Abstract We present numerical results from a parameter study of the standing accretion shock instability (SASI), investigating the impact of general relativity (GR) on the dynamics. Using GR ...hydrodynamics with GR gravity, and nonrelativistic (NR) hydrodynamics with Newtonian gravity, in an idealized model setting, we vary the initial radius of the shock, and by varying its mass and radius in concert, the proto-neutron star compactness. We investigate four compactnesses expected in a post-bounce core-collapse supernova (CCSN). We find that GR leads to a longer SASI oscillation period, with ratios between the GR and NR cases as large as 1.29 for the highest-compactness suite. We also find that GR leads to a slower SASI growth rate, with ratios between the GR and NR cases as low as 0.47 for the highest-compactness suite. We discuss implications of our results for CCSN simulations.
Abstract
We present strong gravitational lensing models for 37 galaxy clusters from the Sloan Digital Sky Survey Giant Arcs Survey. We combine data from multi-band
Hubble Space Telescope
Wide Field ...Camera 3 (WFC3) imaging, with ground-based imaging and spectroscopy from
Magellan
, Gemini, Apache Point Observatory, and the Multiple Mirror Telescope, in order to detect and spectroscopically confirm new multiply imaged lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong-lensing mass models for these galaxy clusters. The clusters span a redshift range of 0.176 <
z
< 0.66 with a median redshift of
z
= 0.45, and sample a wide range of dynamical masses, 1.5 <
M
200
< 35 × 10
14
, as estimated from their velocity dispersions. As these clusters were selected as lenses primarily owing to a fortuitous alignment with background galaxies that results in giant arcs, they exhibit a wide range in Einstein radii, 1.″3 <
θ
E
< 23.″1 for a source at
z
= 2, with a median
θ
E
= 10.″8. The reduced
HST
images and lens model outputs are made available to the scientific community as high-level data products with this publication.
Abstract
This paper describes algorithms for nonrelativistic hydrodynamics in the toolkit for high-order neutrino radiation hydrodynamics (
thornado
), which is being developed for multiphysics ...simulations of core-collapse supernovae (CCSNe) and related problems with Runge–Kutta discontinuous Galerkin (RKDG) methods. More specifically,
thornado
employs a spectral-type nodal collocation approximation, and we have extended limiters—a slope limiter to prevent nonphysical oscillations and a bound-enforcing limiter to prevent nonphysical states—from the standard RKDG framework to be able to accommodate a tabulated nuclear equation of state (EoS). To demonstrate the efficacy of the algorithms with a nuclear EoS, we first present numerical results from basic test problems in idealized settings in one and two spatial dimensions, employing Cartesian, spherical-polar, and cylindrical coordinates. Then, we apply the RKDG method to the problem of adiabatic collapse, shock formation, and shock propagation in spherical symmetry, initiated with a 15
M
⊙
progenitor. We find that the extended limiters improve the fidelity and robustness of the RKDG method in idealized settings. The bound-enforcing limiter improves the robustness of the RKDG method in the adiabatic collapse application, while we find that slope limiting in characteristic fields is vulnerable to structures in the EoS—more specifically, in the phase transition from nuclei and nucleons to bulk nuclear matter. The success of these applications marks an important step toward applying RKDG methods to more realistic CCSN simulations with
thornado
in the future.
Discontinuous Galerkin (DG) methods provide a means to obtain high-order accurate solutions in regions of smooth fluid flow while still resolving strong shocks. These and other properties make DG ...methods attractive for solving problems involving hydrodynamics; e.g., the core-collapse supernova problem. With that in mind we are developing a DG solver for the general relativistic, ideal hydrodynamics equations under a 3+1 decomposition of spacetime, assuming a conformally-flat approximation to general relativity. With the aid of limiters we verify the accuracy and robustness of our code with several difficult test-problems: a special relativistic Kelvin-Helmholtz instability problem, a two-dimensional special relativistic Riemann problem, and a one- and two-dimensional general relativistic standing accretion shock (SAS) problem. We find good agreement with published results, where available. We also establish sufficient resolution for the 1D SAS problem and find encouraging results regarding the standing accretion shock instability (SASI) in 2D.
We present Hubble Space Telescope (HST) imaging and grism spectroscopy of a strongly lensed LIRG at z = 0.816, SGAS 143845.1+145407, and use the magnification boost of gravitational lensing to study ...the distribution of star formation throughout this galaxy. Based on the HST imaging data, we create a lens model for this system; we compute the mass distribution and magnification map of the z = 0.237 foreground lens. We find that the magnification of the lensed galaxy ranges between 2 and 10, with a total magnification (measured over all the images of the source) of = . We find that the total projected mass density within ∼34 kpc of the brightest cluster galaxy is . Using the lens model we create a source reconstruction for SGAS 143845.1+145407, which, paired with a faint detection of H in the grism spectroscopy, allows us to finally comment directly on the distribution of star formation in a z ∼ 1 LIRG. We find widespread star formation across this galaxy, in agreement with the current understanding of these objects. However, we note a deficit of H emission in the nucleus of SGAS 143845.1+145407, likely due to dust extinction.
