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2009

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Articles 181 - 210 of 245

Full-Text Articles in Astrophysics and Astronomy

An Extended Dust Disk In A Spiral Galaxy : An Occulting Galaxy Pair In The Acs Nearby Galaxy Survey Treasury., Benne W. Holwerda, W. C. Keel, B. Williams, J. J. Dalcanton, R. S. De Jong Feb 2009

An Extended Dust Disk In A Spiral Galaxy : An Occulting Galaxy Pair In The Acs Nearby Galaxy Survey Treasury., Benne W. Holwerda, W. C. Keel, B. Williams, J. J. Dalcanton, R. S. De Jong

Faculty and Staff Scholarship

We present an analysis of an occulting galaxy pair, serendipitously discovered in the ACS Nearby Galaxy Survey Treasury observations of NGC 253 taken with the Hubble Space Telescope’s (HST) Advanced Camera for Surveys in F475W, F606W, and F814W (SDSS − g, broad V, and I). The foreground disk system (at z 0.06) shows a dusty disk much more extended than the starlight, with spiral lanes seen in extinction out to 1.5 R25, approximately 6 half-light radii. This pair is the first where extinction can be mapped reliably out to this distance from the center. The spiral arms of the extended …

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Investigating The Tev Morphology Of Mgro J1908+06 With Veritas, P. T. Reynolds, Et. Al. Jan 2009

Investigating The Tev Morphology Of Mgro J1908+06 With Veritas, P. T. Reynolds, Et. Al.

Physical Sciences Publications

We report on deep observations of the extended TeV gamma-ray source MGRO J1908+06 made with the VERITAS very high energy gamma-ray observatory. Previously, the TeV emission has been attributed to the pulsar wind nebula (PWN) of the Fermi-LAT pulsar PSR J1907+0602. We detect MGRO J1908+06 at a significance level of 14 standard deviations (14σ) and measure a photon index of 2.20 ± 0.10stat ± 0.20sys. The TeV emission is extended, covering the region near PSR J1907+0602 and also extending toward SNR G40.5-0.5. When fitted with a two-dimensional Gaussian, the intrinsic extension has a standard deviation of σsrc = 0fdg44 ± …

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Spectropolarimetric Variability And Co-Rotating Structure In Hd 92207., Richard Ignace, S. Hubrig, M. Schöller Jan 2009

Spectropolarimetric Variability And Co-Rotating Structure In Hd 92207., Richard Ignace, S. Hubrig, M. Schöller

ETSU Faculty Works

We report on low resolution (R~3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well-known for significant spectral variability. The source was observed on seven different nights spanning approximately 3 months in time. With a rotation period of approximately 1 year, our data covers approximately a quarter of the star's rotational phase. Variability in the continuum polarization level is observed over this period of time. The polarization across the Halpha line on any given night is typically different from the degree and position angle of the polarization in the continuum. Interestingly, Hbeta is not in emission and …

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Phase Shift Sequences For An Adding Interferometer, Peter Hyland, Brent Follin, Emory F. Bunn Jan 2009

Phase Shift Sequences For An Adding Interferometer, Peter Hyland, Brent Follin, Emory F. Bunn

Physics Faculty Publications

Cosmic microwave background (CMB) polarimetry has the potential to provide revolutionary advances in cosmology. Future experiments to detect the very weak B-mode signal in CMB polarization maps will require unprecedented sensitivity and control of systematic errors. Bolometric interferometry may provide a way to achieve these goals. In a bolometric interferometer (or other adding interferometer), phase shift sequences are applied to the inputs in order to recover the visibilities. Noise is minimized when the phase shift sequences corresponding to all visibilities are orthogonal. We present a systematic method for finding sequences that produce this orthogonality, approximately minimizing both the length of …

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Dark Matter Scaling Relations And The Assembly Epoch Of Coma Early-Type Galaxies, J. Thomas, R. P. Saglia, R. Bender, D. Thomas, K. Gebhardt, J Magorrian, E. M. Corsini, G. Wegner Jan 2009

Dark Matter Scaling Relations And The Assembly Epoch Of Coma Early-Type Galaxies, J. Thomas, R. P. Saglia, R. Bender, D. Thomas, K. Gebhardt, J Magorrian, E. M. Corsini, G. Wegner

