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Articles 31 - 60 of 179
Full-Text Articles in Astrophysics and Astronomy
Defect Assisted Growth Of Copper-Silicide Nanostructures On Si(100) And Si(111), Endu Sekhar Srinadhu
Defect Assisted Growth Of Copper-Silicide Nanostructures On Si(100) And Si(111), Endu Sekhar Srinadhu
All Dissertations
As the dimensions of the smallest feature on the integrated circuit has minia-turized into the range of tens of nanometers, patterning of highly ordered nanos-tructures with tunable size and shape in large scale on the surface of substrate is highly demanding and increasingly challenges the limits of nanolithography. To over-come the conventional lithographic limitations, self assembled methods have been explored. While strain driven self assembly is widely viewed as a promising technique for patterning at the nanoscale, to follow this approach and create structures in a desired manner, a reliable means to engineer and characterize the shape and sizes of …
Ion Transport Through Macrocapillaries – Oscillations Due To Charge Patch Formation, Dhruva Kulkarni, L.A.M. Lyle, Chad E. Sosolik
Ion Transport Through Macrocapillaries – Oscillations Due To Charge Patch Formation, Dhruva Kulkarni, L.A.M. Lyle, Chad E. Sosolik
Publications
We present results on ion transport through large bore capillaries (macrocapillaries) that probe both the geometric and ion-guided aspects of this ion delivery mechanism. We have demonstrated that guiding in macrocapillaries exhibits position- and angle-dependent transmission properties which are directly related to the capillary material (either metal or insulator) and geometry. Specifically, we have passed 1 keV Rb+ ions through glass and metal macrocapillaries, and have observed oscillations for the transmitted ion current passing through the insulating capillaries. Straightforward calculations show that these oscillations can be attributed to beam deflections from charge patches that form on the interior walls …
Scalable Synthesis And Energy Applications Of Defect Engineered Nano Materials, Mehmet Karakaya
Scalable Synthesis And Energy Applications Of Defect Engineered Nano Materials, Mehmet Karakaya
All Dissertations
Nanomaterials and nanotechnologies have attracted a great deal of attention in a few decades due to their novel physical properties such as, high aspect ratio, surface morphology, impurities, etc. which lead to unique chemical, optical and electronic properties. The awareness of importance of nanomaterials has motivated researchers to develop nanomaterial growth techniques to further control nanostructures properties such as, size, surface morphology, etc. that may alter their fundamental behavior. Carbon nanotubes (CNTs) are one of the most promising materials with their rigidity, strength, elasticity and electric conductivity for future applications. Despite their excellent properties explored by the abundant research works, …
A Spectroscopic Study Of Anomalous Stellar Populations In M67, Courtney Mcgahee
A Spectroscopic Study Of Anomalous Stellar Populations In M67, Courtney Mcgahee
All Dissertations
A population of stars exists in the old, open cluster M67, whose photometry, color magnitude diagram locations and associated evolutionary states cannot be explained by current, standard single star evolution theory. These stars are often referred to as ``yellow straggler' stars. Yellow stragglers have been identified in multiple star clusters suggesting that these stars constitute a real population. Additionally, according to independent studies, at least some of the yellow straggler stars in M67 are likely cluster members. Therefore, cluster non-membership is not a sufficient explanation for the observed anomalous photometry of these stars. It is possible that the yellow stragglers …
