SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 10 - MAY 19, 2006
89 ASTRONOMY
Includes observations of celestial bodies; astronomical instruments and techniques; radio, gamma-ray, x-ray, ultraviolet, and infrared astronomy; and astrometry.
20060012178 NASA Goddard Space Flight Center, Greenbelt, MD, USA
A Search for X-ray Emission in Isolated Compact Triplets
Brown, Beth A.;Williams, Barbara; [2006]; 1 pp.; In English; 207th Meeting of the American Astronomical Society, 8-12 Jan. 2006, Washington, DC, USA; No Copyright; Avail.: Other Sources; Abstract Only
We describe preliminary results of an exploratory search for diffuse X-ray emission in a sample of the poorest galaxy groups, i.e., isolated compact triplets of galaxies. These systems represent the simplest forms of galaxy clustering while manifesting all the complexities inherent in other groups. We have selected 20 compact triplets for this initial study. The component galaxies are expected to interact with each other and with the group's intergalactic medium, if present, in complex ways that trigger high-energy processes. Author
X Rays; Emission; Compact Galaxies; Intergalactic Media; Galactic Clusters
20060012179 Colorado Univ., CO, USA
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The 3D Structure of Eta Carinae's Nebula: A Definitive Picture from High-Dispersion Near-IR Spectra
Smith, N.; Bulletin of the American Astronomical Society; [2006]; Volume 37, No. 4; 1 pp.; In English; AAS 207th Meeting: Massive Binaries, 8-12 Jan. 2006, Washington, DC, USA; Copyright; Avail.: Other Sources; Abstract Only
High resolution long-slit spectra obtained with the Phoenix spectrograph on Gemini South provide our most accurate probe of the 3D structure of the Homunculus Nebula around Eta Carinae. Emission from molecular hydrogen at 2.122 microns traces a very thin outer skin, which contains the vast majority of the more than 10 solar masses of material in the nebula. This emission, in turn, yields our first definitive picture of the exact shape of the nebula, plus the latitude dependence of the mass-loss rate, speed, kinetic energy, shell thickness, and other properties associated with Eta Car's 19th century explosion. This will be critical for testing any models for the outburst mechanism. A preliminary analysis suggests that explosion from a critically rotating star was the dominant mechanism that gave rise to both the bipolar shape of the nebula and the production of its equatorial disk. [Fe II] emission in the near IR traces a geometrically thicker but less massive shell found on the inner surface of the H2 skin --- this is either a reverse shock that decelerates Eta Car's wind or a warm PDR. [Fe Ill emission also clarifies the structure of an inner 'Little Homunculus' seen previously in HST/STlS spectra. Comparing these two tracers of cool molecular gas and warm partially-ionized gas resolves some significant confusion about the complex structure noted in previous studies. Author
Nebulae; Stellar Mass; Near Infrared Radiation; Ionized Gases; Molecular Gases; Bipolarity; High Resolution
20060012180 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Eta Carinae: Orientation of The Orbital Plane
Gull, T. R.; Nielsen, K. E.; Ivarsson, S.; Corcoran, M. F.; Verner, E.; Hillier, J. D.; Bulletin of the American Astronomical Society; [2006]; Volume 37, No. 4; 2 pp.; In English; AAS 207th Meeting: Massive Binaries, 8-12 Jan. 2006, Washington, DC, USA; Copyright; Avail.: Other Sources; Abstract Only
Evidence continues to build that Eta Carinae is a massive binary system with a hidden hot companion in a highly elliptical orbit. We present imaging and spectroscopic evidence that provide clues to the orientation of the orbital plane.
The circumstellar ejecta, known as the Homunculus and Little Homunculus, are hourglass-shaped structures, one encapsulated within the other, tilted at about 45 degrees from the sky plane. A disk region lies between the bipolar lobes. Based upon their velocities and proper motions,Weigelt blobs B, C and D, very bright emission clumps 0.1 to 0.3' Northwest from Eta Carinae, lie in the disk. UV flux from the hot companion, Eta Car B, photoexcites the Weigelt blobs. Other clumps form a complete chain around the star, but are not significantly photoexcited. The strontium filament, a 'neutral' emission structure, lies in the same general direction as the Weigelt blobs and exhibits peculiar properties indicative that much mid-UV, but no hydrogen-ionizing radiation impinges on this structure. It is shielded by singly-ionized iron. P Cygni absorptions in Fe I I lines, seen directly in line of sight from Eta Carinae, are absent in the stellar light scattered by theWeigelt blobs. Rather than a strong absorption extending to -600 km/s, a low velocity absorption feature extends from -40 to -150 km/s.