Dartmouth Scholarship

Axisymmetric, orbit-based dynamical models are used to derive dark matter scaling relations for Coma early-type galaxies. From faint to bright galaxies, halo core radii and asymptotic circular velocities increase. Compared to spirals of the same brightness, the majority of Coma early-type galaxies—those with old stellar populations—have similar halo core radii but more than two times larger asymptotic halo velocities. The average dark matter density inside 2 r eff decreases with increasing luminosity and is 6.8 times larger than in disk galaxies of the same B-band luminosity. Compared at the same stellar mass, dark matter densities in ellipticals are 13.5 …

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Einstein@Home Search For Periodic Gravitational Waves In Ligo S4 Data, B. Abbott, R. Abbott, R. Adhikari, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Joseph D. Romano Jan 2009

Einstein@Home Search For Periodic Gravitational Waves In Ligo S4 Data, B. Abbott, R. Abbott, R. Adhikari, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Joseph D. Romano

Physics & Astronomy Faculty Publications

A search for periodic gravitational waves, from sources such as isolated rapidly spinning neutron stars, was carried out using 510 h of data from the fourth LIGO science run (S4). The search was for quasimonochromatic waves in the frequency range from 50 to 1500 Hz, with a linear frequency drift ˙�� (measured at the solar system barycenter) in the range −��/��<˙��<0.1⁢��/��, where the minimum spin-down age �� was 1000 yr for signals below 300 Hz and 10 000 yr above 300 Hz. The main computational work of the search was distributed over approximately 100 000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 h, despite the large parameter space searched. No statistically significant signals were found. The sensitivity of the search is estimated, along with the fraction of parameter space that was vetoed because of contamination by instrumental artifacts. In the 100 to 200 Hz band, more than 90% of sources with dimensionless gravitational-wave strain amplitude greater than 10−23 would have been detected.

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Hubble Space Telescope Observations Of The Quasar Pks 0637-752: Equipartition Electron-Proton Jet From The Most Complete Spectral Coverage To Date, Kushal T. Mehta, Markos Georganopoulos, Eric S. Perlman, Charles A. Padgett, George Chartas Jan 2009

Hubble Space Telescope Observations Of The Quasar Pks 0637-752: Equipartition Electron-Proton Jet From The Most Complete Spectral Coverage To Date, Kushal T. Mehta, Markos Georganopoulos, Eric S. Perlman, Charles A. Padgett, George Chartas

Aerospace, Physics, and Space Science Faculty Publications

We present new Near-Infrared Camera and Multi-Object Spectrometer and attitude control system observations of the quasar jet PKS 0637-752, and we use them, together with existing multiwavelength observations, to produce the most complete spectral coverage of the source to date. We explore the implications of these observations in the context of models for the jet X-ray emission. By relaxing the assumption of equipartition, we undertake an exhaustive study of the parameter space for external Compton off the cosmic microwave background (CMB) (EC/CMB) model. We find that the multiwavelength observations exclude a magnetic-field-dominated jet. Using the method proposed by Georganopoulos et …

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Einstein@Home Search For Periodic Gravitational Waves In Ligo S4 Data, B. Abbott, R. Abbott, R. Adhikari, P. Ajith, B. Allen, G. Allen, R. Amin, D. P. Anderson, S. B. Anderson, W. G. Anderson, M. A. Arain, M. Araya, H. Armandula, P. Armor, Y. Aso, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, M. Bastarrika, K. Bayer, J. Betzwieser, P. T. Beyersdorf, Tiffany Z. Summerscales Jan 2009

Einstein@Home Search For Periodic Gravitational Waves In Ligo S4 Data, B. Abbott, R. Abbott, R. Adhikari, P. Ajith, B. Allen, G. Allen, R. Amin, D. P. Anderson, S. B. Anderson, W. G. Anderson, M. A. Arain, M. Araya, H. Armandula, P. Armor, Y. Aso, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, M. Bastarrika, K. Bayer, J. Betzwieser, P. T. Beyersdorf, Tiffany Z. Summerscales

Faculty Publications

A search for periodic gravitational waves, from sources such as isolated rapidly spinning neutron stars, was carried out using 510 h of data from the fourth LIGO science run (S4). The search was for quasimonochromatic waves in the frequency range from 50 to 1500 Hz, with a linear frequency drift ḟ (measured at the solar system barycenter) in the range -f/τ<ḟ

