Journal article
Uncovering the orbital dynamics of stars hidden inside their powerful winds: application to $η$ 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.
- Publication status:
- Published
- Peer review status:
- Peer reviewed
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- Files:
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(Preview, Accepted manuscript, 3.9MB, Terms of use)
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- Publisher copy:
- 10.1093/mnras/staa669
Authors
- Publisher:
- Oxford University Press
- Journal:
- Monthly Notices of the Royal Astronomical Society More from this journal
- Volume:
- 494
- Issue:
- 1
- Pages:
- 17-35
- Publication date:
- 2020-03-13
- Acceptance date:
- 2020-03-05
- DOI:
- EISSN:
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1365-2966
- ISSN:
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0035-8711
- Language:
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English
- Keywords:
- Pubs id:
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1092736
- Local pid:
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pubs:1092736
- Deposit date:
-
2020-04-03
Terms of use
- Copyright holder:
- Grant et al.
- Copyright date:
- 2020
- Rights statement:
- © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
- Notes:
- This is the accepted manuscript version of the article. The final version is available from Oxford University Press at: https://doi.org/10.1093/mnras/staa669
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