GRAVITY chromatic imaging of Eta Car's core

Abstract

Eta Car is one of the most intriguing luminous blue variables in the Galaxy. Observations and models at different wavelengths suggest a central binary with a 5.54 yr period residing in its core. 2D and 3D radiative transfer and hydrodynamic simulations predict a primary with a dense and slow stellar wind that interacts with the faster and lower density wind of the secondary. The wind-wind collision scenario suggests that the secondary's wind penetrates the primary's wind creating a low-density cavity in it, with dense walls where the two winds interact. We aim to trace the inner ~5-50 au structure of Eta Car's wind-wind interaction, as seen through BrG and, for the first time, through the He I 2s-2p line. We have used spectro-interferometric observations with GRAVITY at the VLTI. Our modeling of the continuum allows us to estimate its FWHM angular size close to 2 mas and an elongation ratio of 1.06 +/- 0.05 over a PA = 130 +/- 20 deg. Our CMFGEN modeling helped us to confirm that the role of the secondary should be taken into account to properly reproduce the observed BrG and He I lines. Chromatic images across BrG reveal a southeast arc-like feature, possibly associated to the hot post-shocked winds flowing along the cavity wall. The images of He I 2s-2p served to constrain the 20 mas structure of the line-emitting region. The observed morphology of He I suggests that the secondary is responsible for the ionized material that produces the line profile. Both the BrG and the He I 2s-2p maps are consistent with previous hydrodynamical models of the colliding wind scenario. Future dedicated simulations together with an extensive interferometric campaign are necessary to refine our constraints on the wind and stellar parameters of the binary, which finally will help us predict the evolutionary path of Eta Car.

arXiv comment32 pages, 27 figures (14 in the main body, 13 in the appendices), accepted for publication in AA

References in corpus (39)

• Models of Stars, Brown Dwarfs and Exoplanets
• First Light for GRAVITY: Phase Referencing Optical Interferometry for the Very Large Telescope Interferometer
• Line formation in solar granulation VI. [C I], C I, CH and C2 lines and the photospheric C abundance
• CERES: A Set of Automated Routines for Echelle Spectra
• In Hot Pursuit of the Hidden Companion of Eta Carinae: An X-ray Determination of the Wind Parameters
• A Census of the Carina Nebula. I: Cumulative Energy Input from Massive Stars
• The periodicity of the eta Carinae events
• 3D modelling of the colliding winds in Eta Carinae - evidence for radiative inhibition
• Spiralling out of control: 3D hydrodynamical modelling of the colliding winds in $\eta$Carinae
• Near-Infrared interferometry of Eta Carinae with high spatial and spectral resolution using the VLTI and the AMBER instrument
• Direct measurement of the size and shape of the present-day stellar wind of Eta Carinae
• High-excitation emission lines near eta Carinae, and its likely companion star
• The UV Scattering Halo of the Central Source Associated with Eta Carinae
• Constraining the Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical Model for the Broad [Fe III] Emission
• Constraints on decreases in Eta Carinae's mass loss from 3D hydrodynamic simulations of its binary colliding winds
• A multispectral view of the periodic events in eta Carinae
• Direct constraint on the distance of y2 Velorum from AMBER/VLTI observations
• Modeling the RXTE light curve of $\eta$ Carinae from a 3-D SPH simulation of its binary wind collision
• The Early Spectra of Eta Carinae 1892 to 1941 and the Onset of Its High Excitation Emission Spectrum
• Episodic mass loss in binary evolution to the Wolf-Rayet phase: Keck and HST proper motions of RY Scuti's nebula
• He II $\lambda$4686 emission from the massive binary system in $\eta$ Car: constraints to the orbital elements and the nature of the periodic minima
• $\eta$ Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
• Submillimetre Variability of Eta Carinae: cool dust within the outer ejecta
• Secular Changes in Eta Carinae's Wind 1998-2011
• Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage
• The three-dimensional structure of the Eta Carinae Homunculus
• Is Eta Carinae a fast rotator, and how much does the companion influence the inner wind structure?
• The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle
• Imaging with HST the time evolution of Eta Carinae's colliding winds
• 3D radiative transfer simulations of Eta Carinae's inner colliding winds - I. Ionization structure of helium at apastron
• Near-infrared integral field spectroscopy of the Homunculus nebula around Eta Carinae using Gemini/CIRPASS
• A Lighthouse Effect in Eta Carinae
• A companion as the cause of latitude-dependent effects in the wind of Eta Carinae
• To $v_{\infty }$ and beyond! The He I absorption variability across the 2014.6 periastron passage of $\eta$ Carinae
• Eta Carinae's 2014.6 Spectroscopic Event: The Extraordinary He II and N II Features
• VLTI-AMBER velocity-resolved aperture-synthesis imaging of Eta Carinae with a spectral resolution of 12000. Studies of the primary star wind and innermost wind-wind collision
• Near-Infrared Evidence for a Sudden Temperature Increase in Eta Carinae
• GRAVITY: the Calibration Unit
• Galactic Twins of the Nebula Around SN 1987A: Hints that LBVs may be supernova progenitors

Cited by in corpus (1)

• Optical/near-infrared observations of the Fried Egg Nebula: Multiple shell ejections on a 100 yr timescale from a massive yellow hypergiant