Multidimensional Simulations Of Non-Linear Cosmic Ray Production In Supernova Remnant Evolution, Joshua Wood
Multidimensional Simulations Of Non-Linear Cosmic Ray Production In Supernova Remnant Evolution, Joshua Wood
All Dissertations
When a high-mass star (& 4Msun) explodes at the end of its life, a supernova occurs, leaving its degenerate core and a fast-moving shell of matter, known as a supernova remnant (SNR). The SNR shell lasts for many thousands of years, generating emissions from low-frequency radio (~ 10-7 eV) up to γ-ray regime (~ 1015 eV). It is also believed that SNRs are the predominant source of galactic cosmic rays, accelerating a population of thermal ions, primarily protons, up to relativistic energies by means of the diffusive shock acceleration (DSA) mechanism. The small population of thermal (Boltzmann) particles, p ~ …
Three X-Ray Transients In M31 Oberserved With Swift, R. Voss, W. Pietsch, F. Haberl, H. Stiele, J. Greiner, G. Sala, Dieter H. Hartmann, D. Hatzidimitriou
Three X-Ray Transients In M31 Oberserved With Swift, R. Voss, W. Pietsch, F. Haberl, H. Stiele, J. Greiner, G. Sala, Dieter H. Hartmann, D. Hatzidimitriou
Publications
Aims.The purpose of this study is to find transient X-ray sources in M 31, and to investigate and classify their nature.Methods.Three X-ray transients were observed with Swift. For each of the three X-ray transients we use the Swift X-ray and opticaldata together with observations from XMM-Newton and Chandra to investigate the lightcurves and the spectra of the outburst, andthereby to identify the source types. Results.The outburst of XMMU J004215.8+ 411924 lasted for about one month. The source had a hard power-law spectrum with aphoton index of 1.6. It was previously identified as a Be/X-ray binary based on the optical identification …
Supernova Neutrino Nucleosynthesis Of Light Elements With Neutrino Oscillations, Takashi Yoshida, Toshitaka Kajino, Hidekazu Yokomakura, Keiichi Kimura, Akira Takamura, Dieter H. Hartmann
Supernova Neutrino Nucleosynthesis Of Light Elements With Neutrino Oscillations, Takashi Yoshida, Toshitaka Kajino, Hidekazu Yokomakura, Keiichi Kimura, Akira Takamura, Dieter H. Hartmann
Publications
Light element synthesis in supernovae through neutrino-nucleus interactions, i.e., the ν-process, is affected by neutrino oscillations in the supernova environment. There is a resonance of 13-mixing in the O/C layer, which increases the rates of charged-current ν-process reactions in the outer He-rich layer. The yields of 7Li and 11B increase by about a factor of 1.9 and 1.3, respectively, for a normal mass hierarchy and an adiabatic 13-mixing resonance, compared to those without neutrino oscillations. In the case of an inverted mass hierarchy and a non-adiabatic 13-mixing resonance, the increase in the 7Li and 11B yields is much smaller. Observations …
Chemical Evolution Of The Neutron-Rich Iron-Group Isotopes And Implications For The Formation Of Fun Cais, Tianhong Yu
Chemical Evolution Of The Neutron-Rich Iron-Group Isotopes And Implications For The Formation Of Fun Cais, Tianhong Yu
All Dissertations
Calcium-aluminum-rich inclusions (CAIs) are millimeter-sized refractory objects found in primitive meteorites. CAIs are considered as some of the first solids to form in the solar system, because they are refractory. FUN CAIs, those with Fractionated and Unknown Nuclear effects, are a small subset of CAIs. These FUN CAIs show correlated excesses and deficits in the neutron-rich iron-group isotopes such as 48 Ca and 50 Ti which regular CAIs do not. Interestingly, these isotopes are most likely produced infrequently but in huge quantities in a rare class of thermonuclear (Type Ia) supernovae. I propose that the isotopic effects in the neutron-rich …
High-Resolution Near-Infrared Spectroscopy Of Hd 100546. Ii. Analysis Of Variable Rovibrational Co Emission Lines, Sean D. Brittain, Joan Najita, John S. Carr, Joseph Liskowsky, Matthew R. Troutman, Greg W. Doppmann
