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  • 1
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    Periodic Eclipse Variations in Asynchronous Polar V1432 Aql: Evidence of a Shifting Threading Region (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We report the results of a 28-month photometric campaign studying V1432 Aql, the only known eclipsing, asynchronous polar. Our data show that both the residual eclipse flux and eclipse OC timings vary strongly as a function of the spin-orbit beat period. Relying upon a new model of the system, we show that cyclical changes in the location of the threading region along the ballistic trajectory of the accretion stream could produce both effects. This model predicts that the threading radius is variable, in contrast to previous studies which have assumed a constant threading radius. Additionally, we identify a very strong photometric maximum which is only visible for half of the beat cycle. The exact cause of this maximum is unclear, but we consider the possibility that it is the optical counterpart of the third accreting polecap proposed by Rana et al. Finally, the rate of change of the white dwarf's spin period is consistent with it being proportional to the difference between the spin and orbital periods, implying that the spin period is approaching the orbital period asymptotically.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN35009 , Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711) (e-ISSN 1365-2966); 449; 3; 3107-3120
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  • 2
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    The Extreme Spin of the Black Hole in Cygnus X-1 (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observatIOns. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these.results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum.spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-I contains a near-extreme Kerr black hole with a spin parameter a* 〉 0.95 (3(sigma)). For a less probable (synchronous) dynamIcal model, we find a* 〉 0.92 (3(sigma)). In our analysis, we include the uncertainties in black hole mass orbital inclination angle and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk's low luminosity.
    Keywords: Astrophysics
    Type: GSFC.JA.5551.2011
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  • 3
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    Habex 4-Meter Off-Axis Primary Mirror Study (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Astrophysics
    Type: MSFC-E-DAA-TN45461 , SPIE Optics + Photonics; Aug 06, 2017 - Aug 10, 2017; San Diego, CA; United States
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  • 4
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    Following the Water: the Evolution of Ice-forming Regions in the Early Solar Nebula (2006)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The abundances of water-vapor and water-ice during the first ten million years of the protoplanetary solar nebula are simulated using a new condensation/sublimation model. This study builds on a "snow line" model reported in ApJ 627 L153 (2005); it uses a simple phenomenological model where water vapor molecules evolve from solar atomic abundance and eventually condenses to ice at colder points in the nebula once the water-vapor partial pressure exceeds a value determined by the phase diagram for water. The synthesis of water vapor from elementary species is modeled with a chemical network consisting of about 400 species and 4000 reactions. The evolution of the icy zone (and its relative abundance of solid ice) is traced from a limited region in the early hotter disk to its final state at the time when the gas is expelled and a planetary system begins to form. Possible effects of this dynamic motion on disk chemistry and organic molecule formation are also described.
    Keywords: Astrophysics
    Type: 4th Astrobiology Science Conference; Mar 26, 2006 - Mar 30, 2006; Washington, DC; United States
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  • 5
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    The Minimum-Mass Surface Density of the Solar Nebula using the Disk Evolution Equation (2005)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The Hayashi minimum-mass power law representation of the pre-solar nebula (Hayashi 1981, Prog. Theo. Phys.70,35) is revisited using analytic solutions of the disk evolution equation. A new cumulative-planetary-mass-model (an integrated form of the surface density) is shown to predict a smoother surface density compared with methods based on direct estimates of surface density from planetary data. First, a best-fit transcendental function is applied directly to the cumulative planetary mass data with the surface density obtained by direct differentiation. Next a solution to the time-dependent disk evolution equation is parametrically adapted to the planetary data. The latter model indicates a decay rate of r -1/2 in the inner disk followed by a rapid decay which results in a sharper outer boundary than predicted by the minimum mass model. The model is shown to be a good approximation to the finite-size early Solar Nebula and by extension to extra solar protoplanetary disks.
    Keywords: Astrophysics
    Type: 2005 DPS Meeting; Sep 02, 2005 - Sep 09, 2005; Cambridge; United Kingdom
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  • 6
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    Deterministic Polishing of Replicating Grazing-Incidence Mandrels (2019)
    In:  CASI
    Details
    Publication Date: 2019-10-12
    Description: In an effort to manufacture high-angular-resolution, grazing-incidence, x-ray optics, Marshall Space Flight Center (MSFC) is taking measures to improve its electroformed replicated optics. A key development is the use of computer-numerical control (CNC) polishing to deterministically improve the surface of electroless nickel mandrels used to replicate grazing- incidence optics. Metrology, control software and polishing parameters must function together seamlessly to reach the specifications required to replicate sub-arcsecond optics. Each change in polishing parameters effects the wear pattern of the polishing head. Using Richardson-Lucy deconvolution, the controller software fits the wear pattern to metrology data to calculate the changing feedrates across the mandrel. Here we present an overview of our process, and early results showing the effectiveness of deterministic polishing for replicated optics.
    Keywords: Astrophysics
    Type: MSFC-E-DAA-TN73695 , SPIE Optics & Photonics; Aug 13, 2019 - Aug 15, 2019; San Diego, CA; United States
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  • 7
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    XMM Observations of Low Mass Groups (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: The contents of this report contains discussion of the two-dimensional XMM-Newton group survey. The analysis of the NGC 2300 and Pavo observations indicated by the azimuthally averaged analysis that the temperature structure is minimal to the NGC2300 system; however, the Pavo system shows signs of a merger in progress. XMM data is used to generate two dimensional maps of the temperature and abundance used to generate maps of pressure and entropy.
    Keywords: Astrophysics
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  • 8
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    Observations of the Li, Be, and B Isotopes and Constraints on Cosmic-ray Propagation (2007)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: The abundance of Li, Be, and B isotopes in galactic cosmic rays (GCR) between E=50-200 MeV/nucleon has been observed by the Cosmic Ray Isotope Spectrometer (CRIS) on NASA's ACE mission since 1997 with high statistical accuracy. Precise observations of Li, Be, B can be used to constrain GCR propagation models. We find that a diffusive reacceleration model with parameters that best match CRIS results (e.g. B/C, Li/C, etc) are also consistent with other GCR observations. A approx. 15-20% overproduction of Li and Be in the model predictions is attributed to uncertainties in the production cross-section data. The latter becomes a significant limitation to the study of rare GCR species that are generated predominantly via spallation.
    Keywords: Astrophysics
    Type: To appear in Journal of Advances in Space Research
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  • 9
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    Deterministic Polishing of Replicating Grazing-Incidence Mandrels (2019)
    In:  CASI
    Details
    Publication Date: 2019-10-16
    Description: No abstract available
    Keywords: Astrophysics
    Type: MSFC-E-DAA-TN73696 , SPIE Optics & Photonics; Aug 13, 2019 - Aug 15, 2019; San Diego, CA; United States
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  • 10
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    X-Ray Polarimetry with the Polarization Spectroscopic Telescope Array (PolSTAR) (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA's 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3-50 keV (requirement; goal: 2.5-70 keV) X-rays probing the behavior of matter, radiation and the very fabric of spacetime under the extreme conditions close to the event horizons of black holes, as well as in and around magnetars and neutron stars. The PolSTAR design is based on the technology developed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission launched in June 2012. In particular, it uses the same X-ray optics, extendable telescope boom, optical bench, and CdZnTe detectors as NuSTAR. The mission has the sensitivity to measure approx. 1% linear polarization fractions for X-ray sources with fluxes down to approx. 5 mCrab. This paper describes the PolSTAR design as well as the science drivers and the potential science return.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN54093 , Astroparticle Physics (ISSN 0927-6505); 75; 8-28
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