36 research outputs found
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
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
The security and quality of drinking water supply in Austria – factors, present requirements and initiatives
A catalog of potential post-common envelope binaries
We present a catalog containing 839 candidate post–common envelope systems. Common envelope evolution is very important in stellar astrophysics, particularly in the context of very compact and short-period binaries, including cataclysmic variables, as progenitors of, e.g., supernovae Type Ia or mergers of black holes and/or neutron stars. At the same time, it is a barely understood process in binary evolution. Due to limitations, since partially remedied, on direct simulation, early investigations were mainly focused on providing analytic prescriptions of the outcome of common envelope evolution. In recent years, detailed hydrodynamical calculations have produced deeper insight into the previously elusive process of envelope ejection. However, a direct link between the observations and theory of this relatively short-lived phase in binary evolution has not been forthcoming. Therefore, the main insight to be gained from observations has to be derived from the current state of systems likely to have gone through a common envelope. Here we present an extensive catalog of such observations as found in the literature. The aim of this paper is to provide a reliable set of data, obtained from observations, to be used in the theoretical modeling of common envelope evolution. In this catalog, the former common envelope donor star is commonly observed as a white dwarf or hot subdwarf star. This catalog includes period and mass estimates wherever obtainable. Some binaries are borderline cases to allow an investigation of the transition between a common envelope formation and other mass-transfer processes
Triple Evolution: An Important Channel in the Formation of Type Ia Supernovae
Type Ia supernovae (SNe Ia) are thought to be the result of thermonuclear explosions in white dwarfs (WDs). Commonly considered formation pathways include two merging WDs (the double-degenerate channel) and a single WD accreting material from a H or He donor (the single-degenerate channel). Since the predicted SN Ia rates from WDs in binaries are thought to be insufficient to explain the observed SN Ia rate, it is important to study similar interactions in higher-order multiple-star systems such as triple systems. We use the evolutionary population synthesis code Multiple Stellar Evolution (MSE) to study the stellar evolution, binary interactions, and gravitational dynamics of the triple-star systems. Also, unlike previous studies, prescriptions are included to simultaneously take into account the single- and double-degenerate channels, and we consider triples across the entire parameter space (including those with tight inner binaries). We explore the impact of typically ignored or uncertain physics such as flybys and common envelope prescription parameters on our results. The majority of systems undergo circular mergers to explode as SNe Ia, while eccentric collisions contribute to 0.44integrated SN Ia rate from the triple channel is found to be ( 3.60 ± 0.04 ) x 10−4 M⊙−1 , which is, surprisingly, similar to that of the isolated binary channel, where the SN Ia rate is ( 3.2 ± 0.1 ) x 10−4 M⊙−1 . This implies that triples, when considering their entire parameter space, yield an important contribution to the overall SN Ia rate