A reassessment of ground‐based observations confirms to better than a 98% confidence level that the Galileo probe entered a 5‐μm hot spot, a region of unusual clarity and dryness, some 900±300 km north of its southern boundary. Cloud conditions at that point were similar to those in the center of this region, some 600 km further north. At the time of the probe entry, the region was evolving to a slightly larger size and even thinner cloud conditions, as evidenced by its rapidly brightening appearance at 4.78 μm. The low reflectivity of the region in red light is highly anticorrelated with 4.78‐μm thermal emission, but this correlation breaks down in the blue. In general, the reflectivity of most hot spots is remarkably uniform, although the 4.78‐μm thermal emission is highly variable. A cloud structure most consistent with both the observed reflected sunlight and thermal emission properties consists of two layers: (1) a cloud layer above the 450‐mbar level extending up to the 150‐mbar level that probably consists of submicron sized particles and (2) a tropospheric cloud that is probably below the 1‐bar level, possibly ammonia hydrosulfide, with low optical thickness in the infrared. A population of particles larger than ∼3 μm, clearly present at the NH 3 ice cloud level outside hot spots, is absent inside them. The NH 3 gas abundance near 300–400 mbar pressure does not appear to be unusually depleted in hot spots. Zonal structures in the tropospheric temperature field near the probe entry site were not correlated with the location of 5‐μm hot spots but moved at speeds closer to the internal rotation rate of the planet. The properties of the tropospheric thermal waves at the probe entry latitude show little correlation to the properties of the 5‐μm hot spot waves. Temperatures at the probe entry site derived from remote sensing are warmer than the Atmospheric Structure Instrument (ASI) experiment results near the tropopause, probably because the low‐temperature ASI features are confined to regions smaller than the ∼6000‐km resolution characteristic of the remote sensing.
Abstract The James Webb Space Telescope (JWST) has opened up a new window to study highly reddened explosive transients. We present results from late-time JWST follow-up spectroscopic observations with NIRSpec and MIRI-LRS of the intermediate-luminosity red transient (ILRT) AT 2019abn. ILRTs represent a mysterious class of transients that exhibit peak luminosities between those of classical novae and supernovae and that are known to be highly dust obscured. Similar to the prototypical examples of this class of objects, NGC 300 2008-OT and SN 2008S, AT 2019abn has an extremely red and dusty progenitor detected only in pre-explosion Spitzer/IRAC imaging at 3.6 and 4.5 μ m and not in deep optical or near-infrared Hubble Space Telescope images. We find that late-time observations of AT 2019abn from NEOWISE and JWST are consistent with the late-time evolution of SN 2008S. In part because they are so obscured by dust, it is unknown what produces an ILRT, with hypotheses including high-mass stellar merger events, nonterminal stellar outbursts, and terminal supernova explosions through electron capture in super-AGB (SAGB) stars. Our JWST observations show strong mid-IR class C polycyclic aromatic hydrocarbon features at 6.3 and 8.25 μ m typical of carbon-rich post-AGB sources. These features suggest that the dust around AT 2019abn is composed of carbonaceous grains, which are not typically observed around red supergiants. However, depending on the strength and temperature of hot bottom burning, SAGB stars may be expected to exhibit a carbon-rich chemistry. Thus, our JWST observations are consistent with AT 2019abn having an SAGB progenitor and exploding as an electron-capture supernova.
We describe the operations concept and data reduction plan for the Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope (JWST). The overall JWST operations concept is to use observation templates (OTs) to provide a straightforward and intuitive way for users to specify observations. MIRI has four OTs that correspond to the four observing modes: (1) imaging, (2) coronagraphy, (3) low-resolution spectroscopy, and (4) medium-resolution spectroscopy. We outline the user choices and expansion of these choices into detailed instrument operations. The data reduction plans for MIRI are split into three stages, where the specificity of the reduction steps to the observation type increases with stage. The reduction starts with integration ramps: stage 1 yields uncalibrated slope images; stage 2 calibrates the slope images; and then stage 3 combines multiple calibrated slope images into high-level data products (e.g., mosaics, spectral cubes, and extracted source information). Finally, we give examples of the data and data products that will be derived from each of the four different OTs.
Abstract : An early function of the FMU-98 fuze mounted on the 2.75-in. rocket occurred approximately 0.1 sec after mechanical arming. Circumstantial evidence is documented that indicates the 600-G, Skinny inertial switch to be the cause. The theory is that the switch had a deformed gap and was excited into closure by rattling of the rocket fins and sputtering of the rocket motor. Although the evidence is not conclusive on the cause of the early function, a precautionary change to the less resonant, 600-G, low cost switch is recommended.
