We propose that the intermediate luminosity optical transient NGC 300 OT2008-1 was powered by a mass transfer episode from an extreme Asymptotic Giant Branch star to a Main Sequence companion. We find a remarkable similarity of the shapes of the light curves of the several months long NGC 300 OT2008-1 outburst, of the three months long 2002 enigmatic outburst of the B star V838 Mon, and the twenty-years long Great Eruption of the massive binary system Eta Carinae that occurred in the 19th century. Their similar decline properties hint to a common energy source: a gravitational energy that is released by accretion onto a main sequence star. These events populate a specific strip in the total energy vs. outburst duration diagram. The strip is located between novae and supernovae. We add recent transient events to that diagram and find them to occupy the same strip. This suggests that some intermediate luminosity optical transients are powered by accretion onto a compact object (not necessarily a main sequence star). These transients are expected to produce bipolar ejecta as a result of the geometry of the accretion process.
$η$ Carinae is an extraordinary massive star famous for its 19th century Great Eruption and the surrounding Homunculus nebula ejected in that event. The cause of this eruption has been the centre of a long-standing mystery. Recent observations, including light-echo spectra of the eruption, suggest that it most likely resulted from a stellar merger in an unstable triple system. Here we present a detailed set of theoretical calculations for this scenario; from the dynamics of unstable triple systems and the mass ejection from close binary encounters, to the mass outflow from the eruption caused …
During the years 1838-1858, the very massive star η Carinae became the prototype supernova impostor: it released nearly as much light as a supernova explosion and shed an impressive amount of mass, but survived as a star.1 Based on a light-echo spectrum of that event, Rest et al.2 conclude that "a new physical mechanism" is required to explain it, because the gas outflow appears cooler than theoretical expectations. Here we note that (1) theory predicted a substantially lower temperature than they quoted, and (2) their inferred observational value is quite uncertain. Therefore, analyses so far…
Gaia parallaxes for the star cluster Tr 16 reveal a discrepancy in the oft-quoted distance of Eta Carinae. It is probably more distant and more luminous. Moreover, many presumed members may not belong to Tr 16.
We present preliminary results of our analysis on the long-term variations observed in the optical spectrum of the LBV star Eta Carinae. Based on the hydrogen line profiles, we conclude that the physical parameters of the primary star did not change in the last 15 years.
A series of three HST/STIS spectroscopic mappings, spaced approximately one year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving outward from eta Carinae. We identify these arcs with the shell-like structures, seen in the 3D hydrodynamical simulations, formed by compression of the primary wind by the secondary wind during periastron passages.
We argue that the emission and the absorption components of he N II lines recently observed in Eta Carinae can originate in the secondary's wind acceleration zone. We base this claim in part on the presence of these lines in hot nitrogen rich stars, such as WN 8 stars, and on the expected clumpy nature of such winds. The envelope of the secondary star in Eta Carinae is expected to be nitrogen rich due to accretion of few solar masses of the primary luminous blue variable's nitrogen rich material during the nineteenth century Great Eruption. Another argument in support of N II lines origin in t…
Major stellar-wind emission features in the spectrum of Eta Car have recently decreased by factors of order 2 relative to the continuum. This is unprecedented in the modern observational record. The simplest, but unproven, explanation is a rapid decrease in the wind density.