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Absolute Magnitude Distribution And Light Curves Of Gamma-Ray Burst Supernovae., D. Richardson Jan 2009

Absolute Magnitude Distribution And Light Curves Of Gamma-Ray Burst Supernovae., D. Richardson

Faculty and Staff Publications

Photometry data were collected from the literature and analyzed for supernovae (SNe) that are thought to have a gamma-ray burst (GRB) association. There are several GRBs afterglow light curves that appear to have an SN component. For these light curves, the SN component was extracted and analyzed. An SN light-curve model was used to help determine the peak absolute magnitudes as well as estimates for the kinetic energy, ejected mass, and nickel mass in the explosion. The peak absolute magnitudes are, on average, brighter than those of similar SNe (stripped-envelope SNe) that do not have a GRB association, but this …

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An Intensive Hst Survey For Z>1 Supernovae By Targeting Galaxy Clusters, K S. Dawson, G Aldering, R Amanullah, K Barbary, L F. Barrientos, M Brodwin, N Connolly, A Dey, M Doi, M Donahue, P Eisenhardt, E Ellingson, L Faccioli, V Fadeyev, H K. Fakhouri, A S. Fruchter, D G. Gilbank, M D. Gladders, G Goldhaber, A H. Gonzalez, A Goobar, A Gude, T Hattori, H Hoekstra, Xiaosheng Huang, Y Ihara, B T. Jannuzi, D Johnston, K Kashikawa, B Koester, K Konishi, M Kowalski, C Lidman, E V. Linder, L Lubin, J Meyers, T Morokuma, F Munshi, C Mullis, T Oda, N Panagia, S Perlmutter, M Postman, T Pritchard, J Rhodes, P Rosati, D Rubin, D J. Schlegel, A Spadafora, S A. Stanford, V Stanishev, D Stern, M Strovink, N Suzuki, N Takanashi, K Tokita, M Wagner, L Wang, N Yasuda, H. K. C. Yee, Supernova Cosmology Project Jan 2009

An Intensive Hst Survey For Z>1 Supernovae By Targeting Galaxy Clusters, K S. Dawson, G Aldering, R Amanullah, K Barbary, L F. Barrientos, M Brodwin, N Connolly, A Dey, M Doi, M Donahue, P Eisenhardt, E Ellingson, L Faccioli, V Fadeyev, H K. Fakhouri, A S. Fruchter, D G. Gilbank, M D. Gladders, G Goldhaber, A H. Gonzalez, A Goobar, A Gude, T Hattori, H Hoekstra, Xiaosheng Huang, Y Ihara, B T. Jannuzi, D Johnston, K Kashikawa, B Koester, K Konishi, M Kowalski, C Lidman, E V. Linder, L Lubin, J Meyers, T Morokuma, F Munshi, C Mullis, T Oda, N Panagia, S Perlmutter, M Postman, T Pritchard, J Rhodes, P Rosati, D Rubin, D J. Schlegel, A Spadafora, S A. Stanford, V Stanishev, D Stern, M Strovink, N Suzuki, N Takanashi, K Tokita, M Wagner, L Wang, N Yasuda, H. K. C. Yee, Supernova Cosmology Project

Physics and Astronomy

We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9<zHST field survey and a factor of three improvement in the total yield of SN detections in relatively dust-free red-sequence galaxies. In total, sixteen SNe were discovered at z>0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the …

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Dearth Of Dark Matter Or Massive Dark Halo? Mass-Shape-Anisotropy Degeneracies Revealed By Nmagic Dynamical Models Of The Elliptical Galaxy Ngc 3379, F. De Lorenzi, O. Gerhard, L. Coccato, M. Arnaboldi, M. Capaccioli, K. C. Freeman, K. Kuijken, M. R. Merrifield, N. R. Napolitano, E. Noordermeer, Aaron J. Romanowsky, V. P. Debattista Jan 2009

Dearth Of Dark Matter Or Massive Dark Halo? Mass-Shape-Anisotropy Degeneracies Revealed By Nmagic Dynamical Models Of The Elliptical Galaxy Ngc 3379, F. De Lorenzi, O. Gerhard, L. Coccato, M. Arnaboldi, M. Capaccioli, K. C. Freeman, K. Kuijken, M. R. Merrifield, N. R. Napolitano, E. Noordermeer, Aaron J. Romanowsky, V. P. Debattista

