The UV Scattering Halo of the Central Source Associated with η Carinae

Hillier, D. J.; Gull, Theodore R.; Nielsen, K. E.; Sonneborn, G.; Iping, R. C.; Smith, Nathan; Corcoran, M. F.; Damineli, A.; Hamann, Fred; Martin, John; Weis, Karsten

doi:10.1086/501225

Cited by 95 publications

(198 citation statements)

References 73 publications

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“…3. Eta Car's visual extinction is A V ∼ 6-7 mag (Hillier et al 2006) and small (<1-2 mag) at L. Thus the relative fluxes between V (≈ 4.5 mag in 2013) and L (≈ −1.6 mag in 2013) are consistent without invoking a large dust emission component in L.…”

Section: Possible Scenarios For the Observed Changes In η Carmentioning

confidence: 74%

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Mehner¹,

Ishibashi²,

Whitelock³

et al. 2014

A&A

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Aims. Eta Car's ultra-violet, optical, and X-ray light curves and its spectrum suggest a physical change in its stellar wind over the last decade. It was proposed that the mass-loss rate decreased by a factor of about 2 in the last 15 years. We complement these recent results by investigating the past evolution and the current state of η Car in the near-infrared (IR). Results. The long-term brightening trends in η Car's JHKL light curves were discontinuous around the 1998 periastron passage. After 1998, the star shows excess emission above the extrapolated trend from earlier dates, foremost in J and H, and the blueward, cyclical progression in its near-IR colors is accelerated. The near-IR color evolution is strongly correlated with the periastron passages. After correcting for the secular trend we find that the color evolution matches an apparent increase in blackbody temperature of an optically thick near-IR emitting plasma component from about 3500 to 6000 K over the last 20 years. Conclusions. We suggest that the changing near-IR emission may be caused by variability in optically thick bremsstrahlung emission. Periastron passages play a key role in the observed excess near-IR emission after 1998 and the long-term color evolution. We thus propose as a hypothesis that angular momentum transfer (via tidal acceleration) during periastron passages leads to sudden changes in η Car's atmosphere resulting in a long-term decrease in the mass-loss rate.

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Section: Possible Scenarios For the Observed Changes In η Carmentioning

confidence: 74%

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Mehner¹,

Ishibashi²,

Whitelock³

et al. 2014

A&A

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“…17 in Teodoro et al (2016), we derived the projected binary separation of approximately 4.9 mas (11.5 au) and PA of 315 • at the time of observation. The secondary star is not visible in our images, because it is at least about 100 times fainter than the primary star (e.g., Hillier et al 2006;Weigelt et al 2007). The primary is also not visible due to high extinction.…”

Section: A106 Page 7 Of 19mentioning

confidence: 89%

“…Infrared long-baseline interferometry provides us with a unique opportunity to study the mass loss from the colliding wind binary η Car. The primary star of the system is an extremely luminous and massive (M ∼ 100 M ) unstable luminous blue variable star (LBV) with a high mass-loss rate of ∼10 −3 M yr −1 (Davidson & Humphreys 1997;Davidson et al 2001;Hillier et al 2001Hillier et al , 2006Groh et al 2012b). A decrease in the observed strength of Hα and Fe ii emission lines, and a change in the strength of N ii lines, provide indications that the primary wind density has decreased, either due to a global reduction in mass loss or to latitudinal changes (e.g., Davidson et al 2015;Mehner et al 2012Mehner et al , 2010b.…”

Section: Introductionmentioning

confidence: 99%

VLTI-AMBER velocity-resolved aperture-synthesis imaging ofηCarinae with a spectral resolution of 12 000

