Eta Carinae, the closest, active, massive binary containing a highly unstable Luminous Blue Variable, exhibits expanding, compressed wind shells, seen in emission, that are spatially and spectrally ...resolved by Hubble Space Telescope/Space Telescope Imaging Spectrograph. Starting in 2009 June, these structures were mapped across its 5.54-yr, highly elliptical, binary orbit to follow temporal changes in the light of Fe iii 4659 Å and Fe ii 4815 Å. The emissions trace portions of fossil wind shells, that were formed by wind–wind interactions across each cycle. Over the high-ionization state, dense arcs, photoionized by far-ultraviolet radiation from the hot secondary, are seen in Fe iii. Other arcs, ionized by mid-ultraviolet radiation from the primary star, are seen in Fe ii. The Fe iii structures tend to be interior to Fe ii structures that trace extensive, less disturbed primary wind. During the brief periastron passage when the secondary plunges deep into the primary's extremely dense wind, on the far side of primary star, high-ionization Fe iii structures fade and reappear in Fe ii. Multiple fossil wind structures were traced across the 5.7-yr monitoring interval. The strong similarity of the expanding Fe ii shells suggests that the wind and photoionization properties of the massive binary have not changed substantially from one orbit to the next over the past several orbital cycles. These observations trace structures that can be used to test 3D hydrodynamical and radiative-transfer models of massive, interacting winds. They also provide a baseline for following future changes in η Car, especially of its winds and photoionization properties.
We have monitored the massive binary star ... Carinae with the CTIO/Small and Moderate Aperture Research Telescope System 1.5 m telescope and CHIRON spectrograph from the previous apastron passage of ...the system through the recent 2014.6 periastron passage. Our monitoring has resulted in a large, homogeneous data set with an unprecedented time-sampling, spectral resolving power, and signal to noise. This allowed us to investigate temporal variability previously unexplored in the system and discover a kinematic structure in the P Cygni absorption troughs of neutral helium wind lines. The features observed occurred prior to the periastron passage and are seen as we look through the trailing arm of the wind-wind collision shock cone. We show that the bulk of the variability is repeatable across the last five periastron passages, and that the absorption occurs in the inner 230 au of the system. In addition, we found an additional, high-velocity absorption component superimposed on the P Cygni absorption troughs that has been previously unobserved in these lines, but which bears resemblance to the observations of the He I ...10830 A feature across previous cycles. Through a comparison of the current smoothed particle hydrodynamical simulations, we show that the observed variations are likely caused by instabilities in the wind-wind collision region in our line of sight, coupled with stochastic variability related to clumping in the winds. (ProQuest: ... denotes formulae/symbols omitted.)
We have monitored the massive binary star ... Carinae with the CTIO/Small and Moderate Aperture Research Telescope System 1.5 m telescope and CHIRON spectrograph from the previous apastron passage of ...the system through the recent 2014.6 periastron passage. Our monitoring has resulted in a large, homogeneous data set with an unprecedented time-sampling, spectral resolving power, and signal to noise. This allowed us to investigate temporal variability previously unexplored in the system and discover a kinematic structure in the P Cygni absorption troughs of neutral helium wind lines. The features observed occurred prior to the periastron passage and are seen as we look through the trailing arm of the wind-wind collision shock cone. We show that the bulk of the variability is repeatable across the last five periastron passages, and that the absorption occurs in the inner 230 au of the system. In addition, we found an additional, high-velocity absorption component superimposed on the P Cygni absorption troughs that has been previously unobserved in these lines, but which bears resemblance to the observations of the He I ...10830 A feature across previous cycles. Through a comparison of the current smoothed particle hydrodynamical simulations, we show that the observed variations are likely caused by instabilities in the wind-wind collision region in our line of sight, coupled with stochastic variability related to clumping in the winds. (ProQuest: ... denotes formulae/symbols omitted.)