Faculty Publications

Recent results from the Planetary Nebula Spectrograph (PNS) survey have revealed a rapidly falling velocity dispersion profile in the nearby elliptical galaxy NGC 3379, casting doubts on whether this intermediate-luminosity galaxy has the kind of dark matter (DM) halo expected in Λ cold dark matter (ΛCDM) cosmology. We present a detailed dynamical study of this galaxy, combining ground based long-slit spectroscopy, integral-field data from the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) instrument and PNS data reaching to more than seven effective radii. We construct dynamical models with the flexible χ2-made-to-measure (χ2M2M) particle method implemented in the NMAGIC …

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Hubble Space Telescope Discovery Of A Z = 3.9 Multiply Imaged Galaxy Behind The Complex Cluster Lens Warps J1415.1+36 At Z = 1.026, Xiaosheng Huang, T Morokuma, Hk Fakhouri, G Aldering, R Amanullah, K Barbary, M Brodwin, Nv Connolly, Ks Dawson, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, Md Gladders, Jf Hennawi, Y Ihara, Mj Jee, M Kowalski, K Konishi, C Lidman, J Meyers, La Moustakas, S Perlmutter, D Rubin, Dj Schlegel, Al Spadafora, N Suzuki, N Takanashi, N Yasuda Jan 2009

Hubble Space Telescope Discovery Of A Z = 3.9 Multiply Imaged Galaxy Behind The Complex Cluster Lens Warps J1415.1+36 At Z = 1.026, Xiaosheng Huang, T Morokuma, Hk Fakhouri, G Aldering, R Amanullah, K Barbary, M Brodwin, Nv Connolly, Ks Dawson, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, Md Gladders, Jf Hennawi, Y Ihara, Mj Jee, M Kowalski, K Konishi, C Lidman, J Meyers, La Moustakas, S Perlmutter, D Rubin, Dj Schlegel, Al Spadafora, N Suzuki, N Takanashi, N Yasuda

Physics and Astronomy

We report the discovery of a multiply lensed Ly Alpha (Lya) emitter at z = 3.90 behind the massive galaxy cluster WARPS J1415.1+3612 at z = 1.026. Images taken by the Hubble Space Telescope(HST) using ACS reveal a complex lensing system that produces a prominent, highly magnified arc and a triplet of smaller arcs grouped tightly around a spectroscopically confirmed cluster member. Spectroscopic observations using FOCAS on Subaru confirm strong Lya emission in the source galaxy and provide redshifts for more than 21 cluster members, from which we obtain a velocity dispersion of 807+/-185 km/s. Assuming a singular isothermal sphere …

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Kinematic Properties Of Early-Type Galaxy Haloes Using Planetary Nebulae, L. Coccato, O. Gerhard, M. Arnaboldi, P. Das, N. G. Douglas, K. Kuijken, M. R. Merrifield, N. R. Napolitano, Aaron J. Romanowsky, E. Noordermeer, M. Capaccioli, A. Cortesi, F. De Lorenzi, K. C. Freeman Jan 2009

Kinematic Properties Of Early-Type Galaxy Haloes Using Planetary Nebulae, L. Coccato, O. Gerhard, M. Arnaboldi, P. Das, N. G. Douglas, K. Kuijken, M. R. Merrifield, N. R. Napolitano, Aaron J. Romanowsky, E. Noordermeer, M. Capaccioli, A. Cortesi, F. De Lorenzi, K. C. Freeman

Faculty Publications

We present new planetary nebulae (PNe) positions, radial velocities and magnitudes for six early-type galaxies obtained with the Planetary Nebulae Spectrograph (PNS), along with derived two-dimensional velocity and velocity dispersion fields, and the α parameters (i.e. the number of PNe per unit luminosity). We also present new deep absorption-line long-slit kinematics for three galaxies in the sample, obtained with the FOcal Reducer and low dispersion Spectrograph (FORS2) at the Very Large Telescope (VLT). We extend this study to include additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, including previous PNS studies, in order to obtain …

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Discovery Of An Unusual Optical Transient With The Hubble Space Telescope, K Barbary, Ks Dawson, K Tokita, G Aldering, R Amanullah, Nv Connolly, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, A Goobar, A Gude, Xiaosheng Xiaosheng Huang, Y Ihara, K Konishi, M Kowalski, C Lidman, J Meyers, T Morokuma, P Nugent, S Perlmutter, D Rubin, D Schlegel, Al Spadafora, N Suzuki, Hk Swift, N Takanashi, Rc Thomas, N Yasuda, Supernova Cosmology Project Jan 2009

