Characterising the orbit and circumstellar environment of the high-mass binary MWC 166 A

Abstract

Context: Stellar evolution models are highly dependent on accurate mass estimates, especially for high-mass stars in the early stages of evolution. The most direct method for obtaining model-independent masses is derivation from the orbit of close binaries. Aims: To derive the first astrometric+RV orbit solution for the single-lined spectroscopic binary MWC 166 A, based on CHARA and VLTI near-infrared interferometry over multiple epochs and ~100 archival radial velocity measurements, and to derive fundamental stellar parameters from this orbit. We also sought to model circumstellar activity in the system from K-band spectral lines. Methods: We geometrically modelled the dust continuum to derive astrometry at 13 epochs and constrain individual stellar parameters. We used the continuum models as a base to examine differential phases, visibilities and closure phases over the Br-$\gamma$ and He-I emission lines. Results: Our orbit solution suggests a period of $367.7\pm 0.1$ d, twice as long as found with previous RV orbit fits, subsequently constraining the component masses to $M_1=12.2\pm 2.2M_{\odot }$ and $M_2=4.9\pm 0.5M_{\odot }$. The line-emitting gas was found to be localised around the primary and is spatially resolved on scales of ~11 stellar radii, with the spatial displacement between the line wings consistent with a rotating disc. Conclusions: The large radius and stable orientation of the line emission are inconsistent with magnetospheric or boundary-layer accretion, but indicate an ionised inner gas disk around MWC 166 Aa. We observe line variability that could be explained either with generic line variability in a Herbig star disc or V/R variations in a decretion disc. We also constrained the age of the system to ~$(7\pm 2)\times 10^5$ yr, consistent with the system being comprised of a main-sequence primary and a secondary still contracting towards the main sequence.

24 pages, 19 figures, 7 tables, 1 appendix. Accepted in A&A

References in corpus (14)

• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Improving PARSEC models for very low mass stars
• New PARSEC evolutionary tracks of massive stars at low metallicity: testing canonical stellar evolution in nearby star forming dwarf galaxies
• Constraining the thermally-pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud
• Structure of Herbig AeBe disks at the milliarcsecond scale A statistical survey in the H band using PIONIER-VLTI
• Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage
• Empirical Tests of Pre-Main-Sequence Stellar Evolution Models with Eclipsing Binaries
• Precession and accretion in circumbinary discs: The case of HD 104237
• The VLTI / PIONIER near-infrared interferometric survey of southern T Tauri stars. I. First results
• A spectroscopic survey of Herbig Ae/Be stars with X-Shooter II: Accretion diagnostic lines
• HR 6819 is a binary system with no black hole -- revisiting the source with infrared interferometry and optical integral field spectroscopy
• The Inner Disk and Accretion Flow of the Close Binary DQ Tau
• A method to deconvolve mass ratio distribution from binary stars