5 results
New orbital analysis of stars at the Galactic center using speckle holography and orbital priors
- Anna Boehle, Rainer Schödel, Leo Meyer, Andrea M. Ghez
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- Journal:
- Proceedings of the International Astronomical Union / Volume 9 / Issue S303 / October 2013
- Published online by Cambridge University Press:
- 22 May 2014, pp. 242-244
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- October 2013
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We present initial results of a study that has more than doubled the time baseline for astrometric measurements of faint stars orbiting the supermassive black hole (SMBH) at the Galactic center. The advent of adaptive optics has enabled stars as faint as K = 19 mag to be tracked at 50 mas resolution for the last decade. While similar resolution images exist from the prior decade, they were obtained from speckle imaging data analyzed with the technique of shift-and-add, which limited detections to stars brighter than K = 16 mag. By improving the speckle data analysis technique with speckle holography and using prior orbital knowledge, we are now able to track stars as faint as ∼18 mag at 50 mas resolution through the early Keck speckle data sets (1995-2005). This methodology has already led to the detection of two short-period stars never previously seen in speckle images, such that our data now spans their full orbits. We can now better constrain the orbital parameters of all stars in the intriguing “S-star cluster,” which will ultimately give us insight into the origin of these stars and be used to probe the curvature of space-time in the unexplored regime near a SMBH.
Contributors
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- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. Deichmann Edwards, Miguel A. De La Torre, George E. Demacopoulos, Thomas de Mayo, Leah DeVun, Beatriz de Vasconcellos Dias, Dennis C. Dickerson, John M. Dillon, Luis Miguel Donatello, Igor Dorfmann-Lazarev, Susanna Drake, Jonathan A. Draper, N. Dreher Martin, Otto Dreydoppel, Angelyn Dries, A. J. Droge, Francis X. D'Sa, Marilyn Dunn, Nicole Wilkinson Duran, Rifaat Ebied, Mark J. Edwards, William H. Edwards, Leonard H. Ehrlich, Nancy L. Eiesland, Martin Elbel, J. Harold Ellens, Stephen Ellingson, Marvin M. Ellison, Robert Ellsberg, Jean Bethke Elshtain, Eldon Jay Epp, Peter C. Erb, Tassilo Erhardt, Maria Erling, Noel Leo Erskine, Gillian R. Evans, Virginia Fabella, Michael A. Fahey, Edward Farley, Margaret A. Farley, Wendy Farley, Robert Fastiggi, Seena Fazel, Duncan S. Ferguson, Helwar Figueroa, Paul Corby Finney, Kyriaki Karidoyanes FitzGerald, Thomas E. FitzGerald, John R. Fitzmier, Marie Therese Flanagan, Sabina Flanagan, Claude Flipo, Ronald B. Flowers, Carole Fontaine, David Ford, Mary Ford, Stephanie A. Ford, Jim Forest, William Franke, Robert M. Franklin, Ruth Franzén, Edward H. Friedman, Samuel Frouisou, Lorelei F. Fuchs, Jojo M. Fung, Inger Furseth, Richard R. Gaillardetz, Brandon Gallaher, China Galland, Mark Galli, Ismael García, Tharscisse Gatwa, Jean-Marie Gaudeul, Luis María Gavilanes del Castillo, Pavel L. Gavrilyuk, Volney P. Gay, Metropolitan Athanasios Geevargis, Kondothra M. George, Mary Gerhart, Simon Gikandi, Maurice Gilbert, Michael J. Gillgannon, Verónica Giménez Beliveau, Terryl Givens, Beth Glazier-McDonald, Philip Gleason, Menghun Goh, Brian Golding, Bishop Hilario M. Gomez, Michelle A. Gonzalez, Donald K. Gorrell, Roy Gottfried, Tamara Grdzelidze, Joel B. Green, Niels Henrik Gregersen, Cristina Grenholm, Herbert Griffiths, Eric W. Gritsch, Erich S. Gruen, Christoffer H. Grundmann, Paul H. Gundani, Jon P. Gunnemann, Petre Guran, Vidar L. Haanes, Jeremiah M. 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- Edited by Daniel Patte, Vanderbilt University, Tennessee
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- The Cambridge Dictionary of Christianity
- Published online:
- 05 August 2012
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- 20 September 2010, pp xi-xliv
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Atomic Force Microscope Study on Native Aluminum Nitride Substrates
- Sandra Schujman, Wayne Liu, Nicholas Meyer, Joseph A. Smart, Leo J. Scholwalter
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- MRS Online Proceedings Library Archive / Volume 892 / 2005
- Published online by Cambridge University Press:
- 01 February 2011, 0892-FF30-05
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- 2005
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Native aluminum nitride (AlN) single crystal substrates are promising for use in epitaxial growth of III-nitride materials for fabrication of reliable deep UV light emitting and high power RF devices. Furthermore, the single crystals can be cut into different orientations, such as non-polar or pre-determined and specific misorientations, which will open a door for growing device structures with specially desired properties.
