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Register a new userThe Eta Carinae optical 2009.0 event, a new eclipse-like phenomenon
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Added by
Eduardo Fern\\'andez Laj\\'us
Publication date
2009
fields
Physics
and research's language is
English
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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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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 component (near -144 km/s and probably associated with intervening gas from the Little Homunculus Nebula). All these features were observed during the last event in 2003.5 and are probably related to the close periastron passage of the companion. We argue that these variations are consistent with qualitative expectations about changes in the primary stars stellar wind that result from the wind-wind collision with a massive binary companion and from atmospheric eclipses of the companion.
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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.
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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$gamma$ line emitted by clumps close to the binary system. We also base our orientation on observations of asymmetric molecular clumps that were recently observed by ALMA around the binary system, and were claimed to compose a torus with a missing segment. The orientation has implications for the modeling of the binary interaction during the nineteenth century Great Eruption (GE) of Eta Carinae that occurred close to periastron passage. The orientation where the secondary is closer to us at periastron leads us to suggest that the mass-missing side of the molecular clumps is a result of accretion onto the secondary star during the periastron passage when the clumps were ejected, probably during the GE. The secondary star accreted a few solar masses during the GE and the energy from the accretion process consists the majority of the GE energy. This in turn strengthens the more general model according to which many intermediate-luminosity optical transients (ILOTs) are powered by accretion onto a secondary star.
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