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Post Info TOPIC: eta Carinae
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Title: A Sea Change in Eta Carinae
Authors: Andrea Mehner, Kris Davidson, Roberta M. Humphreys, John C. Martin, Kazunori Ishibashi, Gary J. Ferland, Nolan R. Walborn
(Version v3)

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.

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Using adaptive optics to remove atmospheric blurring, Gemini Observatory released an image today showing previously hidden forensic secrets at the ballistic core of the Homunculus Nebula, part of the explosive Eta Carinae star system.
The infrared image, revealed at the 215th American Astronomical Society meeting in Washington DC, is a high-resolution view of the complex tendrils and puffs of glowing gas and dust surrounding the violent and convulsive death of an exceptionally massive, short-lived star.

Carinae.jpg
Image Credit:J.C. Martin et. al., Gemini Observatory/AURA

Eta Carinae as imaged by the Gemini South telescope in Chile with the Near Infrared Coronagraphic Imager (NICI) using adaptive optics to reduce blurring by turbulence in the Earth's atmosphere. In this image the bipolar lobes of the Homunculus Nebula are visible with the never-before imaged "Little Homunculus Nebula" visible as a faint blue glow, mostly in the lower lobe. The Butterfly Nebula is visible (region circled) as the yellowish glow with dark filamentary structure close to, and mostly below/left, of the central star system (the central star system appears as a dark spot due to the coronagraphic blocking (occulting) disk used to eliminate the star's bright glare). This image is a colour composite using three infrared filters:

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Blobrana


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eacra2.gif
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Credit: Eduardo Fernández-Lajús et al.

This light curve depicts the visual apparent brightness of Eta Car since 1822 up to date.
Eta Carinae is one of the most massive and luminous stars in our galaxy, and is suspected to be a binary system with a period of 5.54 years. In 2003.5 it was expected to undergo an X-ray eclipse.

Position(2000): RA 10 45 03.591, Dec -59 41 04.26

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Blobrana


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Observers have reported that Eta Carinae has brighten.

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Blobrana


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Eta Carinae optical 2009.0 event
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Title: The Eta Carinae optical 2009.0 event, a new "eclipse-like" phenomenon
Authors: E. Fernandez-Lajus, C. Farina, J.P. Calderon, N. Salerno, A.F. Torres, M.A. Schwartz, C. von Essen, F. Giudici, F.A. Bareilles

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 observation program included a new telescope to obtain information from other photometric bands. The daily monitoring consists of the acquisition of CCD images through standard UBVRI filters and a narrow Halpha passband. The subsequent differential photometry includes the central region of the object and the whole Homunculus nebula. The results of our relative UBVRIHalpha photometry, performed from November 2008 up to the end of March 2009, are presented in this work, which comprises the totality of the event. The initial rising branch, the maximum, the dip to the minimum and the recovering rising phase strongly resemble a kind of eclipse. All these features happened on time - according to that predicted - although there are some photometric differences in comparison with the previous event. We made a new determination of 2022.8 days for the period value using the present and previous "eclipse-like" event data. These results strongly support the binarity hypothesis for Eta Car. In this paper, the complete dataset with the photometry of the 2009.0 event is provided to make it readily available for further analysis.

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Eta Carinae
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Title: Deducing the Orientation of the Semimajor Axis of the Eta Carinae Binary System from X-ray Observations
Authors: Amit Kashi, Noam Soker

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-ray emission measure, on the other hand, impose strong constrains on the orientation. We improve our previous calculations and show that the column density is more compatible with an orientation where for most of the time the secondary - the hotter, less massive star - is behind the primary star. The secondary comes closer to the observer only for a short time near periastron passage. The ten-week X-ray deep minimum, which results from a large decrease in the emission measure, implies that the regular secondary wind is substantially suppressed during that period. This suppression is most likely resulted by accretion of mass from the dense wind of the primary luminous blue variable (LBV) star. The accretion from the equatorial plane might lead to the formation of a polar outflow. We suggest that the polar outflow contributes to the soft X-ray emission during the X-ray minimum; the other source is the shocked secondary wind in the tail. The conclusion that accretion occurs at each periastron passage, every five and a half years, implies that accretion had occurred at a much higher rate during the 20 Great Eruption of Eta Carinae in the 19th century.

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A new "event" was predicted for 11 January 2009. the uncertainty is less than 2 days, due to the excellent monitoring made at the Pico dos Dias Observatory in 2003. The next event offers the best perspective for the ground-based telescopes, until the year 2020! A large network of observers in Argentina, Chile and Brazil is working and the preliminary results indicate that everything is following the predictions. This is a confirmation of the binarity nature of the central object. However, new details are showing up, indicating that the periastron passage is traumatic, as opposed to a simple eclipse.
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Obesity has apparently reached galactic proportions, apparently - even stars have a problem with over-eating, a stellar mystery that has astronomers asking how some stars grow to be so large. A supercomputer scientist team may have the answer, in a demonstration of how nature can take something simple and make it complex.
About 7,500 light years away resides the star Eta Carinae, first noted in a star catalogue by the venerable astronomer Edmond Halley (best known for Halley's comet) in 1677. Since then, the star has bedazzled astronomers by brightening every century or so, most notably in an 1843 outburst that briefly made it the brightest star in the sky, despite its distance (one light year is about 5.9 trillion miles.) To add to the mystery, the star is a porker, about 120 times heavier than the sun, embedded in a star-forming gas cloud called the Carina Nebula.
University of California, Berkeley, astronomer Nathan Smith proposed last year in the journal Nature that 1843 outburst arose from an explosion deep in the star that spat out a blob of star-stuff perhaps ten times as heavy as the sun. The report counts the explosion as a newly-discovered mechanism for how gigantic stars, which only live a million years or so, start to break down prior to their final implosion (the process that forms black holes.)

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080910-eta-carinae_big.jpg
Photograph courtesy NASA

A Hubble Space Telescope image of the massive star Eta Carinae shows two large bubbles of gas expanding in opposite directions from its bright central region.
The star`s sudden brightening in 1843 was caused by a mysterious explosion of a type never before identified - not stellar winds as previously thought, experts said in September 2008.

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Title: A Blast Wave from the 1843 Eruption of Eta Carinae
Authors: Nathan Smith

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.

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