We reconstruct the evolution of Eta Carinae in the last two centuries, under the assumption that the two 19th century eruptions were triggered by periastron passages, and by that constrain the binary parameters. The beginning of the Lesser Eruption (LE) at the end of the 19th century occurred when the system was very close to periastron passage, suggesting that the secondary triggered the LE. We assume that the 1838-1858 Great Eruption (GE) was triggered by a periastron passage as well. We also assume that mass transferred from the primary to the secondary star accounts for the extra energy of…
We have observed Eta Carinae over 34 nights between 4th January 2009 and 27th March 2009 covering the estimated timeframe for a predicted spectroscopic event related to a suspected binary system concealed within the homunculus nebula. A photometric minimum feature was confirmed to be periodic and comparison to a previous event indicated that the period to within our error at 2022.6 +/-1.0 d. Using the E-region standard star system, the apparent V magnitudes determined for the local comparison stars were HD303308 8.14+/-0.02, HD 93205 7.77 +/-0.03 and HD93162 8.22 +/-0.05. The latter star was f…
Eta Carinae's spectroscopic events (periastron passages) in 2003, 2009, and 2014 differed progressively. He II 4687 and nearby N II multiplet 5 have special significance because they respond to very soft X-rays and the ionizing UV radiation field (EUV). HST/STIS observations in 2014 show dramatic increases in both features compared to the previous 2009.1 event. These results appear very consistent with a progressive decline in the primary wind density, proposed years ago on other grounds. If material falls onto the companion star near periastron, the accretion rate may now have become too low …
We analyze eight epochs of Hubble Space Telescope H$α$+[N II] imaging of Eta Carinae's outer ejecta. Proper motions of nearly 800 knots reveal that the detected ejecta are divided into three apparent age groups, dating to around 1250 A.D., to around 1550 A.D., and to during or shortly before the Great Eruption of the 1840s. Ejecta from these groups reside in different locations and provide a firm constraint that Eta Car experienced multiple major eruptions prior to the 19th century. The 1250 and 1550 events did not share the same axisymmetry as the Homunculus; the 1250 event was particularly a…
The detection by Rest et al. (2012) of light echoes from $η$ Carinae has provided important new observational constraints on the nature of its 1840's era giant eruption. Spectra of the echoes suggest a relatively cool spectral temperature of about 5500K, lower than the lower limit of about 7000K suggested in the optically thick wind outflow analysis of Davidson (1987). This has lead to a debate about the viability of this steady wind model relative to alternative, explosive scenarios. Here we present an updated analysis of the wind outflow model using newer low-temperature opacity tabulations …
We use recent observations of the He I $\lambda10830 Å$ absorption line and 3D hydrodynamical numerical simulations of the winds collision, to strengthen the case for an orientation of the semimajor axis of the massive binary system Eta Carinae where the secondary star is toward us at periastron passage. Those observations show that the fast blue absorption component exists for only several weeks prior to the periastron passage. We show that the transient nature of the fast blue absorption component supports a geometry where the fast secondary wind, both pre and post-shock material, passes in …
In this work, we present new two-dimensional hydrodynamical simulations of the major eruption of $η$ Car in the 1840s, which resulted in the formation of a bipolar nebula that is commonly known as the large Homunculus. In our numerical models, we have included the high-speed component of 10000 km s$^{-1}$, detected in recent observations, that provides direct evidence of an explosive event. Here, we investigate whether such a violent explosion is able to explain both the shape and the dynamical evolution of $η$ Car's nebula. As in our previous work, we have assumed a two-stage scenario for $η$…
We conduct 3D numerical simulations of the winds collision process in the massive binary system Eta Carinae, and conclude that accretion occurs during periastron passage. We include radiative cooling of the two winds, one from each star, and the gravity of the secondary and primary stars. Our new numerical finding is that at an orbital separation of ~3-4AU, about three weeks before periastron passage, accretion of dense primary wind gas onto the secondary star begins. To isolate the basic role of the secondary stellar gravity, we neglect the orbital motion and the acceleration zone of the prim…
