Jess Johnson's Publications & Other Writings |
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| Journal Articles | ||
Ultraviolet
Spectroscopic Analysis of Mass Flow in the Interacting Binary U Cephei American Astronomical Society, 201st AAS Meeting, #04.02; Bulletin of the American Astronomical Society, Vol. 34, p.1095 |
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Twenty-nine far-ultraviolet and forty-seven near-ultraviolet high resolution International Ultraviolet Explorer (IUE) Satellite archival spectra of the interacting Algol-type binary U Cephei ( B7 V + G8 III-IV ) have been analyzed in order to determine the nature of the variable mass flow occurring in this system. Relatively good phase coverage was obtained in 1989 with fourteen far-ultraviolet and fifteen near-ultraviolet spectra spread over 1.2 orbits. The effects of gas streaming within and out of the system and of pseudophotospheric flow on the primary star are clearly seen in the ultraviolet resonance lines of Si IV (lambda lambda 1393, 1402 ), CIV (lambda lambda 1548, 1550), Al II (lambda 1670 ), Al III (lambda lambda 1854, 1862 ), Fe II (lambda 2599 ), and Mg II (lambda lambda 2795, 2802 ). A major mass flow outburst occurred in 1986 and a weaker outburst appears in some of the 1989 spectra. Light curves were constructed at a number of ultraviolet wavelengths. These light curves show significant departures from those expected from quiescent eclipsing binaries. It may be concluded that U Cep, and a number of other Algol-type binaries studied elsewhere, show pseudophotospheric accretion phenomena, mass exchange and systemic mass loss with occasional, variable, short-term increases in activity. |
| Pyramid
Wavefront Sensing: Theory and Component Technology Development at LAO Jess A. Johnson; Renate Kupke; Donald Gavel; Brian Bauman Proc. SPIE 6272, 62724R (2006) |
Pyramid wavefront sensors offer an alternative to traditional Hartmann
sensing for wavefront measurement in astronomical adaptive optics systems.
The Pyramid sensor has been described as a slope sensor with potential
sensitivity gains over the Shack Hartmann sensor, but in actuality seems
to exhibit traits of both a slope sensor and a direct phase sensor. The
original configuration, utilizing glass pyramids and modulation techniques,
is difficult to implement. We present results of laboratory experiments
using a Pyramid sensor that utilizes a micro-optic lenslet array in place
of a glass pyramid, and does not require modulation. A group of four lenslets
forms both the pyramid knife-edge and the pupil reimaging functions. The
lenslet array is fabricated using a technique that pays careful attention
to the quality of the edges and corners of the lenslets. The devices we
have tested show less than 1 micron edge and corner imperfections, making
them some of the sharpest edges available. We finish by comparing our results
to theoretical wave optic predictions which clearly show the dual nature
of the sensor. |
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First
Results from the UCSC Laboratory for Adaptive Optics Multi-conjugate
and Multi-object Adaptive Optics Testbed Proc. SPIE 6272, 627202 (2006) |
We present first results from the Multi-Conjugate and Multi-Object Adaptive Optics (MCAO and MOAO) testbed, at the UCO/Lick Laboratory for Adaptive Optics (LAO) facility at U.C. Santa Cruz. This testbed is constructed to simulate a 30-m telescope executing MCAO and/or open loop MOAO atmospheric compensation and imaging over 5 arcminutes. It is capable of performing Shack-Hartmann wavefront sensing on up to 8 natural or laser guide stars and 2-3 additional tip/tilt stars. In this paper, we demonstrate improved on-axis correction relative to ground layer adaptive optics (~ 15% Strehl relative to ~ 12%) with a simulated 28-m aperture at a D/r0 corresponding to a science wavelength of 2.6 microns using three laser guide stars on a simulated 41 arcsec radius with a central science object and one deformable mirror at the ground layer. | |
| Other Articles | ||
Zonal-Trigonal
Implementation of Shack-Hartman Wavefront Sensing: Application to the
Surface Figures of the Keck Telescope Segments National
Science Foundation Research Experience for Undergraduates Journal of
the UC Irvine REU Program, Summer 2000 |