No absorbing Fe II exists between Eta Carinae and Weigelt D, but the outer reaches of the wind are intercepted in line of sight from Weigelt D to the observer. This indicates that the UV radiation is constrained by the dominating wind of Eta Car A to a small cavity carved out by the weaker wind of Eta Car B. Since the high excitation nebular lines are seen in the Weigelt blobs at most phases, the cavity, and hence the major axis of the highly elliptical orbit, must lie in the general direction of the Weigelt blobs. The evidence is compelling that the orbital major axis of Eta Carinae is projected at -45 degrees position angle on the sky. Moreover the milliarcsecond-scale extended structure of Eta Carinae, recently detected by VLTI, may be evidence of the binary companion in the disk plane, not necessarily of a single star as a prolate spheroid extending along the ejecta polar axis. Author
Stellar Envelopes; Ejecta; Bipolarity; Stars; Photoexcitation; Ionizing Radiation; Ultraviolet Radiation
20060012181 NASA Goddard Space Flight Center, Greenbelt, MD, USA
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A non-PRE double-peaked burst with oscillations: burning front propagation and stalling
Bhattacharyya, Sudip; Strohmayer, Tod E.; [2006]; 12 pp.; In English; Original contains black and white illustrations; No Copyright; Avail.: CASI: A03, Hardcopy
Non-photospheric-radius-expansion (non-PRE) double-peaked bursts may be explained in terms of spreading (and temporary stalling) of thermonuclear flames from a rotational pole on the neutron star surface, as we argued in a previous study. Here we analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of such a burst from the low mass X-ray binary (LMXB) system 4U 1636-536, and show that our model (with ignition at high latitudes) can qualitatively explain the observed burst profile, and spectral evolution. Moreover, the evolution of the source radius inferred from the data shows a strong signature of temporary stalling of the burning front, which is an essential ingredient of our model. This implies that an understanding of thermonuclear flame spreading on neutron stars can be achieved by a simultaneous study of the evolution of intensity and spectrum of these bursts. We also report the discovery of millisecond period brightness oscillations from this burst, which is the first such observation from a non-PRE double-peaked burst. Our model can explain the corresponding oscillation amplitude during the first (weaker) peak, and the absence of oscillations during the second peak. We discuss how observations of oscillations during non-PRE double-peaked bursts provide an additional t 001 for understanding thermonuclear flame spreading successfully. Author
X Ray Binaries; Neutron Stars; Brightness; X Ray Timing Explorer; Oscillations; Flames; Accretion Disks
20060012183 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Character and Variability of the Eta Carinae Wind Lines
Nielsen, K. E.; Corcoran, M. F.; Gull, T. R.; Ivarsson, S.; Hillier, J. D.; Bulletin of the American Astronomical Society; [2006]; Volume 37, No. 4; 1 pp.; In English; AAS 207th Meeting: Massive BInaries, 8-12 Jan. 2006, Washington, DC, USA; Copyright; Avail.: Other Sources; Abstract Only
The binarity of Eta Carinae has been debated for a long time. We have searched for more evidence for a companion star in a spectroscopic investigation of the Eta Carinae stellar wind lines, using moderate spectral and high angular resolution HST/STIS data. Over Eta Carinae's 5.54 year spectroscopic period many of the observable wind lines in the NUV/Optical spectral region exhibit peculiar line profiles with unusual velocity shifts relative to the system velocity. Some of the lines are exclusively blue-shifted over the entire cycle. Their ionization/excitation imply formation not in the stellar wind but rather in the interface between the two massive stars. We have analyzed velocity and intensity variations over the spectroscopic period and interpreted what the variations tell us about the geometry of the nebular structure close to Eta Carinae. Author
Binary Stars; Companion Stars; Variability; Stellar Winds; Spectral Resolution; Massive Stars; Spectral Bands
20060012260 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Spreading of thermonuclear flames on the neutron star in SAX J1808.4-3658: an observational tool
Bhattacharyya, Sudip; Strohmayer, Tod E.; [2005]; 13 pp.; In English; No Copyright; Avail.: CASI: A03, Hardcopy
