The variability of warm absorbers in Active Galactic Nuclei

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 171-184).This thesis presents three studies of warm (photoionized) absorber variability in Active Galactic Nuclei (AGN) using high-resolution X-ray spectra provided by the Chandra High Energy Transmission Grating (HETG). The first study is a single observation of the AGN MR 2251-178, which is known to have a highly variable warm absorber (WA). We find an unusually thin effective hydrogen column density along the line of sight compared to previous observations. Strong line emission without corresponding absorption indicates significant WA geometric structure. Strong absorption features in the spectrum are evidence of a highly-ionized, high-velocity outflow, which could be carrying a large amount of mass and energy out of the AGN. In the second study, we search for absorption lines variability in the well-studied WA of MCG -6-30-15. We find a significant anti-correlation over time between at least two ions, with suggestions of additional time variation in other ions. At least one line, the is - 2p resonance line of Mg XII, varies as a function of 2-10 keV continuum luminosity. Luminosity-driven ionization changes alone are insufficient to explain the observed variation.(cont.) Either multiple factors influence line strength on observable time scales, or the line of sight to the central source varies over time through a structured absorber. In the third study, we survey spectra from the HETG data archive. We model the normalized excess variance (NEV) spectrum of a varying WA and find that it does not explain high-energy (> 2 keV) spectral variation, nor does it generally fit NEV spectra at lower energies (< 2 keV). We also search through each spectrum at high resolution (AA = 0.01 A) for bins which vary more than expected due to normal Poissonian fluctuations. We find some evidence for such variation in the aggregate sample, though not in AGN individually. Our results show that WA structure is more complicated than pictured in contemporary models. Future high-resolution spectroscopic variability studies are certainly warranted. AGN models should eventually consider the effects of WA structure and the influence of continuum variation on the WA.by Robert R. Gibson.Ph.D

The X-Ray Variability of a Large, Serendipitous Sample of Spectroscopic Quasars

We analyze the X-ray variability of 264 Sloan Digital Sky Survey spectroscopic quasars using the Chandra public archive. This data set consists of quasars with spectroscopic redshifts out to z~5 and covers rest-frame time scales up to Delta t_sys 2000 d, with 3 or more X-ray observations available for 82 quasars. It therefore samples longer time scales and higher luminosities than previous large-scale analyses of AGN variablity. We find significant (>3 sigma) variation in ~30% of the quasars overall; the fraction of sources with detected variability increases strongly with the number of available source counts up to ~70% for sources with >1000 counts per epoch. Assuming the distribution of fractional variation is Gaussian, its standard deviation is ~16% on >1 week time scales, which is not enough to explain the observed scatter in quasar X-ray-to-optical flux ratios as due to variability alone. We find no evidence in our sample that quasars are more variable at higher redshifts (z > 2), as has been suggested in previous studies. Quasar X-ray spectra vary similarly to some local Seyfert AGN in that they steepen as they brighten, with evidence for a constant, hard spectral component that is more prominent in fainter stages. We identify one highly-variable Narrow Line Seyfert 1-type spectroscopic quasar in the Chandra Deep Field-North. We constrain the rate of kilosecond-timescale flares in the quasar population using ~8 months of total exposure and also constrain the distribution of variation amplitudes between exposures; extreme changes (>100%) are quite rare, while variation at the 25% level occurs in <25% of observations. [OIII] 5007A emission may be stronger in sources with lower levels of X-ray variability; if confirmed, this would represent an additional link between small-scale (corona) and large-scale (narrow line region) AGN properties.Comment: Submitted to Ap

Image Texture Characterization Using the Discrete Orthonormal S-Transform

We present a new efficient approach for characterizing image texture based on a recently published discrete, orthonormal space-frequency transform known as the DOST. We develop a frequency-domain implementation of the DOST in two dimensions for the case of dyadic frequency sampling. Then, we describe a rapid and efficient approach to obtain local spatial frequency information for an image and show that this information can be used to characterize the horizontal and vertical frequency patterns in synthetic images. Finally, we demonstrate that DOST components can be combined to obtain a rotationally invariant set of texture features that can accurately classify a series of texture patterns. The DOST provides the computational efficiency and multi-scale information of wavelet transforms, while providing texture features in terms of Fourier frequencies. It outperforms leading wavelet-based texture analysis methods

The Baryon Oscillation Spectroscopic Survey of SDSS-III

The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7. Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000 quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyman alpha forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance D_A to an accuracy of 1.0% at redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyman alpha forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.Comment: 49 pages, 16 figures, accepted by A

