What is the role of wind mass transfer in the progenitor evolution of Type Ia Supernovae? [SSA]


Type Ia supernovae (SNe Ia) are thermonuclear explosions of carbon-oxygen white dwarfs (WDs) that accrete mass from a binary companion, which can be either a non-degenerate star (a main-sequence star or a giant) or an other WD in a binary merger (single- and double-degenerate scenario, respectively). In population-synthesis studies of SNe Ia the contribution of asymptotic giant branch (AGB) stars to either scenario is marginal. However, most of these studies adopt simplified assumptions to compute the effects of wind mass loss and accretion in binary systems. This work investigates the impact of wind mass transfer on a population of binary stars and discusses the role of AGB stars as progenitors of SNe Ia.

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C. Abate
Wed, 26 Jul 17

Comments: Conference proceeding of the meeting “The AGB-Supernovae Mass Transition” which took place in Frascati (Rome) between 27th and the 31st of March 2017

ChromaStarDB: SQL database-driven spectrum synthesis, and more [SSA]


We present an alternate deployment of the GrayStarServer (now ChromaStarServer (CSS)) pedagogical stellar atmosphere and spectrum synthesis WWW-application, namely ChromaStarDB (CSDB), in which the atomic line list used for spectrum synthesis is implemented as an SQL database table rather than as a more conventional byte-data file. This allows for very flexible selection criteria to determine which transitions are extracted from the line list for inclusion in the synthesis, and enables novel pedagogical and research experiments in spectrum synthesis. This line selection flexibility is reflected in the CSDB UI. The database extraction is very fast and would be appropriate for the larger line lists of research-grade modeling codes. We also take the opportunity to present major additions to the ChromaStar and CSS codes that are also reflected in CSDB: i) TiO band opacity in the JOLA approximation, ii) Metal b-f and Rayleigh scattering opacity, iii) 2D implementation of the flux integral, iv) Improvement of the N_e convergence, and v) Expansion of the exo-planet modeling parameters, and vi) General improvements to the UI. The applications may be found at the home page of the OpenStar project: www.ap.smu.ca/OpenStars/.

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C. Short
Wed, 26 Jul 17

Comments: Accepted for publication in PASP

Candidate exoplanet host HD131399A: a nascent Am star [SSA]


Direct imaging suggests that there is a Jovian exoplanet around the primary A-star in the triple-star system HD131399. We investigate a high-quality spectrum of the primary component HD131399A obtained with FEROS on the ESO/MPG 2.2m telescope, aiming to characterise the star’s atmospheric and fundamental parameters, and to determine elemental abundances at high precision and accuracy. The aim is to constrain the chemical composition of the birth cloud of the system and therefore the bulk composition of the putative planet. A hybrid non-local thermal equilibrium (non-LTE) model atmosphere technique is adopted for the quantitative spectral analysis. Comparison with the most recent stellar evolution models yields the fundamental parameters. The atmospheric and fundamental stellar parameters of HD131399A are constrained to Teff=9200+-100 K, log g=4.37+-0.10, M=1.95+0.08-0.06 Msun, R=1.51+0.13-0.10 Rsun, and log L/Lsun=1.17+-0.07, locating the star on the zero-age main sequence. Non-LTE effects on the derived metal abundances are often smaller than 0.1dex, but can reach up to ~0.8dex for individual lines. The observed lighter elements up to calcium are overall consistent with present-day cosmic abundances, with a C/O ratio of 0.45$\pm$0.07 by number, while the heavier elements show mild overabundances. We conclude that the birth cloud of the system had a standard chemical composition, but we witness the onset of the Am phenomenon in the slowly rotating star. We furthermore show that non-LTE analyses have the potential to solve the remaining discrepancies between observed abundances and predictions by diffusion models for Am stars. Moreover, the present case allows mass loss, not turbulent mixing, to be identified as the main transport process competing with diffusion in very young Am stars.