High-Resolution Near-Infrared Spectroscopy Of Hd 100546. Ii. Analysis Of Variable Rovibrational Co Emission Lines, Sean D. Brittain, Joan Najita, John S. Carr, Joseph Liskowsky, Matthew R. Troutman, Greg W. Doppmann
Publications
We present observations of rovibrational CO in HD 100546 from four epochs spanning 2003 January through 2010 December. We show that the equivalent widths of the CO lines vary during this time period with the v = 1–0 CO lines brightening more than the UV fluoresced lines from the higher vibrational states.While the spectroastrometric signal of the hot band lines remains constant during this period, the spectroastrometric signal of the v = 1–0 lines varies substantially. At all epochs, the spectroastrometric signals of the UV fluoresced lines are consistent with the signal one would expect from gas in an axisymmetric …
High-Resolution Near-Infrared Spectroscopy Of Hd 100546. I. Analysis Of Asymmetric Ro-Vibrational Oh Emission Lines, Joseph Liskowsky, Sean D. Brittain, Joan R. Najita, John S. Carr, Greg W. Doppman, Matthew R. Troutman
High-Resolution Near-Infrared Spectroscopy Of Hd 100546. I. Analysis Of Asymmetric Ro-Vibrational Oh Emission Lines, Joseph Liskowsky, Sean D. Brittain, Joan R. Najita, John S. Carr, Greg W. Doppman, Matthew R. Troutman
Publications
We present observations of ro-vibrational OH and CO emission from the Herbig Be star HD 100546. The emission from both molecules arises from the inner region of the disk extending from approximately 13 AU from the central star. The velocity profiles of the OH lines are narrower than the velocity profile of the [O i] λ6300 line, indicating that the OH in the disk is not cospatial with the Oi. This suggests that the inner optically thin region of the disk is largely devoid of molecular gas. Unlike the ro-vibrational CO emission lines, the OH lines are highly asymmetric. We …
Broadband Monitoring Tracing The Evolution Of The Jet And Disk In The Black Hole Candidate X-Ray Binary Maxi J1659-152, A. J. Horst, P. A. Curran, J. C. A. Miller-Jones, J. D. Linford, J. Gorosabel, D. M. Russell, A. De Ugarte Postigo, A. A. Lundgren, G. B. Taylor, D Maitra, S Guziy, T M. Belloni, C Kouveliotou, P G. Jonker, A Kamble, Z Paragi, J Homan, E Kuulkers, J Granot, D Altamirano, M M. Buxton, A Castro-Tirado, R P. Fender, M A. Garrett, N Gehrels, Dieter H. Hartmann, J A. Kennea, H A. Krimm, V Mangano, E Ramirez-Ruiz, P Romano, R.A.M.J. Wijers, R Wijnands, Y J. Yang
Broadband Monitoring Tracing The Evolution Of The Jet And Disk In The Black Hole Candidate X-Ray Binary Maxi J1659-152, A. J. Horst, P. A. Curran, J. C. A. Miller-Jones, J. D. Linford, J. Gorosabel, D. M. Russell, A. De Ugarte Postigo, A. A. Lundgren, G. B. Taylor, D Maitra, S Guziy, T M. Belloni, C Kouveliotou, P G. Jonker, A Kamble, Z Paragi, J Homan, E Kuulkers, J Granot, D Altamirano, M M. Buxton, A Castro-Tirado, R P. Fender, M A. Garrett, N Gehrels, Dieter H. Hartmann, J A. Kennea, H A. Krimm, V Mangano, E Ramirez-Ruiz, P Romano, R.A.M.J. Wijers, R Wijnands, Y J. Yang
Publications
MAXI J1659−152 was discovered on 2010 September 25 as a new X-ray transient, initially identified as a gamma-ray burst, but was later shown to be a new X-ray binary with a blackhole as the most likely compact object. Dips in the X-ray light curves have revealed that MAXI J1659−152 is the shortest period black hole candidate identified to date. Here we present the results of a large observing campaign at radio, submillimetre, near-infrared (nIR), optical and ultraviolet (UV) wavelengths. We have combined this very rich data set with the available X-ray observations to compile a broad-band picture of the evolution …
Near-Infrared Spectroscopic Study Of V1647 Ori, Sean D. Brittain, T W. Rettig, Theodore Simon, Erika L. Gibb, Joseph Liskowsky
