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NASA NTRS1994

On massive carbide precipitation during high temperature low cycle fatigue in alloy 800H

The effect of strain rate on massive precipitation and the mechanism for the occurrence of massive precipitation of M23C6 in alloy 800H is investigated during elevated temperature low cycle fatigue testing. It was observed that large M23C6 platelets were in the vicinity of grain and incoherent twin boundaries. The strain controlled fatigue testing at higher strain rates that promoted cyclic hardening enabled massive precipitation to occur more easily.

CARBON SUPERSATURATION↗
NASA NTRS2014

The Rise and Fall of the Type Ib Supernova iPTF13bvn Not a Massive Wolf-Rayet Star

Context. We investigate iPTF13bvn, a core-collapse (CC) supernova (SN) in the nearby spiral galaxy NGC 5806. This object was discovered by the intermediate Palomar Transient Factory (iPTF) very close to the estimated explosion date and was classified as a stripped-envelope CC SN, likely of Type Ib. Furthermore, a possible progenitor detection in pre-explosion Hubble Space Telescope (HST) images was reported, making this the only SN Ib with such an identification. Based on the luminosity and color of the progenitor candidate, as well as on early-time spectra and photometry of the SN, it was argued that the progenitor candidate is consistent with a single, massive Wolf-Rayet (WR) star. Aims. We aim to confirm the progenitor detection, to robustly classify the SN using additional spectroscopy, and to investigate if our follow-up photometric and spectroscopic data on iPTF13bvn are consistent with a single-star WR progenitor scenario. Methods. We present a large set of observational data, consisting of multi-band light curves (UBVRI, g′r′i′z′) and optical spectra. We perform standard spectral line analysis to track the evolution of the SN ejecta. We also construct a bolometric light curve and perform hydrodynamical calculations to model this light curve to constrain the synthesized radioactive nickel mass and the total ejecta mass of the SN. Late-time photometry is analyzed to constrain the amount of oxygen. Furthermore, image registration of pre- and post-explosion HST images is performed. Results. Our HST astrometry confirms the location of the progenitor candidate of iPTF13bvn, and follow-up spectra securely classify this as a SN Ib. We use our hydrodynamical model to fit the observed bolometric light curve, estimating the total ejecta mass to be 1.9 solar mass and the radioactive nickel mass to be 0.05 solar mass. The model fit requires the nickel synthesized in the explosion to be highly mixed out in the ejecta. We also find that the late-time nebular r′-band luminosity is not consistent with predictions based on the expected oxygen nucleosynthesis in very massive stars. Conclusions. We find that our bolometric light curve of iPTF13bvn is not consistent with the previously proposed single massive WR-star progenitor scenario. The total ejecta mass and, in particular, the late-time oxygen emission are both significantly lower than what would be expected from a single WR progenitor with a main-sequence mass of at least 30 solar mass.

massive↗
NASA NTRS2013

A Panchromatic View of the Restless SN 2009ip Reveals the Explosive Ejection of a Massive Star Envelope

The double explosion of SN 2009ip in 2012 raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the Very Large Array, Swift, Fermi, Hubble Space Telescope, and XMM) constrain SN 2009ip to be a low energy (E (is) approximately 10(exp 50) erg for an ejecta mass approximately 0.5 solar mass) and asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at approximately 5 × 10( exp 14) cm with M approximately 0.1 solar mass, ejected by the precursor outburst approximately 40 days before the major explosion. We interpret the NIR excess of emission as signature of material located further out, the origin of which has to be connected with documented mass-loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic-ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, which later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the massive luminous progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass loss, the physical origin of which has yet to be identified.

view↗
NASA NTRS2013

A Panchromatic View of the Restless SN 2009ip Reveals the Explosive Ejection of a Massive Star Envelope

The double explosion of SN 2009ip in 2012 raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the Very Large Array, Swift, Fermi, Hubble Space Telescope, and XMM) constrain SN 2009ip to be a low energy (E approximating 10(exp 50) ergs for an ejecta mass approximating 0.5 M solar mass) and asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at approximately 5 times 10 (exp 14) cm with M approximating 0.1 solar mass, ejected by the precursor outburst approximately 40 days before the major explosion. We interpret the NIR (Near Infrared) excess of emission as signature of material located further out, the origin of which has to be connected with documented mass-loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic-ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, which later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the massive luminous progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass loss, the physical origin of which has yet to be identified.

