VLTI-AMBER velocity-resolved aperture-synthesis imaging ofηCarinae with a spectral resolution of 12 000 (original) (raw)
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VLTI-MATISSE chromatic aperture-synthesis imaging of η Carinae’s stellar wind across the Brα line
Astronomy & Astrophysics, 2021
Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis ~15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, η Car A, is a luminous blue variable (LBV); the secondary, η Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV η Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of η Car’s WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Brα imaging of η Car’s distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of η Car A’s stellar windin several spectral channels distributed across the Brα 4.052 μm line (spectral resolving power R ~ 960). Our observations were performed close to periastron passage in Feb...
New Astronomy Reviews, 2007
We report spectro-interferometric observations of the Luminous Blue Variable (LBV) η Car using the AMBER instrument of ESO's Very Large Telescope Interferometer (VLTI) . The observations around the He I 2.059 µm and the Brγ 2.166 µm emission lines allow us to investigate the wavelength dependence of the visibility, differential phase, and closure phase of η Car's stellar wind region. If we fit visibility profiles derived from Hillier et al. models to the AMBER visibilities, we obtain 50% encircled-energy diameters of 4.3, 6.5, and 9.6 mas in the 2.17 µm continuum, the He I, and the Brγ emission lines, respectively. For the interpretation of the non-zero differential and closure phases measured within the Brγ line, we developed a simple wind model. Our observations support theoretical models of winds from fast-rotating, luminous hot stars. 2 Weigelt et al.
Direct measurement of the size and shape of the present-day stellar wind of ?�Carinae
Astronomy and Astrophysics, 2003
We present new high angular resolution observations at near-IR wavelengths of the core of the Luminous Blue Variable η Carinae, using NAOS-CONICA at the VLT and VINCI at the VLT Interferometer (VLTI). The latter observations provide spatial information on a scale of 5 milli-arcsec or ∼11 AU at the distance of η Carinae. The present-day stellar wind of η Carinae is resolved on a scale of several stellar radii. Assuming spherical symmetry, we find a mass loss rate of 1.6×10 −3 M⊙/yr and a wind clumping factor of 0.26. The VLTI data taken at a baseline of 24 meter show that the object is elongated with a de-projected axis ratio of approximately 1.5; the major axis is aligned with that of the large bi-polar nebula that was ejected in the 19th century. The most likely explanation for this observation is a counter-intuitive model in which stellar rotation near the critical velocity causes enhanced mass loss along the rotation axis. This results from the large temperature difference between pole and equator in rapidly rotating stars. η Carinae must rotate in excess of 90 per cent of its critical velocity to account for the observed shape. The large outburst may have been shaped in a similar way. Our observations provide strong support for the existence of a theoretically predicted rotational instability, known as the Ω limit.
Astronomy & Astrophysics, 2007
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.
A multispectral view of the periodic events in η Carinae
Monthly Notices of the Royal Astronomical Society, 2008
A full description of the 5.5-yr low excitation events in η Carinae is presented. We show that they are not as simple and brief as previously thought, but a combination of two components. The first, the slow variation component, is revealed by slow changes in the ionization level of circumstellar matter across the whole cycle and is caused by gradual changes in the windwind collision shock-cone orientation, angular opening and gaseous content. The second, the collapse component, is restricted to around the minimum, and is due to a temporary global collapse of the wind-wind collision shock. High-energy photons (E > 16 eV) from the companion star are strongly shielded, leaving the Weigelt objects at low-ionization state for more than six months. High-energy phenomena are sensitive only to the collapse, low energy only to the slow variation and intermediate energies to both components. Simple eclipses and mechanisms effective only near periastron (e.g. shell ejection or accretion on to the secondary star) cannot account for the whole 5.5-yr cycle.
Latitude‐dependent Effects in the Stellar Wind of η Carinae
The Astrophysical Journal, 2003
The Homunculus reflection nebula around η Carinae provides a rare opportunity to observe the spectrum of a star from more than one direction. In the case of η Car, the nebula's geometry is known well enough to infer how line profiles vary with latitude. We present STIS spectra of several positions in the Homunculus, showing directly that η Car has an aspherical stellar wind. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the polar axis. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from radiative driving with equatorial gravity darkening on a rotating star. Reflected profiles of He i lines are more puzzling, offering clues to the wind geometry and ionization structure. During η Car's high-excitation state in March 2000, the wind was fast and dense at the poles, with higher ionization at low latitudes.
