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Register a new userPrediction for the He I 10830A Absorption Wing in the Coming Event of Eta Carinae
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We propose an explanation to the puzzling appearance of a wide blue absorption wing in the He I 10830A P-Cygni profile of the massive binary star Eta Carinae several months before periastron passage. Our basic assumption is that the colliding winds region is responsible for the blue wing absorption. By fitting observations, we find that the maximum outflow velocity of this absorbing material is ~2300 km/s. We also assume that the secondary star is toward the observer at periastron passage. With a toy-model we achieve two significant results. (1) We show that the semimajor axis orientation we use can account for the appearance and evolution of the wide blue wing under our basic assumption. (2) We predict that the Doppler shift (the edge of the absorption profile) will reach a maximum 0-3 weeks before periastron passage, and not necessarily exactly at periastron passage or after periastron passage.
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We report the detection of the emission line He II 4686 A in eta Carinae. The equivalent width of this line is ~100 mA along most of the 5.5-yr cycle and jumps to ~900 mA just before phase 1.0, followed by a brief disappearance. The similarity between the intensity variations of this line and of the X-ray light curve is remarkable, suggesting that they are physically connected. We show that the number of ionizing photons in the ultraviolet and soft X-rays, expected to be emitted in the shock wave from the colliding winds, is of the order of magnitude required to produce the He II emission via photoionization. The emission is clearly blueshifted when the line is strong. The radial velocity of the line is generally -100 Km/s, decreases steadily just before the event, and reaches -400 Km/s at ph = 1.001. At this point, the velocity gradient suddenly changes sign, at the same time that the emission intensity drops to nearly zero. Possible scenarios for explaining this emission are briefly discussed. The timing of the peak of He II intensity is likely to be associated to the periastron and may be a reliable fiduciary mark, important for constraining the orbital parameters.
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.
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.
During the years 1838-1858, the very massive star {eta} 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 do not reveal any significant contradiction between the observed spectrum and most previous discussions of the Great Eruption and its physics.
Using the high dispersion NUV mode of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST) to observe Eta Carinae, we have resolved and identified over 500 sharp, circumstellar absorption lines of iron-group singly-ionized and neutral elements with ~20 velocity components ranging from -146 km/s to -585 km/s. These lines are from transitions originating from ground and metastable levels as high as 40,000 cm-1 above ground. The absorbing material is located either in dense inhomogeneities in the stellar wind, the warm circumstellar gas immediately in the vicinity of Eta Carinae, or within the cooler foreground lobe of the Homunculus. We have used classical curve-of-growth analysis to derive atomic level populations for FeII at -146 km/s and for TiII at -513 km/s. These populations, plus photoionization and statistical equilibrium modeling, provide electron temperatures, Te, densities, n, and constraints on distances from the stellar source, r. For the -146 km/s component, we derive Te = 6400 K, n(H)>10e7 - 10e8 cm-3, and d ~1300 AU. For the -513 km/s component, we find a much cooler temperature, Te= 760 K, with n(H)> 10e7cm-3, we estimate d~10,000 AU. The large distances for these two components place the absorptions in the vicinity of identifiable ejecta from historical events, not near or in the dense wind of Eta Carinae. Further analysis, in parallel with obtaining improved experimental and theoretical atomic data, is underway to determine what physical mechanisms and elemental abundances can explain the large number of strong circumstellar absorption features in the spectrum of Eta Carinae.
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