We report on the N II 5668-5712 emission and absorption lines in the spectrum of Eta Carinae. Spectral lines of the stellar wind regions can be classified into four physically distinct categories: 1) low-excitation emission such as H I and Fe II, 2) higher excitation He I features, 3) the N II lines discussed in this paper, and 4) He II emission. These categories have different combinations of radial velocity behavior, excitation processes, and dependences on the secondary star. The N II lines are the only known features that originate in "normal" undisturbed zones of the primary wind but depe…
We discuss the events that led to the giant eruption of Eta Carinae, and find that the mid-nineteenth century (in 1838-1843) giant mass-loss outburst has the characteristics of being produced by the merger event of a massive close binary, triggered by the gravitational interaction with a massive third companion star, which is the current binary companion in the Eta Carinae system. We come to this conclusion by a combination of theoretical arguments supported by computer simulations using the Astrophysical Multipurpose Software Environment. According to this model the $\sim 90$\,\MSun\, present…
We present evidence that the Boorong Aboriginal people of northwestern Victoria observed the Great Eruption of Eta (η) Carinae in the nineteenth century and incorporated the event into their oral traditions. We identify this star, as well as others not specifically identified by name, using descriptive material presented in the 1858 paper by William Edward Stanbridge in conjunction with early southern star catalogues. This identification of a transient astronomical event supports the assertion that Aboriginal oral traditions are dynamic and evolving, and not static. This is the only definitive…
The Weigelt knots, dense slow-moving ejecta near eta Car, are mysterious in structure as well as in origin. Using a special set of spectrograms obtained with the HST/STIS, we have partially resolved the ionization zones of one knot to an accuracy of about 10 mas. Contrary to simple models, higher ionization levels occur on the_outer_ side of the knot, i.e., farther from the star. They cannot represent a bow shock, and no truly satisfying explanation is yet available -- though we sketch one tentative possibility. We emphasize that STIS spectrograms provide far more reliable spatial measurements…
During the past decade several observational and theoretical works provided evidences of the binary nature of Eta Carinae. Nevertheless, there is still no direct determination of the orbital parameters, and the different current models give contradictory results. The orbit is, in general, assumed to coincide with the Homunculus equator although the observations are not conclusive. Among all systems, Eta Carinae has the advantage that it is possible to observe both the direct emission of line transitions in the central source and its reflection by the Homunculus, which are dependent on the orbi…
Eta Carinae is considered to be a massive colliding wind binary system with a highly eccentric (e \sim 0.9), 5.54-yr orbit. However, the companion star continues to evade direct detection as the primary dwarfs its emission at most wavelengths. Using three-dimensional (3-D) SPH simulations of Eta Car's colliding winds and radiative transfer codes, we are able to compute synthetic observables across multiple wavebands for comparison to the observations. The models show that the presence of a companion star has a profound influence on the observed HST/STIS UV spectrum and H-alpha line profiles, a…
Stellar wind-emission features in the spectrum of eta Carinae have decreased by factors of 1.5-3 relative to the continuum within the last 10 years. We investigate a large data set from several instruments (STIS, GMOS, UVES) obtained between 1998 and 2011 and we analyze the progression of spectral changes in the direct view of the star, in the reflected polar-on spectra at FOS4, and at the Weigelt knots. We find that the spectral changes occurred gradually on a time scale of about 10 years and that they are dependent on the viewing angle. The line strengths declined most in our direct view of …
We report on H-alpha spectroscopy of the 2009.0 spectroscopic event of eta Carinae collected via SMARTS observations using the CTIO 1.5 m telescope and echelle spectrograph. Our observations were made almost every night over a two month interval around the predicted minimum of eta Car. We observed a significant fading of the line emission that reached a minimum seven days after the X-ray minimum. About 17 d prior to the H-alpha flux minimum, the H-alpha profile exhibited the emergence of a broad, P Cygni type, absorption component (near a Doppler shift of -500 km/s) and a narrow absorption com…
