Academic Commons Search Results
http://academiccommons.columbia.edu/catalog.rss?f%5Bpub_date_facet%5D%5B%5D=2011&f%5Bsubject_facet%5D%5B%5D=Astrophysics&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usFe15+ dielectronic recombination and the effects of configuration interaction between resonances with different captured electron principal quantum numbers
http://academiccommons.columbia.edu/catalog/ac:158735
Savin, Daniel Wolf; Kwon, D. H.http://hdl.handle.net/10022/AC:P:19543Fri, 29 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) of Na-like Fe15+ forming Mg-like Fe14+ via excitation of a 2l core electron has been investigated. We find that configuration interaction (CI) between DR resonances with different captured electron principal quantum numbers n can lead to a significant reduction in resonance strengths for n≥5. Previous theoretical work for this system has not considered this form of CI. Including it accounts for most of the discrepancy between previous theoretical and experimental results.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesDifferential Emission Measure Analysis of a Polar Coronal Hole During the Solar Minimum in 2007
http://academiccommons.columbia.edu/catalog/ac:158020
Hahn, Michael; Landi, E.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19399Fri, 22 Mar 2013 00:00:00 +0000We have performed a differential emission measure (DEM) analysis for a polar coronal hole observed during solar minimum in 2007. Five observations are analyzed spanning the coronal hole from the central meridian to the boundary with the quiet-Sun corona. The observed heights ranged from 1.05 to 1.20 R ☉. The analysis shows that the plasma is not strictly isothermal anywhere, but rather has a high-temperature component that extends up to log T(K) = 6.2-6.3. The size and importance of this component depend on location, and its evolving magnitude with height marks the boundary between the coronal hole and the quiet corona, where it becomes dominant. The DEM of the coronal hole plasma below log T(K) = 6.0 decreases faster with height than that of the high-temperature component. We discuss the possible nature of the high-temperature component. Our results highlight the potential limitations of isothermal analyses. Such methods actually measure a DEM-weighted average temperature and as a result can infer artificial temperature gradients. Assuming the gas is isothermal along the line of sight can also yield incorrect electron densities. By revealing structures along the line of sight, a DEM analysis can also be used to more reliably interpret electron temperature and density measurements.Astrophysics, Plasma physicsmh2451, dws26Astronomy and AstrophysicsArticlesStorage Ring Cross Section Measurements for Electron Impact Ionization of Fe12 + Forming Fe13 + and Fe14 +
http://academiccommons.columbia.edu/catalog/ac:158017
Hahn, Michael; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19398Fri, 22 Mar 2013 00:00:00 +0000We report electron impact ionization cross section measurements for electron impact single ionization of Fe12 + forming Fe13 + and electron impact double ionization of Fe12 + forming Fe14 +. These are the first electron impact ionization data for any Si-like ion uncontaminated by an unknown metastable fraction. Recent distorted wave calculations agree with our single ionization results to within ~15%. Double ionization is dominated by inner shell ionization of a 2l electron resulting in autoionization of a second electron as the inner shell hole is filled.Astrophysics, Atomic physics, Plasma physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesStorage Ring Cross Section Measurements for Electron Impact Ionization of Fe11+ Forming Fe12+ and Fe13+
http://academiccommons.columbia.edu/catalog/ac:157901
Hahn, Michael; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Muller, A.; Novotny, Oldrich; Repnow, R.