Uncovering the orbital dynamics of stars hidden inside their powerful winds: application to $\eta$ Carinae and RMC 140

Abstract

Determining accurate orbits of binary stars with powerful winds is challenging. The dense outflows increase the effective photospheric radius, precluding direct observation of the Keplerian motion; instead the observables are broad lines emitted over large radii in the stellar wind. Our analysis reveals strong, systematic discrepancies between the radial velocities extracted from different spectral lines: the more extended a line's emission region, the greater the departure from the true orbital motion. To overcome these challenges, we formulate a novel semi-analytical model which encapsulates both the star's orbital motion and the propagation of the wind. The model encodes the integrated velocity field of the out-flowing gas in terms of a convolution of past motion due to the finite flow speed of the wind. We test this model on two binary systems. (1), for the extreme case $\eta$ Carinae, in which the effects are most prominent, we are able to fit the model to 10 Balmer lines from H-alpha to H-kappa concurrently with a single set of orbital parameters: time of periastron $T_0=2454848$ (JD), eccentricity $e=0.91$, semi-amplitude $k=69$ km/s and longitude of periastron $\omega =241^{\circ }$. (2) for a more typical case, the Wolf-Rayet star in RMC 140, we demonstrate that for commonly used lines, such as He II and N III/IV/V, we expect deviations between the Keplerian orbit and the predicted radial velocities. Our study indicates that corrective modelling, such as presented here, is necessary in order to identify a consistent set of orbital parameters, independent of the emission line used, especially for future high accuracy work.

arXiv comment20 pages, 15 figures, accepted for publication in MNRAS

References in corpus (40)

• The NumPy array: a structure for efficient numerical computation
• Binary interaction dominates the evolution of massive stars
• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars
• A Comprehensive Study of Binary Compact Objects as Gravitational Wave Sources: Evolutionary Channels, Rates, and Physical Properties
• An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent
• The VLT-FLAMES Tarantula Survey I: Introduction and observational overview
• The Structure of the Homunculus: I. Shape and Latitude Dependence from H2 and [Fe II] Velocity Maps of Eta Carinae
• A Porosity-Length Formalism for Photon-Tiring-Limited Mass Loss from Stars Above the Eddington Limit
• In Hot Pursuit of the Hidden Companion of Eta Carinae: An X-ray Determination of the Wind Parameters
• Latitude-dependent effects in the stellar wind of Eta Carinae
• The periodicity of the eta Carinae events
• High resolution X-ray spectroscopy of bright O type stars
• 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
• Chemical evolution of galaxies. I. A composition-dependent SPH model for chemical evolution and cooling
• The UV Scattering Halo of the Central Source Associated with Eta Carinae
• GaussPy+: A fully automated Gaussian decomposition package for emission line spectra
• High precision orbital and physical parameters of double-lined spectroscopic binary stars - HD78418, HD123999, HD160922, HD200077 and HD210027
• Constraining the Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical Model for the Broad [Fe III] Emission
• Eta Carinae across the 2003.5 minimum: Spectroscopic Evidence for Massive Binary Interactions
• Modeling the RXTE light curve of $\eta$ Carinae from a 3-D SPH simulation of its binary wind collision
• On the influence of the companion star in Eta Carinae: 2D radiative transfer modeling of the ultraviolet and optical spectra
• Detection of He II 4686 in eta Carinae
• Anisotropy of X-ray bursts from neutron stars with concave accretion disks
• Precision radial velocities of double-lined spectroscopic binaries with an iodine absorption cell
• 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
• Fluctuations and symmetry in the speed and direction of the jets of SS433 on different timescales
• He II 4686 in eta Carinae: collapse of the wind-wind collision region during periastron passage
• X-ray Emission from Eta Carinae near Periastron in 2009 I: A Two State Solution
• A search for transits of GJ 581\lowercase{e} and characterization of the host star variability using MOST space telescope photometry
• Critical Differences and Clues in Eta Car's 2009 Event
• SS433's accretion disc, wind and jets: before, during and after a major flare
• 3D radiative transfer simulations of Eta Carinae's inner colliding winds - I. Ionization structure of helium at apastron
• A companion as the cause of latitude-dependent effects in the wind of Eta Carinae
• The H-alpha Variations of eta Carinae During the 2009.0 Spectroscopic Event
• Eta Carinae's 2014.6 Spectroscopic Event: The Extraordinary He II and N II Features
• Orbital Parameters for the $250M_{\odot }$ Eta Carinae Binary System
• 3D radiative transfer simulations of Eta Carinae's inner colliding winds - II: Ionization structure of helium at periastron
• The Optical Wind Line Variability of $\eta$ Carinae During the 2009.0 Event
• Resolving the H-alpha-emitting Region in the Wind of Eta Carinae

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