Near-Infrared Spectroscopic Study Of V1647 Ori, Sean D. Brittain, T W. Rettig, Theodore Simon, Erika L. Gibb, Joseph Liskowsky
Publications
We present new high-resolution infrared echelle spectra of V1647 Ori, the young star that illuminates McNeil's nebula. From the start, V1647 Ori has been an enigmatic source that has defied classification, in some ways resembling eruptive stars of the FUor class and in other respects the EXor variables. V1647 Ori underwent an outburst in 2003 before fading back to its pre-outburst brightness in 2006. In 2008, it underwent a new outburst. In this paper we present high-resolution K-band and M-band spectra from the W. M. Keck Observatory that were acquired during the 2008 outburst. We compare the spectra to spectra …
Nitrogen Abundances And The Distance Moduli Of The Pleiades And Hyades, Blake Miller, Jeremy R. King, Yu Chen, Ann Merchant Boesgaard
Nitrogen Abundances And The Distance Moduli Of The Pleiades And Hyades, Blake Miller, Jeremy R. King, Yu Chen, Ann Merchant Boesgaard
Publications
Recent reanalyses of HIPPARCOS parallax data confirm a previously noted discrepancy with the Pleiades distance modulus estimated from main-sequence fitting in the color-magnitude diagram. One proposed explanation of this distance modulus discrepancy is a Pleiades He abundance that is significantly larger than the Hyades value. We suggest that, based on our theoretical and observational understanding of Galactic chemical evolution, nitrogen abundances may serve as a proxy for helium abundances of disk stars. Utilizing high-resolution near-UV Keck/HIRES spectroscopy, we determine N abundances in the Pleiades and Hyades dwarfs from NH features in the λ3330 region. While our Hyades N abundances show …
Gas Lines From The 5-Myr Old Optically Thin Disk Around Hd141569a, W F. Thi, C Pinte, E Pantin, J C. Augereau, G Meeus, F Menard, C Martin-Zaidi, P Woitke, P Riviere-Marichalar, I Kamp, A Carmona, G Sandell, C Eiroa, W Dent, B Montesinos, G Aresu, R Meijerink, M Spaans, G White, D Ardila, J Lebreton, I Mendigutia, Sean D. Brittain
Gas Lines From The 5-Myr Old Optically Thin Disk Around Hd141569a, W F. Thi, C Pinte, E Pantin, J C. Augereau, G Meeus, F Menard, C Martin-Zaidi, P Woitke, P Riviere-Marichalar, I Kamp, A Carmona, G Sandell, C Eiroa, W Dent, B Montesinos, G Aresu, R Meijerink, M Spaans, G White, D Ardila, J Lebreton, I Mendigutia, Sean D. Brittain
Publications
At the distance of 99-116 pc, HD141569A is one of the nearest HerbigAe stars that is surrounded by a tenuous disk, probably in transition between a massive primordial disk and a debris disk. We observed the fine-structure lines of OI at 63 and 145 micron and the CII line at 157 micron with the PACS instrument onboard the Herschel Space Telescope as part of the open-time large programme GASPS. We complemented the atomic line observations with archival Spitzer spectroscopic and photometric continuum data, a ground-based VLT-VISIR image at 8.6 micron, and 12CO fundamental ro-vibrational and pure rotational J=3-2 observations. We …
Accretion Variability Of Herbig Ae/Be Stars Observed By X-Shooter Hd 31648 And Hd 163296, I Mendigutia, Sean D. Brittain, C Eiroa, G Meeus, B Montesinos, A Mora, J Muzerolle, R D. Oudmaijer, E Rigliaco
Accretion Variability Of Herbig Ae/Be Stars Observed By X-Shooter Hd 31648 And Hd 163296, I Mendigutia, Sean D. Brittain, C Eiroa, G Meeus, B Montesinos, A Mora, J Muzerolle, R D. Oudmaijer, E Rigliaco
Publications
This work presents X-Shooter/Very Large Telescope spectra of the prototypical, isolated Herbig Ae stars HD 31648 (MWC 480) and HD 163296 over five epochs separated by timescales ranging from days to months. Each spectrum spans over a wide wavelength range covering from 310 to 2475 nm. We have monitored the continuum excess in the Balmer region of the spectra and the luminosity of 12 ultraviolet, optical, and near-infrared spectral lines that are commonly used as accretion tracers for T Tauri stars. The observed strengths of the Balmer excesses have been reproduced from a magnetospheric accretion shock model, providing a mean …