Discovery Of An Unusual Optical Transient With The Hubble Space Telescope, K Barbary, Ks Dawson, K Tokita, G Aldering, R Amanullah, Nv Connolly, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, A Goobar, A Gude, Xiaosheng Xiaosheng Huang, Y Ihara, K Konishi, M Kowalski, C Lidman, J Meyers, T Morokuma, P Nugent, S Perlmutter, D Rubin, D Schlegel, Al Spadafora, N Suzuki, Hk Swift, N Takanashi, Rc Thomas, N Yasuda, Supernova Cosmology Project

Physics and Astronomy

We present observations of SCP 06F6, an unusual optical transient discovered during the Hubble Space Telescope Cluster Supernova Survey. The transient brightened over a period of ~;;100 days, reached a peak magnitude of ~;;21.0 in both i_775 and z_850, and then declined over a similar timescale. There is no host galaxy or progenitor star detected at the location of the transient to a 3 sigma upper limit of i_775 = 26.4 and z_850 = 26.1, giving a corresponding lower limit on the flux increase of a factor of ~;;120. Multiple spectra show five broad absorption bands between 4100 AA and …

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Central Mass-To-Light Ratios And Dark Matter Fractions In Early-Type Galaxies, C. Tortora, N. R. Napolitano, Aaron J. Romanowsky, M. Capaccioli, G. Covone Jan 2009

Central Mass-To-Light Ratios And Dark Matter Fractions In Early-Type Galaxies, C. Tortora, N. R. Napolitano, Aaron J. Romanowsky, M. Capaccioli, G. Covone

Faculty Publications

Dynamical studies of local elliptical galaxies and the Fundamental Plane point to a strong dependence of the total mass-to-light ratio (M/L) on luminosity with a relation of the form M/L∝Lγ. The ‘tilt’γ may be caused by various factors, including stellar population properties (metallicity, age and star formation history), initial mass function, rotational support, luminosity profile non-homology and dark matter (DM) fraction. We evaluate the impact of all these factors using a large uniform data set of local early-type galaxies from Prugniel & Simien. We take particular care in estimating the stellar masses, using a general star formation history, and comparing …

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Magnetic Hole Formation From The Perspective Of Inverse Scattering Theory, Robert L. Hamilton, D A. Peterson, S M. Libby Jan 2009

Magnetic Hole Formation From The Perspective Of Inverse Scattering Theory, Robert L. Hamilton, D A. Peterson, S M. Libby

Faculty Publications - Department of Mathematics

The dynamics of oblique, weakly dispersive nonlinear Alfven waves in the presence of weak resistive damping are investigated numerically through an extension of the derivative nonlinear Schrodinger (DNLS) equation. It is observed numerically that the nonlinear dynamics are organized around the dynamics and allowed interactions of the underlying DNLS soliton families. There are three types of oblique Alfven solitons: the compressive two-parameter soliton and one-parameter bright soliton along with the rare factive one-parameter dark soliton. The damping of either of these compressive solitons is accompanied by the formation of one or more dark solitons. The implication of these processes is …

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Nuclear Resonances: The Quest For Large Column Densities And A New Tool, J. Greiner, S. Boggs, G. Dicocco, K. T. Freese, N. Gehrels, Dieter H. Hartmann, A. Iyudin, G. Kanbach, A. A. Zdziarski Jan 2009

Nuclear Resonances: The Quest For Large Column Densities And A New Tool, J. Greiner, S. Boggs, G. Dicocco, K. T. Freese, N. Gehrels, Dieter H. Hartmann, A. Iyudin, G. Kanbach, A. A. Zdziarski

Publications

Nuclear physics offers us a powerful tool: using nuclear resonance absorption lines to infer the physical conditions in astrophysical settings which are otherwise diffcult to deduce. Present-day technology provides an increase in sensitivity over previous gamma-ray missions large enough to utilize this tool for the first time. The most exciting promise is to measure gamma-ray bursts from the first star(s) at redshifts 20–60, but also active galactic nuclei are promising targets.

