The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures; https://iopscience.iop.org/article/10.1088/1538-3873/acb29

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Spatial and Temporal Dependence of Temperature Variations Induced by Atmospheric Pressure Variations in Shallow Underground Cavities

International audiencePressure-induced temperature (PIT) variations are systematically observed in the atmosphere of underground cavities. Such PIT variations are due to the compressibility of the air, damped by heat exchange with the rock surface. It is important to characterize such processes for numerous applications, such as the preservation of painted caves or the assessment of the long-term stability of underground laboratories and underground waste repositories. In this paper we thoroughly study the spatiotemporal dependence of the PIT response versus frequency using vertical and horizontal profiles of temperature installed in an abandoned underground quarry located in Vincennes, near Paris. The PIT response varies from about 20 × 10-3°C hPa-1 at a frequency of 2 × 10-4 Hz to 2-3 × 10-3°C hPa-1 at a frequency of one cycle per day. An analytical expression based on a simple heat exchange model accounts for the observed features of the PIT response and allows for correcting the measured time series, having standard deviations of about 10-2°C, to residual variations with a standard deviation of about 2 × 10-3°C. However, a frequency-dependent attenuation of the response, corresponding to a reduction in amplitude with a factor varying from 2 to 3, is observed near the walls. This effect is not included in the simple analytical expression, but it can be accounted for by a one-dimensional differential equation, solved numerically, where temperature variations in the atmosphere are damped by an effective radiative coupling with the rock surface, complemented by a diffusive coupling near the walls. The TIP response is observed to remain stable over several years, but a large transient enhancement of about a factor of two is observed near the roof at one location from July to October 2005. In a cavity located below the Paris Observatory, an additional contribution is identified in the PIT response function versus frequency for frequencies smaller than 2 × 10-5 Hz. This contribution can be described using a modified analytical expression that includes the effect of heat diffusion into the surrounding rock. Using this expression, in this case also, the temperature time series can then be corrected, giving a residual standard deviation smaller than 1.6 × 10-3°C. Transient temporal variations of the PIT response are observed in all sites, with possible nonlinear components in the PIT. Such effects are not properly understood at this stage, and limit the reduction of time series to standard deviations of the order of 2 × 10-3°C, and consequently limit the search for new transient or seasonal temperature signals, for example due to the presence of tiny heat sources in the cavity or to geodynamical effects

Detectability and significance of 12 hr barometric tide in radon-222 signal, dripwater flow rate, air temperature and carbon dioxide concentration in an underground tunnel

International audienceSearching for small periodic signals, such as the 12 hr (S 2) barometric tide, and monitoring their amplitude as a function of time, can provide important clues on the complex processes affecting fluid transport in unsaturated fractured media under multiple influences. Here, first, we show that a modified spectrogram analysis (MSA) is more efficient than simple Fourier transform to reveal weak periodic signals. Secondly, we show how transient periodic signals can be monitored as a function of time using spectrograms. These methods are applied to time-series of radon and carbon dioxide concentration, dripwater flow rates and air temperature measured during several years in the Roselend dead-end tunnel, located in the French Alps near an artificial lake. A weak S 2 line is evidenced in radon concentration, with enhanced amplitude during transient radon bursts. Similarly, the S 2 line is observed using MSA in dripwater flow rates which sample mainly fracture flow, as suggested by a hydrochemical analysis, while it is not seen in dripwater flow rates sampling matrix flow. In the absence of a strong 24 hr line, the presence of a S 2 line suggests sensitivity to barometric pressure , and thus a significant advective contribution in radon and some dripwater transport. No S 2 line is observed in the carbon dioxide time-series. The temporal structure of the S 2 component, however, is not similar in the radon concentration and the dripwater flow rates, suggesting, in particular, that dripwater does not play a significant role in the generation of radon bursts. Temperature time-series exhibit a significant S 2 contribution, induced by atmospheric pressure, spatially organised in the tunnel, decreasing vertically upwards. A remarkable transient temperature inversion during radon bursts suggests that the additional advective air contributions responsible for the radon bursts occur from the non-saturated rocks below the tunnel

Evidence of both M2 and O1 Earth tide waves in radon-222 air concentration measured in a subglacial laboratory

International audienceMany earthquake-related radon-222 temporal changes have been recorded since the 1960s and are frequently discussed, sometimes initiating a controversial debate on the relevance of radon-222 as an earthquake precursory signal. The diurnal S1-O1 and semidiurnal S2-M2 Earth tide signatures in radon signals are acquired in a natural context. This can be used to calibrate the radon changes under strain accumulation close to epicentral areas, which are often discussed but are rarely evidenced by experimental data. The analysis of a 10 month time series acquired in the subglacial laboratory of the Argentière glacier, Mont Blanc Massif, French Alps, demonstrates here the unambiguous episodic appearance of the M2-O1 waves in the radon signal with significant amplitudes of 36 and 50 Bq m 3, respectively. We thus prove that radon variations induced by gravitational M2 and O1 waves are detectable in a natural environment. In this particular place, the radon response is probably amplified by cyclic stress variations applied on the upstream side of the natural rock dam into which the laboratory is drilled. The amplification of the radon signal is induced by poroelastic deformation under this particular mechanical forcing. This can elucidate why most precedent studies failed to detect M2-O1 signatures in radon signals recorded in other underground laboratories