We have found several novel patterns on different orientation AlN substrates using Atomic Force Microscope (AFM). Aluminum nitride substrates with chemical-mechanical-polishing (CMP) finished surfaces, for a number of different misorientations with respect to the main hexagonal axis, that is, c-, a- and b-axis, show well differentiated structures. The AFM images reveal atomic level closed-loop rings. We believe these closed-loop rings are indicative of edge-dislocations. These structures are mostly seen on the near and on-axis aluminum polar surfaces. Atomic steps are not visible on the non-polar bare surfaces and for larger deviations from the polar axis (i.e., larger than 6 degrees from the c-axis). It is also noticed that even though atomic level steps are not always visible on the bare substrate for non-polar and large misorientations from the polar aluminum face, they can be observed after homoepitaxial and heteroepitaxial growth on these orientations. The research results indicate that both substrate orientation and surface treatment play an important role in forming different kinds of surface morphologies.
A Low-Temperature Process for Device Quality Si/SiO2 Interfaces on Si(111)
- T. Yasuda, D. R. Lee, C. H. Bjorkman, Y. Ma, G. Lucovsky, U. Emmerichs, C. Meyer, K. Leo, H. Kurz
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- MRS Online Proceedings Library Archive / Volume 315 / 1993
- Published online by Cambridge University Press:
- 21 February 2011, 375
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- 1993
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Device-quality Si/SiO2 interfaces with an interface trap density as low as ∼2 × 1010cm−2 eV−1 were formed on Si( 111) surfaces by a low-temperature, two-step oxidation/deposition process using a remote plasma enhanced CVD system. The micromorphology of the initial Si(1 11) surface was changed i) by controlling the roughness of the initial Si surface through the pH of HF/NH4F treatments, and ii) by an introduction of surface steps using Si(111) wafers that were cut off the axis in the direction. When the Si wafer was subjected to a pre-deposition rinse in a 40 wt-% NH4F solution to develop an atomically smooth surface, the SiO2/Si(111) interface displayed a midgap interface trap density, Dit, of 2∼3 × 1010cm−2 eV−1 with Al as an electrode material. The Dit values increased systematically up to about 1 × 1011cm−2 eV−1 as the pH of the HF/NH4F treatment was decreased. The density of surface steps had a lesser effect on Dit. MOS capacitors with an n-type poly-Si electrode also showed Dit of ∼2 × 1010cm−2 eV−1. The effects of the hightemperature processing associated with poly-Si deposition and doping are discussed in conjunction with our recent study on second harmonic generation from the SiO2/Si interfaces.
Chemically Modified Second Harmonic Generation at Surfaces on Vicinal Si(111) Wafers
- U. Emmerichs, C. Meyer, K. Leo, H. Kurz, C. H. Bjorkman, C. E. Shearon, Jr, Y. Ma, T. Yasuda, G. Lucovsky
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- MRS Online Proceedings Library Archive / Volume 281 / 1992
- Published online by Cambridge University Press:
- 25 February 2011, 815
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- 1992
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Using surface second harmonic generation (SSHG) at 1053nm, we study the influence of off-axis orientation and surface structure of silicon (111) surfaces. We study wafers cut at angles between 0° and 5° in the [112] direction. The surface structure is varied by thermal oxidation at 850°C, annealing, and thinning the oxide in a HF solution. For comparison, nitride films are also investigated. The characteristic rotational symmetry of the SSHG-signal for (111) flat (non-vicinal) surfaces is enhanced by a Si/SiO2 interface. The oxide layer also influences the signals due to the steps on vicinal surfaces. The results are discussed in comparison with a microscopic model of the oxidized misoriented surface.