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19396Fri, 22 Mar 2013 00:00:00 +0000We report ionization cross section measurements for electron impact single ionization (EISI) of Fe11+ forming Fe12+ and electron impact double ionization (EIDI) of Fe11+ forming Fe13+. The measurements cover the center-of-mass energy range from approximately 230 eV to 2300 eV. The experiment was performed using the heavy-ion storage ring TSR located at the Max-Planck-Institut für Kernphysik in Heidelberg, Germany. The storage ring approach allows nearly all metastable levels to relax to the ground state before data collection begins. We find that the cross section for single ionization is 30% smaller than was previously measured in a single-pass experiment using an ion beam with an unknown metastable fraction. We also find some significant differences between our experimental cross section for single ionization and recent distorted wave (DW) calculations. The DW Maxwellian EISI rate coefficient for Fe11+ forming Fe12+ may be underestimated by as much as 25% at temperatures for which Fe11+ is abundant in collisional ionization equilibrium. This is likely due to the absence of 3s excitation-autoionization (EA) in the calculations. However, a precise measurement of the cross section due to this EA channel was not possible because this process is not distinguishable experimentally from electron impact excitation of an n = 3 electron to levels of n ≥ 44 followed by field ionization in the charge state analyzer after the interaction region. Our experimental results also indicate that the EIDI cross section is dominated by the indirect process in which direct single ionization of an inner shell 2l electron is followed by autoionization, resulting in a net double ionization.Astrophysics, Atomic physics, Plasma physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesEffects of Configuration Interaction for Dielectronic Recombination of Na-like Ions Forming Mg-like Ions
http://academiccommons.columbia.edu/catalog/ac:157904
Kwon, D. H.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19397Fri, 22 Mar 2013 00:00:00 +0000Theoretical dielectronic recombination (DR) rate coefficient calculations can be sensitive to configuration interaction (CI) between resonances with different captured electron principle quantum numbers n. Here we explore the importance of this multi-n CI process for DR via 2l → 3l' core excitations and its effect on the total DR rate coefficient. Results are presented for selected Na-like ions from Ca9 + to Zn19 +. We find that including this multi-n CI can reduce the DR rate coefficient by up to ~10% at temperatures where an ion is predicted to form in collisional ionization equilibrium and up to ~15% at higher temperatures. To a first approximation, this will translate into a corresponding increase in the ion abundance. Charge state distributions calculation seeking to be accurate to better than 10% will thus need to take this effect into account. We also present simple fits to the calculated rate coefficients for ease of incorporation into plasma models.Astrophysics, Atomic physics, Plasma physicsdws26Astronomy and AstrophysicsArticlesDielectronic recombination of xenonlike tungsten ions
http://academiccommons.columbia.edu/catalog/ac:158065
Lestinsky, M.; Bernhardt, D.; Grieser, M.; Hahn, Michael; Krantz, C.; Novotny, Oldrich; Repnow, R.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolfhttp://hdl.handle.net/10022/AC:P:19414Fri, 22 Mar 2013 00:00:00 +0000Dielectronic recombination (DR) of xenonlike W20+ forming W19+ has been studied experimentally at a heavy-ion storage ring. A merged-beams method has been employed for obtaining absolute rate coefficients for electron-ion recombination in the collision-energy range 0–140 eV. The measured rate coefficient is dominated by strong DR resonances even at the lowest experimental energies. At plasma temperatures where the fractional abundance of W20+ is expected to peak in a fusion plasma, the experimentally derived plasma recombination rate coefficient is over a factor of 4 larger than the theoretically calculated rate coefficient which is currently used in fusion plasma modeling. The largest part of this discrepancy stems most probably from the neglect in the theoretical calculations of DR associated with fine-structure excitations of the W20+([Kr]4d10 4f8) ion core.Astrophysics, Plasma physics, Atomic physicsmh2451, on2138, dws26Astronomy and AstrophysicsArticlesAssociative detachment of H− + H → H2 + e−
http://academiccommons.columbia.edu/catalog/ac:158068
