Wind-Wind Collision in the eta Carinae Binary System: a Shell-Like Event Near Periastron

The exact nature of eta Carinae is still an open issue. In this paper we assume a binary system to explain the strong X-ray emission, but we also take into account that, near periastron and because of the highly eccentric orbit, the wind emerging from eta Carinae accumulates behind the shock and can mimic a shell-like ejection event. For this process to be effective, at periastron the secondary star should be located between eta Carinae and the observer, solving also the discrepancy between the orbital parameters derived from ground and space based observations. We show that, as the secondary moves in its orbit, the shell cools down and the number of available stellar ionizing photons is not enough to maintain the shell temperature at its equilibrium value of about 7500 K. The central part of the shell remains cold and under these conditions grain formation and growth can take place in timescales of hours. Using recently published HST data for the optical and UV continuum during the 2003 shell event, we estimated that a fraction of 0.01 of the interstellar dust to H ratio is enough to explain the observations. We also calculated the neutral gas column density intercepting the line of sight at each point of the orbit near periastron, and were able to reproduce the form and duration of the X-ray light curve without any change in the eta Carinae mass loss rate. This same column density can explain the observed H$\alpha$ light curve observed during the 2003 event.Comment: accepted to MNRA

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This chapter describes lasers and other sources of coherent light that operate in a wide wavelength range. First, the general principles for the generation of coherent continuous-wave and pulsed radiation are treated including the interaction of radiation with matter, the properties of optical resonators and their modes as well as such processes as Q-switching and mode-locking. The general introduction is followed by sections on numerous types of lasers, the emphasis being on todayʼs most important sources of coherent light, in particular on solid-state lasers and several types of gas lasers. An important part of the chapter is devoted to the generation of coherent radiation by nonlinear processes with optical parametric oscillators, difference- and sum-frequency generation, and high-order harmonics. Radiation in the extended ultraviolet (EUV) and x-ray ranges can be generated by free electron lasers (FEL) and advanced x-ray sources. Ultrahigh light intensities up to 1021 W/cm2 open the door to studies of relativistic laser–matter interaction and laser particle acceleration. The chapter closes with a section on laser stabilization