Physical plausibility of cold star models satisfying Karmarkar conditions

2017 ◽  
Vol 53 (11) ◽  
Author(s):  
Pratibha Fuloria ◽  
Neeraj Pant
Keyword(s):  
Star Models ◽  
Cold Star

scholarly journals Sea stars generate downforce to stay attached to surfaces

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mark Hermes ◽  
Mitul Luhar
Keyword(s):  
Body Shape ◽  
Control Volume ◽  
Water Channel ◽  
Morphological Plasticity ◽  
The Body ◽  
Sea Star ◽  
Sea Stars ◽  
Hydrodynamic Loads ◽  
Spherical Dome ◽  
Star Models

AbstractIntertidal sea stars often function in environments with extreme hydrodynamic loads that can compromise their ability to remain attached to surfaces. While behavioral responses such as burrowing into sand or sheltering in rock crevices can help minimize hydrodynamic loads, previous work shows that sea stars also alter body shape in response to flow conditions. This morphological plasticity suggests that sea star body shape may play an important hydrodynamic role. In this study, we measured the fluid forces acting on surface-mounted sea star and spherical dome models in water channel tests. All sea star models created downforce, i.e., the fluid pushed the body towards the surface. In contrast, the spherical dome generated lift. We also used Particle Image Velocimetry (PIV) to measure the midplane flow field around the models. Control volume analyses based on the PIV data show that downforce arises because the sea star bodies serve as ramps that divert fluid away from the surface. These observations are further rationalized using force predictions and flow visualizations from numerical simulations. The discovery of downforce generation could explain why sea stars are shaped as they are: the pentaradial geometry aids attachment to surfaces in the presence of high hydrodynamic loads.

scholarly journals The effects of surface fossil magnetic fields on massive star evolution: III. The case of τ Sco

2021 ◽  
Author(s):  
Z Keszthelyi ◽  
G Meynet ◽  
F Martins ◽  
A de Koter ◽  
A David-Uraz
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Massive Star ◽  
Slow Rotation ◽  
Single Star ◽  
Surface Magnetic Field ◽  
Fundamental Parameters ◽  
Chemical Enrichment ◽  
Star Models ◽  
Nitrogen Excess

Abstract τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

scholarly journals Neutrinos in Proto-neutron Star Models

2013 ◽  
Vol 44 (11) ◽  
pp. 2389
Author(s):  
M. Pieńkos
Keyword(s):  
Neutron Star ◽  
Star Models ◽  
Proto Neutron Star

Variable selection in STAR models with neighbourhood effects using genetic algorithms

2010 ◽  
Vol 29 (8) ◽  
pp. 728-750 ◽  
Author(s):  
Isolina Alberto ◽  
Asunción Beamonte ◽  
Pilar Gargallo ◽  
Pedro M. Mateo ◽  
Manuel Salvador
Keyword(s):  
Genetic Algorithms ◽  
Variable Selection ◽  
Neighbourhood Effects ◽  
Star Models

Nonadiabatic Observables in β Cephei Star Models

1994 ◽  
pp. 15-16
Author(s):  
H. Cugier ◽  
W. A. Dziembowski ◽  
A. A. Pamyatnykh
Keyword(s):  
Star Models

scholarly journals Local star-forming dwarf galaxies as windows on reionization-era stellar populations

2019 ◽  
Vol 15 (S352) ◽  
pp. 316-316
Author(s):  
Peter Senchyna
Keyword(s):  
Line Emission ◽  
Stellar Populations ◽  
Star Forming ◽  
Star Models ◽  
Relative Paucity ◽  
High Ionization ◽  
Low Metallicity ◽  
Nearby Galaxies ◽  
A New Technique

AbstractThe recent detections of high-ionization nebular line emission from species including CIV in a number of z > 6 galaxies have highlighted substantial deficiencies in our understanding of metal poor stars. Prominent nebular CIV has never been detected in purely star-forming systems locally, and the massive star models used to model this emission in photoionization codes have not been empirically calibrated below the metallicity of the SMC (20% solar). As a result, we are presently entirely unprepared to correctly interpret nebular emission from metal-poor stars observed with JWST and ALMA in the reionization era. We present results from a multi-pronged ongoing local ultraviolet/optical observation campaign with HST/COS, Keck/ESI, and MMT designed to address this issue by locating and characterizing stellar populations capable of powering such high-ionization emission. This work has already demonstrated that strong nebular CIV can be powered by extremely metal-poor (< 10% solar) massive stars, indicating that we may already have evidence of such low-metallicity populations in the reionization era. However, CIV at the equivalent widths detected at z > 6 remains elusive locally, potentially in part due to the relative paucity of known nearby galaxies at these metallicities with massive stellar populations comparable to those in z > 6 systems. We present a new technique to locate such nearby galaxies, and results from optical follow-up which indicate that a substantial population of highly star- forming metal-poor galaxies likely resides just below the detection limits of previous large spectroscopic surveys.

scholarly journals Close Binary Perspectives

Galaxies ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 57
Author(s):  
R.E. Wilson
Keyword(s):  
Fluid Dynamic ◽  
Binary Star ◽  
Cataclysmic Variables ◽  
Morphological Type ◽  
Close Binary ◽  
Paradigm Shifts ◽  
Star Models ◽  
Unified Algorithm ◽  
Logical Errors ◽  
Analytic Models

Development of analytic binary star models is discussed in historical and on-going perspective, beginning with an overview of paradigm shifts, the merits of direct (rectification-free) models, and fundamental four-type binary system morphology. Attention is called to the likelihood that many or even most cataclysmic variables may be of the double contact morphological type. Eclipsing binary distance estimates differ from those of standard candles in being individually measurable—without reliance on (usually nearby) objects that are assumed similar. Recent progress on circumstellar accretion disk models is briefly summarized, with emphasis on the separate roles of fluid dynamic, structural, and analytic models. Time-related parameters (ephemeris, apsidal motion, and light travel time) now can be found with a unified algorithm that processes light curves, velocity curves, and pre-existing eclipse timings together, without need to compute any new timings. Changes in data publication practices are recommended and logical errors and inconsistencies in terminology are noted. Parameter estimation strategies are discussed.

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