We analyse archival Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) data of thermonuclear X-ray bursts from the 2002 outburst of the accreting millisecond pulsar SAX 51808.4-3658. We present evidence of a complex frequency modulation of oscillations during burst rise, and correlations among the time evolution of the oscillation frequency, amplitude, and the inferred burning region area. We discuss these findings in the context of a model, based on thermonuclear flame spreading on the neutron star surface, that can qualitatively explain these features. From our model, we infer that for the 2002 Oct. 15 thermonuclear burst, the ignition likely occurred in the mid-latitudes, the burning region took approx. 0.2 s to nearly encircle the equatorial region of the neutron star, and after that the lower amplitude oscillation originated from the remaining asymmetry of the burning front in the same hemisphere where the burst ignited. We emphasize that studies of the evolution of burst oscillation properties during burst rise can provide a powerful tool to understand thermonuclear flame spreading on neutron star surfaces under extreme physical conditions. Author
Flames; Neutron Stars; Ignition; X Ray Timing Explorer; Frequency Modulation; Oscillations; Combustion; Spreading
20060012287 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Detection of a Hot Binary Companion of eta Carinae
Sonnebom, G.; Iping, R. C.; Gull, T. R.; Massa, D. L.; Hillier, D. J.; Bulletin of the American Astronomical Society; [2006]; Volume 37, No. 4; 1 pp.; In English; AAS 207th Meeting, 8-12 Jan. 2006, Washington, DC, USA; Copyright; Avail.: Other Sources; Abstract Only
A hot companion of eta Carinae has been detected using high resolution spectra (905 - 1180 A) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Observations were obtained at two epochs of the 2024-day orbit: 2003 June during ingress to the 2003.5 X-ray eclipse and 2004 April several months after egress. These data show that essentially all the far-UV flux from eta Car shortward of Lyman alpha disappeared at least two days before the start of the X-ray eclipse (2003 June 29), implying that the hot companion, eta Car B, was also eclipsed by the dense wind or extended atmosphere of eta Car A. Analysis of the far-UV spectrum shows that eta Car B is a luminous hot star. N II 1084-1086 emission disappears at the same time as the far-UV continuum, indicating that this feature originates from eta Car B itself or in close proximity to it. The strong N II emission also raises the possibility that the companion star is nitrogen rich. The observed FUV flux levels and spectral features, combined with the timing of their disappearance, is consistent with eta Carinae being a massive binary system Author
Far UV Spectroscopic Explorer; Binary Stars; Explorer Satellites; Hot Stars; X Rays; Eclipses; Companion Stars
20060012288 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Strings of Eta Carina: The HST/STIS Spectra and [Ca II]
Melendez, M. B.; Gull, T. R.; Bautista, M. A.; Badnell, N. R.; Bulletin of the American Astronomical Society; January 2006; Volume 37, No. 4; 2 pp.; In English; AAS 207th Meeting: Massive Binaries, 8-12 Jan. 2006, Washington, DC, USA; No Copyright; Avail.: Other Sources; Abstract Only
Long linear, filamentary ejecta, are found to move at very high velocity external to the Homunculus, the circumstellar hourglass-shaped ejecta surrounding Eta Carinae. The origin of the strings is a puzzle. As an example, the Weigelt Blobs have N at 10X solar and C, O at 0.01X solar abundance, along with He/H significantly enhanced. This abundance pattern is evidence for extreme CNO-processing. Similarly, the Strontium Filament has Ti/Ni at 100X solar, presumably due to the lack of oxygen to form Ti-oxide precipitates onto dust grains. We have obtained 2-D spectra with the HST/STIS of the Strontium Filament and a portion of a string. These deep spectral exposures, at moderate dispersion, span much of the near red spectral region from 5000 to 9000A. We have identified twelve emission lines in these spectra with proper velocities and spatial structure of this string and obtained line ratios for [Ca II] (7293/7325A) and [Fe Ill (7157/8619A) which are useful for determining physical conditions in this nebulosity. In an attempt to use the [Ca II] ratio to determine the physical parameters, and ultimately the abundances in the strings, we have constructed a statistical equilibrium model for Ca II , including radiative and collisional rates. These results incorporate our newly calculated atomic data for levels n = 3,4,5 and 6 configurations of Ca II. The aim is to compute the [Ca II] line ratios and use them as a diagnostic of the physical parameters. Using the [FeII] ratio we find that for Te=10,000 K, the electron density is Ne approx.10(exp 6)/cu cm. We plan to use the [Ca II] ratio to confirm this result. Then, we will extend the use of this multilevel model Ca II atom to study the physical conditions of the Strontium filament where eight lines of Ca II, both allowed and forbidden, had been identified. With the physical conditions determined, we will be able to derive reliable estimates for the gas phase abundances in the strings. Author
Stellar Envelopes; Spectral Bands; Strings; Abundance; Electron Density (Concentration); Strontium; Vapor Phases; Ejecta
20060012289 NASA Goddard Space Flight Center, Greenbelt, MD, USA
NUV Spectroscopic Studies of Eta Car's Weigelt D across the 2003.5 Minimum