Eta Carinae is the most massive active binary within 10,000 light-years and is famous for the largest non-terminal stellar explosion ever recorded. Observations reveal that the supermassive (~120 M⊙) ...binary, consisting of an LBV and either a WR or extreme O star, undergoes dramatic changes every 5.54 years due to the stars’ very eccentric orbits (e ≈ 0.9). Many of these changes are caused by a dynamic wind-wind collision region (WWCR) between the stars, plus expanding fossil WWCRs formed one, two, and three 5.54-year cycles ago. The fossil WWCRs can be spatially and spectrally resolved by the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS). Starting in June 2009, we used the HST/STIS to spatially map Eta Carinae’s fossil WWCRs across one full orbit, following temporal changes in several forbidden emission lines (e.g. Feiii 4659 Å, Feii 4815 Å), creating detailed data cubes at multiple epochs. Multiple wind structures were imaged, revealing details about the binary’s orbital motion, photoionization properties, and recent (~5 − 15 year) mass-loss history. These observations allow us to test 3-D hydrodynamical and radiative-transfer models of the interacting winds. Our observations and models strongly suggest that the wind and photoionization properties of Eta Carinae’s binary have not changed substantially over the past several orbital cycles. They also provide a baseline for following future changes in Eta Carinae, essential for understanding the late-stage evolution of this nearby supernova progenitor. For more details, see Gull et al. (2016) and references therein.
The material lost through stellar winds of Asymptotic Giant Branch (AGB) stars is one of the main contributors to the chemical enrichment of galaxies. The general hypothesis of the mass loss ...mechanism of AGB winds is a combination of stellar pulsations and radiative pressure on dust grains, yet current models still suffer from limitations. Among others, they assume chemical equilibrium of the gas, which may not be justified due to rapid local dynamical changes in the wind. This is important as it is the chemical composition that regulates the thermal structure of the wind, the creation of dust grains in the wind, and ultimately the mass loss by the wind. Using a self-consistent hydrochemical model, we investigated how non-equilibrium chemistry affects the dynamics of the wind. This paper compares a hydrodynamical and a hydrochemical dust-free wind, with focus on the chemical heating and cooling processes. No sustainable wind arises in a purely hydrodynamical model with physically reasonable pulsations. Moreover, temperatures are too high for dust formation to happen, rendering radiative pressure on grains impossible. A hydrochemical wind is even harder to initiate due to efficient chemical cooling. However, temperatures are sufficiently low in dense regions for dust formation to take place. These regions occur close to the star, which is needed for radiation pressure on dust to sufficiently aid in creating a wind. Extending this model self-consistently with dust formation and evolution, and including radiation pressure, will help to understand the mass loss by AGB winds.
The highly eccentric binary system Eta Carinae shows numerous time-variable emission and absorption features. These observational signatures are the result of interactions between the complex ...three-dimensional (3D) wind-wind collision regions and photoionization by the luminous stars. Specifically, helium presents several interesting spectral features that provide important clues on the geometry and physical properties of the system and the individual stars. We use the SimpleX algorithm to post-process 3D smoothed particle hydrodynamics simulation output of the interacting winds in Eta Car in order to obtain the fractions of ionized helium assuming three different primary star mass-loss rates. The resultant ionization maps constrain the regions where helium is singly- and doubly-ionized. We find that reducing the primary's mass-loss rate increases the volume of He+. Lowering the primary mass-loss rate produces large variations in the volume of He+ in the pre-shock primary wind on the periastron side of the system. Our results show that binary orientations in which apastron is on our side of the system are more consistent with available observations. We suggest that small variations in the primary's mass-loss rate might explain the observed increase in HeI absorption in recent decades, although numerous questions regarding this scenario remain open. We also propose that the absence of broad HeI lines in the spectra of Eta Car between its 1890's eruption and 1944 might be explained by the companion star's He0+ ionizing photons not being able to penetrate the wind-wind interaction region, due to a higher primary mass-loss rate at that time (by a factor >2, compared to the present value).