Savin, Daniel Wolf; Bruhns, H.; Kreckel, H.; Miller, Kenneth; Urbain, X.; Eliasek, J.; Cizek, M.http://hdl.handle.net/10022/AC:P:19415Fri, 22 Mar 2013 00:00:00 +0000Using a merged-beams apparatus, we have measured the associative detachment (AD) reaction of H−+H→H2+e− for relative collision energies up to Er≤4.83 eV. These data extend above the 1-eV limit of our earlier results. We have also updated our previous theoretical work to account for AD via the repulsive 2Σg+ H2− potential energy surface and for the effects at Er≥0.76 eV on the experimental results due to the formation of long-lived H2 resonances lying above the H+H separated atoms limit. Merging both experimental data sets, our results are in good agreement with our new theoretical calculations and confirm the prediction that this reaction essentially turns off for Er≳2 eV. Similar behavior has been predicted for the formation of protonium from collisions of antiprotons and hydrogen atoms.Astrophysics, Atomic physicsdws26, kam2211Astronomy and AstrophysicsArticlesSpinning Black Hole Pairs: Dynamics and Gravitational Waves
http://academiccommons.columbia.edu/catalog/ac:141916
Grossman, Rebecca I.http://hdl.handle.net/10022/AC:P:11791Fri, 11 Nov 2011 00:00:00 +0000Black hole binaries will be an important source of gravitational radiation for both ground-based and future space-based gravitational wave detectors. The study of such systems will offer a unique opportunity to test the dynamical predictions of general relativity when gravity is very strong. To date, most investigations of black hole binary dynamics have focused attention on restricted scenarios in which the black holes do not spin (and thus are confined to move in a plane) and/or in which they stay on quasi-circular orbits. However, spinning black hole pairs in eccentric orbits are now understood to be astrophysically equally important. These spinning binaries exhibit a range of complicated dynamical behaviors, even in the absence of radiation reaction. Their conservative dynamics is complicated by extreme perihelion precession compounded by spin-induced precession. Although the motion seems to defy simple decoding, we are able to quantitatively define and describe the fully three-dimensional motion of arbitrary mass-ratio binaries with at least one black hole spinning and expose an underlying simplicity. To do so, we untangle the dynamics by constructing an instantaneous orbital plane and showing that the motion captured in that plane obeys elegant topological rules. In this thesis, we apply the above prescription to two formal systems used to model black hole binaries. The first is defined by the conservative 3PN Hamiltonian plus spin-orbit coupling and is particularly suitable to comparable-mass binaries. The second is defined by geodesics of the Kerr metric and is used exclusively for extreme mass-ratio binaries. In both systems, we define a complete taxonomy for fully three-dimensional orbits. More than just a naming system, the taxonomy provides unambiguous and quantitative descriptions of the orbits, including a determination of the zoom-whirliness of any given orbit. Through a correspondence with the rational numbers, we are able to show that all of the qualitative features of the well-studied equatorial geodesic motion around Schwarzschild and Kerr black holes are also present in more general black hole binary systems. This includes so-called zoom-whirl behavior, which turns out to be unexpectedly prevalent in comparable-mass binaries in the strong-field regime just as it is for extreme mass-ratio binaries. In each case we begin by thoroughly cataloging the constant radius orbits which generally lie on the surface of a sphere and have acquired the name "spherical orbits". The spherical orbits are significant as they energetically frame the distribution of all orbits. In addition, each unstable spherical orbit is asymptotically approached by an orbit that whirls an infinite number of times, known as a homoclinic orbit. We further catalog the homoclinic trajectories, each of which is the infinite whirl limit of some part of the zoom-whirl spectrum and has a further significance as the separatrix between inspiral and plunge for eccentric orbits. We then show that there exists a discrete set of orbits that are geometrically closed n-leaf clovers in a precessing orbital plane. When viewed in the full three dimensions, these orbits do not close, but they are nonetheless periodic when projected into the orbital plane. Each n-leaf clover is associated with a rational number, q, that measures the degree of perihelion precession in the precessing orbital plane. The rational number q varies monotonically with the orbital energy and with the orbital eccentricity. Since any bound orbit can be approximated as near one of these periodic n-leaf clovers, this special set offers a skeleton that illuminates the structure of all bound orbits in both systems, in or out of the equatorial plane. A first significant conclusion that