Abertura

The new event in eta Carinae is approaching:11/Jan/2009!
A new "event" was predicted for 11 January 2009. the uncertainty is less than 2 days, due to the excelent 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 Argentine, 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. The wind-wind collision shcok seems to collapse at periastron passage. One of the best indicators of the wind-wind shock that can be assessed from the ground is the HeII4686 line, which is one of the major targets for the monitoring caimpaign .

Observations have shown that eta Carinae undergoes low excitation events every 5.5 years. The event predicted to occur on late June 2003 came on schedule. It was observed in many ground and space-based observatories. A specially dense monitoring was done at the Pico dos Dias Observatory in South Brazil. The minimum (defined by the disappearance of the narrow component in the HeI 6678 A line) started on 2003 June 29. The observations permitted to refine the length of the period to P= 5.538 +- 0.0007 years. The binary hypothesis raised by Damineli in 1996 is stronghly supported by the confirmation of true periodicity. In the 2003.5 event it was possible to see that the "event" is composed by 2 parts. The first one works along the whole period and corresponds to a slow obscuration of the secondary star. The second component shows up only 3 weeks before the minimum and lasts for 70 days. This second component seems to be due to a kind of eclipse of the secondary star. It was not yet possible to detect the secondary star directely. A surprise, also arised from the Pico dos Dias Observatory, was the detection of the spectral line HeII 4686 A by Steriner and Damineli. The ionized Helium plasma indcates that there is a huge UV source of light inside the system, that is more luminous than 100 times the solar bolometric luminosity. This is much more than what we see in X-rays: 10 Lsun. This remains a mistery, linked to the secondary star in the system. We beth that someone will detect directely the secondary star during the next event predicted to star on 11 January 2009 (plus or minus 2 days).

The binary scenario assumes that the primary star is the more luminous and colder (T~20 000K) of the pair. The companion star would be smaller and hotter .(T~37 000K). The animation below shows what should be the orbit of the secondary star (blue) in the rest frame of the primary (red). Notice that the excentricity is very large, making the periastron passage (minimum separation) very fast. The primary star has dense and slow wind (V~600 km/s) - represented as gray discs - and the secondary should have fast (V~3 000 km/s) and low density wind. Since the secondary star is much less luminous, its stellar spectrum has not been observed yet. The wind of the secondary star is easier to see in X-rays and possibly at far UV. The high temperature of the secondary companion could explain also the presence of high excitation lines ([Ne III], [Ar III] etc.), unlikely to be produced by the soft spectrum of the primary star. The hard (and absorbed) X-rays would be produced by the wind wind collision. Several authors have reasons to believe that the binary scenario is correct (visit the links shown in this page), we hope to come up with the "smoking gun" along the 2003.5 event.

The animation above displays the behaviour of the HeI 10830 line intensity along the last orbital revolution. Notice that that line fades fast as it approaches the periastron and recovers a little slower after the event. The orbital inclination seems not to be enough as to produce an eclipse between the stars. The ideia is that the ionizing radiation from the secondary star is obscured more and more, as it plunges into deeper and deeper zones of the primary star wind. Only the central parts of the primary star wind is shown here, in reality, it extends far beyound the binary system.