Spectral observations of the massive colliding wind binary Eta Carinae show phase-dependent variations, in intensity and velocity, of numerous helium emission and absorption lines throughout the ...entire 5.54-year orbit. Approaching periastron, the 3D structure of the wind-wind interaction region (WWIR) gets highly distorted due to the eccentric (\(e \sim 0.9\)) binary orbit. The secondary star (\(\eta_{\mathrm{B}}\)) at these phases is located deep within the primary's dense wind photosphere. The combination of these effects is thought to be the cause of the particularly interesting features observed in the helium lines at periastron. We perform 3D radiative transfer simulations of \(\eta\) Car's interacting winds at periastron. Using the SimpleX radiative transfer algorithm, we post-process output from 3D smoothed particle hydrodynamic simulations of the inner 150 au of the \(\eta\) Car system for two different primary star mass-loss rates (\(\dot{M}_{\eta_{\mathrm{A}}}\)). Using previous results from simulations at apastron as a guide for the initial conditions, we compute 3D helium ionization maps. We find that, for higher \(\dot{M}_{\eta_{\mathrm{A}}}\), \(\eta_{\mathrm{B}}\) He\(^{0+}\)-ionizing photons are not able to penetrate into the pre-shock primary wind. He\(^{+}\) due to \(\eta_{\mathrm{B}}\) is only present in a thin layer along the leading arm of the WWIR and in a small region close to the stars. Lowering \(\dot{M}_{\eta_{\mathrm{A}}}\) allows \(\eta_{\mathrm{B}}\)'s ionizing photons to reach the expanding unshocked secondary wind on the apastron side of the system, and create a low fraction of He\(^{+}\) in the pre-shock primary wind. With apastron on our side of the system, our results are qualitatively consistent with the observed variations in strength and radial velocity of \(\eta\) Car's helium emission and absorption lines, which helps better constrain the regions where these lines arise.
We present results of full 3D hydrodynamical and radiative transfer simulations of the colliding stellar winds in the massive binary system Eta Carinae. We accomplish this by applying the SimpleX ...algorithm for 3D radiative transfer on an unstructured Voronoi-Delaunay grid to recent 3D smoothed particle hydrodynamics (SPH) simulations of the binary colliding winds. We use SimpleX to obtain detailed ionization fractions of hydrogen and helium, in 3D, at the resolution of the original SPH simulations. We investigate several computational domain sizes and Luminous Blue Variable primary star mass-loss rates. We furthermore present new methods of visualizing and interacting with output from complex 3D numerical simulations, including 3D interactive graphics and 3D printing. While we initially focus on Eta Car, the methods employed can be applied to numerous other colliding wind (WR 140, WR 137, WR 19) and dusty 'pinwheel' (WR 104, WR 98a) binary systems. Coupled with 3D hydrodynamical simulations, SimpleX simulations have the potential to help determine the regions where various observed time-variable emission and absorption lines form in these unique objects.
We have monitored the massive binary star $\eta$ Carinae with the CTIO/SMARTS
1.5~m telescope and CHIRON spectrograph from the previous apastron passage of
the system through the recent 2014.6 ...periastron passage. Our monitoring has
resulted in a large, homogeneous data set with an unprecedented time-sampling,
spectral resolving power, and signal-to-noise. This allowed us to investigate
temporal variability previously unexplored in the system and discover a
kinematic structure in the P Cygni absorption troughs of neutral helium wind
lines. The features observed occurred prior to the periastron passage and are
seen as we look through the trailing arm of the wind-wind collision shock cone.
We show that the bulk of the variability is repeatable across the last five
periastron passages, and that the absorption occurs in the inner 230 AU of the
system. In addition, we found an additional, high-velocity absorption component
super-imposed on the P Cygni absorption troughs that has been previously
un-observed in these lines, but which bears resemblance to the observations of
the He~I $\lambda$10830 \AA\ feature across previous cycles. Through a
comparison of the current smoothed particle hydrodynamical simulations, we show
that the observed variations are likely caused by instabilities in the
wind-wind collision region in our line-of-sight, coupled with stochastic
variability related to clumping in the winds.
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