The massive evolved star Eta Carinae is the most luminous star in the Milky Way and has the highest steady wind mass-loss rate of any known star. Radiative transfer models of the spectrum by Hillier et al. predict that H-alpha is mostly emitted in regions of the wind at radii of 6 to 60 AU from the star (2.5 to 25 mas at 2.35 kpc). We present diffraction-limited images (FWHM ~25 mas) with Magellan adaptive optics in two epochs, showing that Eta Carinae consistently appears ~2.5 to 3 mas wider in H-alpha emission compared to the adjacent 643 nm continuum. This implies that the H-alpha line-form…
We present an analysis of the visible through near infrared spectrum of Eta Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES at the ESO VLT". This is a part of larger effort to present a complete Eta Carinae spectrum, and extends the previously presented analyses with the HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near UV is characterized by the ejecta absorption. At longer wavelengths, stellar wind features from the central source and narrow emission lines from the Weigelt condensations dominate the spectrum. However, narrow absorpt…
We present high resolution numerical simulations of the colliding wind system $η$ Carinae, showing accretion onto the secondary star close to periastron passage. Our hydrodynamical simulations include self gravity and radiative cooling. The smooth stellar winds collide and develop instabilities, mainly the non-linear thin shell instability, and form filaments and clumps. We find that a few days before periastron passage the dense filaments and clumps flow towards the secondary as a result of its gravitational attraction, and reach the zone where we inject the secondary wind. We run our simulat…
Homunculus Nebula is surrounding the star system Eta Carinae. The nebula is embedded within a much larger ionized hydrogen region, which is the Carina Nebula. Homunculus is believed to have been ejected in a huge outburst from Eta Carinae in 1841, so brightly to be visible from Earth. This massive explosion produced two polar lobes and an equatorial disc, moving outwards. Though Eta Carinae is quite away, approximately 7,500 light-years, it is possible to distinguish in the nebula, many structures with the size of about the diameter of our solar system. Knots, dust lanes and radial streaks app…
The binary eta Carinae is the closest example of a very massive star, which may have formed through a merger during its Great Eruption in the mid-nineteenth century. We aimed to confirm and improve the kinematics using a spectroscopic data set taken with the CTIO 1.5 m telescope over the time period of 2008-2020, covering three periastron passages of the highly eccentric orbit. We measure line variability of H-alpha and H-beta, where the radial velocity and orbital kinematics of the primary star were measured from the H-beta emission line using a bisector method. At phases away from periastron…
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-l…
We use the accretion model to explain the early exit of Eta Carinae from its 2009 X-ray minimum. In the accretion model the secondary star accretes mass from the primary wind near periastron passage, a process that suppresses the secondary wind. As the shocked secondary wind is responsible for most of the X-ray emission, the accretion process accounts for the X-ray minimum. The early exit from the 2009 X-ray minimum after four weeks, instead of ten weeks as in the two previous minima, is attributed to the primary wind that during the last minimum was somewhat faster and of lower mass loss rate…
Contrary to recent claims, we argue that the orientation of the massive binary system Eta Carinae is such that the secondary star is closer to us at periastron passage, and it is on the far side during most of the time of the eccentric orbit. The binary orientation we dispute is based on problematic interpretations of recent observations. Among these observations are the radial velocity of the absorption component of He I P-Cyg lines, of the He II $\lambda4686$ emission line, and of the Br$γ$ line emitted by clumps close to the binary system. We also base our orientation on observations of asy…
Existing HST UV data offer many previously neglected clues to eta Car's behavior since 2000. Here we examine a subset of observations with diverse results. (1) The star's rapid change of state is confirmed by major changes in UV absorption lines, circumstellar extinction, and other features. (2) N III] 1750 is one of the two most luminous emission features in eta Car's observable spectrum, comparable to H-alpha. This and other semi-forbidden lines are useful because they have no P Cyg absorption. (3) N III] multiplet ratios provide the first direct diagnostic of gas densities in eta Car's outf…
We present the first 3D prints of output from a supercomputer simulation of a complex astrophysical system, the colliding stellar winds in the massive (>120 M_Sun), highly eccentric (e ~ 0.9) binary star system Eta Carinae. We demonstrate the methodology used to incorporate 3D interactive figures into a PDF journal publication and the benefits of using 3D visualization and 3D printing as tools to analyze data from multidimensional numerical simulations. Using a consumer-grade 3D printer (MakerBot Replicator 2X), we successfully printed 3D smoothed particle hydrodynamics (SPH) simulations of Et…
