Resolving the dynamical mass tension of the massive binary 9 Sagittarii. (arXiv:2105.09968v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Fabry_M/0/1/0/all/0/1">M. Fabry</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Hawcroft_C/0/1/0/all/0/1">C. Hawcroft</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Frost_A/0/1/0/all/0/1">A. J. Frost</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Mahy_L/0/1/0/all/0/1">L. Mahy</a> (2, 1), <a href="http://arxiv.org/find/astro-ph/1/au:+Marchant_P/0/1/0/all/0/1">P. Marchant</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Bouquin_J/0/1/0/all/0/1">J-B. Le Bouquin</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Sana_H/0/1/0/all/0/1">H. Sana</a> (1) ((1) Institute of Astronomy, Leuven, Belgium, (2) Royal Observatory of Belgium, Brussels, Belgium, (3) Institute of Planetology and Astrophysics, Grenoble, France)
Direct dynamical mass measurements of stars with masses above 30 M${}_odot$
are rare. This is the result of the low yield of the upper initial mass
function and the limited number of such systems in eclipsing binaries.
Long-period, double-lined spectroscopic binaries that are also resolved
astrometrically offer an alternative for obtaining absolute masses of stellar
objects. 9 Sgr is one such long-period, high-mass binary. Unfortunately, a
large amount of tension exists between its total dynamical mass inferred from
radial velocity measurements and that from astrometric data. We obtained the
astrometric orbit from VLTI/PIONIER and VLTI/GRAVITY interferometric
measurements. Using archival and new spectroscopy, we performed a grid-based
spectral disentangling search to constrain the semi-amplitudes of the radial
velocity curves. We computed atmospheric parameters and surface abundances by
adjusting textsc{fastwind} atmosphere models and we compared our results with
evolutionary tracks computed with the Bonn Evolutionary Code (BEC). Grid
spectral disentangling of 9 Sgr supports the presence of a 53 M${}_odot$
primary and a 39 M${}_odot$ secondary. Comparison with BEC evolutionary tracks
shows the components of 9 Sgr are most likely coeval with an age of roughly 1
Myr. Our analysis clears up the contradiction between mass and orbital
inclination estimates reported in previous studies. We detect the presence of
significant CNO-processed material at the surface of the primary, suggesting
enhanced internal mixing compared to currently implemented in the BEC models.
The present measurements provide a high-quality high-mass anchor to validate
stellar evolution models and to test the efficiency of internal mixing
processes.
Direct dynamical mass measurements of stars with masses above 30 M${}_odot$
are rare. This is the result of the low yield of the upper initial mass
function and the limited number of such systems in eclipsing binaries.
Long-period, double-lined spectroscopic binaries that are also resolved
astrometrically offer an alternative for obtaining absolute masses of stellar
objects. 9 Sgr is one such long-period, high-mass binary. Unfortunately, a
large amount of tension exists between its total dynamical mass inferred from
radial velocity measurements and that from astrometric data. We obtained the
astrometric orbit from VLTI/PIONIER and VLTI/GRAVITY interferometric
measurements. Using archival and new spectroscopy, we performed a grid-based
spectral disentangling search to constrain the semi-amplitudes of the radial
velocity curves. We computed atmospheric parameters and surface abundances by
adjusting textsc{fastwind} atmosphere models and we compared our results with
evolutionary tracks computed with the Bonn Evolutionary Code (BEC). Grid
spectral disentangling of 9 Sgr supports the presence of a 53 M${}_odot$
primary and a 39 M${}_odot$ secondary. Comparison with BEC evolutionary tracks
shows the components of 9 Sgr are most likely coeval with an age of roughly 1
Myr. Our analysis clears up the contradiction between mass and orbital
inclination estimates reported in previous studies. We detect the presence of
significant CNO-processed material at the surface of the primary, suggesting
enhanced internal mixing compared to currently implemented in the BEC models.
The present measurements provide a high-quality high-mass anchor to validate
stellar evolution models and to test the efficiency of internal mixing
processes.
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