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3d Reconnection And Flow Dynamics In The Ssx Experiment, Michael R. Brown, C. D. Cothran, David H. Cohen, Jason Alexander Horwitz , '07, Vernon Hampden Chaplin , '07 Jan 2009

3d Reconnection And Flow Dynamics In The Ssx Experiment, Michael R. Brown, C. D. Cothran, David H. Cohen, Jason Alexander Horwitz , '07, Vernon Hampden Chaplin , '07

Physics & Astronomy Faculty Works

Several new experimental results are reported from plasma merging studies at the Swarthmore Spheromak Experiment (SSX) with relevance to collisionless three-dimensional magnetic reconnection in laboratory and space plasmas. First, recent high-resolution velocity measurements of impurity ions using ion Doppler spectroscopy (IDS) show bi-directional outflow jets at 40 km/s (nearly the Alfven speed). The SSX IDS instrument measures with 1 mu s or better time resolution the width and Doppler shift of the C-III impurity (H plasma) 229.7 nm line to determine the temperature and line-averaged flow velocity during spheromak merging events. High flow speeds are corroborated using an in situ …

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X-Ray Spectroscopy Of The Radiation-Driven Winds Of Massive Stars: Line Profile And Line Ratio Diagnostics, David H. Cohen Jan 2009

X-Ray Spectroscopy Of The Radiation-Driven Winds Of Massive Stars: Line Profile And Line Ratio Diagnostics, David H. Cohen

Physics & Astronomy Faculty Works

Massive stars drive powerful, supersonic winds via the radiative momentum associated with the thermal UV emission from their photospheres. Shock phenomena are ubiquitous in these winds, heating them to millions, and sometimes tens of millions, of degrees. The emission line spectra from the shock-heated plasma provide powerful diagnostics of the winds' physical conditions, which in turn provide constraints on models of wind shock heating. Here I show how x-ray line transfer is affected by photoelectric absorption in the partially ionized component of the wind and how it can be modeled to determine the astrophysically important mass-loss rates of these stellar …

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Grb Polarimetry With Poet, Mark L. Mcconnell, L Angelini, Matthew Baring, Scott Barthelmy, J Kevin Black, Peter F. Bloser, B Dennis, A G. Emslie, J Greiner, W Hajdas, A K. Harding, H Hartmann, J E. Hill, Kunihito Ioka, Philip Kaaret, G Kanbach, D Kniffen, Jason S. Legere, John R. Macri, R Morris, Takashi Nakamura, N Produit, James M. Ryan, Takanori Sakamoto, Kenji Toma, X Wu, Ryo Yamazaki, Bing Zhang Jan 2009

Grb Polarimetry With Poet, Mark L. Mcconnell, L Angelini, Matthew Baring, Scott Barthelmy, J Kevin Black, Peter F. Bloser, B Dennis, A G. Emslie, J Greiner, W Hajdas, A K. Harding, H Hartmann, J E. Hill, Kunihito Ioka, Philip Kaaret, G Kanbach, D Kniffen, Jason S. Legere, John R. Macri, R Morris, Takashi Nakamura, N Produit, James M. Ryan, Takanori Sakamoto, Kenji Toma, X Wu, Ryo Yamazaki, Bing Zhang

Space Science Center

POET (Polarimeters for Energetic Transients) represents a concept for a Small Explorer (SMEX) satellite mission, whose principal scientific goal is to understand the structure of GRB sources through sensitive X‐ray and γ‐ray polarization measurements. The payload consists of two wide field‐of‐view (FoV) instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2–15 keV and a high energy polarimeter (Gamma‐Ray Polarimeter Experiment or GRAPE) that would measure polarization in the 60–500 keV energy range. The POET spacecraft provides a zenith‐pointed platform for maximizing the exposure to deep space. Spacecraft rotation provides a means of effectively …

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Statistical Properties Of Gamma‐Ray Burst Polarization, Kenji Toma, Takanori Sakamoto, Bing Zhang, J E. Hill, Mark L. Mcconnell, Peter F. Bloser, Ryo Yamazaki, Kunihito Ioka, Takashi Nakamura Jan 2009

Statistical Properties Of Gamma‐Ray Burst Polarization, Kenji Toma, Takanori Sakamoto, Bing Zhang, J E. Hill, Mark L. Mcconnell, Peter F. Bloser, Ryo Yamazaki, Kunihito Ioka, Takashi Nakamura