massive↗
NASA NTRS1994

Massively Parallel Algorithms for Real-Time Wavefront Control of a Dense Adaptive Optics System

In this paper massively parallel algorithms and architectures for real-time wavefront control of a dense adaptive optic system (SELENE) are presented. We have already shown that the computation of a near optimal control algorithm for SELENE can be reduced to the solution of a discrete Poisson equation on a regular domain. Although this represents an optimal computation, due the large size of the system and the high sampling rate requirement, the implementation of this control algorithm poses a computationally challenging problem since it demands a sustained computational throughput of the order of 10 GFlops. We develop a novel algorithm, designated as Fast Invariant Imbedding algorithm, which offers a massive degree of parallelism with simple communication and synchronization requirements. Due to these features, our algorithm is significantly more efficient than other Fast Poisson Solvers for implementation on massively parallel architectures.

massively↗
NASA NTRS2022

Planet Hunters TESS IV: A Massive, Compact Hierarchical Triple Star System TIC 470710327

We report the discovery and analysis of a massive, compact, hierarchical triple system (TIC 470710327) initially identified by citizen scientists in data obtained by NASA’s Transiting Exoplanet Survey Satellite (TESS). Spectroscopic follow-up observations obtained with the HERMES spectrograph, combined with eclipse-timing variations (ETVs), confirm that the system is comprised of three OB stars, with a compact 1.10 d eclipsing binary and a non-eclipsing tertiary on a 52.04 d orbit. Dynamical modelling of the system (from radial velocity and ETVs) reveal a rare configuration wherein the tertiary star (O9.5-B0.5V; 14–17 M ꙩ ) is more massive than the combined mass of the inner binary (10.9–13.2 M ꙩ ). Given the high mass of the tertiary, we predict that this system will undergo multiple phases of mass transfer in the future, and likely end up as a double neutron star gravitational wave progenitor or an exotic Thorne–Żytkow object. Further observational characterization of this system promises constraints on both formation scenarios of massive stars as well as their exotic evolutionary end-products.

NASA's Transiting Exoplanet Survey Satellite (TESS↗
NASA NTRS2022

UV Spectropolarimetry with Polstar: Massive Star Binary Colliding Winds

The winds of massive stars are important for their direct impact on the interstellar medium, and for their influence on the final state of a star prior to it exploding as a supernova. However, the dynamics of these winds is understood primarily via their illumination from a single central source. The Doppler shift seen in resonance lines is a useful tool for inferring these dynamics, but the mapping from that Doppler shift to the radial distance from the source is ambiguous. Binary systems can reduce this ambiguity by providing a second light source at a known radius in the wind, seen from orbitally modulated directions. From the nature of the collision between the winds, a massive companion also provides unique additional information about wind momentum fluxes. Since massive stars are strong ultraviolet (UV) sources, and UV resonance line opacity in the wind is strong, UV instruments with a high resolution spectroscopic capability are essential for extracting this dynamical information. Polarimetric capability also helps to further resolve ambiguities in aspects of the wind geometry that are not axisymmetric about the line of sight, because of its unique access to scattering direction information. We review how the proposed MIDEX-scale mission Polstar can use UV spectropolarimetric observations to critically constrain the physics of colliding winds, and hence radiatively-driven winds in general. We propose a sample of 20 binary targets, capitalizing on this unique combination of illumination by companion starlight, and collision with a companion wind, to probe wind attributes over a range in wind strengths. Of particular interest is the hypothesis that the radial distribution of the wind acceleration is altered significantly, when the radiative transfer within the winds becomes optically thick to resonance scattering in multiple overlapping UV lines.

Ultraviolet Astronomy↗
NASA NTRS1973

Gyromagnetic ratio of a massive body.

It is well known that the gyromagnetic ratio (g factor) of a classical, slowly rotating body whose charge density is proportional to its mass density must be equal to unity. However, if the body is very massive, the spacetime curvature effects of general relativity become important and the result g = 1 is no longer valid. We calculate here the gyromagnetic ratio of a slowly rotating, massive shell with uniform charge density. When the shell is large compared with the Schwarzschild radius we have g = 1, but as the shell becomes more massive the g factor increases. In the limit as the shell approaches its Schwarzschild radius we obtain g approaching 2 (the same value as for an electron).

