Explosion of white dwarfs harboring hybrid CONe cores

Recently, it has been found that off-centre carbon burning in a subset of intermediate-mass stars does not propagate all the way to the center, resulting in a class of hybrid CONe cores. Here, we consider the possibility that stars hosting these hybrid CONe cores might belong to a close binary system and, eventually, become white dwarfs accreting from a non-degenerate companion at rates leading to a supernova explosion. We have computed the hydrodynamical phase of the explosion of Chandrasekhar-mass white dwarfs harboring hybrid cores, assuming that the explosion starts at the center, either as a detonation (as may be expected in some degenerate merging scenarios) or as a deflagration (that afterwards transitions into a delayed detonation). We assume these hybrid cores are made of a central CO volume, of mass M(CO), surrounded by an ONe shell. We show that, in case of a pure detonation, a medium-sized CO-rich region, M(CO)<0.4 Msun, results in the ejection of a small fraction of the mantle while leaving a massive bound remnant. Part of this remnant is made of the products of the detonation, Fe-group nuclei, but they are buried in its inner regions, unless convection is activated during the ensuing cooling and shrinking phase of the remnant. In contrast, and somehow paradoxically, delayed detonations do not leave remnants but for the minimum M(CO) we have explored, M(CO)=0.2 Msun, and even in this case the remnant is as small as 0.13 Msun. The ejecta produced by these delayed detonations are characterized by slightly smaller masses of 56Ni and substantially smaller kinetic energies than obtained for a delayed detonation of a 'normal' CO white dwarf. The optical emission expected from these explosions would hardly match the observational properties of typical Type Ia supernovae, although they make interesting candidates for the subluminous class of SN2002cx-like or SNIax.Comment: Accepted for Astronomy and Astrophysics, 11 pages, 4 figure

Super-AGB Stars and their role as Electron Capture Supernova progenitors

We review the lives, deaths and nucleosynthetic signatures of intermediate mass stars in the range approximately 6.5-12 Msun, which form super-AGB stars near the end of their lives. We examine the critical mass boundaries both between different types of massive white dwarfs (CO, CO-Ne, ONe) and between white dwarfs and supernovae and discuss the relative fraction of super-AGB stars that end life as either an ONe white dwarf or as a neutron star (or an ONeFe white dwarf), after undergoing an electron capture supernova. We also discuss the contribution of the other potential single-star channels to electron-capture supernovae, that of the failed massive stars. We describe the factors that influence these different final fates and mass limits, such as composition, the efficiency of convection, rotation, nuclear reaction rates, mass loss rates, and third dredge-up efficiency. We stress the importance of the binary evolution channels for producing electron-capture supernovae. We discuss recent nucleosynthesis calculations and elemental yield results and present a new set of s-process heavy element yield predictions. We assess the contribution from super-AGB star nucleosynthesis in a Galactic perspective, and consider the (super-)AGB scenario in the context of the multiple stellar populations seen in globular clusters. A brief summary of recent works on dust production is included. Lastly we conclude with a discussion of the observational constraints and potential future advances for study into these stars on the low mass/high mass star boundary.Comment: 28 pages, 11 figures. Invited review for Publications of the Astronomical Society of Australia, to be published in special issue on "Electron Capture Supernovae". Submitte

Reducing sample variance: halo biasing, non-linearity and stochasticity

Comparing clustering of differently biased tracers of the dark matter distribution offers the opportunity to reduce the cosmic variance error in the measurement of certain cosmological parameters. We develop a formalism that includes bias non-linearities and stochasticity. Our formalism is general enough that can be used to optimise survey design and tracers selection and optimally split (or combine) tracers to minimise the error on the cosmologically interesting quantities. Our approach generalises the one presented by McDonald & Seljak (2009) of circumventing sample variance in the measurement of $f\equiv d \ln D/d\ln a$. We analyse how the bias, the noise, the non-linearity and stochasticity affect the measurements of $Df$ and explore in which signal-to-noise regime it is significantly advantageous to split a galaxy sample in two differently-biased tracers. We use N-body simulations to find realistic values for the parameters describing the bias properties of dark matter haloes of different masses and their number density. We find that, even if dark matter haloes could be used as tracers and selected in an idealised way, for realistic haloes, the sample variance limit can be reduced only by up to a factor $\sigma_{2tr}/\sigma_{1tr}\simeq 0.6$. This would still correspond to the gain from a three times larger survey volume if the two tracers were not to be split. Before any practical application one should bear in mind that these findings apply to dark matter haloes as tracers, while realistic surveys would select galaxies: the galaxy-host halo relation is likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA