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N. Przybilla, P. Aschenbrenner and S. Buder
Wed, 26 Jul 17

Comments: 5 pages + 3 pages appendix, 3 figures. Accepted for publication in A&A

Verification of operational solar flare forecast: Case of Regional Warning Center Japan [SSA]


In this article, we discuss a verification study of an operational solar flare forecast in the Regional Warning Center (RWC) Japan. The RWC Japan has been issuing four-categorical deterministic solar flare forecasts for a long time. In this forecast verification study, we used solar flare forecast data accumulated over 16 years (from 2000 to 2015). We compiled the forecast data together with solar flare data obtained with the Geostationary Operational Environmental Satellites (GOES). Using the compiled data sets, we estimated some conventional scalar verification measures with 95% confidence intervals. We also estimated a multi-categorical scalar verification measure. These scalar verification measures were compared with those obtained by the persistence method and recurrence method. As solar activity varied during the 16 years, we also applied verification analyses to four subsets of forecast-observation pair data with different solar activity levels. We cannot conclude definitely that there are significant performance difference between the forecasts of RWC Japan and the persistence method, although a slightly significant difference is found for some event definitions. We propose to use a scalar verification measure to assess the judgment skill of the operational solar flare forecast. Finally, we propose a verification strategy for deterministic operational solar flare forecasting.

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Y. Kubo, M. Den and M. Ishii
Wed, 26 Jul 17

Comments: 29 pages, 7 figures and 6 tables. Accepted for publication in Journal of Space Weather and Space Climate (SWSC)

The Non-Linear Growth of the Magnetic Rayleigh-Taylor Instability [SSA]


This work examines the effect of the embedded magnetic field strength on the non-linear development of the magnetic Rayleigh-Taylor Instability (RTI) (with a field-aligned interface) in an ideal gas close to the incompressible limit in three dimensions. Numerical experiments are conducted in a domain sufficiently large so as to allow the predicted critical modes to develop in a physically realistic manner. The ratio between gravity, which drives the instability in this case (as well as in several of the corresponding observations), and magnetic field strength is taken up to a ratio which accurately reflects that of observed astrophysical plasma, in order to allow comparison between the results of the simulations and the observational data which served as inspiration for this work. This study finds reduced non-linear growth of the rising bubbles of the RTI for stronger magnetic fields, and that this is directly due to the change in magnetic field strength, rather than the indirect effect of altering characteristic length scales with respect to domain size. By examining the growth of the falling spikes, the growth rate appears to be enhanced for the strongest magnetic field strengths, suggesting that rather than affecting the development of the system as a whole, increased magnetic field strengths in fact introduce an asymmetry to the system. Further investigation of this effect also revealed that the greater this asymmetry, the less efficiently the gravitational energy is released. By better understanding the under-studied regime of such a major phenomenon in astrophysics, deeper explanations for observations may be sought, and this work illustrates that the strength of magnetic fields in astrophysical plasmas influences observed RTI in subtle and complex ways.

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J. Carlyle and A. Hillier
Wed, 26 Jul 17

Comments: Accepted for publication by A&A. 10 pages, 9 figures

Partially Ionized Plasmas in Astrophysics [SSA]


Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress.

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J. Ballester, I. Alexeev, M. Collados, et. al.
Wed, 26 Jul 17

Comments: 163 pages, submitted to Space Science Reviews

Production, Processing and Consumption of the Dust in the Galaxy [SSA]


The recent results obtained by the modern telescopes and spacecrafts allow us for the first time to compare directly the mass, spatial density and size distribution of the dust grains in the regions of their production, processing and consumption in our Galaxy. The ALMA and VLT/SPHERE telescopes allow us to estimate the production of the dust by supergiants and collapsing core supernovae. The 2MASS, WISE, SDSS, Planck and other telescopes allow us to estimate the processing of the dust in the interstellar medium. After renewed Besan\c{c}on Galaxy model the medium appears to contain about half the local mass of matter (both baryonic and dark) in the Galactic neighborhood of the Sun. The Helios, Ulysses, Galileo, Cassini and New Horizons spacecrafts allow us to estimate the consumption of the dust into large solid bodies. The results are consistent each other assuming the local mean spatial density of the dust is about of $3.5\times10^{-26}$ g/cm$^3$, mean density of the grain is about 1 g/cm$^3$, and the dust production rate is about of 0.015 Solar mass per year for whole the Galaxy.

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G. Gontcharov
Wed, 26 Jul 17

Comments: 4 pages, 1 figure, conference proceedings Stars: From Collapse to Collapse, Proceedings of a conference held at Special Astrophysical Observatory, Nizhny Arkhyz, Russia 3-7 October 2016. Edited by Yu. Yu. Balega, D. O. Kudryavtsev, I. I. Romanyuk, and I. A. Yakunin. San Francisco: Astronomical Society of the Pacific, 2017, p.71