James Webb Space Telescope (JWST) transmission and emission spectra will provide invaluable glimpses of transiting exoplanet atmospheres, including possible biosignatures. This promising science from ...JWST, however, will require exquisite precision and understanding of systematic errors that can impact the time series of planets crossing in front of and behind their host stars. Here, we provide estimates of the random noise sources affecting JWST Near-Infrared Camera (NIRCam) time-series data on the integration-to-integration level. We find that 1/ f noise can limit the precision of grism time series for two groups (230–1000 ppm depending on the extraction method and extraction parameters) but will average down like the square root of N frames/reads. The current NIRCam grism time-series mode is especially affected by 1/ f noise because its GRISMR dispersion direction is parallel to the detector fast-read direction, but could be alleviated in the GRISMC direction. Care should be taken to include as many frames as possible per visit to reduce this 1/ f noise source: thus, we recommend the smallest detector subarray sizes one can tolerate, four output channels, and readout modes that minimize the number of skipped frames (RAPID or BRIGHT2). We also describe a covariance-weighting scheme that can significantly lower the contributions from 1/ f noise as compared to sum extraction. We evaluate the noise introduced by preamplifier offsets, random telegraph noise, and high dark current resistor capacitor (RC) pixels and find that these are correctable below 10 ppm once background subtraction and pixel masking are performed. We explore systematic error sources in a companion paper.
Abstract
Exoplanet CoRoT-1 b is intriguing because we predict it to be a transitional planet between hot Jupiters (equilibrium temperatures ∼1500 K) and ultrahot Jupiters (equilibrium temperatures ...>2000 K). In 2012, observations of CoRoT-1 b included one primary transit and three secondary eclipses with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) combined with the G141 grism (1.1–1.7
μ
m) in stare mode. We aimed to further investigate CoRoT-1 b through its secondary eclipses, producing spectrophotometric light curves corrected for charge trapping, also known as the ramp effect in time-series observations with the WFC3. We found that, when correcting for the ramp effect and using the typically discarded first orbit, we are better capable of constraining and optimizing the emission and transmission spectra. We did a grid retrieval in this transitional temperature regime and found the spectra for CoRoT-1 b to be featureless and to agree with an inverted temperature–pressure (
T
–
P
) profile. We note, however, that the contribution function for the WFC3 indicates pressures probed near 10
−3
to 10
0
bar, which correspond to a nearly isothermal region in our
T
–
P
profile, thereby indicating that the inversion at high altitude is model-dependent. Despite no distinct features, the analysis done on CoRoT-1 b paves the way to high-precision results with stare mode spectroscopy. As a new generation of observations from the James Webb Space Telescope (JWST) approaches, CoRoT-1 b might be an interesting follow-up target because the time-series spectroscopic modes of JWST’s NIRSpec, MIRI, and NIRCam instruments will be analogous to HST’s stare mode.
The James Webb Space Telescope (JWST) will measure exoplanet transmission and eclipse spectroscopy at unprecedented precisions to better understand planet structure, dynamics, chemistry, and ...formation. These are essential tools on the march toward biosignature searches on potentially habitable planets. We explore a range of exoplanet atmospheric conditions and forecast the expected results with JWST. We take realistic CHIMERA models that match existing Spitzer and Hubble Space Telescope results and simulate the spectra achievable with the JWST MIRI+NIRCam Guaranteed Time Observations survey, which includes observations of HD 189733 b, WASP-80 b, HAT-P-19 b, WASP-107 b, GJ 436 b, and HAT-P-26 b. We then retrieve atmospheric parameters from these spectra to estimate the precision to which the planets' atmospheric compositions can be measured. We find that emission spectra have well-constrained unimodal solutions but transmission spectra near 10× solar abundance and solar C/O ratios can suffer from bimodal solutions. Broad wavelength coverage as well as higher-precision data can resolve bimodal solutions and provide dramatically better atmospheric parameter constraints. We find that metallicities can be measured to within 20%-170%, which approaches the precisions on solar system planets, and C/O ratios can be constrained to ∼10%-60%, assuming that observers can leverage short wavelength data to select the correct solution from the bimodal posteriors. These compositional precisions are sufficient to validate or refute predictions from disk formation models on final atmospheric abundances as long as their history is not erased by planet evolution processes. We also show the extent to which eclipse mapping with JWST is possible on our brightest system HD 189733 b.
Performance of NIRCam on JWST in Flight Rieke, Marcia J.; Kelly, Douglas M.; Misselt, Karl ...
Publications of the Astronomical Society of the Pacific,
02/2023, Volume:
135, Issue:
1044
Journal Article
Peer reviewed
Open access
Abstract
The Near Infrared Camera for the James Webb Space Telescope (JWST) is delivering the imagery that astronomers have hoped for ever since JWST was proposed back in the 1990s. In the ...Commissioning Period that extended from right after launch to early 2022 July, NIRCam has been subjected to a number of performance tests and operational checks. The camera is exceeding prelaunch expectations in virtually all areas, with very few surprises discovered in flight. NIRCam also delivered the imagery needed by the Wavefront Sensing Team for use in aligning the telescope mirror segments.
Abstract We demonstrate an approach to determine spectral energy distribution (SED) templates that are accurate to the 1% level from the visible through the infrared for nearby (unextincted) ...solar-type stars. Our approach is based only on measurements of T eff , log( g ), and M/H and the use of standard theoretical SED models. The success of this approach confirms that the existing absolute calibration is likely to be accurate to this level throughout this spectral range. We then demonstrate how to measure and correct for extinction, allowing extension of this calibration approach to faint levels (and more distant stars). We provide template SEDs in digital form for 11 G-dwarf stellar calibrators.
