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The wind-wind collision hole in eta Car

Published online by Cambridge University Press:  28 July 2017

A. Damineli ,
M. Teodoro ,
N. D. Richardson ,
T. R. Gull ,
M. F. Corcoran ,
K. Hamaguchi ,
J. H. Groh ,
G. Weigelt ,
D. J. Hillier  and
C. Russell
...Show all authors
A. Damineli
Affiliation:
Inst. de Astron., Geofísica e Ciências Atmosféricas, Univ. de São Paulo, R. do Matão 1226, São Paulo 05508-900, Brazil email: augusto.damineli@iag.usp.br
M. Teodoro
Affiliation:
Astroph. Sci. Division, Code 660, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA USRA, 7178 Columbia, MD 20146, USA
N. D. Richardson
Affiliation:
Ritter Observ., Depart. of Phys. and Astr., The University of Toledo, Toledo, OH 43606-3390, USA
T. R. Gull
Affiliation:
Astroph. Sci. Division, Code 660, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
M. F. Corcoran
Affiliation:
Astroph. Sci. Division, Code 660, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA USRA, 7178 Columbia, MD 20146, USA
K. Hamaguchi
Affiliation:
Astroph. Sci. Division, Code 660, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA USRA, 7178 Columbia, MD 20146, USA
J. H. Groh
Affiliation:
School of Physiscs, Trinity College Dublin, The Un. of Dublin, Dublin 2, Ireland
G. Weigelt
Affiliation:
Max-Planck-Institut for Radioastronomy, Auf dem Hügel 69, D-53121 Bonn, Germany
D. J. Hillier
Affiliation:
Depart. of Phys. and Astr., Univ. of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260, USA
C. Russell
Affiliation:
Astroph. Sci. Division, Code 660, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
A. Moffat
Affiliation:
Départ. de Physique, Univ. de Montréal, CP 6128, Succursale: Centre-Ville, Montréal, QC, H3C 3J7, Canada
K. R. Pollard
Affiliation:
Department of Physics and Astronomy, University of Canterbury, Chirstchurch, New Zealand
T. I. Madura
Affiliation:
San Jose State University, Depart. of Physics and Astronomy, San Jose, CA, USA
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Abstract

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Eta Carinae is one of the most massive observable binaries. Yet determination of its orbital and physical parameters is hampered by obscuring winds. However the effects of the strong, colliding winds changes with phase due to the high orbital eccentricity. We wanted to improve measures of the orbital parameters and to determine the mechanisms that produce the relatively brief, phase-locked minimum as detected throughout the electromagnetic spectrum. We conducted intense monitoring of the He ii λ4686 line in η Carinae for 10 months in the year 2014, gathering ~300 high S/N spectra with ground- and space-based telescopes. We also used published spectra at the FOS4 SE polar region of the Homunculus, which views the minimum from a different direction. We used a model in which the He ii λ4686 emission is produced by two mechanisms: a) one linked to the intensity of the wind-wind collision which occurs along the whole orbit and is proportional to the inverse square of the separation between the companion stars; and b) the other produced by the ‘bore hole’ effect which occurs at phases across the periastron passage. The opacity (computed from 3D SPH simulations) as convolved with the emission reproduces the behavior of equivalent widths both for direct and reflected light. Our main results are: a) a demonstration that the He ii λ4686 light curve is exquisitely repeatable from cycle to cycle, contrary to previous claims for large changes; b) an accurate determination of the longitude of periastron, indicating that the secondary star is ‘behind’ the primary at periastron, a dispute extended over the past decade; c) a determination of the time of periastron passage, at ~4 days after the onset of the deep light curve minimum; and d) show that the minimum is simultaneous for observers at different lines of sight, indicating that it is not caused by an eclipse of the secondary star, but rather by the immersion of the wind-wind collision interior to the inner wind of the primary.

Keywords

stars: individual (η Carinae)stars: massivebinaries: generalstars: circumstellar matteratomic dataatomic processesradiation mechanisms: generalplasmas
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 12 , Symposium S329: The Lives and Death-Throes of Massive Stars , November 2016 , pp. 186 - 190
Copyright
Copyright © International Astronomical Union 2017 

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