can be drawn from this analysis is that all generic orbits in the final stages of inspiral under gravitational radiation losses are characterized by precessing clovers with few leaves, and that no orbit will behave like the tightly precessing ellipse of Mercury. We close with a practical application of our taxonomy beyond the illumination of conservative dynamics. The numerical calculation of the first-order (adiabatic) approximation to radiatively evolving inspiral motion in extreme mass-ratio binaries is currently hindered by prohibitive computational cost. Motivated by this limitation, we explain how a judicious use of periodic orbits can dramatically expedite both that calculation and the generation of snapshot gravitational waves from geodesic sources.Physics, Astrophysicsrg420Physics, Physics and Astronomy (Barnard College)DissertationsResults from the QUIET Q-Band Observing Season
http://academiccommons.columbia.edu/catalog/ac:141910
Dumoulin, Robert Nicolashttp://hdl.handle.net/10022/AC:P:11789Fri, 11 Nov 2011 00:00:00 +0000The Q/U Imaging ExperimenT (QUIET) is a ground-based telescope located in the high Atacama Desert in Chile, and is designed to measure the polarization of the Cosmic Microwave Background (CMB) in the Q and W frequency bands (43 and 95 GHz respectively) using coherent polarimeters. From 2008 October to 2010 December, data from more than 10,000 observing hours were collected, first with the Q-band receiver (2008 October to 2009 June) and then with the W-band receiver (until the end of the 2010 observing season). The QUIET data analysis effort uses two independent pipelines, one consisting of a maximum likelihood framework and the other consisting of a pseudo-C` framework. Both pipelines employ blind analysis methods, and each provides analysis of the data using large suites of null tests specific to the pipeline. Analysis of the Q-band receiver data was completed in November of 2010, confirming the only previous detection of the first acoustic peak of the EE power spectrum and setting competitive limits on the scalar-totensor ratio, r. In this dissertation, the results from the Q-band observing season using the maximum likelihood pipeline will be presented.Physics, AstrophysicsPhysicsDissertationsHEFT measurement of the hard X-ray size of the Crab Nebula and the hard X-ray optics of the Nuclear Spectroscopic Telescope Array (NuSTAR)
http://academiccommons.columbia.edu/catalog/ac:141649
An, Hongjunhttp://hdl.handle.net/10022/AC:P:11786Wed, 09 Nov 2011 00:00:00 +0000In this thesis, I discuss two topics: The High Energy Focusing Telescope (HEFT) and the Nuclear Spectroscopic Telescope Array (NuSTAR). HEFT is the first experiment done with imaging telescopes in the hard X-ray energy band (~20-70 keV). I briefly describe the instrument and the balloon campaign. The inflight calibration of the Point Spread Function (PSF) is done with a point source observation (~50 minutes of Cyg X-1 observation). With the PSF calibrated, I attempt to measuring the size of the Crab Nebula in this energy band. Analysis for aspect reconstruction, optical axis determination and the size measurement are described in detail. The size of the Crab Nebula is energy dependent due to synchrotron burn-off. The measurement of the size at different energies can provide us with important parameters for the pulsar wind nebula (PWN) model such as the magnetization parameter. With ~60 minutes of observation of the Crab Nebula with HEFT, I measure the size of the Crab Nebula at energies of 25-58 keV. The analysis technique I used for the size measurement here can be used for measuring the size of astrophysical objects whose sizes are comparable to the width of the PSF. NuSTAR is a satellite version of the HEFT experiment although the spatial and spectral resolution of the optics are improved significantly. And thus, the fabrication technique for the HEFT optics needed to be modified. I describe the fabrication technique for the NuSTAR optics, focusing on the epoxy selection and process development and the metrology systems for characterizing the figure of the glass surfaces.Physics, Astrophysicsha2153PhysicsDissertationsMergers of Supermassive Black Hole Binaries in Gas-rich Environments: Models of Event Rates and Electromagnetic Signatures
http://academiccommons.columbia.edu/catalog/ac:138452
