2,308 research outputs found
Considerations on the Role of Fall-Back Discs in the Final Stages of the Common Envelope Binary Interaction
The common envelope interaction is thought to be the gateway to all evolved
compact binaries and mergers. Hydrodynamic simulations of the common envelope
interaction between giant stars and their companions are restricted to the
dynamical, fast, in-spiral phase. They find that the giant envelope is lifted
during this phase, but remains mostly bound to the system. At the same time,
the orbital separation is greatly reduced, but in most simulations it levels
off? at values larger than measured from observations. We conjectured that
during the post-in-spiral phase the bound envelope gas will return to the
system. Using hydrodynamic simulations, we generate initial conditions for our
simulation that result in a fall-back disk with total mass and angular momentum
in line with quantities from the simulations of Passy et al. We find that the
simulated fall-back event reduces the orbital separation efficiently, but fails
to unbind the gas before the separation levels off once again. We also find
that more massive fall-back disks reduce the orbital separation more
efficiently, but the efficiency of unbinding remains invariably very low. From
these results we deduce that unless a further energy source contributes to
unbinding the envelope (such as was recently tested by Nandez et al.), all
common envelope interactions would result in mergers. On the other hand,
additional energy sources are unlikely to help, on their own, to reduce the
orbital separation. We conclude by discussing our dynamical fall-back event in
the context of a thermally-regulated post-common envelope phase.Comment: 12 pages, 12 pages, Accepted to MNRA
L\u27Azur: February 1966
Parents\u27 Weekend Editionhttps://spiral.lynn.edu/studentnews/1004/thumbnail.jp
L\u27Azur: May 1964
The first student newspaper published by the school.https://spiral.lynn.edu/studentnews/1000/thumbnail.jp
L\u27Azur: February 1965
Parents\u27 Weekend Editionhttps://spiral.lynn.edu/studentnews/1001/thumbnail.jp
Quark deconfinement in neutron star cores: The effects of spin-down
We study the role of spin-down in driving quark deconfinement in the high
density core of isolated neutron stars. Assuming spin-down to be solely due to
magnetic braking, we obtain typical timescales to quark deconfinement for
neutron stars that are born with Keplerian frequencies. Employing different
equations of state (EOS), we determine the minimum and maximum neutron star
masses that will allow for deconfinement via spin-down only. We find that the
time to reach deconfinement is strongly dependent on the magnetic field and
that this time is least for EOS that support the largest minimum mass at zero
spin, unless rotational effects on stellar structure are large. For a fiducial
critical density of for the transition to the quark phase
(g/cm is the saturation density of nuclear
matter), we find that neutron stars lighter than cannot reach a
deconfined phase. Depending on the EOS, neutron stars of more than
can enter a quark phase only if they are spinning faster than
about 3 milliseconds as observed now, whereas larger spin periods imply that
they are either already quark stars or will never become one.Comment: 4 pages, 4 figures, submitted to ApJ
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
Childhood intelligence and personality traits neuroticism and openness contributes to social mobility : A study in the Aberdeen 1936 Birth Cohort
Peer reviewedPostprin
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