Browsing by Subject "images"
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Item GEMS Survey Data and Catalog(2008-01) Caldwell, John A. R.; McIntosh, Daniel H.; Rix, Hans-Walter; Barden, Marco; Beckwith, Steven V. W.; Bell, Eric F.; Borch, Andrea; Heymans, Catherine; Haeussler, Boris; Jahnke, Knud; Jogee, Shardha; Meisenheimer, Klaus; Peng, Chien Y.; Sanchez, Sebastian F.; Somerville, Rachel S.; Wisotzki, Lutz; Wolf, Christian; Caldwell, John A. R.We describe the data reduction and object cataloging for the GEMS survey, a large-area (800 arcmin(2)) two-band (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on the Hubble Space Telescope, centered on the Chandra Deep Field-South.Item Optimized Retinal Nerve Fiber Layer Segmentation Based On Optical Reflectivity And Birefringence For Polarization-Sensitive Optical Coherence Tomography(2011-09) Wang, Bingqing; Paranjape, Amit S.; Yin, Biwei; Liu, Shuang; Markey, Markey K.; Milner, Thomas E.; Rylander, H. Grady; Wang, Bingqing; Paranjape, Amit S.; Yin, Biwei; Liu, Shuang; Markey, Markey K.; Milner, Thomas E.; Rylander, H. GradySegmentation of the retinal nerve fiber layer (RNFL) from swept source polarization-sensitive optical coherence tomography (SS-PSOCT) images is required to determine RNFL thickness and calculate birefringence. Traditional RNFL segmentation methods based on image processing and boundary detection algorithms utilize only optical reflectivity contrast information, which is strongly affected by speckle noise. We present a novel approach to segment the retinal nerve fiber layer (RNFL) using SS-PSOCT images including both optical reflectivity and phase retardation information. The RNFL anterior boundary is detected based on optical reflectivity change due to refractive index difference between the vitreous and inner limiting membrane. The posterior boundary of the RNFL is a transition zone composed of birefringent axons extending from retinal ganglion cells and may be detected by a change in birefringence. A posterior boundary detection method is presented that segments the RNFL by minimizing the uncertainty of RNFL birefringence determined by a Levenberg-Marquardt nonlinear fitting algorithm. Clinical results from a healthy volunteer show that the proposed segmentation method estimates RNFL birefringence and phase retardation with lower uncertainty and higher continuity than traditional intensity-based approaches.Item The Quasar SDSS J105041.35+345631.3: Black Hole Recoil Or Extreme Double-Peaked Emitter?(2009-12) Shields, Gregory A.; Rosario, D. J.; Smith, K. L.; Bonning, E. W.; Salviander, Sarah; Kalirai, J. S.; Strickler, R.; Ramirez-Ruiz, E.; Dutton, A. A.; Treu, T.; Marshall, P. J.; Shields, Gregory A.; Smith, K. L.; Salviander, SarahThe quasar SDSS J105041.35+345631.3 (z = 0.272) has broad emission lines blueshifted by 3500 km s(-1) relative to the narrow lines and the host galaxy. Such an object may be a candidate for a recoiling supermassive black hole, a binary black hole, a superposition of two objects, or an unusual geometry for the broad emission-line region. The absence of narrow lines at the broad line redshift argues against superposition. New Keck spectra of J1050+3456 place tight constraints on the binary model. The combination of large velocity shift and symmetrical H beta profile, as well as aspects of the narrow line spectrum, make J1050+3456 an interesting candidate for black hole recoil. Other aspects of the spectrum, however, suggest that the object is most likely an extreme case of a "double-peaked emitter." We discuss possible observational tests to determine the true nature of this exceptional object.Item A Search For Binary Active Galactic Nuclei: Double-Peaked OIII AGNs In The Sloan Digital Sky Survey(2010-06) Smith, K. L.; Shields, Gregory A.; Bonning, E. W.; McMullen, C. C.; Rosario, D. J.; Salviander, Sarah; Smith, K. L.; Shields, Gregory A.; McMullen, C. C.We present active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) having double-peaked profiles of [OIII]lambda lambda 5007, 4959 and other narrow emission lines, motivated by the prospect of finding candidate binary AGNs. These objects were identified by means of a visual examination of 21,592 quasars at z < 0.7 in SDSS Data Release 7 (DR7). Of the spectra with adequate signal-to-noise, 148 spectra exhibit a double-peaked [OIII] profile. Of these, 86 are Type 1 AGNs and 62 are Type 2 AGNs. Only two give the appearance of possibly being optically resolved double AGNs in the SDSS images, but many show close companions or signs of recent interaction. Radio-detected quasars are three times more likely to exhibit a double-peaked [OIII] profile than quasars with no detected radio flux, suggesting a role for jet interactions in producing the double-peaked profiles. Of the 66 broad-line (Type 1) AGNs that are undetected in the FIRST survey, 0.9% show double-peaked [OIII] profiles. We discuss statistical tests of the nature of the double-peaked objects. Further study is needed to determine which of them are binary AGNs rather than disturbed narrow line regions, and how many additional binaries may remain undetected because of insufficient line-of-sight velocity splitting. Previous studies indicate that 0.1% of SDSS quasars are spatially resolved binaries, with typical spacings of similar to 10-100 kpc. If a substantial fraction of the double-peaked objects are indeed binaries, then our results imply that binaries occur more frequently at smaller separations (< 10 kpc). This suggests that simultaneous fueling of both black holes is more common as the binary orbit decays through these spacings.Item The Vega Debris Disc: A View From Herschel(2010) Sibthorpe, B.; Vandenbussche, B.; Greaves, J. S.; Pantin, E.; Olofsson, G.; Acke, B.; Barlow, M. J.; Blommaert, Jadl; Bouwman, J.; Brandeker, A.; Cohen, M.; De Meester, W.; Dent, W. R. F.; Di Francesco, J.; Dominik, C.; Fridlund, M.; Gear, W. K.; Glauser, A. M.; Gomez, H. L.; Hargrave, P. C.; Harvey, P. M.; Henning, T.; Heras, A. M.; Hogerheijde, M. R.; Holland, W. S.; Ivison, R. J.; Leeks, S. J.; Lim, T. L.; Liseau, R.; Matthews, B. C.; Naylor, D. A.; Pilbratt, G. L.; Polehampton, E. T.; Regibo, S.; Royer, P.; Sicilia-Aguilar, A.; Swinyard, B. M.; Waelkens, C.; Walker, H. J.; Wesson, R.; Harvey, P. M.We present five band imaging of the Vega debris disc obtained using the Herschel Space Observatory. These data span a wavelength range of 70-500 mu m with full-width half-maximum angular resolutions of 5.6-36.9 ''. The disc is well resolved in all bands, with the ring structure visible at 70 and 160 mu m. Radial profiles of the disc surface brightness are produced, and a disc radius of 11 '' (similar to 85AU) is determined. The disc is seen to have a smooth structure thoughout the entire wavelength range, suggesting that the disc is in a steady state, rather than being an ephemeral structure caused by the recent collision of two large planetesimals.