Breaking the brightness barrier: JWST/NIRCam DHS spectroscopy for high-precision time-series observations
Abstract
Many of the most scientifically compelling exoplanets orbit bright nearby stars that exceed the brightness limits of existing JWST spectroscopic observing modes. To address this limitation, a new NIRCam Short Wavelength Grism Time-Series mode has been developed by combining the Dispersed Hartmann Sensor (DHS) with a new on-board multistripe detector readout capability. The DHS disperses the incoming light through multiple pupil sub-apertures, reducing the incident flux and providing slitless spectroscopy between approximately 1.0 and 2.3 um. The multistripe readout mode further increases the accessible brightness range (K ~ 2.5 - 5.7 mag, depending on the spectral type of the object), with the previous limit being K ~ 5.7 mag at 1.5 um, by reading only the detector regions containing the DHS spectra, reducing the detector frame time with the standard RAPID readout mode from 10.74 s to 1.36 s over even less when using smaller substripe sizes. Together with the simultaneous long-wavelength grism observations, the new mode provides spectroscopic continuous coverage from approximately 1.0 to 5.0 um for targets as bright as K ~ 2.5 mag. We present the first results of on-orbit commissioning of this new observing mode with the final stage consisting of observations of a full transit of the exoplanet WASP-18b, which allowed us to demonstrate the feasibility of using NIRCam DHS for high-precision time-series observations. The commissioning presented in this paper marks the first deployment of the multistripe detector readout on JWST. Beyond NIRCam DHS, this new capability will be extended to other spectroscopic modes, including NIRISS SOSS and NIRSpec PRISM. Bright nearby stars host many of the highest-priority targets for exoplanet atmospheric characterization, making multistripe an important new capability for maximizing the scientific return of JWST.
Versions
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BibTeX
@misc{dyrek2026breaking,
title = {{Breaking the brightness barrier: JWST/NIRCam DHS spectroscopy for high-precision time-series observations}},
author = {Achrene Dyrek and John Stansberry and Louis E. Bergeron and Everett Schlawin and Nestor Espinoza and Brian Brooks and Mario Gennaro and Martha L. Boyer and Russell Ryan and Bryan Hilbert and Munazza K. Alam and Aarynn L. Carter and Norbert Pirzkal and Julien H. Girard and Anton M. Koekemoer},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.04109},
eprint = {2608.04109},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.04109},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Breaking the brightness barrier: JWST/NIRCam DHS spectroscopy for high-precision time-series observations
AU - Achrene Dyrek
AU - John Stansberry
AU - Louis E. Bergeron
AU - Everett Schlawin
AU - Nestor Espinoza
AU - Brian Brooks
AU - Mario Gennaro
AU - Martha L. Boyer
AU - Russell Ryan
AU - Bryan Hilbert
AU - Munazza K. Alam
AU - Aarynn L. Carter
AU - Norbert Pirzkal
AU - Julien H. Girard
AU - Anton M. Koekemoer
PY - 2026
DA - 2026/08/04
PB - arXiv
DO - 10.48550/arxiv.2608.04109
UR - https://arxiv.org/abs/2608.04109
AB - Many of the most scientifically compelling exoplanets orbit bright nearby stars that exceed the brightness limits of existing JWST spectroscopic observing modes. To address this limitation, a new NIRCam Short Wavelength Grism Time-Series mode has been developed by combining the Dispersed Hartmann Sensor (DHS) with a new on-board multistripe detector readout capability. The DHS disperses the incoming light through multiple pupil sub-apertures, reducing the incident flux and providing slitless spectroscopy between approximately 1.0 and 2.3 um. The multistripe readout mode further increases the accessible brightness range (K ~ 2.5 - 5.7 mag, depending on the spectral type of the object), with the previous limit being K ~ 5.7 mag at 1.5 um, by reading only the detector regions containing the DHS spectra, reducing the detector frame time with the standard RAPID readout mode from 10.74 s to 1.36 s over even less when using smaller substripe sizes. Together with the simultaneous long-wavelength grism observations, the new mode provides spectroscopic continuous coverage from approximately 1.0 to 5.0 um for targets as bright as K ~ 2.5 mag. We present the first results of on-orbit commissioning of this new observing mode with the final stage consisting of observations of a full transit of the exoplanet WASP-18b, which allowed us to demonstrate the feasibility of using NIRCam DHS for high-precision time-series observations. The commissioning presented in this paper marks the first deployment of the multistripe detector readout on JWST. Beyond NIRCam DHS, this new capability will be extended to other spectroscopic modes, including NIRISS SOSS and NIRSpec PRISM. Bright nearby stars host many of the highest-priority targets for exoplanet atmospheric characterization, making multistripe an important new capability for maximizing the scientific return of JWST.
ER -