Abstract
It is critical for James Webb Space Telescope (JWST) science that instrumental units are converted to physical units. We detail the design of the JWST absolute flux calibration program that ...has the core goal of ensuring a robust flux calibration internal to and between all the science instruments for both point and extended source science. This program will observe a sample of calibration stars that have been extensively vetted based mainly on Hubble Space Telescope, Spitzer Space Telescope, and Transiting Exoplanet Survey Satellite observations. The program uses multiple stars of three different, well-understood types (hot stars, A dwarfs, and solar analogs) to allow for the statistical (within a type) and systematic (between types) uncertainties to be quantified. The program explicitly includes observations to calibrate every instrument mode, further vet the set of calibration stars, measure the instrumental repeatability, measure the relative calibration between subarrays and full frame, and check the relative calibration between faint and bright stars. For photometry, we have set up our calibration to directly support both the convention based on the band average flux density and the convention based on the flux density at a fixed wavelength.
Abstract
High-precision lightcurves combined with eclipse-mapping techniques can reveal the horizontal and vertical structure of a planet’s thermal emission and the dynamics of hot Jupiters. Someday, ...they even may reveal the surface maps of rocky planets. However, inverting lightcurves into maps requires an understanding of the planet, star, and instrumental trends because they can resemble the gradual flux variations as the planet rotates (i.e., partial phase curves). In this work, we simulate lightcurves with baseline trends and assess the impact on planet maps. Baseline trends can be erroneously modeled by incorrect astrophysical planet map features, but there are clues to avoid this pitfall in both the residuals of the lightcurve during eclipse and sharp features at the terminator of the planet. Models that use a Gaussian process or polynomial to account for a baseline trend successfully recover the input map even in the presence of systematics but with worse precision for the
m
= 1 spherical harmonic terms. This is also confirmed with the ThERESA eigencurve method where fewer lightcurve terms can model the planet without correlations between the components. These conclusions help aid the decision on how to schedule observations to improve map precision. If the
m
= 1 components are critical, such as measuring the east/west hot-spot shift on a hot Jupiter, better characterization of baseline trends can improve the
m
= 1 terms’ precision. For latitudinal north/south information from
m
≠ 1 mapping terms, it is preferable to obtain high signal to noise at ingress/egress with more eclipses.
Abstract
We report Spitzer 3.6 and 4.5
μ
m photometry of 11 bright stars relative to Sirius, exploiting the unique optical stability of the Spitzer Space Telescope point-spread function (PSF). ...Spitzer's extremely stable beryllium optics in its isothermal environment enables precise comparisons in the wings of the PSF from heavily saturated stars. These bright stars stand as the primary sample to improve stellar models, and to transfer the absolute flux calibration of bright standard stars to a sample of fainter standards useful for missions like JWST and for large ground-based telescopes. We demonstrate that better than 1% relative photometry can be achieved using the PSF wing technique in the radial range of 20″–100″ for stars that are fainter than Sirius by 8 mag (from outside the saturated core to a large radius where a high signal-to-noise ratio profile can still be obtained). We test our results by (1) comparing the 3.6−4.5 color with that expected between the WISE W1 and W2 bands, (2) comparing with stars where there is accurate
K
S
photometry, and (3) also comparing with relative fluxes obtained with the DIRBE instrument on COBE. These tests confirm that relative photometry is achieved to better than 1%.
Abstract
We report on five years of 3–5
μ
m photometry measurements obtained by warm Spitzer to track the dust debris emission in the terrestrial zone of HD 166191 in combination with simultaneous ...optical data. We show that the debris production in this young (∼10 Myr) system increased significantly in early 2018 and reached a record high level (almost double by mid 2019) by the end of the Spitzer mission (early 2020), suggesting intense collisional activity in its terrestrial zone likely due to either initial assembling of terrestrial planets through giant impacts or dynamical shake-up from unseen planet-mass objects or recent planet migration. This intense activity is further highlighted by detecting a star-size dust clump, passing in front of the star, in the midst of its infrared brightening. We constrain the minimum size and mass of the clump using multiwavelength transit profiles and conclude that the dust clump is most likely created by a large impact involving objects of several hundred kilometers in size with an apparent period of 142 days (i.e., 0.62 au, assuming a circular orbit). The system’s evolutionary state (right after the dispersal of its gas-rich disk) makes it extremely valuable to learn about the process of terrestrial-planet formation and planetary architecture through future observations.
Abstract
The disintegrating planet candidate K2-22 b shows periodic and stochastic transits best explained by an escaping debris cloud. However, the mechanism that creates the debris cloud is ...unknown. The grain size of the debris as well as its sublimation rate can be helpful in understanding the environment that disintegrates the planet. Here, we present simultaneous photometry with the
g
band at 0.48
μ
m and
K
S
band at 2.1
μ
m using the Large Binocular Telescope. During an event with very low dust activity, we put a new upper limit on the size of the planet of 0.71
R
⊕
or 4500 km. We also detected a medium depth transit that can be used to constrain the dust particle sizes. We find that the median particle size must be larger than about 0.5–1.0
μ
m, depending on the composition of the debris. This leads to a high mass-loss rate of about 3 × 10
8
kg s
−1
, which is consistent with hydrodynamic escape models. If they are produced by some alternate mechanism such as explosive volcanism, it would require extraordinary geological activity. Combining our upper limits on the planet size with the high mass-loss rate, we find a lifetime of the planet of less than 370 Myr. This drops to just 21 Myr when adopting the 0.02
M
⊕
mass predicted from hydrodynamical models.
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