Magnetic Field Generation In A Jet-Sheath Plasma Via The Kinetic Kelvin-Helmholtz Instability, K.-I. Nishikawa, P. Hardee, B. Zhang, I. Dutan, M. Medvedev, E. J. Choi, K. W. Min, J. Niemiec, Y. Mizuno, A Nordlund, J T. Frederiksen, H Sol, M Pohl, Dieter H. Hartmann
Magnetic Field Generation In A Jet-Sheath Plasma Via The Kinetic Kelvin-Helmholtz Instability, K.-I. Nishikawa, P. Hardee, B. Zhang, I. Dutan, M. Medvedev, E. J. Choi, K. W. Min, J. Niemiec, Y. Mizuno, A Nordlund, J T. Frederiksen, H Sol, M Pohl, Dieter H. Hartmann
Publications
We have investigated the generation of magnetic fields associated with velocity shear between an unmagne-tized relativistic jet and an unmagnetized sheath plasma. We have examined the strong magnetic fields generated by ki-netic shear (Kelvin–Helmholtz) instabilities. Compared to the previous studies using counter-streaming performed by Alves et al. (2012), the structure of the kinetic Kelvin– Helmholtz instability (KKHI) of our jet-sheath configura-tion is slightly different, even for the global evolution of the strong transverse magnetic field. In our simulations the major components of growing modes are the electric field Ez, perpendicular to the flow boundary, and the magnetic field By, transverse …
A Spectroscopic Analysis Of The Eclipsing Short-Period Binary V505 Persei And The Origin Of The Lithium Dip, Patrick Baugh, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard
A Spectroscopic Analysis Of The Eclipsing Short-Period Binary V505 Persei And The Origin Of The Lithium Dip, Patrick Baugh, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard
Publications
As a test of rotationally-induced mixing causing the well-known Li dip in older mid-F dwarfs in the local Galactic disk, we utilize high-resolution and -S/N Keck/HIRES spectroscopy to measure the Li abundance in the components of the ∼1 Gyr, [Fe/H]= −0.15 eclipsing short-period binary V505 Per. We find A(Li) ∼ 2.7 ± 0.1 and 2.4 ± 0.2 in the Teff∼6500 and 6450K primary and sec-ondary components, respectively. Previous Teff determinations and uncertainties suggest that each component is located in the midst of the Li dip. If so, their A(Li) are ≥2–5 times larger than A(Li) detections and upper limits observed …
Co-Production Of Nitrogen-15 And Oxygen-18 In Explosive Helium Burning And Implications For Supernova Graphite Grains, Michael Bojazi
Co-Production Of Nitrogen-15 And Oxygen-18 In Explosive Helium Burning And Implications For Supernova Graphite Grains, Michael Bojazi
All Theses
My Masters research involves simulations of a supernova whereby a shock wave of constant Mach number is sent through a 15-solar-mass star evolved to the point of core-collapse. The resulting nucleosynthesis is examined with the intent of explaining the overproduction, relative to solar values, of nitrogen-15 and oxygen-18 abundances in supernova presolar graphite grains, as experimentally determined by Groopman et al. via a NanoSIMS analysis. We find such overabundances to be present in the helium-rich zone. Oxygen-18 is leftover from presupernova helium burning while nitrogen-15 is produced by explosive helium burning. Interestingly, anomalous excesses in molybdenum-95 and molybdenum-97 abundances in …
X-Ray Source Variability Study Of The M31 Central Field Using Chandra Hrc-1, F. Hofmann, W. Pietsch, M. Henze, F. Haberl, R. Sturm, M. Della Valle, Dieter H. Hartmann, D. Hatzidimitriou
X-Ray Source Variability Study Of The M31 Central Field Using Chandra Hrc-1, F. Hofmann, W. Pietsch, M. Henze, F. Haberl, R. Sturm, M. Della Valle, Dieter H. Hartmann, D. Hatzidimitriou
