NIRCam Coronagraphy was declared ready for science in the early summer 2022. Several impactful science results have since been obtained using the NIRCam coronagraphs, mainly on known exoplanetary systems. In this contribution we give an update on all improvements we have implemented to make this mode more efficient and perform better. With tight timing constraints in commissioning, we focused on the long wavelengths occulter MASK335R. Here we describe how we improved the target acquisition for all five masks, the distortion correction and global alignment, the absolute flux calibration, etc. We also implemented the default dual channel operations mid-Cycle 1 (simultaneous short and long wavelengths). While not trivial, this new capability improves the efficiency and the impact NIRCam Coronagraphy can have in the field of exoplanets. We discuss the current on-sky contrasts and astrometric performances which are now better understood and can be compared to other high contrast facilities. We demonstrate that NIRCam Coronagraphy is transformative in characterizing known objects but also discovering colder and/or more mature exoplanets.
Backgrounds observed by JWST will be a critical parameter for overall observatory sensitivity. JWST’s background, sensitivity and other performance requirements drove the observatory’s open architecture, sunshield geometry, orbit at L2 and other unique characteristics. These requirements were verified by analysis, to be measured for the first time on-orbit. Modeling JWSTs backgrounds is complex, as JWST backgrounds have multiple components including: backgrounds from in-field sources (such as Zodiacal Light) and stray light from scattering of sky sources outside the field; thermal selfemission of optical surfaces; and scattering of thermal self-emission from other Observatory surfaces. The unbaffled telescope design allows stray light paths from multiple directions. The 5-layer sunshield passively cools and shades the telescope and science instruments; however, there are thermal paths that may affect thermal performance. In-field backgrounds and stray light from sky sources can depend on the telescope’s pointing and observation date. The thermal emission contributions will depend on the Observatory’s sun orientation and recent history. The JWST Background Tool (JBT) uses the stray light models, in-field backgrounds, and thermal models to predict the expected backgrounds. Onorbit, several positions were measured at multiple wavelengths with NIRCam and MIRI to probe JWST’s backgrounds and validate model predictions. These results may be used to update the JWST Exposure Time Calculator in preparation for the Cycle 2 proposal call. This conference proceeding will provide a summary of the modeling backgrounds and report on the measured on-orbit backgrounds.
The James Webb Space Telescope (JWST) will revolutionize the field of high-contrast imaging and enable both the direct detection of Saturn-mass planets and the characterization of substellar companions in the mid-infrared. While JWST will feature unprecedented sensitivity, angular resolution will be the key factor when competing with ground-based telescopes. Here, we aim to characterize the performance of several extreme angular resolution imaging techniques available with JWST in the 3–5 µm regime based on data taken during the instrument commissioning. Firstly, we introduce custom tools to simulate, reduce, and analyze JWST NIRCam and MIRI coronagraphy data and use these tools to extract companion detection limits from on-sky NIRCam round and bar mask coronagraphy observations. Secondly, we present on-sky JWST NIRISS aperture masking interferometry (AMI) and kernel phase imaging (KPI) observations from which we extract companion detection limits using the publicly available fouriever tool. Scaled to a total integration time of one hour and a target of the brightness of AB Dor (W1 ≈ 4.4 mag, W2 ≈ 3.9 mag), we find that NIRISS AMI and KPI reach contrasts of ∼ 7–8 mag at ∼ 70 mas and ∼ 9 mag at ∼ 200 mas. Beyond ∼ 250 mas, NIRCam coronagraphy reaches deeper contrasts of ∼ 13 mag at ∼ 500 mas and ∼ 15 mag at ∼ 2 arcsec. While the bar mask performs ∼ 1 mag better than the round mask at small angular separations ≲ 0.75 arcsec, it is the other way around at large angular separations ≳ 1.5 arcsec. Moreover, the round mask gives access to the full 360 deg field-of-view which is beneficial for the search of new companions. We conclude that already during the instrument commissioning, JWST high-contrast imaging in the L- and M-bands performs close to its predicted limits and is a factor of ∼ 10 times better at large separations than the best ground-based instruments operating at similar wavelengths despite its < 2 times smaller collecting area.
KEYWORDS: Coronagraphy, Stars, James Webb Space Telescope, Point spread functions, Distortion, Telescopes, Signal to noise ratio, Calibration, Target acquisition, Exoplanets, Astronomical imaging, Near infrared, Direct methods, Astronomical instrumentation
In a cold and stable space environment, the James Webb Space Telescope (JWST or ”Webb”) reaches unprecedented sensitivities at wavelengths beyond 2 microns, serving most fields of astrophysics. It also extends the parameter space of high-contrast imaging in the near and mid-infrared. Launched in late 2021, JWST underwent a six month commissioning period. In this contribution we focus on the NIRCam Coronagraphy mode which was declared ”science ready” on July 10 2022, the last of the 17 JWST observing modes. Essentially, this mode enables the detection of fainter/redder/colder (less massive for a given age) self-luminous exoplanets as well as other faint astrophysical signal in the vicinity of any bright object (stars or galaxies). Here we describe some of the steps and hurdles the commissioning team went through to achieve excellent performances. Specifically, we focus on the Coronagraphic Suppression Verification activity. We were able to produce firm detections at 3.35µm of the white dwarf companion HD 114174 B which is at a separation of ' 0.500and a contrast of ' 10 magnitudes (104 fainter than the K∼5.3 host star). We compare these first on-sky images with our latest, most informed and realistic end-to-end simulations through the same pipeline. Additionally we provide information on how we succeeded with the target acquisition with all five NIRCam focal plane masks and their four corresponding wedged Lyot stops.
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