Ivarsson, S.; Nielsen, K. E.; Gull, T. R.; Hillier, J. D.; Bulletin of the American Astronomical Society; [2006]; Volume 37, No. 4; 1 pp.; In English; AAS 207th Meeting, 8-12 Jan. 2006, Washington, DC, USA; Copyright; Avail.: Other Sources; Abstract Only
HST/STIS high dispersion, high spatial resolution spectra in the near UV (2424-2705A) were recorded of Weigelt D, located 0.25' from Eta Carinae, before, during and after the star's 2003.5 minimum. Most nebular emission, including Lyman-alpha pumped Fe II and [Fe III] lines show phase dependent variations with disappearance at the minimum and reappearance a few months later. Circumstellar absorptions increase at minimum, especially in the Fe II resonance lines originating not only from ground levels but also meta stable levels well above the ground levels. These ionization/excitation effects can be explained by a sudden change in UV flux reaching the blobs, likely due to a line-of-sight obscuration of the hotter companion star, Eta Car B, recently discovered by Iping et al. (poster, this meeting). The scattered starlight seen towards Weigelt D display noticeable different line profiles than the direct starlight from Eta Carinae. P-Cygni absorption profiles in Fe II stellar lines observed directly towards Eta Carinae, show terminal velocities up to -550 km/s. However, scattered starlight of Weigelt D display significant lower velocities ranging from -40 to -150 km/s.We interpret this result to be indicative that no absorbing Fe II wind structure exists between the Central source and Weigelt D. The lower velocity absorption appears to be connected to the outer Fe II wind structure of Eta Car A extending beyond Weigelt D intersecting the observer's line of sight. This result is consistent with the highly extended wind of Eta Car A. Author
Stellar Envelopes; Lyman Alpha Radiation; Companion Stars; Line of Sight; Occultation; Resonance Lines; High Resolution
20060012314 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Constellation-X Reflection Grating Spectrometer
Allen, Jean C.; [2006]; 1 pp.; In English; MSSL Workshop on High Resolution X-Ray Spectroscopy, 25-29 Mar. 2006, Dorking, Surrey, UK; No Copyright; Avail.: Other Sources; Abstract Only
The Reflection Grating Spectrometer on the Constellation-X mission will provide high sensitivity, high-resolution spectra in the soft x-ray band. The RGS performance requirements are specified as a resolving power of greater than 300 and an effective area of greater than 1000 sq cm across most of the 0.25 to 2.0 keV band. These requirements are driven by the science goals of the mission. We will describe the performance requirements and goals, the reference design of the spectrometer, and examples of science cases where we expect data from the RGS to significantly advance our current understanding of the universe. Author
Constellation-X; Spectrometers; X Ray Astronomy; High Resolution
20060012348 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Fundamental Properties of O-Type Stars
Heap, Sara R.; Lanz, Thierry; Hubeny, Ivan; The Astrophysical Journal; [2006]; Volume 638; 25 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): NAS5-26555; NAG5-10895; NAG5-13187; GO-7437; AR-7985; NRA-01-01; ADP-099; Copyright; Avail.: Other Sources
We present a comprehensive analysis of high-resolution, far-ultraviolet HST STIS, FUSE, and optical spectra of 18 O stars in the Small Magellanic Cloud. Our analysis is based on the OSTAR2002 grid of NLTE metal-line-blanketed model atmospheres calculated with our code TLUSTY. We systematically explore and present the sensitivity of various UV and optical lines to different stellar parameters. We have obtained consistent fits of the UV and the optical spectrum to derive the effective temperature, surface gravity, surface composition, and microturbulent velocity of each star. Stellar radii, masses, and luminosities follow directly. For stars of the same spectral subtype, we find a general good agreement between effective temperature determinations obtained with TLUSTY, CMFGEN, and FASTWIND models, which are all lower than the standard T(sub eff) calibration of O stars. We propose a new calibration between the spectral type and effective temperature based on our results from UV metal lines, as well as optical hydrogen and helium lines. The lower effective temperatures translate into ionizing luminosities that are smaller by a factor of 3 compared to luminosities inferred from previous standard calibrations. The chemical composition analysis reveals that the surface of about 80% of the program stars is moderately to strongly enriched in nitrogen, while showing the original helium, carbon, and oxygen abundances. Our results support the new stellar evolution models that predict that the surface of fast rotating stars becomes nitrogen-rich during the main-sequence phase because of rotationally induced mixing. Enrichment factors are, however, larger than predicted by stellar evolution models. Most stars exhibit the 'mass discrepancy' problem, which we interpret as a result of fast rotation that lowers the measured effective gravity. Nitrogen enrichment and low spectroscopic masses are therefore two manifestations of fast rotation. Our study thus emphasizes the importance of rotation in our understanding of the properties of massive stars and provides a framework for investigating populations of low-metallicity massive stars at low and high redshifts. Author
