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تسجيل مستخدم جديدThe Case for a James Webb Space Telescope Extragalactic Key Project
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Steven L. Finkelstein
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The upcoming launch of the James Webb Space Telescope (JWST) in less than three years is certain to bring a revolution in our understanding of many area of astrophysics, with one of the key goals being galaxy evolution. As the first proposals will be due in a little over two years, the time is ripe to take a holistic look at the science goals which the community would wish to accomplish with this observatory. Contrary to our experiences with the Hubble Space Telescope, which has now operated successfully for over two decades due to several timely servicing missions, the lifetime of JWST is finite and relatively short, with a lifetime requirement of five years, and a ten-year goal. Following the discussion session at the Exploring the Universe with JWST conference at ESA-ESTEC in October 2015, we highlight in this document the (non-local) extragalactic science goals for JWST. We describe how a concerted community effort could best address these, ensuring that the desired survey can be completed during the JWST mission.
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This white paper examines the benefit of the upcoming James Webb Space Telescope for studies of the Solar Systems four giant planets: Jupiter, Saturn, Uranus, and Neptune. JWSTs superior sensitivity, combined with high spatial and spectral resolution
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A which is predicted to be stable within the alpha Cen AB system. We demonstrate that with reasonable performance of the telescope and instrument, a 20 hr program combining on-target and reference star observations at 15.5 um could detect thermal emission from planets as small as ~5 RE. Multiple visits every 3-6 months would increase the geometrical completeness, provide astrometric confirmation of detected sources, and push the radius limit down to ~3 RE. An exozodiacal cloud only a few times brighter than our own should also be detectable, although a sufficiently bright cloud might obscure any planet present in the system. While current precision radial velocity (PRV) observations set a limit of 50-100 ME at 1-3 AU for planets orbiting alpha Cen A, there is a broad range of exoplanet radii up to 10 RE consistent with these mass limits. A carefully planned observing sequence along with state-of-the-art post-processing analysis could reject the light from alpha Cen A at the level of ~10^-5 at 1-2 and minimize the influence of alpha Cen B located 7-8 away in the 2022-2023 timeframe. These space-based observations would complement on-going imaging experiments at shorter wavelengths as well as PRV and astrometric experiments to detect planets dynamically. Planetary demographics suggest that the likelihood of directly imaging a planet whose mass and orbit are consistent with present PRV limits is small, ~5%, and possibly lower if the presence of a binary companion further reduces occurrence rates. However, at a distance of just 1.34 pc, alpha Cen A is our closest sibling star and certainly merits close scrutiny.
The James Webb Space Telescope (JWST) is a large (6.6m), cold (50K), infrared-optimized space observatory that will be launched early in the next decade. The observatory will have four instruments: a near-infrared camera, a near-infrared multi-object
spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 to 5.0 microns, while the mid-infrared instrument will do both imaging and spectroscopy from 5.0 to 29 microns. The JWST science goals are divided into four themes. The End of the Dark Ages: First Light and Reionization theme seeks to identify the first luminous sources to form and to determine the ionization history of the early universe. The Assembly of Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The Birth of Stars and Protoplanetary Systems theme seeks to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The Planetary Systems and the Origins of Life theme seeks to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.
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