This article summarizes a workshop held on March, 2014, on the potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations. JWST's unique combination of high sensitivity and broad wavelength coverage will enable the accurate measurement of transits with high signal-to-noise. Most importantly, JWST spectroscopy will investigate planetary atmospheres to determine atomic and molecular compositions, to probe vertical and horizontal structure, and to follow dynamical evolution, i.e. exoplanet weather. JWST will sample a diverse population of planets of varying masses and densities in a wide variety of environments characterized by a range of host star masses and metallicities, orbital semi-major axes and eccentricities. A broad program of exoplanet science could use a substantial fraction of the overall JWST mission.
We present high-resolution imaging of the nucleus of NGC 4258 from 1 to 18 μm. Our observations reveal that the previously discovered compact source of emission is unresolved even at the near-infrared resolution of ~02 FWHM, which corresponds to about 7 pc at the distance of the galaxy. This is consistent with the source of emission being the region in the neighborhood of the purported 3.5 × 107 M☉ black hole. After correcting for about 18 mag of visual extinction, the infrared data are consistent with an Fν ∝ ν-1.4±0.1 spectrum from 1.1 to 18 μm, implying a nonthermal origin. Based on this spectrum, the total extinction-corrected infrared luminosity (1-20 μm) of the central source is 2 × 108 L☉. We argue that the infrared spectrum and luminosity of the central source obviates the need for a substantial contribution from a standard, thin accretion disk at these wavelengths and calculate the accretion rate through an advection-dominated accretion flow to be ~ 10-3 M☉ yr -1. The agreement between these observations and the theoretical spectral energy distribution for advection-dominated flows provides evidence for the existence of an advection-dominated flow in this low-luminosity active galactic nucleus.
We report on tests of the Mid-Infrared Instrument (MIRI) focal plane electronics (FPE) and detectors conducted at the Jet Propulsion Laboratory (JPL). The goals of these tests are to: characterize the performance of readout modes; establish subarray operations; characterize changes to performance when switching between subarrays and/or readout modes; fine tune detector settings to mitigate residual artifacts; optimize anneal effectiveness; and characterize persistence. The tests are part of a continuing effort to support the MIRI pipeline development through better understanding of the detector behavior. An extensive analysis to determine the performance of the readout modes was performed. We report specifically on the comparison of the fast and slow readout modes and subarray tests.
A long-wavelength large format Quantum Well Infrared Photodetector (QWIP) focal plane array has been successfully used in a ground based astronomy experiment. QWIP arrays afford greater flexibility than the usual extrinsically doped semiconductor infrared (IR) arrays. Recently, we operated an infrared camera with a 256x256 QWIP array sensitive at 8.5 μm at the prime focus of the 5-m Hale telescope, obtaining the images. The remarkable noise stability - and low 1/f noise - of QWIP focal plane arrays enable camera to operate by modulating the optical signal with a nod period up to 100 s. A 500 s observation on dark sky renders a flat image with little indication of the low spatial frequency structures associated with imperfect sky substration or detector drifts. At low operating temperatures for low-background irradiance levels, high resistivity of thick barriers in the active region of QWIPs impeded electrons from entering the detector from the opposite electrode. This could lead to a delay in refilling the space-charge buildup, and result in a lower responsitivity at high optical modulation frequencies. In order to overcome this problem we have designed a new detector structure, the blocked intersubband detector (BID) with separate active quantum well region and blocking barrier.
A long-wavelength large format quantum well infrared photodetector (QWIP) focal plane array has been successfully used in a ground based astronomy experiment. QWIP arrays afford greater flexibility than the usual extrinsically doped semiconductor infrared (IR) arrays. The wavelength of the peak response and cutoff can be continuously tailored over a range wide enough to enable light detection at any wavelength range between 6-20 /spl mu/m. The spectral band width of these detectors can be tuned from narrow (/spl Delta//spl lambda///spl lambda/ /spl sim/ 10%) to wide (/spl Delta//spl lambda///spl lambda/ /spl sim/ 40 %) allowing various applications. Also, QWIP device parameters can be optimized to achieve extremely high performances at lower operating temperatures (/spl sim/ 30 K) due to exponential suppression of dark current. Furthermore, QWIPs offer low cost per pixel and highly uniform large format focal plane arrays (FPAs) mainly due to mature GaAs/AlGaAs growth and processing technologies. The other advantages of GaAs/AlGaAs based QWIPs are higher yield, lower 1/f noise and radiation hardness. Recently, we operated an infrared camera with a 256/spl times/256 QWIP array sensitive at 8.5 /spl mu/m at the prime focus of the 5 m Hale telescope, obtaining the images. The remarkable noise stability - and low 1/f noise - of QWIP focal plane arrays enable cameras to operate by modulating the optical signal with a nod period up to 100 s. A 500 s observation on dark sky renders a flat image with little indication of the low spatial frequency structures associated with imperfect sky subtraction or detector drifts.