Tanaka, Takamitsuhttp://hdl.handle.net/10022/AC:P:11117Fri, 09 Sep 2011 00:00:00 +0000Supermassive black holes permeate the observable Universe, residing in the nuclei of all or nearly all nearby massive galaxies and powering luminous quasars as far as ten billion light years away. These monstrous objects must grow through a combination of gas accretion and mergers of less massive black holes. The direct detection of the mergers by future gravitational-wave detectors will be a momentous scientific achievement, providing tests of general relativity and revealing the cosmic evolution of supermassive black holes. An additional -- and arguably equally rewarding -- challenge is the concomitant observation of merging supermassive black holes with both gravitational and electromagnetic waves. Such synergistic, "multi-messenger" studies can probe the expansion history of the Universe and shed light on the details of accretion astrophysics. This thesis examines the mergers of supermassive black hole binaries and the observable signatures of these events. First, we consider the formation scenarios for the earliest supermassive black holes. This investigation is motivated by the Sloan Digital Sky Survey observation of a quasar that appears to be powered by a supermassive black hole with a mass of billions of solar masses, already in place one billion years after the Big Bang. Second, we develop semianalytic, time-dependent models for the thermal emission from circumbinary gas disks around merging black holes. Our calculations corroborate the qualitative conclusion of a previous study that for black hole mergers detectable by a space-based gravitational-wave observatory, a gas disk near the merger remnant may exhibit a dramatic brightening of soft X-rays on timescales of several years. Our results suggest that this "afterglow" may become detectable more quickly after the merger than previously estimated. Third, we investigate whether these afterglow episodes could be observed serendipitously by forthcoming wide-field, high-cadence electromagnetic surveys. Fourth, we introduce a new subset of time-dependent solutions for the standard equation describing thin, viscous Keplerian disks. Finally, we apply these solutions to model the electromagnetic emission of accretion disks around supermassive black hole binaries that may be detectable with precision pulsar timing.Astrophysics, Astronomytt2196Astronomy and AstrophysicsDissertationsFrom Measure Zero to Measure Hero: Periodic Kerr Orbits and Gravitational Wave Physics
http://academiccommons.columbia.edu/catalog/ac:137822
Perez-Giz, Gabehttp://hdl.handle.net/10022/AC:P:11008Mon, 29 Aug 2011 00:00:00 +0000A direct observational detection of gravitational waves - perhaps the most fundamental prediction of a theory of curved spacetime - looms close at hand. Stellar mass compact objects spiraling into supermassive black holes have received particular attention as sources of gravitational waves detectable by space-based gravitational wave observatories. A well-established approach models such an extreme mass ratio inspirals (EMRI) as an adiabatic progression through a series of Kerr geodesics. Thus, the direct detection of gravitational radiation from EMRIs and the extraction of astrophysical information from those waveforms require a thorough knowledge of the underlying geodesic dynamics. This dissertation adopts a dynamical systems approach to the study of Kerr orbits, beginning with equatorial orbits. We deduce a topological taxonomy of orbits that hinges on a correspondence between periodic orbits and rational numbers. The taxonomy defines the entire dynamics, including aperiodic motion, since every orbit is in or near the periodic set. A remarkable implication of this periodic orbit taxonomy is that the simple precessing ellipse familiar from planetary orbits is not allowed in the strong-field regime. Instead, eccentric orbits trace out precessions of multi-leaf clovers in the final stages of inspiral. Furthermore, for any black hole, there is some orbital angular momentum value in the strong-field regime below which zoom-whirl behavior becomes unavoidable. We then generalize the taxonomy to help identify nonequatorial orbits whose radial and polar frequencies are rationally related, or in resonance. The thesis culminates by describing how those resonant orbits can be leveraged for an order of magnitude or more reduction in the computational cost of adiabatic order EMRI trajectories, which are so prohibitively expensive that no such relativistically correct inspirals have been generated to date.Physics, Astrophysics, Applied mathematicsgep1PhysicsDissertationsAccretion topics in astrophysics
