Very massive stars shed much of their mass in violent precursor eruptions as luminous blue variables (LBVs) before reaching their most likely end as supernovae, but the cause of LBV eruptions is unknown. The 19th century eruption of Eta Carinae, the prototype of these events, ejected about 12 solar masses at speeds of 650 km/s, with a kinetic energy of almost 10^50 ergs. Some faster material with speeds up to 1000-2000 km/s had previously been reported but its full distribution was unknown. Here I report observations of much faster material with speeds up to 3500-6000 km/s, reaching farther from the star than the fastest material in earlier reports. This fast material roughly doubles the kinetic energy of the 19th century event, and suggests that it released a blast wave now propagating ahead of the massive ejecta. Thus, Eta Car's outer shell now mimics a low-energy supernova remnant. The eruption has usually been discussed in terms of an extreme wind driven by the star's luminosity, but fast material reported here suggests that it was powered by a deep-seated explosion rivalling a supernova, perhaps triggered by the pulsational pair instability. This may alter interpretations of similar events seen in other galaxies.
I examine the angular momentum evolution during the 1837-1856 Great Eruption of the massive star Eta Carinae. I find that the new estimate of the mass blown during that eruption implies that the envelope of Eta Car substantially spun-down during the 20 years eruption. Single-star models, most of which require the envelope to rotate close to the break-up velocity, cannot account for the bipolar nebula (the Homunculus) formed from matter expelled in that eruption. The kinetic energy and momentum of the Homunculus further constrains single-star models. I discuss how Eta Car can fit into a unified…
I compare the structures of the bipolar nebulae around the massive binary system Eta Carinae and around the low mass binary system HD 44179. While Eta Carinae is on its way to become a supernova, the Red Rectangle is on its way to form a planetary nebula. Despite the two orders of magnitude difference in mass, these two systems show several similarities, both in the properties of the stellar binary systems and the nebulae. From this comparison and further analysis of the accretion process during the 20 years Great Eruption of Eta Carinae, I strengthen the binary model for the formation of its …
I argue that the large scale departure from axisymmetry of the Eta Carinae nebula can be explained by the binary stars model of Eta Carinae. The companion diverts the wind blown by the primary star, by accreting from the wind and possibly by blowing its own collimated fast wind (CFW). The effect of these processes depends on the orbital separation, hence on the orbital phase of the eccentric orbit. The variation of the mass outflow from the binary system with the orbital phase leads to a large-scale departure from axisymmetry along the equatorial plane, as is observed in Eta Car. I further spe…
I discuss the role of short-duration eruptive mass loss in the evolution of very massive stars. Giant eruptions of Luminous Blue Variables (LBVs) like the 19th century event of $η$ Carinae can remove large quantities of mass almost instantaneously, making them significant in stellar evolution. They can potentially remove more mass from the star than line-driven winds, especially if winds are clumped such that O star mass-loss rates need to be revised downward. When seen in other galaxies as ``supernova impostors'', these eruptions typically last for less than a decade, and they can remove of o…
Eta Carinae was observed by FUSE through the LWRS (30 arcsec x30 arcsec) and HIRS (1.25 arcsec x 20 arcsec) apertures in March and April 2004. There are significant differences between the two spectra. About half of the LWRS flux appears to be due to two B-type stars near the edge of the LWRS aperture, 14 arcsec from eta Carinae. The HIRS spectrum (LiF1 channel) therefore reveals the intrinsic FUV spectrum of eta Carinae without this stellar contamination. The HIRS spectrum contains strong interstellar H2 having high rotational excitation (up to J=8). Most of the atomic species with prominent …
We present thermal infrared images of the bipolar nebula surrounding eta Carinae at six wavelengths from 4.8 to 24.5 microns. These were obtained with the MIRAC3 camera system at the Magellan Observatory. Our images reveal new intricate structure in the bright core of the nebula, allowing us to re-evaluate interpretations of morphology seen in images with lower resolution. Complex structures in the core might not arise from a pair of overlapping rings or a cool (110 K) and very massive dust torus, as has been suggested recently. Instead, it seems more likely that the arcs and compact knots com…
High-resolution spectra of [Fe II] 16435 around eta Carinae provide powerful diagnostics of the geometry and kinematics of the ``Little Homunculus'' (LH) growing inside the larger Homunculus nebula. The LH expansion is not perfectly homologous: while low-latitudes are consistent with linear expansion since 1910, the polar caps imply ejection dates around 1920--1930. However, the expansion speed of the LH is slower than the post-eruption wind, so the star's powerful wind may accelerate it. With an initial ejection speed of 200 km/s in 1890, the LH would have been accelerated to its present spee…