Space Science Center

The emission mechanism and the origin and structure of magnetic fields in gamma‐ray burst (GRB) jets are among the most important open questions concerning the nature of the central engine of GRBs. In spite of extensive observational efforts, these questions remain to be answered and are difficult or even impossible to infer with the spectral and lightcurve information currently collected. Polarization measurements will lead to unambiguous answers to several of these questions. Recent developments in X‐ray and γ‐ray polarimetry techniques have demonstrated a significant increase in sensitivity enabling several new mission concepts, e.g. POET (Polarimeters for Energetic Transients), providing wide …

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Detecting A Stochastic Gravitational-Wave Background: The Overlap Reduction Function, Lee Samuel Finn, Shane L. Larson, Joseph D. Romano Jan 2009

Detecting A Stochastic Gravitational-Wave Background: The Overlap Reduction Function, Lee Samuel Finn, Shane L. Larson, Joseph D. Romano

All Physics Faculty Publications

Detection of a gravitational-wave stochastic background via ground or space-based gravitational-wave detectors requires the cross correlation of the response of two or more independent detectors. The cross correlation involves a frequency-dependent factor—the so-called overlap reduction function or Hellings-Downs curve—that depends on the relative geometry of each detector pair, i.e., the detector separations and the relative orientation of their antenna patterns (beams). An incorrect formulation of this geometrical factor has appeared in the literature, leading to incorrect conclusions regarding the sensitivity of proposed detectors to a stochastic gravitational-wave background. To rectify these errors and as a reference for future work we …

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A Search For Iron Emission Lines In The Chandra X-Ray Spectra Of Neutron Star Low-Mass X-Ray Binaries, E. M. Cackett, J. M. Miller, J. Homan, M. Van Der Klis, W. H. G. Lewin, M. Méndez, J. Raymond, D. Steeghs, R. Wijnands Jan 2009

A Search For Iron Emission Lines In The Chandra X-Ray Spectra Of Neutron Star Low-Mass X-Ray Binaries, E. M. Cackett, J. M. Miller, J. Homan, M. Van Der Klis, W. H. G. Lewin, M. Méndez, J. Raymond, D. Steeghs, R. Wijnands

Physics and Astronomy Faculty Research Publications

While iron emission lines are well studied in black hole systems, both in X-ray binaries and active galactic nuclei, there has been less of a focus on these lines in neutron star low-mass X-ray binaries (LMXBs). However, recent observations with Suzaku and XMM-Newton have revealed broad, asymmetric iron line profiles in three neutron star LMXBs, confirming an inner disk origin for these lines in neutron star systems. Here, we present a search for iron lines in six neutron star LMXBs. For each object we have simultaneous Chandra and RXTE observations at two separate epochs, allowing for both a high-resolution spectrum …

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Winds And Accretion In Young Stars, Suzan Edwards Jan 2009

Winds And Accretion In Young Stars, Suzan Edwards

Astronomy: Faculty Publications

Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star‐disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin‐up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stellar spindown. Although spectroscopic indicators of high velocity T Tauri winds have been known for decades, the line of He I 10830 offers a promising new …

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Uncertainties In Theoretical Hei Emissivities: Hii Regions, Primordial Abundance And Cosmological Recombination, R. L. Porter, Gary J. Ferland, Keith B. Macadam, P. J. Storey Jan 2009

Uncertainties In Theoretical Hei Emissivities: Hii Regions, Primordial Abundance And Cosmological Recombination, R. L. Porter, Gary J. Ferland, Keith B. Macadam, P. J. Storey

Physics and Astronomy Faculty Publications

A number of recent works in astronomy and cosmology have relied upon theoretical He I emissivities, but we know of no effort to quantify the uncertainties in the atomic data. We analyse and assign uncertainties to all relevant atomic data, perform Monte Carlo analyses, and report standard deviations in the line emissivities. We consider two sets of errors, which we call ‘optimistic’ and ‘pessimistic’. We also consider three different conditions, corresponding to prototypical Galactic and extragalactic H IIregions and the epoch of cosmological recombination. In the extragalactic H II case, the errors we obtain are comparable to or larger than …

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General Search For Stars With Rapid Optical Variations: Test Fields, Elizabeth Fagg, Jieun Park, Kelly Pearson, Robert Kehoe Jan 2009

