The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope. III. Single Object Slitless Spectroscopy

Abstract The Near Infrared Imager and Slitless Spectrograph instrument (NIRISS) is the Canadian Space Agency contribution to the suite of four science instruments of the James Webb Space Telescope. As one of the three NIRISS observing modes, the Single Object Slitless Spectroscopy (SOSS) mode is tai...

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Published in:Publications of the Astronomical Society of the Pacific 2023-07, Vol.135 (1049), p.75001
Main Authors: Albert, Loïc, Lafrenière, David, Doyon, René, Artigau, Étienne, Volk, Kevin, Goudfrooij, Paul, Martel, André R., Radica, Michael, Rowe, Jason, Espinoza, Néstor, Roy, Arpita, Filippazzo, Joseph C., Darveau-Bernier, Antoine, Talens, Geert Jan, Sivaramakrishnan, Anand, Willott, Chris J., Fullerton, Alexander W., LaMassa, Stephanie, Hutchings, John B., Rowlands, Neil, Begoña Vila, M., Zhou, Julia, Aldridge, David, Maszkiewicz, Michael, Beaulieu, Mathilde, Cook, Neil J., Piaulet, Caroline, Roy, Pierre-Alexis, Lamontagne, Pierrot, Morel, Kim, Frost, William, Salhi, Salma, Coulombe, Louis-Philippe, Benneke, Björn, MacDonald, Ryan J., Johnstone, Doug, Turner, Jake D., Fournier-Tondreau, Marylou, Allart, Romain, Kaltenegger, Lisa
Format: Article
Language:English
Subjects:
Astronomical instrumentation
Chemical speciation
Exoplanet atmospheres
Extrasolar planets
Gas giant planets
Infrared astronomy
Noise
Space telescopes
Spectroscopy
Spectrum analysis
Terrestrial planets
Time series
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Summary:Abstract The Near Infrared Imager and Slitless Spectrograph instrument (NIRISS) is the Canadian Space Agency contribution to the suite of four science instruments of the James Webb Space Telescope. As one of the three NIRISS observing modes, the Single Object Slitless Spectroscopy (SOSS) mode is tailor-made to undertake time-series observations of exoplanets to perform transit spectroscopy. The SOSS permits observing point sources between 0.6 and 2.8 μ m at a resolving power of 650 at 1.25 μ m using a slitless cross-dispersing grism while its defocussing cylindrical lens enables observing targets as bright as J = 6.7 by spreading light across 23 pixels along the cross-dispersion axis. This paper officially presents the design of the SOSS mode, its operation, characterization, and its performance, from ground-based testing and flight-based commissioning. On-sky measurements demonstrate a peak photon conversion efficiency of 55% at 1.2 μ m. The first time series on the A-type star BD+60°1753 achieves a flux stability close to the photon-noise limit, so far tested to a level of 20 parts per million on a 40 minute timescale after simply subtracting a long-term trend. Uncorrected 1/ f noise residuals underneath the spectral traces add an extra source of noise equivalent to doubling the readout noise. Preliminary analysis of an HAT-P-14b transit time series indicates that it is difficult to remove all of the noise in pixels with partially saturated ramps. Overall, the SOSS delivers performance at the level required to tackle key exoplanetary science programs such as detecting secondary atmospheres on terrestrial planets and measuring abundances of several chemical species in gas giants.
ISSN:0004-6280
1538-3873
DOI:10.1088/1538-3873/acd7a3