The progenitors of type Ia supernovae in the semidetached binaries with red giant donors

Context. The companions of the exploding carbon-oxygen white dwarfs (CO WDs) for producing type Ia supernovae (SNe Ia) are still not conclusively confirmed. A red-giant (RG) star has been suggested to be the mass donor of the exploding WD, named as the symbiotic channel. However, previous studies on the this channel gave a relatively low rate of SNe Ia. Aims. We aim to systematically investigate the parameter space, Galactic rates and delay time distributions of SNe Ia from the symbiotic channel by employing a revised mass-transfer prescription. Methods. We adopted an integrated mass-transfer prescription to calculate the mass-transfer process from a RG star onto the WD. In this prescription, the mass-transfer rate varies with the local material states. Results. We evolved a large number of WD+RG systems, and found that the parameter space of WD+RG systems for producing SNe Ia is significantly enlarged. This channel could produce SNe Ia with intermediate and old ages, contributing to at most 5% of all SNe Ia in the Galaxy. Our model increases the SN Ia rate from this channel by a factor of 5. We suggest that the symbiotic systems RS Oph and T CrB are strong candidates for the progenitors of SNe Ia.Comment: 8 pages, 6 figure

Atomic bonding and electrical characteristics of metallic and semi-metallic elements from the binding energy and bond charge model

In this paper, we use density functional theory to calculate the electronic structure and properties of 47 metallic and semi-metallic elements. The binding energy and bond charge model (BBC) model is combined with the tight binding and density functional tight binding approaches to obtain quantitative information about atomic bonding at the atomic scale and to understand the contributions and effects of deformation energy density, energy shifts, and atomic bonding on the Hamiltonian

Statistical Properties of Brown Dwarf Companions: Implications for Different Formation Mechanisms

The mass domain where massive extrasolar planets and brown dwarfs overlap is still poorly understood due to the paucity of brown dwarfs orbiting close to solar-type stars, the so-called brown dwarf desert. In this paper we collect all of available data about close brown dwarfs around solar type stars and their host stars from literature and study the demographics of the brown dwarf desert. The data clearly show a short period and a medium mass gap in the brown dwarf period-mass distribution diagram ($35<m\sin i<55 M_{\rm Jup}$ and $P<100$ days), representing the "driest land" in the brown dwarf desert. Observation biases are highly unlikely to cause this gap due to its short period and medium mass, of which brown dwarfs can be easily detected by previous RV surveys. Brown dwarfs above and below this gap have significantly different eccentricity distribution, which not only confirms that this gap is real, but also implies that they may have different origins. Our further statistical study indicates that brown dwarfs below this gap may primarily form in the protoplanetary disk through disk gravitational instability, while brown dwarfs above this gap may dominantly form like a stellar binary through molecular cloud fragmentation. Our discoveries have offered important insights about brown dwarf formation mechanisms and their possible relationships with planet and star formation.Comment: 9 pages, 6 figures, 1 table. Submitted to MNRAS. Comments are welcom

Social network characteristics, perceived drinking norms and hazardous alcohol use

Efforts by researchers, policy makers and other stakeholders to bring about significant reductions in alcohol use among the youth appears not to be yielding desired results, as the problem of hazardous drinking among the youth has persisted. One possible problem is that studies and policies on alcohol have not adequately situated the problem within relevant social contexts. This cross-sectional study examined the influence of social network characteristics, perceived drinking norms and demographicvariables on hazardous drinking among 1,315 adult males newly recruited into a youth empowerment scheme in a state in Southwest Nigeria. Data were collected using structured questionnaire. Results showed that about 18% of the respondents reported scores falling within the hazardous drinking zones while 13% were abstainers. Hierarchical multiple regression analyses were performed to explore the extent to which each of the network characteristics and other factors predicted hazardous drinking. Age (â = -.19; p&lt;.05) and educational status (â = -.16; p&lt;.05) of participants significantly predicted hazardous drinking by accounting for about 15% of the explained variance in hazardous drinking. Social network characteristics accounted for about 33% of the explained variance in hazardous drinking. The importance of these and other findings of the study, and the need to factor in normative and social influences in alcohol-reduction intervention programmes were highlighted