Abstract
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 February 2020 (orbital phase ~ 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (~14 au). The radius of the faintest outer wind regions is ~26 mas (~60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 ± 0.06 mas (6.54 ± 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
Highlights
Eta Car is a spectacular, unstable binary system at a distance of ∼2.3 kpc (Davidson & Humphreys 1997; Smith 2006)
In this paper we present the first Brα Very Large Telescope Interferometer (VLTI)-MATISSE aperture-synthesis imaging of η Car’s innermost wind region obtained during its February 2020 periastron passage
Η Car’s 2D wind intensity distribution on wavelength or LOS velocity in several spectral channels distributed across the Brα line
Summary
Eta Car is a spectacular, unstable binary system at a distance of ∼2.3 kpc (Davidson & Humphreys 1997; Smith 2006). The primary star, η Car A, is a very massive (M ∼ 100 M ) luminous blue variable star (LBV) with an optically thick stellar wind, a mass-loss rate of ∼10−3 M yr−1, and a terminal wind speed of ∼420 km s−1 (Davidson & Humphreys 1997, 2012; Davidson et al 2001; Hillier et al 2001, 2006; Smith 2006; Groh et al. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 0104.D-0015A, 0104.D-0015B, 0104.D-0015C, 0106.D-0309(A), 0106.D-0309(B), and 0106.D-0309(C). The orbital eccentricity causes a phase-dependent wind-wind collision (WWC) zone
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