Publications
Context. The central field of the Andromeda galaxy (M 31) has been monitored, using the Chandra HRC-I detector (about 0.1-10 keV energy range) from 2006 to 2012 with the main aim to detect X-rays from optical novae. We present a systematic analysis of all X-ray sources found in the 41 nova monitoring observations, along with 23 M 31 central field HRC-I observations available from the Chandra data archive starting in December 1999. Aims. Based on these observations, we studied the X-ray long-term variability of the source population and especially of X-ray binaries in M 31. Methods. We created a catalogue …
Nature Of The Gas And Dust Around 51 Oph, W F. Thi, F Menard, G Meeus, A Carmona, P Riviere-Marichalar, J C. Augereau, I Kamp, P Woitke, C Pinte, I Mendigutia, C Eiroa, B Montesinos, Sean D. Brittain, W Dent
Nature Of The Gas And Dust Around 51 Oph, W F. Thi, F Menard, G Meeus, A Carmona, P Riviere-Marichalar, J C. Augereau, I Kamp, P Woitke, C Pinte, I Mendigutia, C Eiroa, B Montesinos, Sean D. Brittain, W Dent
Publications
Circumstellar disc evolution is paramount for the understanding of planet formation. The GASPS program aims at determining the circumstellar gas and solid mass around ~250 pre-main-sequence Herbig Ae and TTauri stars. We aim to understand the origin and nature of the circumstellar matter orbiting 51 Oph, a young (Myr) luminous B9.5 star. We obtained continuum and line observations with the PACS instrument on board the Herschel Space Observatory and continuum data at 1.2 mm with the IRAM 30m telescope. The SED and line fluxes were modelled using the physico-chemo radiative transfer code ProDiMo. We detected a strong emission by OI …
Bright Radio Emission From An Ultraluminous Stellar-Mass Microquasar In M31, Matthew J. Middleton, James C. A. Miller-Jones, Sera Markoff, Rob Fender, Martin Henze, Natasha Hurley-Walker, Anna M. M. Scaife, Timorthy P. Roberts, Dominic Walton, John Carpenter, Jean-Pierre Macquart, Geoffrey C. Bower, Mark Gurwell, Wolfgang Pietsch, Frank Haberl, Jonathan Harris, Michael Daniel, Junayd Miah, Chris Done, John Morgan, Hugh Dickinson, Phil Charles, Vadim Burwitz, Massimo Della Valle, Michael Freyberg, Jochen Greiner, Margarita Hernanz, Dieter H. Hartmann, Despina Hatzidimitriou, Arno Riffeser, Gloria Sala, Stella Seitz, Pablo Reig, Arne Rau, Marina Orio, David Titterington, Keith Grainge
Bright Radio Emission From An Ultraluminous Stellar-Mass Microquasar In M31, Matthew J. Middleton, James C. A. Miller-Jones, Sera Markoff, Rob Fender, Martin Henze, Natasha Hurley-Walker, Anna M. M. Scaife, Timorthy P. Roberts, Dominic Walton, John Carpenter, Jean-Pierre Macquart, Geoffrey C. Bower, Mark Gurwell, Wolfgang Pietsch, Frank Haberl, Jonathan Harris, Michael Daniel, Junayd Miah, Chris Done, John Morgan, Hugh Dickinson, Phil Charles, Vadim Burwitz, Massimo Della Valle, Michael Freyberg, Jochen Greiner, Margarita Hernanz, Dieter H. Hartmann, Despina Hatzidimitriou, Arno Riffeser, Gloria Sala, Stella Seitz, Pablo Reig, Arne Rau, Marina Orio, David Titterington, Keith Grainge
Publications
A subset of ultraluminous X-ray sources (those with luminosities < 10^40 erg s^-1)^1 are thought to be powered by the accretion of gas onto black holes with masses of ~5-20 M⊙, probably via an accretion disc. The X-ray and radio emission are coupled in such Galactic sources, with the radio emission originating in a relativistic jet thought to be launched from the innermost regions near the black hole4,5, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium precludes determining the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source whose peak luminosity can exceed 1039 erg s^-1 in the nearby galaxy, M31. The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a stellar mass black hole. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.