Constraining the wind launching region in Herbig Ae stars: AMBER/VLTI spectroscopy of HD 104237
Astronomy & Astrophysics, 2007
Aims:We investigate the origin of the Brγ emission of the Herbig Ae star HD 104237 on Astronomical Unit (AU) scales. Methods: Using AMBER/VLTI at a spectral resolution R=1500 we spatially resolve the emission in both the Brγ line and the adjacent continuum. Results: The visibility does not vary between the continuum and the Brγ line, even though the line is strongly detected in the spectrum, with a peak intensity 35% above the continuum. This demonstrates that the line and continuum emission have similar size scales. We assume that the K-band continuum excess originates in a “puffed-up” inner rim of the circumstellar disk, and discuss the likely origin of Brγ. Conclusions: .We conclude that this emission most likely arises from a compact disk wind, launched from a region 0.2-0.5 AU from the star, with a spatial extent similar to that of the near infrared continuum emission region, i.e., very close to the inner rim location. Based on observations collected at the European Southern Observatory, Paranal, Chile, within the guaranteed time programme 074.A-9025(A).
Interferometric Observations of η Carinae - the VLTI Takes Its First Glimpse at the Central Source
International Astronomical Union Colloquium, 2002
We describe the first long-baseline interferometric measurement ever made of the luminous blue variableηCarinae.ηCar was observed with the Very Large Telescope Interferometer (VLTI) with the 8.2 m Unit Telescopes as well as with the 40 cm test siderostats on three different baselines. We will detail the measurements and data analysis and discuss briefly the implications of the derived visibility on the morphology of the central source. Furthermore we will discuss the future possibilities of interferometric observations and will show thatηCar is one of the prime candidates for imaging with the VLTI.
In hot pursuit of the hidden companion of ?�Carinae: An X-ray determination of the wind parameters
Astronomy and Astrophysics, 2002
We present X-ray spectral fits to a recently obtained Chandra grating spectrum of η Carinae, one of the most massive and powerful stars in the Galaxy and which is strongly suspected to be a colliding wind binary system. Hydrodynamic models of colliding winds are used to generate synthetic X-ray spectra for a range of mass-loss rates and wind velocities. They are then fitted against newly acquired Chandra grating data. We find that due to the low velocity of the primary wind (≈ 500 km s −1 ), most of the observed X-ray emission appears to arise from the shocked wind of the companion star. We use the duration of the lightcurve minimum to fix the wind momentum ratio at η = 0.2. We are then able to obtain a good fit to the data by varying the mass-loss rate of the companion and the terminal velocity of its wind. We find thatṀ 2 ≈ 10 −5 M⊙ yr −1 and v∞ 2 ≈ 3000 km s −1 . With observationally determined values of ≈ 500−700 km s −1 for the velocity of the primary wind, our fit implies a primary mass-loss rate ofṀ 1 ≈ 2.5 × 10 −4 M⊙ yr −1 . This value is smaller than commonly inferred, although we note that a lower mass-loss rate can reduce some of the problems noted by when a value as high as 10 −3 M⊙ yr −1 is used. The wind parameters of the companion are indicative of a massive star which may or may not be evolved. The line strengths appear to show slightly sub-solar abundances, although this needs further confirmation. Based on the over-estimation of the X-ray line strengths in our model, and re-interpretation of the HST/FOS results, it appears that the homunculus nebula was produced by the primary star.
3D modelling of the colliding winds in η Carinae - evidence for radiative inhibition
Monthly Notices of the Royal Astronomical Society, 2009
The X-ray emission from the super-massive star η Car is simulated using a three dimensional model of the wind-wind collision. In the model the intrinsic X-ray emission is spatially extended and energy dependent. Absorption due to the unshocked stellar winds and the cooled postshock material from the primary LBV star is calculated as the intrinsic emission is ray-traced along multiple sightlines through the 3D spiral structure of the circumstellar environment. The observable emission is then compared to available X-ray data, including the lightcurve observed by the Rossi X-ray Timing Explorer (RXTE) and spectra observed by XMM-Newton. The orientation and eccentricity of the orbit are explored, as are the wind parameters of the stars and the nature and physics of their close approach. Our modelling supports a viewing angle with an inclination of ≃ 42 • , consistent with the polar axis of the Homunculus nebula , and the projection of the observer's line-of-sight onto the orbital plane has an angle of ≃ 0 − 30 • in the prograde direction on the apastron side of the semi-major axis.