http://academiccommons.columbia.edu/catalog/ac:137835
Zalamea, Ivanhttp://hdl.handle.net/10022/AC:P:11012Mon, 29 Aug 2011 00:00:00 +0000Accretion theory is essential for understanding a multitude of varied astronomical observations such as X-ray binaries, active galactic nuclei and gamma-ray bursts. In this document three works on accretion will be presented.The first one is on the structure of an inviscid accretion disc with small angular momentum around a rotating black hole. This regime of accretion may occur in X-ray binaries and GRBs. The second work is on neutrino antineutrino annihilation in the vicinity of a hyper-accreting black hole. This work is relevant for the study of GRBs, in particular it singles out when neutrinos may be responsible for powering GRBs. The third work studies the tidal stripping of a white dwarf spiraling into a massive black hole. The stripped matter accretes onto the black hole producing a transient emission, presumably periodic, observable with X-ray and optical telescopes. At the same time the white dwarf emits gravitational waves as it spirals into the black hole.Astrophysicsilz2101PhysicsDissertationsInvestigations in time and of space using the FIRST survey : radio source variability and the evolution of FR II quasars
http://academiccommons.columbia.edu/catalog/ac:129621
Thyagarajan, Nithyanandanhttp://hdl.handle.net/10022/AC:P:9833Fri, 25 Feb 2011 00:00:00 +0000The FIRST survey covered ~ 10,000 deg2 of the sky over a decade, providing unprecedented levels of flux density sensitivity (~ 1 mJy) at 1.4 GHz, uniformity to within 15% (at ~ 0.15 mJy rms), 5".4 angular resolution, astrometric accuracy to better than 1" and has cataloged ≥ 800,000 sources. It has made enormous contributions to diverse scientific ends including such subjects as radio source populations, quasars, large-scale structure and clustering of radio sources, gravitational lensing, cosmology, etc. I present the motivation, analysis and results of two projects also intended to demonstrate the power and expand the scope of the FIRST survey's scientific reach. A comprehensive search for variable and transient radio sources has been conducted using the ~ 55,000 snapshot images of the FIRST survey. An analysis leading to the discovery of 1,651 variable and transient objects down to mJy levels over a wide range of timescales (few minutes to years) is presented. The multi-wavelength matching for counterparts reveals the diverse classes of objects exhibiting variability. Interestingly, ~ 60% of the objects in the sample have either no classified counterparts or no corresponding sources at any other wavelength and require multi-wavelength follow-up observations. I discuss these classes of variables and speculate on the identity of objects that lack multi-wavelength counterparts. Thus, the FIRST survey has yielded the largest sample by far of radio variables and transients to date to unprecedented levels of sensitivity and sky coverage and demonstrates the promise of future radio instruments which have transient-detection as one of their key science projects. For decades, radio astronomers have attempted to use double-lobed radio sources to constrain the angular size-redshift (θ − z) relation and to derive cosmological parameters therefrom. Most of the early attempts have, embarrassingly, shown general consistency with a static Euclidean universe rather than with Friedmann models. These earlier results can be attributed to a combination of selection effects, sample definition problems, and inconsistencies in analysis. However, some recent and more successful analyses have still failed to distinguish among different Friedmann models. A catalog of ~ 680 FR II quasars was constructed from the FIRST sources with redshifts taken from the SDSS spectroscopic QSO catalog and a similar sized sample from the SDSS photometric QSO catalog which are the largest quasar compilations to date. Using statistical analyses, no evidence for intrinsic evolution of sizes with redshift is found. A static Euclidean model for the universe is clearly ruled out. However, new degeneracies between parameters in the multi-dimensional χ2-surface are found which can only be resolved with additional, independent information. Notable differences are found between the spectroscopic and photometric samples raising questions about the nature and origin of these populations.Astronomy, Astrophysicsnt2128AstronomyDissertations