O Stars; Magellanic Clouds; Stellar Evolution; Stellar Mass; Red Shift; Massive Stars; Main Sequence Stars; Gravitation; Luminosity
20060013020 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Status of the PAPPA experiment
Kogut, Alan; [2006]; 1 pp.; In English; Fundamental Physics with Cosmic Microwave Background Radiation 2nd Irvine Cosmology, 22-26 Mar. 2006, Irvine, CA, USA; No Copyright; Avail.: Other Sources; Abstract Only
The Primordial Anisotropy Polarization Pathfinder Array (PAPPA) is a balloonborne instrument to measure the polarization of the cosmic microwave background and search for the signature of primordial gravity waves. PAPPA uses a novel marriage of RF phase modulation and millimeter-wave bolometric detectors to produce a 'polarimeter-on-a-chip' capable of simultaneously measuring the Stokes I, Q, and U parameters on the sky. I will discuss the current status and future plans for PAPPA. Author
Anisotropy; Polarization; Gravity Waves; Protogalaxies; Cosmology
20060013022 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Taking the Measure of the Universe: Cosmology from the WMAP Mission
Hinshaw, Gary F.; [2006]; 1 pp.; In English; Invited talk on WMAP the Fundamental Physics with Cosmic Microwave Background Radiation 2nd Irvine Cosmology Conference, 23-25 Mar. 2006, Irvine, CA, USA; No Copyright; Avail.: Other Sources; Abstract Only
The data from the first three years of operation of the Wilkinson Microwave Anisotropy Probe (WMAP) satellite provide detailed full-sky maps of the cosmic microwave background temperature anisotropy and new full-sky maps of the polarization. Together, the data provide a wealth of cosmological information, including the age of the universe, the epoch when the first stars formed, and the overall composition of baryonic matter, dark matter, and dark energy. The results also provide constraints on the period of inflationary expansion in the very first moments of time. These and other aspects of the mission will be discussed. WMAP, part of NASA's Explorers program, was launched on June 30,2001. The WMAP satellite was produced in a partnership between the Goddard Space Flight Center and Princeton University. The WMAP team also includes researchers at the Johns Hopkins University; the Canadian Institute of Theoretical Astrophysics; University of Texas; Cornel1 University; University of Chicago; Brown University; University of British Columbia; University of Pennsylvania; and University of California, Los Angeles Author
Microwave Anisotropy Probe; Space Missions; NASA Space Programs; Cosmology; Universe
20060013024 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Confirmation of the E(sup src)(sub Peak)-E(sub iso) (Amati) relation from the x-ray flash XRF 050416A observed by the Swift burst alert telescope
Sakamoti, T.; Barbier, L.; Barthelmy, S. D.; Cummings, J. R.; Fenimore, E. E.; Gehrels, N.; Hullinger, D.; Krimm, H. A.; Markwardt, C. B., et al.; The Astrophysical Journal; January 10, 2006; Volume 36; 4 pp.; In English; Original contains black and white illustrations; Copyright; Avail.: Other Sources
We report Swift Burst Alert Telescope (BAT) observations of the X-ray flash (XRF) XRF 050416A. The fluence ratio between the 15-25 and 25-50 keV energy bands of this event is 1.5, thus making it the softest gamma-ray burst (GRB) observed by BAT so far. The spectrum is well fitted by a Band function with E(sup obs)(sub peak) of 15.0(sup +2.3)(sub -2.7) keV. Assuming the redshift of the host galaxy (z = 0.6535), the isotropic equivalent radiated energy E(sub iso) and the peak energy at the GRB rest frame (E(sup src)(sub peak)) of XRF 050416A are not only consistent with the correlation found by Amati et al. and extended to XRFs by Sakamoto et al. but also fill in the gap of this relation around the 30-80 keV range of E(sup src)(sub peak). This result tightens the validity of the E(sup src)(sub Peak)-E(sup src)(sub peak) relation from XRFs to GRBs. We also find that the jet break time estimated using the empirical relation between E(sup src)(sub peak) and the collimation corrected energy E(sub gamma), is inconsistent with the afterglow observation by the Swift X-Ray Telescope. This could be due to the extra external shock emission overlaid around the jet break time or to the nonexistence of a jet break feature for XRFs, which might be a further challenge for GRB jet emission models and XRF/GRB unification scenarios. Author
Swift Observatory; X Ray Telescopes; Gamma Ray Bursts; Galaxies
