SOZZETTI, AlessandroAlessandroSOZZETTISMART, Richard LaurenceRichard LaurenceSMARTDRIMMEL, RonaldRonaldDRIMMELGiacobbe, P.P.GiacobbeLATTANZI, Mario GilbertoMario GilbertoLATTANZI2020-09-162020-09-1620170035-8711http://hdl.handle.net/20.500.12386/27427Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations indicate that CW Leo, the closest carbon-rich asymptotic giant branch star to Sun, might have a low-mass stellar companion. We present archival ground-based astrometric measurements of CW Leo obtained within the context of the Torino Parallax Program and with >6 yr (1995-2001) of time baseline. The residuals to a single-star solution show significant curvature, and they are strongly correlated with the well-known I-band photometric variations due to stellar pulsations. We describe successfully the astrometry of CW Leo with a variability-induced motion (VIM) + acceleration model. We obtain proper motion and parallax of the centre-of-mass of the binary, the former in fair agreement with recent estimates, the latter at the near end of the range of inferred distances based on indirect methods. The VIM + acceleration model results allow us to derive a companion mass in agreement with that inferred by ALMA, they point towards a somewhat longer period than implied by ALMA, but are not compatible with much longer period estimates. These data will constitute a fundamental contribution towards the full understanding of the orbital architecture of the system when combined with Gaia astrometry, providing an ∼25 yr time baseline.STAMPAenArticle10.1093/mnrasl/slx0822-s2.0-85023610565000411640400001https://academic.oup.com/mnrasl/article-abstract/471/1/L1/3860091?redirectedFrom=fulltext2017MNRAS.471L...1SFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation