heating during inter-pulse phases, in contrast to the case of carbon-burning flame where the conduction drives the inward propagation of the flame. We infer that such a low mass double white dwarf system could be a progenitor of the AM CVn stars.
Spectral synthesis in 3-dimensional (3D) space for the earliest spectra of Type Ia supernovae (SNe Ia) is presented. In particular, the high velocity absorption features that are commonly seen at the earliest epochs (∼ 10 days before maximum light) are investigated by means of a 3D Monte Carlo spectral synthesis code. The increasing number of early spectra available allows statistical study of the geometry of the ejecta. The observed diversity in strength of the high velocity features (HVFs) can be explained in terms of a "covering factor", which represents the fraction of the projected photosphere that is concealed by high velocity material. Various geometrical models involving high velocity material with a clumpy structure or a thick torus can naturally account for the observed statistics of HVFs. HVFs may be formed by a combination of density and abundance enhancements. Such enhancements may be produced in the explosion itself or may be the result of interaction with circumstellar material or an accretion disk. Models with 1 or 2 blobs, as well as a thin torus or disk-like enhancement are unlikely as a standard situation.
The James Webb Space Telescope (JWST) was conceived and built to answer one of the most fundamental questions that humans can address empirically: "How did the Universe make its first stars?". This can be attempted in classical stare mode and by still photography -with all the pitfalls of crowding and multiband redshifts of objects of which a spectrum was never obtained. Our First Lights At REionization (FLARE) project transforms the quest for the epoch of reionization from the static to the time domain. It targets the complementary question: "What happened to those first stars?". It will be answered by observations of the most luminous events: supernovae and accretion on to black holes formed by direct collapse from the primordial gas clouds. These transients provide direct constraints on star-formation rates and the truly initial initial mass function, and they may identify possible stellar seeds of supermassive black holes. Furthermore, our knowledge of the physics of these events at ultra-low metallicity will be much expanded. JWST's unique capabilities will detect these most luminous and earliest cosmic messengers easily in fairly shallow observations. However, these events are very rare at the dawn of cosmic structure formation and so require large area coverage. Time domain astronomy can be advanced to an unprecedented depth by means of a shallow field of JWST reaching 27 mag (AB) in 2 µm and 4.4 µm over a field as large as 0.1 square degree visited multiple times each year. Such a survey may set strong constraints or detect massive Population III supernovae at redshifts beyond 10, pinpointing the redshift of the first stars, or at least their death. Based on our current knowledge of superluminous supernovae, such a survey will find one or more superluminous supernovae at redshifts above 6 in five years and possibly several direct collapse black holes.In addition, the large scale structure that is the trademark of the epoch of reion--3ization will be detected. Although JWST is not designed as a wide field survey telescope, we show that such a wide field survey is possible with JWST and is critical in addressing several of its key scientific goals.
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