Weigelt

Hofmann

Schertl

et al. 2016

A&A

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Context. The mass loss from massive stars is not understood well. η Carinae is a unique object for studying the massive stellar wind during the luminous blue variable phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Aims. We want to investigate the structure and kinematics of η Car's primary star wind and wind-wind collision zone with a high spatial resolution of ∼6 mas (∼14 au) and high spectral resolution of R = 12 000. Methods. Observations of η Car were carried out with the ESO Very Large Telescope Interferometer (VLTI) and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision.Results. We present velocity-resolved aperture-synthesis images reconstructed in more than 100 different spectral channels distributed across the Brγ 2.166 µm emission line. The intensity distribution of the images strongly depends on wavelength. At wavelengths corresponding to radial velocities of approximately −140 to −376 km s −1 measured relative to line center, the intensity distribution has a fan-shaped structure. At the velocity of −277 km s −1 , the position angle of the symmetry axis of the fan is ∼126 • . The fan-shaped structure extends approximately 8.0 mas (∼18.8 au) to the southeast and 5.8 mas (∼13.6 au) to the northwest, measured along the symmetry axis at the 16% intensity contour. The shape of the intensity distributions suggests that the obtained images are the first direct images of the innermost wind-wind collision zone. Therefore, the observations provide velocity-dependent image structures that can be used to test three-dimensional hydrodynamical, radiative transfer models of the massive interacting winds of η Car.

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“…The Hillier et al (2001Hillier et al ( , 2006 model was developed to explain STIS HST spectra. The luminosity of the primary (5 × 10 6 L ) was set by observed IR fluxes (see discussion by Davidson & Humphreys 1997) and the known distance of 2.3 kpc to η Car.…”

Section: Introductionmentioning

confidence: 99%

“…With the exception of Na (which was found to be enhanced by at least a factor of 2), the adoption of solar abundances for other metal species was found to yield satisfactory fits to the STIS spectra. A more recent discussion of the basic model, with particular reference to the UV and outer wind, is given by Hillier et al (2006).…”

Section: Introductionmentioning

confidence: 99%

Near-infrared interferometry of η Carinae with spectral resolutions of 1 500 and 12 000 using AMBER/VLTI

Weigelt

Kraus

Driebe

et al. 2006

A&A

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Aims. We present the first NIR spectro-interferometry of the LBV η Carinae. The observations were performed with the AMBER instrument of the ESO Very Large Telescope Interferometer (VLTI) using baselines from 42 to 89 m. The aim of this work is to study the wavelength dependence of η Car's optically thick wind region with a high spatial resolution of 5 mas (11 AU) and high spectral resolution. Methods. The observations were carried out with three 8.2 m Unit Telescopes in the K-band. The raw data are spectrally dispersed interferograms obtained with spectral resolutions of 1500 (MR-K mode) and 12 000 (HR-K mode). The MR-K observations were performed in the wavelength range around both the He i 2.059 µm and the Brγ 2.166 µm emission lines, the HR-K observations only in the Brγ line region.Results. The spectrally dispersed AMBER interferograms allow the investigation of the wavelength dependence of the visibility, differential phase, and closure phase of η Car. In the K-band continuum, a diameter of 4.0 ± 0.2 mas (Gaussian FWHM, fit range 28-89 m baseline length) was measured for η Car's optically thick wind region. If we fit Hillier et al. (2001, ApJ, 553, 837) model visibilities to the observed AMBER visibilities, we obtain 50% encircled-energy diameters of 4.2, 6.5 and 9.6 mas in the 2.17 µm continuum, the He i, and the Brγ emission lines, respectively. In the continuum near the Brγ line, an elongation along a position angle of 120• ±15• was found, consistent with previous VINCI/VLTI measurements by van Boekel et al. (2003, A&A, 410, L37). We compare the measured visibilities with predictions of the radiative transfer model of Hillier et al. (2001), finding good agreement. Furthermore, we discuss the detectability of the hypothetical hot binary companion. For the interpretation of the non-zero differential and closure phases measured within the Brγ line, we present a simple geometric model of an inclined, latitude-dependent wind zone. Our observations support theoretical models of anisotropic winds from fast-rotating, luminous hot stars with enhanced high-velocity mass loss near the polar regions.

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The UV Scattering Halo of the Central Source Associated with η Carinae

Cited by 95 publications

References 73 publications

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Near-infrared evidence for a sudden temperature increase in Eta Carinae

VLTI-AMBER velocity-resolved aperture-synthesis imaging ofηCarinae with a spectral resolution of 12 000

Near-infrared interferometry of η Carinae with spectral resolutions of 1 500 and 12 000 using AMBER/VLTI

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