Supersoft X-Rays Reveal A Classical Nova In The M31 Globular Cluster Bol 126, M. Henze, W. Pietsch, F. Haberl, M. Della Valle, A. Riffeser, G. Sala, D. Hatzidimitriou, F. Hofmann, Dieter H. Hartmann, J. Koppenhoefer
Supersoft X-Rays Reveal A Classical Nova In The M31 Globular Cluster Bol 126, M. Henze, W. Pietsch, F. Haberl, M. Della Valle, A. Riffeser, G. Sala, D. Hatzidimitriou, F. Hofmann, Dieter H. Hartmann, J. Koppenhoefer
Publications
Context. Classical novae (CNe) represent the main class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. Only three confirmed novae and three SSSs have been discovered in globular clusters (GCs) of any galaxy so far, of which one nova and two SSSs (including the nova) were found in M 31 GCs. Aims. To study the SSS state of CNe we carried out a high-cadence X-ray monitoring of the M 31 central area with XMM-Newton and Chandra. This project is supplemented by regular optical monitoring programmes at various observatories. Methods. We analysed X-ray and …
Multi-Color Observations Of Short Grb Afterglows: 20 Events Observed Between 2007 And 2010, A. Nicuesa Guelbenzu, S. Klose, J. Greiner, D. A. Kann, T. Krühler, A. Rossi, S. Schulze, P. M. J. Afonso, J. Elliott, R Filgas, Dieter H. Hartmann, A Kupcu Yoldas, S Mcbreen, M Nardini, F Olivares E., A Rau, S Schmidl, P Schady, V Sudilovsky, A C. Updike, A Yoldas
Multi-Color Observations Of Short Grb Afterglows: 20 Events Observed Between 2007 And 2010, A. Nicuesa Guelbenzu, S. Klose, J. Greiner, D. A. Kann, T. Krühler, A. Rossi, S. Schulze, P. M. J. Afonso, J. Elliott, R Filgas, Dieter H. Hartmann, A Kupcu Yoldas, S Mcbreen, M Nardini, F Olivares E., A Rau, S Schmidl, P Schady, V Sudilovsky, A C. Updike, A Yoldas
Publications
We report on follow-up observations of 20 short-duration gamma-ray bursts (GRBs; T90 <2 >s) performed in g'r'i'z' JHKs with the Gamma-Ray Burst Optical Near-Infrared Detector (GROND) between mid-2007 and the end of 2010. This is one of the most compre-hensive data sets on GRB afterglow observations of short bursts published so far. In three cases, GROND was on target within less than 10 min after the trigger, leading to the discovery of the afterglow of GRB 081226A and its faint underlying host galaxy. In addition, GROND was able to image the optical afterglow and follow the light curve evolution in five …
Planet Formation In Transition Disks: Modeling, Spectroscopy, And Theory, Joseph Liskowsky
Planet Formation In Transition Disks: Modeling, Spectroscopy, And Theory, Joseph Liskowsky
All Dissertations
An important field of modern astronomy is the study of planets. Literally for millennia, careful observers of the night sky have tracked these 'wanderers', with their peculiar motions initiating avenues of inquiry not able to elucidated by a study of the stars alone: we have discovered that the planets (as well as Earth) orbit the sun and that the stars are so far away, even their relative positions do not seem to shift perceptibly when Earth's position moves hundreds of millions of miles. With the advent of the telescope, and subsequent improvements upon it over the course of centuries, accelerating …
Evaluation Of 26al Method As Star Formation Rate Indicator, Manjeet Singh
Evaluation Of 26al Method As Star Formation Rate Indicator, Manjeet Singh
All Theses
The aim of this work is to evaluate the '26Al method' used to determine the Galactic Star Formation Rate (SFR) and compare it to other alternative methods. 26Al is a radioactive isotope produced mainly in massive star winds and in the ensuing core collapse supernova explosion. The radioactive 26Al decays with a life time of 106 years by emitting γ- ray photons in 1.808 MeV band. The 26Al method involves using the Galactic 26Al radioactive flux as a tracer. This approach based on the γ- ray line measurements does not suffer from extinction and small number statistics.
