscopic Time-series Performance of JWST/NIRSpec from Commissioning Observations

Lustig-Yaeger, J., et al. 2023, submitted to Nature Astronomy (arXiv)
A JWST transmission spectrum of a nearby Earth-sized exoplanet

Mikal-Evans, T., et al. 2023 ApJL 943 L17
A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud Formation

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Originally published