20060013031 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Dark Energy, Dark Matter and Science with Constellation-X
Cardiff, Ann Hornschemeier; [2005]; 1 pp.; In English; George Mason University Conference, 7 Dec. 2005,Washington, DC, USA; No Copyright; Avail.: Other Sources; Abstract Only
Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the dark energy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as 'cosmic feedback' whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of Dark Energy. Author
Black Holes (Astronomy); Constellation-X; Dark Energy; Dark Matter
20060013066 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Supercritical Pile Model for GRBs
Kazanas, Demos; [2006]; 1 pp.; In English; University of Crete, Dept. of Physics Conference, 4-7 Apr. 2006, Crete, Greece; No Copyright; Avail.: Other Sources; Abstract Only
We present the spectral and temporal radiative signatures expected within the Supercritical Pile model of Gamma Ray Bursts (GRB). This model is motivated by the need for a process that provides the dissipation necessary in GRB and presents a well defined scheme for converting the energy stored in the relativistic protons of the Relativistic Blast Waves (RBW) associated with GRB into radiation; at the same time it leads to spectra which exhibit a peak in the burst nuF(sub nu) distribution at an energy E(sub p) approximately equal to 1 MeV in the observer s frame, in agreement with observation and largely independent of the Lorentz factor GAMMA of the associated relativistic outflow. Furthermore, this scheme does not require (but does not preclude) acceleration of particles at the shock other than that provided by the isotropization of the flow bulk kinetic energy on the RBW frame. In the present paper we model in detail the evolution of protons, electrons and photons from a RBW to produce detailed spectra of the prompt GRB phase as a function of time from across a very broad range spanning roughly 4 log10 GAMMA decades in frequency. The model spectra are in general agreement with observations and provide a means for the delineating of the model parameters through direct comparison with trends observed in GRB properties. Author
Gamma Ray Bursts; Models; Piles; Spectra
20060013067 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Gamma Ray Burst Discoveries by the Swift Mission
Gehrels, Neil; [2006]; 1 pp.; In English; No Copyright; Avail.: Other Sources; Abstract Only
Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. The NASA Swift mission is an innovative new multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Swift is now in orbit after a beautiful launch on November 20, 2004. A new-technology wide-field gamma-ray camera detects more than a hundred bursts per year. Sensitive narrow-field X-ray and UV/optical telescopes, built in collaboration with UK and Italian partners, are pointed at the burst location in 20 to 70 sec by an autonomously controlled 'swift' spacecraft. For each burst, arcsec positions are determined and optical/UV/X-ray/gamma-ray spectrophotometry performed. Information is also rapidly sent to the ground to a team of more than 50 observers at telescopes around the world. The first year of findings from the mission will be presented. The long-standing mystery of short GRBs has been solved, and the answer is the most interesting possible scenario. High redshift bursts have been detected leading to a better understanding of star formation rates and distant galaxy environments. GRBs have been found with giant X-ray flares occurring in their afterglow. These, and other topics, will be discussed. Author
Gamma Ray Bursts; Cosmology; Swift Observatory; NASA Space Programs
20060013068 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Modeling Gravitational Radiation Waveforms from Black Hole Mergers
Baker, J. G.; Centrelia, J. M.; Choi, D.; Koppitz, M.; VanMeter, J.; [2006]; 1 pp.; In English; American Astronomical Society Meeting, 8-12 Jan. 2006, Washington, DC, USA; No Copyright; Avail.: Other Sources; Abstract Only
Gravitational radiation from merging binary black hole systems is anticipated as a key source for gravitational wave observations. Ground-based instruments, such as the Laser Interferometer Gravitational-wave Observatory (LIGO) may observe mergers of stellar-scale black holes, while the space-based Laser Interferometer Space Antenna (LISA) observatory will be sensitive to mergers of massive galactic-center black holes over a broad range of mass scales. These cataclysmic events may emit an enormous amount of energy in a brief time. Gravitational waves from comparable mass mergers carry away a few percent of the system's mass-energy in just a few wave cycles, with peak gravitational wave luminosities on the order of 10^23 L_Sun. Optimal analysis and interpretation of merger observation data will depend on developing a detailed understanding, based on general relativistic modeling, of the radiation waveforms. We discuss recent progress in modeling radiation from equal mass mergers using numerical simulations of Einstein's gravitational field equations, known as numerical relativity. Our simulations utilize Adaptive Mesh Refinement (AMR) to allow high-resolution near the black holes while simultaneously keeping the outer boundary of the computational domain far from the black holes, and making it possible to read out gravitational radiation waveforms in the weak-field wave zone. We discuss the results from simulations beginning with the black holes orbiting near the system's innermost stable orbit, comparing the recent simulations with earlier 'Lazarus' waveform estimates based on an approximate hybrid numerical/perturbative technique. Author
