Variability of<i>η</i>Carinae - III

Feast, M. W.; Whitelock, P. A.; Marang, F.

doi:10.1046/j.1365-8711.2001.04163.x

Cited by 42 publications

(71 citation statements)

References 33 publications

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“…We suggested that a hot spot could have been created in an interacting binary during the close encounter (van Genderen et al 2001; Paper I). The same suggestion has been made by Feast et al (2001) on account of their NIR results.…”

Section: Discussion Of the Light And Colour Curvessupporting

confidence: 76%

$\mathsf{\eta}$ Car: the optical features at the 2003.5 low-excitation event

Genderen

Sterken

Allen³

et al. 2003

A&A

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Abstract. UBV and BVR photometry of η Car during the 2003.5 low-excitation event -the considered periastron passage of a binary -is presented. The light and colour curves show a number of features, which were also seen at previous periastron passages: a light maximum of long duration with a superimposed flare-like event which is temporarily interrupted by an eclipselike dip, and a steep decline in the U − B color index. The R brightness reached a minimum at the time of mid X-ray totality, probably implying that the Hα emission line reached a minimum. The source of the optical flare-like event is probably not the same as the one causing the the X-ray radiation. It is tempting to consider the epoch of the R minimum and the mid-X ray totality -which roughly coincides with the UBV minimum -as the central moment of the 2003.5 low-excitation event.

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Section: Discussion Of the Light And Colour Curvessupporting

confidence: 76%

$\mathsf{\eta}$ Car: the optical features at the 2003.5 low-excitation event

Genderen

Sterken

Allen³

et al. 2003

A&A

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“…The Mk II photometry from the years 1972-2004 was published in Whitelock et al (1983;, Feast et al (2001), and Whitelock et al (2004). The SAAO IR standard system (Carter 1990) was used and uncertainties range from of about 0.03 mag in JHK to 0.05 mag in L. Here we present the most recent Mk II photometry from [2004][2005][2006][2007][2008][2009][2010][2011][2012][2013] (Table 1).…”

Section: Observations and Data Analysismentioning

confidence: 99%

“…Whitelock et al (2004) rejected an orbital cycle of grain growth and destruction since more dramatic variations in L band than observed would be expected and Chesneau et al (2005) found in near-IR high-angular resolution (60 mas resolution) VLT/NACO images a dust-free area with a radius of 230-350 AU around η Car. Other explanations for the excess emission at periastron include S Doradustype variations (Whitelock et al 1994, Sterken et al 1999, enhanced free-free emission as newly ejected mass joins the material around η Car (Feast et al 2001), and expansion of the primary due to tidal forces (van Genderen et al 2006). It is also possible to envisage the excess emission at periastron as a consequence of grain destruction.…”

Section: Excess Emission Around the Periastron Passagesmentioning

confidence: 99%

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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“…Damineli (1996) first noticed the 5.5-year periodicity in the spectroscopic changes of this object (see Damineli et al 1997Damineli et al , 2000Duncan et al 1999;Ishibashi et al 1999;Davidson et al 1999Davidson et al , 2000van Genderen et al 2003;Steiner & Damineli 2004;Whitelock et al 2004;Corcoran 2005;Weis et al 2005). On the other hand, to date, the binary nature of the central object in η Car and its orbital parameters are still a matter of debate (see, e.g., Zanella et al 1984;Davidson 1999Davidson , 2001Davidson et al 1999Davidson et al , 2000Davidson et al , 2005Ishibashi et al 1999;Smith et al 2000;Feast et al 2001;Ishibashi 2001;Pittard & Corcoran 2002;Smith et al 2003;Martin et al 2006).…”

Section: Introductionmentioning

confidence: 98%

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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Variability ofηCarinae - III

Cited by 42 publications

References 33 publications

$\mathsf{\eta}$ Car: the optical features at the 2003.5 low-excitation event

$\mathsf{\eta}$ Car: the optical features at the 2003.5 low-excitation event

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

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

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