General Search For Stars With Rapid Optical Variations: Test Fields, Elizabeth Fagg, Jieun Park, Kelly Pearson, Robert Kehoe

Journal of Undergraduate Research

We present a search for stars exhibiting short time-scale optical lightvariations. Our search employs archival data taken by the ROTSE1 telephotoarray in two eight degree fields of view. This is a test study considering two fields which overlap fields previously mined for variables, but with different dataand search techniques. Each field was observed for approximately six continuous hours. We employ a general search strategy based on statistical properties of theobserved light curves for each object. The analysis is sensitive to sources with variations < 0.25 day and > 0.1 mag and with mean magnitudes between 9.5 magand 14 mag. We identify 42 variable stars with …

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Tokai To Kamioka: A 2nd Generation Long Baseline Neutrino Experiment, Jessica Danielle Brinson Jan 2009

Tokai To Kamioka: A 2nd Generation Long Baseline Neutrino Experiment, Jessica Danielle Brinson

Honors Capstones

No abstract provided.

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Electron-Impact Excitation Of O Ii Fine-Structure Levels, R. Kisielius, P. J. Storey, Gary J. Ferland, F. P. Keenan Jan 2009

Electron-Impact Excitation Of O Ii Fine-Structure Levels, R. Kisielius, P. J. Storey, Gary J. Ferland, F. P. Keenan

Physics and Astronomy Faculty Publications

Effective collision strengths for forbidden transitions among the five energetically lowest fine-structure levels of O II are calculated in the Breit–Pauli approximation using the R-matrix method. Results are presented for the electron temperature range 100–100 000 K. The accuracy of the calculations is evaluated via the use of different types of radial orbital sets and a different configuration expansion basis for the target wavefunctions. A detailed assessment of previous available data is given, and erroneous results are highlighted. Our results reconfirm the validity of the original Seaton and Osterbrock scaling for the optical O II ratio, a matter of some …

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The Aztec/Sma Interferometric Imaging Survey Of Submillimeter-Selected High-Redshift Galaxies, Joshua D. Younger, Giovanni G. Fazio, Jia Sheng Huang, Min S. Yun, Grant W. Wilson, Matthew L.N. Ashby, Mark A. Gurwell, Alison B. Peck, Glen R. Petitpas, David J. Wilner, David H. Hughes, Itziar Aretxaga, Sungeun Kim, Kimberly S. Scott, Jason Austermann, Thushara Perera, James D. Lowenthal Jan 2009

The Aztec/Sma Interferometric Imaging Survey Of Submillimeter-Selected High-Redshift Galaxies, Joshua D. Younger, Giovanni G. Fazio, Jia Sheng Huang, Min S. Yun, Grant W. Wilson, Matthew L.N. Ashby, Mark A. Gurwell, Alison B. Peck, Glen R. Petitpas, David J. Wilner, David H. Hughes, Itziar Aretxaga, Sungeun Kim, Kimberly S. Scott, Jason Austermann, Thushara Perera, James D. Lowenthal

Astronomy: Faculty Publications

We present results from a continuing interferometric survey of high-redshift submillimeter galaxies (SMGs) with the Submillimeter Array, including high-resolution (beam size ∼ 2 arcsec) imaging of eight additional AzTEC 1.1 mm selected sources in the COSMOS field, for which we obtain six reliable (peak signal-to-noise ratio (S/N) >5 or peak S/N >4 with multiwavelength counterparts within the beam) and two moderate significance (peak S/N >4) detections. When combined with previous detections, this yields an unbiased sample of millimeter-selected SMGs with complete interferometric follow up. With this sample in hand, we (1) empirically confirm the radio-submillimeter association, (2) examine the submillimeter …

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Scattering From A Tenuous Random Medium With Applications In Optics, Jonathan Blackledge Jan 2009

Scattering From A Tenuous Random Medium With Applications In Optics, Jonathan Blackledge

Articles

Mathematical models for the scattering of light (and other radiation) tend to fall into two categories based on a weak field condition (single scattering processes) or a strong field condition (multiple scattering processes). In the latter case, the complexity of deterministic models coupled with available solutions often fail to provide results that are of value to engineering systems (e.g. imaging systems). For this reason, multiple scattering problems are often approached using stochastic modelling methods whose foundations lie in random walk theory where the amplitude and phase of the scattered field are taken to conform to an appropriate statistical process and …

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