The Luminous Blue Variable star Eta Carinae is one of the most massive stars known. It underwent a giant eruption in 1843 in which the Homunculus nebula was created. ROSAT and ASCA data indicate the existence of a hard and a soft X-ray component which appear to be spatially distinct: a softer diffuse shell of the nebula around Eta Carinae and a harder point-like source centered on the star Eta Car. Astonishingly the morphology of the X-ray emission is very different from the optical appearance of the nebula. We present a comparative analysis of optical morphology, the kinematics, and the diffu…
(abridged) We report our discovery and observations of the peculiar Type IIn supernova SN2006gy in NGC1260, revealing that it reached a peak magnitude of -22, making it the most luminous supernova ever recorded. It is not yet clear what powers the total radiated energy of 1e51 erg, but we argue that any mechanism -- thermal emission, circumstellar interaction, or 56Ni decay -- requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star probably experienced an LBV eruption like the 19th century eruption of eta Cari…
Eta Carinae is a very luminous and unstable evolved star. Outflowing material ejected during the star's giant eruption in 1843 surrounds it as a nebula which consists of an inner bipolar region(the Homunculus) and the Outer Ejecta. The outer ejecta is very filamentary and shaped irregularly. Kinematic analysis, however, shows a regular bi-directional expansion despite of the complex morphology. Radial velocities in the outer ejecta reach up to 2000 kms/s and give rise to X-ray emission first detected by ROSAT. We will present a detailed study of the outer ejecta based on HST images, high-resol…
We present a case study of the 13 July 2004 solar event, in which disturbances caused by eruption of a filament from an active region embraced a quarter of the visible solar surface. Remarkable are absorption phenomena observed in the SOHO/EIT 304 A channel; they were also visible in the EIT 195 A channel, in the H-alpha line, and even in total radio flux records. Coronal and Moreton waves were also observed. Multi-spectral data allowed reconstructing an overall picture of the event. An explosive filament eruption and related impulsive flare produced a CME and blast shock, both of which decele…
During $η$ Car's spectroscopic event in mid-2003, the stellar wind's bright H$α$ and H$β$ emission lines temporarily had a distinctive shape unlike that reported on any previous occasion, and particularly unlike the 1997--98 event. Evidently the structure of the wind changed between 1997 and 2003. Combining this with other evidence, we suspect that the star may now be passing through a rapid stage in its recovery from the Great Eruption seen 160 years ago. In any case the data indicate that successive spectroscopic events differ, and the hydrogen line profiles are quantitative clues to the abn…
The extremely luminous and unstable star Eta Carinae is surrounded by ejecta formed during the star's giant eruption around 1843. The optical nebula consists of an inner region, the bipolar Homunculus and the outer ejecta. The X-ray emission as detected in ROSAT and CHANDRA shows a hook shaped emission structure mainly at the position of the outer ejecta substantially larger than the Homunculus. We present results of a comparative study of the optical morphology, the kinematics and the X-ray emission of the outer ejecta around Eta Carinae. In general we find that the X-ray emission traces the …
Stellar explosions such as novae and supernovae produce most of the heavy elements in the Universe. Although the onset of novae from runaway thermonuclear fusion reactions on the surface of a white dwarf in a binary star system is understood[1], the structure, dynamics, and mass of the ejecta are not well known. In rare cases, the white dwarf is embedded in the wind nebula of a red-giant companion; the explosion products plow through the nebula and produce X-ray emission. Early this year, an eruption of the recurrent nova RS Ophiuchi[2,3] provided the first opportunity to perform comprehensive…
We report the first detection of ammonia in the Homunculus nebula around eta Carinae, which is also the first detection of emission from a polyatomic molecule in this or any other luminous blue variable (LBV) nebula. Observations of the NH3 (J,K)=(3,3) inversion transition made with the Australia Telescope Compact Array reveal emission at locations where infrared H2 emission had been detected previously, near the strongest dust emission in the core of the Homunculus. We also detect ammonia emission from the so-called ``strontium filament'' in the equatorial disk. The presence of NH3 around eta…