We show that recent observations of He I and N II lines of $η$ Carinae may provide support for an orbital orientation where the secondary star is closest to us at periastron passages. This conclusion is valid both for the commonly assumed masses of the two stars, and for the higher stellar masses model where the very massive evolved primary star mass is $M_1=170 M_\odot$ and its hot secondary star mass is $M_2 = 80 M_\odot$. The later model better explains the change in the orbital period assuming that the ninetieth century Great Eruption was powered by accretion onto the secondary star. Adopt…
The periodic spectroscopic events in eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of eta Carinae with 5 Southern telescopes during the …
We argue that the asymmetric morphology of the blue and red shifted components of the outflow at hundreds of AU from the massive binary system Eta Carinae can be understood from the collision of the primary stellar wind with the slowly expanding dense equatorial gas. Recent high spatial observations of some forbidden lines, e.g. [Fe III] lambda4659, reveal the outflowing gas within about one arcsecond (2300 AU) from Eta Car. The distribution of the blue and red shifted components are not symmetric about the center, and they are quite different from each other. The morphologies of the blue and …
We perform three-dimensional gas-dynamical simulations and show that the asymmetric morphology of the blue and red-shifted components of the outflow at hundreds of astronomical units (AU) from the massive binary system eta Carinae can be accounted for from the collision of the free primary stellar wind with the slowly expanding dense equatorial gas. Owing to the very complicated structure of the century-old equatorial ejecta, that is not fully spatially resolved by observations, we limit ourselves to modelling the equatorial dense gas by one or two dense spherical clouds. Because of that we re…
We perform 3D hydrodynamical numerical simulations of the winds interaction process in the massive binary system $η$ Carinae, and find the secondary star to accrete mass from the dense primary wind close to periastron passage. This accretion is thought to result in the spectroscopic event and X-ray minimum observed in the system every revolution. In this study we limit ourselves to explore the role of clumps in the primary wind in triggering the accretion process. We include the gravity of the secondary star and the orbital motion starting 19 days (90 degrees) before periastron passage. The ac…
Recent work suggests that the mass-loss rate of the primary star (Eta A) in the massive colliding wind binary Eta Carinae dropped by a factor of 2-3 between 1999 and 2010. We present results from large- (r=1545au) and small- (r=155au) domain, 3D smoothed particle hydrodynamic (SPH) simulations of Eta Car's colliding winds for 3 Eta A mass-loss rates (2.4, 4.8, and 8.5 x 10^-4 M_sun/yr), investigating the effects on the dynamics of the binary wind-wind collision (WWC). These simulations include orbital motion, optically thin radiative cooling, and radiative forces. We find that Eta A's mass-los…
It is believed that eta Carinae is actually a massive binary system, with the wind-wind interaction responsible for the strong X-ray emission. Although the overall shape of the X-ray light curve can be explained by the high eccentricity of the binary orbit, other features like the asymmetry near periastron passage and the short quasi-periodic oscillations seen at those epochs, have not yet been accounted for. In this paper we explain these features assuming that the rotation axis of eta Carinae is not perpendicular to the orbital plane of the binary system. As a consequence, the companion star…
In our ongoing study of eta Carinae's light echoes, there is a relatively bright echo that has been fading slowly, reflecting the 1845-1858 plateau of the eruption. A separate paper discusses its detailed evolution, but here we highlight one important result: the H-alpha line shows extremely broad emission wings that reach -10,000km/s to the blue and +20,000km/s to the red. The line profile shape is inconsistent with electron scattering wings, indicating high-velocity outflowing material. These are the fastest outflow speeds ever seen in a non-terminal massive star eruption. The broad wings ar…
Eta Carinae, the closest, active, massive binary containing a highly unstable LBV, exhibits expanding, compressed wind shells, seen in emission, that are spatially and spectrally resolved by \hst/\stis. Starting in June 2009, these structures were mapped across its 5.54-year, highly elliptical, binary orbit to follow temporal changes in the light of [Fe~III] 4659Å and [Fe~II] 4815Å. 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, photo-ionized by far ultraviolet radiation from the hot …