To evaluate the …
Radiation From Accelerated Particles In Relativistic Jets With Shocks, Shear-Flow, And Reconnection, K.-I. Nishikawa, P. Hardee, Y. Mizuno, I. Dutan, B. Zhang, M. Medvedev, E. J. Chor, K. W. Min, J. Niemiec, Y Mizuno, A Nordlund, J T. Frederiksen, H Sol, M Pohl, Dieter H. Hartmann
Radiation From Accelerated Particles In Relativistic Jets With Shocks, Shear-Flow, And Reconnection, K.-I. Nishikawa, P. Hardee, Y. Mizuno, I. Dutan, B. Zhang, M. Medvedev, E. J. Chor, K. W. Min, J. Niemiec, Y Mizuno, A Nordlund, J T. Frederiksen, H Sol, M Pohl, Dieter H. Hartmann
Publications
We have investigated particle acceleration and shock structure associated with an unmagnetized rel-ativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing jet shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock. We have investigated the generation of magnetic fields associated …
A Deep Search For Host Galaxies Of Grbs With No Detected Optical Afterglow, A. Rossi, S. Klose, P. Ferrero, J. Greiner, L. A. Arnold, E. Gonslaves, Dieter H. Hartmann, A. C. Updike, D. A. Kann, T. Krühler
A Deep Search For Host Galaxies Of Grbs With No Detected Optical Afterglow, A. Rossi, S. Klose, P. Ferrero, J. Greiner, L. A. Arnold, E. Gonslaves, Dieter H. Hartmann, A. C. Updike, D. A. Kann, T. Krühler
Publications
Context. Gamma-ray bursts (GRBs) can provide information about star formation at high redshifts. Even in the absence of a bright optical/near-infrared/radio afterglow, the high detection rate of X-ray afterglows by Swift/XRT and its localization precision of 2–3 arcsec facilitates the identification and the study of GRB host galaxies. Aims. We focus on the search for the host galaxies of 17 bursts with arcsec-sized XRT error circles but no detected long-wavelength afterglow, in spite of their deep and rapid follow-up observations. Three of these events can also be classified as truly dark bursts, i.e., the observed upper limit on the optical …
Star-Disk Interaction In Herbig Ae/Be Stars, Christa Speights
Star-Disk Interaction In Herbig Ae/Be Stars, Christa Speights
All Theses
The question of the mechanism of certain types of stars is important. Classical T Tauri (CTTS) stars accrete magnetospherically, and Herbig Ae/Be stars (higher-mass analogs to CTTS) are thought to also accrete magnetospherically, but the source of a kG magnetic field is unknown, since these stars have radiative interiors. For magnetospheric accretion, an equation has been derived (Hartmann, 2001) which relates the truncation radius, stellar radius, stellar mass, mass accretion rate and magnetic field strength.
Currently the magnetic field of Herbig stars is known to be somewhere between 0.1 kG and 10 kG. One goal of this research is to …
The Power Of Thermonuclear Supernovae After One Year, Ginger Bryngelson
The Power Of Thermonuclear Supernovae After One Year, Ginger Bryngelson
All Dissertations
Type Ia supernovae (SNe Ia), the thermonuclear explosion of a white dwarf, shape our understanding of the expansion of the universe with the use of their uniformity in distance determinations. Powered by radioactivity synthesized in the explosion, they fade slowly over hundreds of days. Sometime after 200 days, the continually expanding ejecta allows γ-rays from 56 Ni and 56 Co decays to escape, and soon any radioactive power contributing to lighting up the SN comes from positrons formed in 19% of 56 Co
decays.
While at first it seemed that positrons escaped through the thinning ejecta, it has become apparent …
The Gas/Dust Ratio Of Circumstellar Disks: Testing Models Of Planetesimal Formation, David Horne, Erika Gibb, Terrence W. Rettig, Sean D. Brittain, David Tilley, Dinshaw Balsara
The Gas/Dust Ratio Of Circumstellar Disks: Testing Models Of Planetesimal Formation, David Horne, Erika Gibb, Terrence W. Rettig, Sean D. Brittain, David Tilley, Dinshaw Balsara
Publications
We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6–5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust columndensity ratio and disk inclination similar to that found by Rettig et al.