Black Holes (Astronomy); Gravitational Waves; Waveforms; Models
20060013069 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Constellation-X Mission: The next giant step in X-ray Astronomy
White, Nicholas E.; [2006]; 1 pp.; In English; Mullard Space Science Lab., High Resolution X-ray Spectroscopy: towards XEUS and Con-X, 27-28 Mar. 2006, Dorking, UK; No Copyright; Avail.: Other Sources; Abstract Only
Constellation-X is the x-ray astronomy equivalent of large ground-based optical telescopes such as the Keck and the VLT, complementing the high spatial resolution capabilities of Chandra. By increasing the telescope aperture and utilizing efficient spectrometers the mission will achieve a factor of 100 increased sensitivity. with its increased capabilities, Constellation-X will address many fundamental astrophysics questions such as observing the formation and evolution of clusters of galaxies, constraining the Baryon content of the Universe, observing the effects of strong gravity close to the event horizon of black holes in AGN and using these effects to determine the black hole rotation. The Constellation-X mission has been under study for eight years and in the Presidents FY04 budget has been given approval to proceed with a launches in 2013 and 2014. In this talk I will review the science goals of the mission, and the implementation approach. Author
Astrophysics; Constellation-X; Telescopes; X Ray Astronomy; Space Missions
20060013073 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The James Webb Space Telescope
Greenhouse, Matthew; [2006]; 1 pp.; In English; Society of Photo Optical Engineering Meeting, 24-26 May 2006, Orlando, FL, USA; No Copyright; Avail.: Other Sources; Abstract Only
The Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is described from a systems perspective with emphasis on unique and advanced technology aspects. The ISIM is one of three elements that comprise the JWST space vehicle and is the science instrument payload of the JWST. The major subsystems of this flight element are described including: structure, thermal, command and data handling, and software. Author
James Webb Space Telescope; Aerospace Vehicles; Instrument Packages; Systems Integration
20060013074 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Stellar Wind from the Central Star of NGC 7009
Sonneborn, George; Iping, Rosina; Chu, You-Hua; Gruendl, Robert; [2006]; 1 pp.; In English; International Astronomical Union Symposium 234, 1-12 Apr. 2006, Kona, HI, USA; Copyright; Avail.: Other Sources; Abstract Only
Observations of NGC 7009, including its central star HD 200516, have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, providing spectra covering 905-1187 A with spectral resolution of 15 km/sec. One observation was made with the 30x30 arcsec aperture and includes the star plus the entire nebula. A second observation used the 1.25x20arcsec slit significantly reducing the nebular 'contamination' of the stellar spectrum. This poster discusses the spectrum of the central star. A strong FUV continuum, as expected for Teff=82,000K, dominates the spectrum. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. This paper presents models of the stellar spectrum and the wind features to further refine the stellar parameters and mass loss rate. Author
Stellar Winds; Stellar Models; Stellar Spectra
20060013075 NASA Goddard Space Flight Center, Greenbelt, MD, USA, NASA Goddard Space Flight Center, Greenbelt,MD, USA
Binary black hole merger dynamics and waveforms
Baker, John G.; Centrella, Joan; Choi, Dae-II; Koppitz, Michael; vanMeter, James; February 7, 2006; 11 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): ATP02-0043-0056; 05-BEFS-05-0044 Report No.(s): arXiv:gr-qc/0602026-v1; No Copyright; Avail.: CASI: A03, Hardcopy