I examine some aspects of the interaction between the massive star Eta Carinae and its companion, in particular during the eclipse-like event, known as the spectroscopic event or the shell event. The spectroscopic event is thought to occur when near periastron passages the stellar companion induces much higher mass loss rate from the primary star, and/or enters into a much denser environment around the primary star. I find that enhanced mass loss rate during periastron passages, if it occurs, might explain the high eccentricity of the system. However, there is not yet a good model to explain t…
In this paper, we present two-dimensional gas dynamic simulations of the formation and evolution of the eta-Car bipolar outflows. Adopting the interacting nonspherical winds model, we have carried out high-resolution numerical simulations, which include explicitly computed time-dependent radiative cooling, for different possible scenarios of the colliding winds. In our simulations, we consider different degrees of non-spherical symmetry for the pre-outburst wind and the great eruption of the 1840s presented by the eta-Car wind. From these models, we obtain important differences in the shape an…
The luminous blue variable Eta Carinae is surrounded by a complex and highly structured nebula of ejected material. The best-studied and axisymmetric components of this outflow consist of bipolar lobes (the ``homunculus'') and an equatorial ``skirt.'' Recent proper motion measurements suggest that the skirt was ejected at the same time as the lobes, contrary to the assumptions of all current theoretical models for the formation of the nebula (which use the skirt to collimate stellar winds into lobes). We present a magnetohydrodynamic (MHD) stellar wind model that produces an outflowing disk an…
High resolution long-slit spectra obtained with the Phoenix spectrograph on Gemini South provide our most accurate probe of the three dimensional structure of the Homunculus around eta Car. The new near-infrared spectra dramatically confirm the double-shell structure inferred previously from thermal dust emission, resolving the nebula into a very thin outer shell seen in H2 21218, and a warmer, thicker inner layer seen in [Fe II] 16435. The thin H2 skin hints that the most important mass loss during the 19th century eruption had a very short duration of less than 5 yr. H2 emission traces the m…
I discuss the role played by short-duration eruptive mass loss in the evolution of very massive stars. Giant eruptions of Luminous Blue Variables (LBVs) like the 19th century event of eta Carinae can remove large quantities of mass almost instantaneously, making them significant in stellar evolution. They can potentially remove much more mass from the star than line-driven winds, especially if stellar winds are highly clumped such that previous estimates of O star mass-loss rates need to be revised downward. When seen in other galaxies as ``supernova impostors'', these LBV eruptions typically …
We have confirmed that the precursor star of the unusual Supernova 1954J (also known as Variable 12) in NGC 2403 survived what appears to have been a super-outburst, similar to the 1843 Great Eruption of eta Carinae in the Galaxy. The apparent survivor has changed little in brightness and color over the last eight years, and a Keck spectrum reveals characteristics broadly similar to those of eta Car. This is further suggested by our identification of the actual outburst-surviving star in high-resolution images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. We reve…
SN2006tf is the third most luminous SN discovered so far, after SN2005ap and SN2006gy. SN2006tf is valuable because it provides a link between two regimes: (1) luminous type IIn supernovae powered by emission directly from interaction with circumstellar material (CSM), and (2) the most extremely luminous SNe where the CSM interaction is so optically thick that energy must diffuse out from an opaque shocked shell. As SN2006tf evolves, it slowly transitions from the second to the first regime as the clumpy shell becomes more porous. This link suggests that the range in properties of the most lum…
We investigate coronal transients associated with a GOES M6.7 class flare and a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were observed. An EIT wave was detected later on. The main features in the radio dynamic spectrum were a frequency-drifting continuum and two type II bursts. Our analysis shows that if the first type II burst was formed in the low corona, the burst heights and speed are close to the projected distances and speed of the Moreton wave (a chromospheric shock wave signatur…
We show that Supernova (SN) 2002kg in NGC 2403, initially classified as Type II-narrow (IIn), has photometric and spectroscopic properties unlike those of normal SNe. Its behavior, instead, is more typical of highly massive stars which experience the short-lived luminous blue variable (LBV) phase toward the end of their lives. The star, in fact, most resembles the LBV S Doradus in outburst. The precursor of SN 2002kg is the irregular, bright blue variable star 37 (V37), catalogued by Tammann & Sandage in 1968. Using high-quality ground-based, multi-band images we can constrain the initial mass…