The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release

We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which contains 105,783 spectroscopically confirmed quasars, represents the conclusion of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS objects that have luminosities larger than M_i = -22.0 (in a cosmology with H_0 = 70 km/s/Mpc Omega_M = 0.3, and Omega_Lambda = 0.7) have at least one emission line with FWHM larger than 1000 km/s or have interesting/complex absorption features, are fainter than i > 15.0 and have highly reliable redshifts. The catalog covers an area of 9380 deg^2. The quasar redshifts range from 0.065 to 5.46, with a median value of 1.49; the catalog includes 1248 quasars at redshifts greater than four, of which 56 are at redshifts greater than five. The catalog contains 9210 quasars with i < 18; slightly over half of the entries have i< 19. For each object the catalog presents positions accurate to better than 0.1" rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 Ang. at a spectral resolution R = 2000 the spectra can be retrieved from the SDSS public database using the information provided in the catalog. Over 96% of the objects in the catalog were discovered by the SDSS. We also include a supplemental list of an additional 207 quasars with SDSS spectra whose archive photometric information is incomplete.Comment: Accepted, to appear in AJ, 7 figures, electronic version of Table 2 is available, see http://www.sdss.org/dr7/products/value_added/qsocat_dr7.htm

Simulação de técnicas de engenharia de reservatórios: exemplo de utilização de opções reais

Este trabalho teve como objetivo incluir flexibilidade gerencial (tais como técnicas de recuperação complementar de óleo) na avaliação de reservatórios. Concluímos que essas técnicas podem aumentar o valor dos reservatórios em até 25% segundo a teoria de opções reais. A principal vantagem da metodologia de teoria de opções em relação à tradicional técnica de fluxo de caixa descontado é levar em conta as questões operacionais da indústria do petróleo. Utilizamos dois modelos clássicos para a precificação de reservatórios de petróleo e aplicamos uma análise de sensibilidade para determinar quais fatores são mais relevantes no seu valor econômico. Como era de se esperar, em ambos os modelos, o tempo de concessão e a taxa de convenience e/ou dividend yield foram os fatores mais importantes

Integrative genomic analysis of childhood acute lymphoblastic leukaemia lacking a genetic biomarker in the UKALL2003 clinical trial

Incorporating genetics into risk-stratification for treatment of childhood B-progenitor acute lymphoblastic leukaemia (B-ALL) has contributed significantly to improved survival. In about 30% B-ALL (B-other-ALL) without well-established chromosomal changes, new genetic subtypes have recently emerged, yet their true prognostic relevance largely remains unclear. We integrated next generation sequencing (NGS): whole genome sequencing (WGS) (n = 157) and bespoke targeted NGS (t-NGS) (n = 175) (overlap n = 36), with existing genetic annotation in a representative cohort of 351 B-other-ALL patients from the childhood ALL trail, UKALL2003. PAX5alt was most frequently observed (n = 91), whereas PAX5 P80R mutations (n = 11) defined a distinct PAX5 subtype. DUX4-r subtype (n = 80) was defined by DUX4 rearrangements and/or ERG deletions. These patients had a low relapse rate and excellent survival. ETV6::RUNX1-like subtype (n = 21) was characterised by multiple abnormalities of ETV6 and IKZF1, with no reported relapses or deaths, indicating their excellent prognosis in this trial. An inferior outcome for patients with ABL-class fusions (n = 25) was confirmed. Integration of NGS into genomic profiling of B-other-ALL within a single childhood ALL trial, UKALL2003, has shown the added clinical value of NGS-based approaches, through improved accuracy in detection and classification into the range of risk stratifying genetic subtypes, while validating their prognostic significance

The Baryon Oscillation Spectroscopic Survey of SDSS-III

The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure. BOSS uses 1.5 million luminous galaxies as faint as i = 19.9 over 10,000 deg(2) to measure BAO to redshifts z < 0.7. Observations of neutral hydrogen in the Ly alpha forest in more than 150,000 quasar spectra (g < 22) will constrain BAO over the redshift range 2.15 < z < 3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Ly alpha forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance d(A) to an accuracy of 1.0% at redshifts z = 0.3 and z = 0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Ly alpha forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D-A(z) and H-1(z) parameters to an accuracy of 1.9% at z similar to 2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS

The Early Royal Society and Visual Culture

Recent studies have fruitfully examined the intersection between early modern science and visual culture by elucidating the functions of images in shaping and disseminating scientific knowledge. Given its rich archival sources, it is possible to extend this line of research in the case of the Royal Society to an examination of attitudes towards images as artefacts –manufactured objects worth commissioning, collecting and studying. Drawing on existing scholarship and material from the Royal Society Archives, I discuss Fellows’ interests in prints, drawings, varnishes, colorants, images made out of unusual materials, and methods of identifying the painter from a painting. Knowledge of production processes of images was important to members of the Royal Society, not only as connoisseurs and collectors, but also as those interested in a Baconian mastery of material processes, including a “history of trades”. Their antiquarian interests led to discussion of painters’ styles, and they gradually developed a visual memorial to an institution through portraits and other visual records.AH/M001938/1 (AHRC

The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III

The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All of the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 deg2 of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include the measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 deg2 of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 deg2; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra. \ua9 2015. The American Astronomical Society