We apply recently developed techniques for simulations of moving black holes to study dynamics and radiation generation in the last few orbits and merger of a binary black hole system. Our analysis produces a consistent picture from the gravitational wave forms and dynamical black hole trajectories for a set of simulations with black holes beginning on circular-orbit trajectories at a variety of initial separations. We find profound agreement at the level of 1% among the simulations for the last orbit, merger and ringdown, resulting in a final black hole with spin parameter a/m = 0.69. Consequently, we are confident that this part of our waveform result accurately represents the predictions from Einstein's General Relativity for the final burst of gravitational radiation resulting from the merger of an astrophysical system of equal-mass non-spinning black holes. We also find good agreement at a level of roughly 10% for the radiation generated in the preceding few orbits. Author
Black Holes (Astronomy); Waveforms; Binary Stars; Astrophysics; Gravitational Waves; Simulation
20060013122 Universities Space Research Association, Greenbelt, MD, USA
The Asymmetrical Wind of the Candidate Luminous Blue Variable MWC 314
Wisniewski, John P.; Babler, Brian L.; Bjorkman, Karen S.; Kurchakov, Anatoly V.; Meade,Marilyn R.; Miroshnichenko, Anatoly S.; January 2006; 19 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): NCC5-637; NAG5-8054; NGT5-50469; NAS5-26777; Copyright; Avail.: CASI: A03, Hardcopy
We present the results of long-term spectropolarimetric and spectroscopic monitoring of MWC 314, a candidate Luminous Blue Variable star.We detect the first evidence of H alpha variability in MWC 314, and find no apparent periodicity in this emission. The total R-band polarization is observed to vary between 2.21% and 3.00% at a position angle consistently around approximately 0 degrees, indicating the presence of a time-variable intrinsic polarization component, hence an asymmetrical circumstellar envelope. We find suggestive evidence that MWC 314's intrinsic polarization exhibits a wavelength-independent magnitude varying between 0.09% and 0.58% at a wavelength-independent position angle covering all four quadrants of the Stokes Q-U plane. Electron scattering off of density clumps in MWC 314's wind is considered as the probable mechanism responsible for these variations. Author
Asymmetry; Spectroscopy; Variable Stars; Polarimetry; Stellar Winds; Blue Stars
20060013146 NASA Goddard Space Flight Center, Greenbelt, MD, USA
A Journey in Space-Time
Kazanas, Demos; [2006]; 1 pp.; In English; 11th Panhellenic Congress of EEF, 28-29 Mar. 2006, Larisa, Greece; No Copyright; Avail.: Other Sources; Abstract Only
The Universe was born about 10 billion years ago in an explosion we now call the Big Bang, which continues until today. While Cosmology was born only after the formulation of General Relativity by Einstein, it is quite amazing that the same equations can be derived from purely Newtonian Physics. I will present such a formulation of the evolution of the Universe and will also present a summary of the developments in Cosmology the past 20 or so years. These have been driven mainly by the development of new techniques and missions to probe the Universe in it's largest scales. At the same time, observations at smaller scales have also given us a picture of the evolution of the structure (galaxies, stars) that are necessary for the development of life. I will close with some speculation on the recently discovered acceleration of the Universe and its implications for it's far future. Author
Universe; Big Bang Cosmology; Galactic Evolution; Space-Time Functions
20060013148 Universities Space Research Association, Greenbelt, MD, USA
Gravitational Rocket from the Merging Massive Black Hole Binaries
Choi, Dale; [2006]; 1 pp.; In English; American Astronomical Society, 8-12 Jan. 2006, Washington, DC, USA Contract(s)/Grant(s): ATP-02-0043-0056; No Copyright; Avail.: Other Sources; Abstract Only
Coalescing massive black hole binaries are expected to be among the most fascinating gravitational wave sources, observable by the NASA/ESA LISA detector. Not only will the merger events reveal the rich phenomenology of extremely strong and dynamical gravity deep inside the potential wells at the centers of galaxies (thus providing an excellent testing ground for general relativity), it will also make important contributions to the astrophysics of massive black hole evolutions. Typical black hole mergers involve asymmetric radiation of gravitational waves and lose linear momentum as well as energy and angular momentum. As a result, the merger remnant receives a kick from the GW emission: a gravitational rocket effect. High kick velocities (higher than the escape velocities of the host structure) would have a strong impact on our understanding of how massive black holes have evolved over time and, in particular, on the estimates of the merger rate for LISA. The main difficulties in calculations of the kick velocities has been in the last moments of the merger where the full theory of general relativity must be employed to accurately model the black hole dynamics. I describe a recent calculation of the kick velocities from numerical relativity simulations of the merging black hole binaries. Author
Black Holes (Astronomy); Gravitational Waves; Massive Stars; Binary Stars
Source: NASA
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