Abstract
The toolkit for high-order neutrino-radiation hydrodynamics (thornado) is being developed for simulations of core-collapse supernovae (CCSNe) and related problems. Current capabilities in ...thornado include solvers for the Euler equations — in non-relativistic and special relativistic limits — and the two-moment model of neutrino transport. The spatial discretization in thornado is based on the discontinuous Galerkin (DG) method, which is receiving increased attention from the computational astrophysics community. In this paper, we provide an overview of the numerical methods for the Euler equations in thornado, and present some encouraging preliminary numerical results from a set of basic tests in one and two spatial dimensions.
The toolkit for high-order neutrino-radiation hydrodynamics (thornado) is being developed for simulations of core-collapse supernovae (CCSNe) and related problems. Current capabilities in thornado ...include solvers for the Euler equations - in non-relativistic and special relativistic limits - and the two-moment model of neutrino transport. The spatial discretization in thornado is based on the discontinuous Galerkin (DG) method, which is receiving increased attention from the computational astrophysics community. In this paper, we provide an overview of the numerical methods for the Euler equations in thornado, and present some encouraging preliminary numerical results from a set of basic tests in one and two spatial dimensions.
The toolkit for high-order neutrino-radiation hydrodynamics (thornado) is being developed for simulations of core-collapse supernovae (CCSNe) and related problems. Current capabilities in thornado ...include solvers for the Euler equations — in non-relativistic and special relativistic limits — and the two-moment model of neutrino transport. The spatial discretization in thornado is based on the discontinuous Galerkin (DG) method, which is receiving increased attention from the computational astrophysics community. In this paper, we provide an overview of the numerical methods for the Euler equations in thornado, and present some encouraging preliminary numerical results from a set of basic tests in one and two spatial dimensions.
We present strong gravitational lensing models for 37 galaxy clusters from the Sloan Digital Sky Survey Giant Arcs Survey. We combine data from multi-band Hubble Space Telescope Wide Field Camera 3 ...(WFC3) imaging, with ground-based imaging and spectroscopy from Magellan, Gemini, Apache Point Observatory, and the Multiple Mirror Telescope, in order to detect and spectroscopically confirm new multiply imaged lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong-lensing mass models for these galaxy clusters. The clusters span a redshift range of 0.176 < z < 0.66 with a median redshift of z = 0.45, and sample a wide range of dynamical masses, 1.5 < M200 < 35 × 1014 , as estimated from their velocity dispersions. As these clusters were selected as lenses primarily owing to a fortuitous alignment with background galaxies that results in giant arcs, they exhibit a wide range in Einstein radii, 1 3 < θE < 23 1 for a source at z = 2, with a median θE = 10 8. The reduced HST images and lens model outputs are made available to the scientific community as high-level data products with this publication.
Swirl mission concept: Unraveling the enigma Robinson, Mark S.; Thangavelautham, Jekan; Anderson, Brian J. ...
Planetary and space science,
11/2018, Letnik:
162
Journal Article
Recenzirano
During the Apollo era of lunar exploration, mysterious albedo patterns, called swirls, captured the imagination of the scientific community. A key aspect of this interest was due to the discovery ...that the swirls are associated with localized relatively strong remnant magnetic fields. Analysis of returned soil samples revealed that solar wind, galactic cosmic rays, and micrometeorite impacts change the albedo of surface soil grains, a process known as space weathering that reduces regolith reflectance over time. Thus it was natural to invoke local magnetic structures as shields that retard space weathering resulting in relatively less space weathering of the regolith in regions with the strongest localized magnetic fields. However, the origins of the magnetic anomalies and associated swirls remain enigmatic to this day.
We designed the Swirl CubeSat to determine the nature of remnant lunar magnetic fields and investigate their role in moderating space weathering of the regolith and assess their suitability for radiation protection of surface assets. Swirl has one focused observational objective: characterize the magnetic field associated with the Reiner Gamma Swirl (RGS) at sub-kilometer spatial sampling, with 0.5 nTesla accuracy and 100 m spatial precision. In the Swirl mission concept, the Swirl spacecraft, a 6U CubeSat, would deploy as a secondary payload from a vehicle on a deep space trajectory. A series of maneuvers would then place the spacecraft in a low orbit that would then be modified to have a periapse of 5–10 km for thirty orbits passing over RGS. Prime Swirl observations were designed during these low-altitude passes and consist of high-resolution vector magnetic field measurements and monochrome navigation imaging.
•Mysterious lunar albedo patterns, called swirls, long ago captured the imagination of the scientific community.•Swirls are co-located with relatively strong magnetic anomalies.•The origin of both the magnetic anomalies and swirls remain enigmatic.•We describe a cubesat mission that could test competing hypotheses for the origin of the magnetic anomalies and swirls.
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