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GRAVITY chromatic imaging of η Car’s core: Milliarcsecond resolution imaging of the wind-wind collision zone (Br γ , He I)
Ist Teil von
Astronomy and astrophysics (Berlin), 2018-10, Vol.618 (125), p.A125-30
Ort / Verlag
EDP Sciences
Erscheinungsjahr
2018
Link zum Volltext
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
Context
.
η
Car is one of the most intriguing luminous blue variables in the Galaxy. Observations and models of the X-ray, ultraviolet, optical, and infrared emission suggest a central binary in a highly eccentric orbit 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. However, the morphology of the cavity and its physical properties are not yet fully constrained.
Aims
. We aim to trace the inner ∼5–50 au structure of
η
Car’s wind-wind interaction, as seen through Br
γ
and, for the first time, through the He
I
2s-2p line.
Methods
. We have used spectro-interferometric observations with the
K
-band beam-combiner GRAVITY at the VLTI. The analyses of the data include (i) parametrical model-fitting to the interferometric observables, (ii) a
CMFGEN
model of the source’s spectrum, and (iii) interferometric image reconstruction.
Results
. Our geometrical modeling of the continuum data allows us to estimate its FWHM angular size close to 2 mas and an elongation ratio
ϵ
= 1.06 ± 0.05 over a PA = 130° ± 20°. Our
CMFGEN
modeling of the spectrum helped us to confirm that the role of the secondary should be taken into account to properly reproduce the observed Br
γ
and He
I
lines. Chromatic images across the Br
γ
line reveal a southeast arc-like feature, possibly associated to the hot post-shocked winds flowing along the cavity wall. The images of the He
I
2s-2p line served to constrain the 20 mas (∼50 au) 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 Br
γ
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
η
Car.