45 research outputs found
The Evolution of Helium Star Plus Carbon-Oxygen White Dwarf Binary Systems and Implications for Diverse Stellar Transients and Hypervelocity Stars
Helium accretion induced explosions in CO white dwarfs (WDs) are considered
promising candidates for a number of observed types of stellar transients,
including supernovae (SNe) of Type Ia and Type Iax. However, a clear favorite
outcome has not yet emerged. We explore the conditions of helium ignition in
the white dwarf and the final fates of helium star-WD binaries as function of
their initial orbital periods and component masses. We compute 274 model binary
systems with the Binary Evolution Code (BEC), where both components are fully
resolved. Stellar and orbital evolution is computed simultaneously, including
mass and angular momentum transfer, tides, and gravitational wave emission, as
well as differential rotation and internal hydrodynamic and magnetic angular
momentum transport. We find that helium detonations are expected only in
systems with the shortest initial orbital periods, and for initially massive
white dwarfs (MWD > 1.0 MSun ) and lower mass donors (Mdonor < 0.8 MSun), with
accumulated helium layers mostly exceeding 0.1 MSun. Upon detonation, these
systems would release the donor as a hypervelocity pre-WD runaway star, for
which we predict the expected range of kinematic and stellar properties.
Systems with more massive donors or initial periods exceeding 1.5 h will likely
undergo helium deflagrations after accumulating 0.1 - 0.001 MSun of helium.
Helium ignition in the white dwarf is avoided in systems with helium donor
stars below - 0.6 MSun, and lead to three distinctly different groups of double
white dwarf systems. The size of the parameter space open to helium detonation
corresponds to only about 3 % of the galactic SN Ia rate, and to 10 % of the SN
Iax rate, while the predicted large amounts of helium (>0.1 MSun) in
progenitors cannot easily be reconciled with observations of archetypical SN
Ia. ...Comment: Accepted for publication in A&A, 28 pages, 16 figures, 6 table
Properties and applications of a predicted population of runaway He-sdO/B stars ejected from single degenerate He-donor SNe
Properties and applications of a predicted population of runaway He-sdO/B stars ejected from single degenerate He-donor SNe
This study builds on previous works, producing the most extensive prediction
of the properties of such a hypothetical population to date, taking into
account both Chandrasekhar and non-Chandrasekhar mass events. These results are
then used to define criteria for membership of this population and characterise
putative subpopulations
This study contains 6x10^6 individual ejection trajectories out of the
Galactic plane calculated with the stellar kinematics framework SHyRT, which
are analysed with regard to their bulk observational properties. These are then
put into context with the only previously identified population member US\,708
and applied to a number of other possible candidate objects.
We find that two additional previously observed objects possess properties to
warrant a designation as candidate objects. Characterisation of these object
with respect to the predicted population finds all of them to be extreme in at
least one astrometric observable. We find that current observations support a
Galactic SN rate on the order of ~3x10^-7/yr to ~2x10^-6/yr, three orders of
magnitude below the inferred Galactic SN Ia rate and two orders of magnitude
below the formation rate of predicted He-donor progenitors. The number of
currently observed population members suggests that the He-donor scenariois not
a dominant contributor to the number of observed SNe Ia. However, we find that,
even at the low event rate suggested, the majority of possibly detectable
population members is still undetected. The extreme nature of current
population members suggests that a still larger number of objects has simply
evaded detection up to this point, hinting at a higher contribution than is
currently supported by observation. - abridged -Comment: 26 pages, 23 figures, 5 tables - accepted in A&
TW Hya: an old protoplanetary disc revived by its planet
Dark rings with bright rims are the indirect signposts of planets embedded in protoplanetary discs. In a recent first, an azimuthally elongated AU-scale blob, possibly a planet, was resolved with ALMA in TW Hya. The blob is at the edge of a cliff-like rollover in the dust disc rather than inside a dark ring. Here we build time-dependent models of TW Hya disc. We find that the classical paradigm cannot account for the morphology of the disc and the blob. We propose that ALMA-discovered blob hides a Neptune mass planet losing gas and dust. We show that radial drift of mm-sized dust particles naturally explains why the blob is located on the edge of the dust disc. Dust particles leaving the planet perform a characteristic U-turn relative to it, producing an azimuthally elongated blob-like emission feature. This scenario also explains why a 10 Myr old disc is so bright in dust continuum. Two scenarios for the dust-losing planet are presented. In the first, a dusty pre-runaway gas envelope of a ∼40M⊕ Core Accretion planet is disrupted, e.g. as a result of a catastrophic encounter. In the second, a massive dusty pre-collapse gas giant planet formed by Gravitational Instability is disrupted by the energy released in its massive core. Future modelling may discriminate between these scenarios and allow us to study planet formation in an entirely new way – by analysing the flows of dust and gas recently belonging to planets, informing us about the structure of pre-disruption planetary envelopes
Chlamydophila abortus Pelvic Inflammatory Disease
We report the first documented case of an extragestational infection with Chlamydophila abortus in humans. The pathogen was identified in a patient with severe pelvic inflammatory disease (PID) by sequence analysis of the ompA gene. Our findings raise the possibility that Chlamydiaceae other than Chlamydia trachomatis are involved in PID
On the fate of the secondary white dwarf in double-degenerate double-detonation Type Ia supernovae
The progenitor systems and explosion mechanism of Type Ia supernovae are
still unknown. Currently favoured progenitors include double-degenerate systems
consisting of two carbon-oxygen white dwarfs with thin helium shells. In the
double-detonation scenario, violent accretion leads to a helium detonation on
the more massive primary white dwarf that turns into a carbon detonation in its
core and explodes it. We investigate the fate of the secondary white dwarf,
focusing on changes of the ejecta and observables of the explosion if the
secondary explodes as well rather than survives. We simulate a binary system of
a and a carbon-oxygen white dwarf with
helium shells each. We follow the system self-consistently from
inspiral to ignition, through the explosion, to synthetic observables. We
confirm that the primary white dwarf explodes self-consistently. The helium
detonation around the secondary white dwarf, however, fails to ignite a carbon
detonation. We restart the simulation igniting the carbon detonation in the
secondary white dwarf by hand and compare the ejecta and observables of both
explosions. We find that the outer ejecta at are
indistinguishable. Light curves and spectra are very similar until d
after explosion and the ejecta are much more spherical than for violent merger
models. The inner ejecta differ significantly which slows down the decline rate
of the bolometric light curve after maximum of the model with a secondary
explosion by about 20 per cent. We expect future synthetic 3D nebular spectra
to confirm or rule out either model.Comment: 12 pages, 7 figures, submitted to MNRAS, comments welcom
First Experimental Characterization of Microwave Emission from Cosmic Ray Air Showers
We report the first direct measurement of the overall characteristics of
microwave radio emission from extensive air showers. Using a trigger provided
by the KASCADE-Grande air shower array, the signals of the microwave antennas
of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have
been read out and searched for signatures of radio emission by high-energy air
showers in the GHz frequency range. Microwave signals have been detected for
more than 30 showers with energies above 3*10^16 eV. The observations presented
in this Letter are consistent with a mainly forward-directed and polarised
emission process in the GHz frequency range. The measurements show that
microwave radiation offers a new means of studying air showers at energies
above 10^17 eV.Comment: Accepted for publication in PR