Eta Carinae shows broad peaks in near-infrared (IR) JHKL photometry, roughly correlated with times of periastron passage in the eccentric binary system. After correcting for secular changes attributed to reduced extinction from the thinning Homunculus Nebula, these peaks have IR spectral energy distributions (SEDs) consistent with emission from hot dust at 1400-1700 K. The excess SEDs are clearly inconsistent, however, with the excess being entirely due to free-free wind or photospheric emission. One must conclude, therefore, that the broad near-IR peaks associated with Eta Carinae's 5.5 yr va…
We study the usage of the X-ray light curve, column density toward the hard X-ray source, and emission measure (density square times volume), of the massive binary system Eta Carinae to determine the orientation of its semi-major axis. The source of the hard X-ray emission is the shocked secondary wind. We argue that, by itself, the observed X-ray flux cannot teach us much about the orientation of the semi-major axis. Minor adjustment of some unknown parameters of the binary system allows to fit the X-ray light curve with almost any inclination angle and orientation. The column density and X-r…
We present multi-epoch photometry and spectroscopy of a light echo from eta Carinae's 19th century Great Eruption. This echo shows a steady decline over a decade, sampling the 1850s plateau of the eruption. Spectra show the bulk outflow speed increasing from 150 km/s at early times, up to 600 km/s in the plateau. Later phases also develop remarkably broad emission wings indicating mass accelerated to more than 10,000 km/s. Together with other clues, this provides direct evidence for an explosive ejection. This is accompanied by a transition from narrow absorption lines to emission lines, often…
In late 2006, ground-based photometry of $η$ Car plus the Homunculus showed an unexpected decrease in its integrated apparent brightness, an apparent reversal of its long-term brightening. Subsequent HST/WFPC2 photometry of the central star in the near-UV showed that this was not a simple reversal. This multi-wavelength photometry did not support increased extinction by dust as the explanation for the decrease in brightness. A spectrum obtained with GMOS on the Gemini-South telescope, revealed subtle changes mid-way in $η$ Car's 5.5 yr spectroscopic cycle 0when compared with HST/STIS spectra a…
FUV spectra of Eta Car, recorded across two decades with HST/STIS, document multiple changes in resonant lines caused by dissipating extinction in our line of sight. The FUV flux has increased nearly ten-fold which has led to increased ionization of the multiple shells within the Homunculus and photo-destruction of molecular hydrogen. Comparison of observed resonant line profiles with CMFGEN model profiles allows separation of wind-wind collision and shell absorptions from the primary wind, P Cygni profiles.The dissipating occulter preferentially obscured the central binary and interacting win…
Near-infrared adaptive optics imaging with NICI and NaCO reveal what appears to be a three-winged or lobed pattern, the "butterfly nebula", outlined by bright Br$γ$ and H$_{2}$ emission and light scattered by dust. In contrast, the [Fe II] emission does not follow the outline of the wings, but shows an extended bipolar distribution which is tracing the Little Homunculus ejected in $η$ Car's second or lesser eruption in the 1890's. Proper motions measured from the combined NICI and NaCO images together with radial velocities show that the knots and filaments that define the bright rims of the b…
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 …
Context. Colliding-wind binaries are massive stellar systems featuring strong, interacting winds. These binaries may be actual particle accelerators, making them variable gamma-ray sources due to changes in the wind collision region along the orbit. However, only two of these massive stellar binary systems have been identified as high-energy sources. The first and archetypical system of this class is Eta Carinae, a bright gamma-ray source with orbital variability peaking around its periastron passage. Aims. The origin of the high energy emission in Eta Carinae is still unclear, with both lepto…
We present a new model for the behavior of scattered time-dependent, asymmetric near-UV emission from the nearby ejecta of η Car. Using a 3-D hydrodynamical simulation of η Car's binary colliding winds, we show that the 3-D binary orientation derived by Madura et al. (2012) is capable of explaining the asymmetric near-UV variability observed in the Hubble Space Telescope Advanced Camera for Surveys/High Resolution Camera (HST ACS/HRC) F220W images of Smith et al. (2004b). Models assuming a binary orientation with i ~ 130 to 145 degrees, ω ~ 230 to 315 degrees, PAz ~ 302 to 327 degrees are cons…
