50 research outputs found
Introduction to the Anthropocene
https://nanocrit.com/issues/issue13/Editors-Introduction-for-NANO-Special-Issue-13-The-Anthropocenehttps://nanocrit.com/issues/issue13/Editors-Introduction-for-NANO-Special-Issue-13-The-AnthropoceneAccepted manuscrip
The role of dredge-up in double white dwarf mergers
We present the results of an investigation of the dredge-up and mixing during
the merger of two white dwarfs with different chemical compositions by
conducting hydrodynamic simulations of binary mergers for three representative
mass ratios. In all the simulations, the total mass of the two white dwarfs is
. Mergers involving a CO and a He white dwarf have
been suggested as a possible formation channel for R Coronae Borealis type
stars, and we are interested in testing if such mergers lead to conditions and
outcomes in agreement with observations. Even if the conditions during the
merger and subsequent nucleosynthesis favor the production of , the merger must avoid dredging up large amounts of , or
else it will be difficult to produce sufficient to explain
the oxygen ratio observed to be of order unity. We performed a total of 9
simulations using two different grid-based hydrodynamics codes using fixed and
adaptive meshes, and one smooth particle hydrodynamics (SPH) code. We find that
in most of the simulations, of is
indeed dredged up during the merger. However, in SPH simulations where the
accretor is a hybrid He/CO white dwarf with a layer of
helium on top, we find that no is being dredged up, while in
the simulation of has been
brought up, making a WD binary consisting of a hybrid CO/He WD and a companion
He WD an excellent candidate for the progenitor of RCB stars.Comment: Accepted for publication in Ap
Emission from Pair-Instability Supernovae with Rotation
Pair Instability Supernovae have been suggested as candidates for some Super
Luminous Supernovae, such as SN 2007bi, and as one of the dominant types of
explosion occurring in the early Universe from massive, zero-metallicity
Population III stars. The progenitors of such events can be rapidly rotating,
therefore exhibiting different evolutionary properties due to the effects of
rotationally-induced mixing and mass-loss. Proper identification of such events
requires rigorous radiation hydrodynamics and radiative transfer calculations
that capture not only the behavior of the light curve but also the spectral
evolution of these events. We present radiation hydrodynamics and radiation
transport calculations for 90-300 Msun rotating pair-instability supernovae
covering both the shock break-out and late light curve phases. We also
investigate cases of different initial metallicity and rotation rate to
determine the impact of these parameters on the detailed spectral
characteristics of these events. In agreement with recent results on
non-rotating pair instability supernovae, we find that for a range of
progenitor masses and rotation rates these events have intrinsically red colors
in contradiction with observations of super-luminous supernovae. The
spectroscopic properties of rotating pair instability supernovae are similar to
those of non-rotating events with stripped hydrogen and helium envelopes. We
find that the progenitor metallicity and rotation rate properties are erased
after the explosion and cannot be identified in the resulting model spectra. It
is the combined effects of pre-supernova mass-loss and the basic properties of
the supernova ejecta such as mass, temperature and velocity that have the most
direct impact in the model spectra of pair instability supernovae.Comment: 15 pages, 22 figures, submitted to Ap
Self-Help: Extrajudicial Rights, Privileges and Remedies in Contemporary American Society
This Special Project examines the myriad forms of self-help currently available to persons in American society. It groups and discusses notable self-help rights, privileges, and remedies under topical classifications that parallel traditional jurisprudential categories. Parts H through VI of the Special Project sketch the legally fashioned contours and explore the legal, social, and political consequences of self-help methods in tort law, criminal law and law enforcement, commercial transactions, landlord-tenant relations,and family law matters. Part VII explores the attorney\u27s role in the development and implementation of curative self-help procedures such as mediation. Special Project concludes by examining the function, mechanisms, and merits of two increasingly popular alternative dispute resolution processes--rent-a-judge programs and the ombudsman--that offer hope for continued peaceable dispute resolution