To achieve optimal performance, the mirror segments in segmented telescopes such as the Keck must not only be phased with respect to one another, but must also individually have surface errors no larger than about 40 nanometers. At the Keck, this is accomplished by discerning the characteristics of the segment surface through Shack-Hartman wavefront sensing, and then physically correcting the surface to the desired accuracy through the use of "warping harnesses" built into the segment support system. Currently, the algorithm that processes the wavefront data uses a modal approach, which assumes that the wavefront distortions due to segment aberrations can be described in terms of Zernike polynomials. This approach simplifies the requisite calculations, but leads to inaccuracies in surface description. A new computational algorithm is therefore desired to increase the accuracy of such surface characterization; this paper presents and discusses such a new algorithm. | |
| Poster Presentations | ||
| The Microbial Seeding
of the Galaxy, or Panspermia Revisited Jess A. Johnson, Jonathen Langton, Greg Laughlin |
The word 'Panspermia' is from the Greek, and literally means ‘seeds everywhere.’ In its modern usage, it refers to the concept that life exists and is distributed throughout space in the form of microbes or spores, which pass from world to world and spark the growth of life. Panspermia as a valid scientific hypothesis has a long and pedigreed history, originating with the Greeks and passing through many modern theoretical incarnations. | |
| Detecting Turbulence with Pyramids Jess Johnson, Reni Kupke, Donald Gavel |
This project deals with one component of an adaptive optics system...
the portion that attempts to detect the nature of the change that has occurred
to the light. The name for the process by which it does this is Wavefront
Sensing. |
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| PWFS With Lenslet Arrays Jess Johnson, Reni Kupke, Donald Gavel |
Although PWFS shows great promise as a next generation wavefront sensing
scheme, its implementation has been hindered by the difficulty of manufacturing
extremely small glass-facet pyramids with precisely machined apexes. In his 2003 Ph.D. dissertation, Brian Bauman, an optical researcher with the Laboratory for Adaptive Optics, proposed that lenslet arrays might be used to replace glass pyramids in PWFS systems. Lenslet arrays represent a ubiquitous and well established technology; they are far less expensive, more durable, and easier to manufacture then glass pyramids. In addition, because they are easier to handle and mount, lenslet arrays make PWFS systems physically less awkward to assemble. Successful implementation of lenslet-based PWFS will open the door to the more widespread adaptation of this novel wavefront sensor technology. |
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| Pyramid
Wavefront Sensing: Theory and Component Technology Development at
LAO Jess Johnson, Renate Kupke, Donald Gavel, Brian Bauman |
Pyramid wavefront sensors offer an alternative to traditional Hartmann
sensing for wavefront measurement in astronomical adaptive optics systems.
The Pyramid sensor has been described as a slope sensor with potential
sensitivity gains over the Shack Hartmann sensor, but in actuality seems
to exhibit traits of both a slope sensor and a direct phase sensor. The original configuration, utilizing glass pyramids and modulation techniques, is difficult to implement. We present results of laboratory experiments using a Pyramid sensor that utilizes a micro-optic lenslet array in place of a glass pyramid, and does not require modulation. A group of four lenslets forms both the pyramid knife-edge and the pupil reimaging functions. The lenslet array is fabricated using a technique that pays careful attention to the quality of the edges and corners of the lenslets. The devices we have tested show less than 1 micron edge and corner imperfections, making them some of the sharpest edges available. We finish by comparing our results to theoretical wave optic predictions which clearly show the dual nature of the sensor. |
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| Other Writings, Graduate (LAO Research Memos, Class Assignments, etc.) | ||
| (Under Construction...) | ||
| Other Writings, Undergraduate (Internship Reports, Class Assignments, etc.) | ||
| (Under Construction...) | ||
| Home | Research | Publications | Teaching | Education | Photos | Health | Interests | Links & References |