We report new HST/STIS observations that map the high-ionization forbidden line emission in the inner arcsecond of Eta Car, the first that fully image the extended wind-wind interaction region of the massive colliding wind binary. These observations were obtained after the 2009.0 periastron at orbital phases 0.084, 0.163, and 0.323 of the 5.54-year spectroscopic cycle. We analyze the variations in brightness and morphology of the emission, and find that blue-shifted emission (-400 to -200 km s-1) is symmetric and elongated along the northeast-southwest axis, while the red-shifted emission (+10…
We use high resolution 3D hydrodynamical simulations to quantify the amount of mass accreted onto the secondary star of the binary system Eta Carinae, exploring two sets of stellar masses that had been proposed for the system, the conventional mass model ($M_1=120 M_{\odot}$ and $M_2=30 M_{\odot}$) and the high mass model ($M_1=170 M_{\odot}$ and $M_2=80 M_{\odot}$). The system consists of two very massive stars in a highly eccentric orbit. Every cycle close to periastron passage the system experiences a spectroscopic event during which many lines change their appearance, accompanied by a decl…
The accretion model for the nineteenth century Great Eruption (GE) of $η$ Carinae suggests that mass outflowing from the primary was accreted onto the secondary, and the gravitational energy of that mass accounts for the increase in luminosity and most of the kinetic energy of the ejecta. It further argues that the accretion was accompanied by the ejection of two jets that shaped the bipolar Homunculus nebula. Observations of echos from the GE found emission lines with broad wings suggesting some of the mass in equatorial directions reached more than $10\,000 \,\rm{km\,s^{-1}}$. We run hydrody…
While SN impostors resemble the Great Eruption of eta Car in the sense that their spectra show narrow H lines and they have typical peak absolute magnitudes of -13 to -14 mag, most extragalactic events observed so far are quite different from eta Car in duration. Their bright phases typically last for 100~d or less, rather than persisting for several years. The transient object UGC2773-OT had a similar peak absolute magnitude to other SN impostors, but with a gradual 5-yr prediscovery rise. In the 6 yr since discovery, it has faded very slowly (0.26 mag/yr). Overall, we suggest that its decade…
We present a three-dimensional (3-D) dynamical model for the broad [Fe III] emission observed in Eta Carinae using the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS). This model is based on full 3-D Smoothed Particle Hydrodynamics (SPH) simulations of Eta Car's binary colliding winds. Radiative transfer codes are used to generate synthetic spectro-images of [Fe III] emission line structures at various observed orbital phases and STIS slit position angles (PAs). Through a parameter study that varies the orbital inclination i, the PA θ that the orbital plane projection of…
The periodic events occurring in Eta Carinae have been widely monitored during the last three 5.5-year cycles. The last one recently occurred in January 2009 and more exhaustive observations have been made at different wavelength ranges. If these events are produced when the binary components approach periastron, the timing and sampling of the photometric features can provide more information about the geometry and physics of the system. Thus, we continued with our ground-based optical photometric campaign started in 2003 to record the behaviour of the 2009.0 event in detail. This time the obs…
The HST archive contains a large collection of images of eta Carinae, and this paper analyzes those most suitable for measuring its expanding Homunculus Nebula. Multiple intensity tracings through the Homunculus reveal the fractional increase in the overall size of the nebula; this avoids registration uncertainty, mitigates brightness fluctuations, and is independent of previous methods. Combining a 13-yr baseline of Wide Field Planetary Camera 2 (WFPC2) images in the F631N filter, with a 4-yr baseline of Advanced Camera for Surveys/High Resolution Channel (ACS/HRC) images in the F550M filter,…
In order to study the distribution of gas and ionizing radiation around eta Car and their implications for its likely companion star, we have examined high-excitation emission lines of [Ne III], [Fe III], etc., in spectra obtained with the HST/STIS instrument during 1998-2004. Our principal results, some of them unexpected, are: (1) The high-excitation fluxes varied systematically and non-trivially throughout eta Car's 5.5-year spectroscopic cycle. Instead of rising to a plateau after the 1998 "event," they changed continuously with a maximum in mid-cycle. (2) At one significant location a bri…