Physician-Patient Communication Among Southern European Cancer Physicians: the Influence of Psychosocial Orientation and Burnout

Physician-patient communication is a critical factor for comprehensive care in oncology. Although a number of studies have been carried out in Northern Europe and the US on this subject, no data are available in Southern European countries. As a part of a multicenter Southern European Psycho-Oncology study (SEPOS), the present investigation was conducted to examine communication skills and related variables (i.e. psychosocial orientation, and burnout) among 125 physicians from Italy, Portugal, and Spain. The Self-Confidence in Communication Skills (SCCS) scale was given to assess physicians' perception of their communication skills and the Expected Outcome of Communication (EOC) scale was administered to examine the physicians' expectations about the effects of communicating with their patients. Doctors' psychosocial orientation was measured by using the Physician Belief Scale (PBS) and burnout was measured by using the Maslach Burnout Inventory (MBI). Although the physicians reported receiving minimal training in communication during their education, they tended to perceive themselves as skilled in patient communication, apart from some areas (e.g. dealing with denial, managing uncertainty, assessing anxiety and depression, and promoting patient-family openness). Low psychosocial orientation and burnout symptoms (i.e. emotional exhaustion, depersonalization, and poor personal accomplishment in their job) were associated with lower confidence in communication skills and higher expectations of a negative outcome, following physician-patient communication. The results suggest that there is a need for training cancer physicians in communication and for increasing a more definite psychosocially oriented approach in cancer care in Mediterranean countries.info:eu-repo/semantics/publishedVersio

GCRT J1745-3009 as a Transient White Dwarf Pulsar

A transient radio source in the direction of the Galactic Center, GCRT J1745-3009, exhibited 5 peculiar consecutive outbursts at 0.33 GHz with a period of 77.13 minutes and a duration of ~10 minutes for each outburst. It has been claimed to be the prototype of a hitherto unknown class of transient radio sources. We interpret it as a transient white dwarf pulsar with a period of 77.13 minutes. The ~10-minute flaring duration corresponds to the epoch when the radio beam sweeps our line of sight. The bursting epoch corresponds to the episodes when stronger sunspot-like magnetic fields emerge into the white dwarf polar cap region during which the pair production condition is satisfied and the white dwarf behaves like a radio pulsar. It switches off as the pair production condition breaks down.Comment: minor changes, ApJL, in pres

Determining the regimes of cold and warm inflation in the susy hybrid model

The SUSY hybrid inflation model is found to dissipate radiation during the inflationary period. Analysis is made of parameter regimes in which these dissipative effects are significant. The scalar spectral index, its running, and the tensor-scalar ratio are computed in the entire parameter range of the model. A clear prediction for strong dissipative warm inflation is found for n_S-1 \simeq 0.98 and a low tensor-scalar ratio much below 10^{-6}. The strong dissipative warm inflation regime also is found to have no \eta-problem and with the field amplitude much below the Planck scale. As will be discussed, this has important theoretical implications in permitting a much wider variety of SUGRA extensions to the basic model.Comment: paragraph added at the end of section V; references added; accepted for publication in Phys. Rev.

WKB formalism and a lower limit for the energy eigenstates of bound states for some potentials

In the present work the conditions appearing in the WKB approximation formalism of quantum mechanics are analyzed. It is shown that, in general, a careful definition of an approximation method requires the introduction of two length parameters, one of them always considered in the text books on quantum mechanics, whereas the second one is usually neglected. Afterwards we define a particular family of potentials and prove, resorting to the aforementioned length parameters, that we may find an energy which is a lower bound to the ground energy of the system. The idea is applied to the case of a harmonic oscillator and also to a particle freely falling in a homogeneous gravitational field, and in both cases the consistency of our method is corroborated. This approach, together with the Rayleigh--Ritz formalism, allows us to define an energy interval in which the ground energy of any potential, belonging to our family, must lie.Comment: Accepted in Modern Physics Letters