Cohen, J. M.↗
NASA NTRS1974

Do massive Brans-Dicke theories of gravitation imitate Brans-Dicke theories with nonzero divergence of energy-momentum tensor

Acharya and Hogan (1973) have introduced a massive scalar field into the usual Brans-Dicke (1961) theory of gravitation. Formally they obtain certain field equations. The assumption of a nonzero divergence for T mu nu (or equivalently the introduction of sources) formally imitates a massive Brans-Dicke and satisfies the condition of Acharya and Hogan that the theory be indistinguishable with the classical test of the Einstein theory. Although it was shown elsewhere that the modified Brans-Dicke theory agrees with the classical test under certain conditions, there were no specified limits on omega, a similar circumstance discovered by Acharya and Hogan for the massive scalar field.

Smalley, L. L.↗
NASA NTRS1979

Massively parallel information processing systems for space applications

NASA is developing massively parallel systems for ultra high speed processing of digital image data collected by satellite borne instrumentation. Such systems contain thousands of processing elements. Work is underway on the design and fabrication of the 'Massively Parallel Processor', a ground computer containing 16,384 processing elements arranged in a 128 x 128 array. This computer uses existing technology. Advanced work includes the development of semiconductor chips containing thousands of feedthrough paths. Massively parallel image analog to digital conversion technology is also being developed. The goal is to provide compact computers suitable for real-time onboard processing of images.

Schaefer, D. H.↗
NASA NTRS1981

Predicted star counts in selected fields and photometric bands Applications to galactic structure, the disk luminosity function, and the detection of a massive halo

Tables are presented of predicted star counts in 17 selected directions on the sky as a function of apparent B, V, R, and I magnitudes and absolute visual magnitudes calculated from the Bahcall-Soneira Galaxy model. It is noted that eight of the fields were selected ab initio for their usefulness in determining from star counts either parameters of galactic structure, the faint end of the disk luminosity function, or the detection of a massive stellar halo. Star counts in specified fields to m sub I = 19 mag are able to reveal the faint end of the disk luminosity function down to the end of the hydrogen-burning main sequence. It is thought that star counts at high galactic latitudes to m sub I = 22 mag should reveal the stellar constituents of a massive halo if they are massive enough to be on the hydrogen-burning main sequence.

Bahcall, J. N.↗
NASA NTRS1985

Inconsistency of topologically massive hypergravity

The coupled topologically massive spin-5/2 gravity system in D = 3 dimensions whose kinematics represents dynamical propagating gauge invariant massive spin-5/2 and spin-2 excitations, is shown to be inconsistent, or equivalently, not locally hypersymmetric. In contrast to D = 4, the local constraints on the system arising from failure of the fermionic Bianchi identities do not involve the 'highest spin' components of the field, but rather the auxiliary spinor required to construct a consistent massive model.

Aragone, C.↗
NASA NTRS1987

An analysis of the crossover between local and massive separation on airfoils

Massive separation on airfoils operating at high Reynolds number is an important problem to the aerodynamicist, since its onset generally determines the limiting performance of an airfoil, and it can lead to serious problems related to aircraft control as well as turbomachinery operation. The phenomenon of crossover between local separation and massive separation on realistic airfoil geometries induced by airfoil thickness is investigated for low speed (incompressible) flow. The problem is studied both for the asymptotic limit of infinite Reynolds number using triple-deck theory, and for finite Reynolds number using interacting boundary-layer theory. Numerical results are presented which follow the evolution of the flow as it develops from a mildly separated state to one dominated by the massively separated flow structure as the thickness of the airfoil geometry is systematically increased. The effect of turbulence upon the evolution of the flow is considered, and the impact is significant, with the principal effect being the suppression of the onset of separation. Finally, the effect of surface suction and injection for boundary-layer control is considered. The approach which was developed provides a valuable tool for the analysis of boundary-layer separation up to and beyond stall. Another important conclusion is that interacting boundary-layer theory provides an efficient tool for the analysis of the effect of turbulence and boundary-layer control upon separated vicsous flow.

