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Sembach, Kenneth

Publications and source records attributed to Sembach, Kenneth.

Advanced Technology Large-Aperture Space Telescope: Science Drivers and Technology Developments

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8- to 16-m ultraviolet optical near Infrared space observatory for launch in the 2025 to 2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including: Is there life elsewhere in the Galaxy? We present a range of science drivers and the resulting performance requirements for ATLAST (8- to 16-marcsec angular resolution, diffraction limited imaging at 0.5 micron wavelength, minimum collecting area of 45 sq m, high sensitivity to light wavelengths from 0.1 to 2.4 micron, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to that of current generation observatory-class space missions.

Postman, Marc↗

The Advanced Technology Large Aperture Space Telescope (ATLAST): Science Drivers, Technology Developments, and Synergies with Other Future Facilities

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers that define the main performance requirements for ATLAST (8 to 16 milliarcsec angular resolution, diffraction limited imaging at 0.5 m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 m to 2.4 m, high stability in wavefront sensing and control). We will also discuss the synergy between ATLAST and other anticipated future facilities (e.g., TMT, EELT, ALMA) and the priorities for technology development that will enable the construction for a cost that is comparable to current generation observatory-class space missions.

Postman, Marc↗

The Advanced Technology Large Aperture Space Telescope (ATLAST): Science Drivers and Technology Developments

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers and the resulting performance requirements for ATLAST (8 to 16 milliarcsecond angular resolution, diffraction limited imaging at 0.5 m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 m to 2.4 m, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to current generation observatory-class space missions. Keywords: Advanced Technology Large-Aperture Space Telescope (ATLAST); ultraviolet/optical space telescopes; astrophysics; astrobiology; technology development.

Postman, Marc↗

The Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph with unprecedented sensitivity that was installed into the Hubble Space Telescope (HST) in May 2009, during HST Servicing Mission 4 (STS-125). We present the design philosophy and summarize the key characteristics of the instrument that will be of interest to potential observers. For faint targets, with flux F(sub lambda) approximates 1.0 X 10(exp -14) ergs/s/cm2/Angstrom, COS can achieve comparable signal to noise (when compared to STIS echelle modes) in 1-2% of the observing time. This has led to a significant increase in the total data volume and data quality available to the community. For example, in the first 20 months of science operation (September 2009 - June 2011) the cumulative redshift pathlength of extragalactic sight lines sampled by COS is 9 times that sampled at moderate resolution in 19 previous years of Hubble observations. COS programs have observed 214 distinct lines of sight suitable for study of the intergalactic medium as of June 2011. COS has measured, for the first time with high reliability, broad Lya absorbers and Ne VIII in the intergalactic medium, and observed the HeII reionization epoch along multiple sightlines. COS has detected the first CO emission and absorption in the UV spectra of low-mass circumstellar disks at the epoch of giant planet formation, and detected multiple ionization states of metals in extra-solar planetary atmospheres. In the coming years, COS will continue its census of intergalactic gas, probe galactic and cosmic structure, and explore physics in our solar system and Galaxy.

Green, James C.↗

Monitoring the Intrinsic Absorption Complex Toward RXJ123.8+0115

The main focus of this study was changed after it became clear that the object to be observed by the Far Ultraviolet Spectroscopic Explorer (FUSE) could not be observed because of spacecraft attitude control system limitations. Therefore, we replaced the prime object for the program (RXJ1230.8+0115) with a secondary object (H1821+643) and began an analysis of a similar quasar spectrum for comparison with the extant RXJ1230.8+0115 spectrum obtained previously by FUSE. Using high-resolution spectra of the radio-quiet, X-ray bright quasar HE0226-4110 obtained with the Hubble Space Telescope (HST) and FUSE, we have examined the remarkable associated absorption line system. The redshift of the quasar is roughly 0.5 so the FUSE+HST spectra cover the rest-frame wavelength in the extreme ultraviolet range 610-1 160A. In this range, we detect transitions from a wide range of ionization species, including the H I Lyman series, Ne VIII, and, for the first time at this resolution, four adjacent stages of oxygen O III-VI. The high quality of these spectra allow us to disentangle the structure of the gas using the complex kinematics to guide the assessments of the multi-component and multi-phase nature of the system. The kinematics of the absorber indicate that all the H I, C 111, and 0 III reside in a single component, while higher ionization species largely arise in a separate, more kinematically complex structure. An analysis of a ground-based spectrum of the quasar covering the H-beta and [0 III] 5007 emission lines reveal excellent agreement in redshift between the 0 III absorption and emission. Thus, for the first time, we are able to use absorption line diagnostics to place interesting constraints on the location and structure of the narrow emission line region around a quasar. In addition, we detect a narrow absorption line that is only seen O VI and lies roughly 50 km/s redward of the narrow emission line component. Absorption from 0 V, and Ne VIII is also detected at this velocity, but as part of broader, more redshifted, component. The line width of this narrow component imply a maximum temperature that is too small to produce O VI through collisional process, suggesting instead that photoionization from the quasar is the dominant ionization mechanism. The photoionization constraints imply that O VII should be the dominant ionization stage in the component.

Sembach, Kenneth↗

Ultraviolet interstellar absorption toward HD 163522, a halo star at 9 kiloparsecs in the direction l = 350 deg and b = -9 deg

UV interstellar absorption line measurements obtained by the IUE satellite toward HD 163522 in the direction l = 349.6 deg and b = -9 deg are analyzed. The UV stellar spectrum of HD 163522 places the star beyond the Galactic center at a distance away from the Galactic plane of z = -1.5 kpc. An absorption-line spectrum with S/N approximately equal to 15-25 is produced. The UV interstellar absorption lines for neutral, and weakly and highly ionized gas are examined, as well as the correlation between profiles and the Galactic rotation. Simple model calculations are performed to quantitatively determine the characteristics of the profiles. The observed absorption-line profiles for Al III, Si IV, C IV, and N V are converted into plots of optical depths vs velocity. A comparison of these plots for the weak and strong member of each doublet reveals that the profiles are not strongly influenced by the presence of unresolved saturated absorption, and the optical depth profiles can therefore be directly converted into measures of N(v), the column density per km/s. The converted column densities are examined.

Savage, Blair D.↗