Barnett, M.↗
NASA NTRS1987

Analysis of crossover between local and massive separation on airfoils

The occurrence of massive separation on airfoils operating at high Reynolds number poses an important problem to the aerodynamicist. In the present study, the phenomenon of crossover, induced by airfoil thickness, between local separation and massive separation is investigated for low speed (incompressible), symmetric flow past realistic airfoil geometries. This problem is studied both for the infinite Reynolds number asymptotic limit using triple-deck theory and for finite Reynolds number using interacting boundary-layer theory. Numerical results are presented which illustrate how the flow evolves from local to massive separation as the airfoil thickness is increased. The results of the triple-deck and the interacting boundary-layer analyses are found to be in qualitative agreement for the NACA four digit series and an uncambered supercritical airfoil. The effect of turbulence on the evolution of the flow is also considered. Solutions are presented for turbulent flows past a NACA 0014 airfoil and a circular cylinder. For the latter case, the calculated surface pressure distribution is found to agree well with experimental data if the proper eddy pressure level is specified.

Barnett, Mark↗
NASA NTRS1987

Conditions for the formation of massive stars

Upper limits on the masses of stars that can form are reexamined and models for the inflow of matter through cocoons around stars of 60, 100, and 200 solar masses are calculated. Consideration is given to the general conditions that must hold at the inner and outer boundaries of a protostellar cocoon; limits on the dust-to-gas ratios and mass inflow rates that will permit inflow onto very massive stars are determined. It is found that inflow can occur if intermediate-sized grains (0.05-0.25 micron) are missing from the initial gas/dust mixture. The existence of massive stars in certain locations in galaxies indicates that preconditioning of the interstellar medium by shocks or turbulence is necessary for massive star formation.

Wolfire, Mark G.↗
NASA NTRS1991

Wolf-Rayet stars as starting points or as endpoints of the evolution of massive stars?

The paper investigates the evidence for the two interpretations of Wolf-Rayet stars suggested in the literature: (1) massive premain-sequence stars with disks and (2) massive stars which have lost most of their H-rich layers in a stellar wind is investigated. The abundance determinations which are done in two different ways and which lead to different conclusions are discussed. The composition is solar, which would suggest interpretation (1), or the CNO abundances are strongly anomalous, which would suggest interpretation (2). Results from evolutionary calculations, stellar statistics, the existence of Ofpe/WN9 transition stars and W-R stars with evolved companions show overwhelming evidence that W-R stars are not premain-sequence stars but that they are in a late stage of evolution. Moreover, the fact that W-R stars are usually in clear regions of space, whereas massive premain-sequence stars are embedded in ultracompact H II regions also shows that W-R stars are not young premain-sequence stars.

Lamers, H. J. G. L. M.↗
NASA NTRS1991

Massive star evolution and SN 1987A

The evolution of massive stars through hydrogen and helium burning is addressed. A set of stellar evolutionary sequences for mass/solar mass of 15, 20, and 25, and metallicity of 0.002, 0.005, 0.007, 0.010, and 0.20 are presented; semiconvection is restricted to operating slower than the local thermal time scale. Using these sequences, simple models of the massive star content of the LMC are found to agree moderately well with the new observational data of Fitzpatrick and Garmany (1990). LMC supergiants were detected only in their postmain-sequence phases, so that 5-10 times more massive stars are there but not identified as such. It is argued that SN 1987A exhibits the normal evolution of a single star of about 20 solar mases having LMC abundances. Despite the variety of envelope behavior, the structure of the core at collapse is rather similar for the stars of a given mass. Variations due to different rates of mass loss are likely to be larger than those due to composition.

Arnett, David↗
NASA NTRS1992

Presupernova evolution in massive interacting binaries

The way in which binary interaction affects the presupernova evolution of massive close binaries and the resulting supernova explosions is investigated systematically by means of a Henyey-type stellar evolution code that was modified to allow its application to binary stellar evolution calculations. The code makes it possible to trace the effects of mass and angular momentum loss from the binary, as well as mass transfer within the binary system. It is found that a large number of binary scenarios can be distinguished, depending on the type of binary interaction and the evolutionary stage of the supernova progenitor at the time of the interaction. Monte Carlo simulations are performed to estimate the frequencies of the occurrence of various scenarios. It is found that, because of a previous binary interaction, 15-30 percent of all massive stars (with initial masses greater than about 8 solar masses) become helium stars, and another 5 percent of all massive stars end their lives as blue supergiants rather than as red supergiants.

Podsiadlowski, PH.↗