Evidence for orbital motion of CW Leonis from ground-based astrometry

A. Sozzetti, R. L. Smart, R. Drimmel, P. Giacobbe, Mario G. Lattanzi

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    Recent 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 correlatedwith thewell-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.
    Original languageEnglish
    Article numberslx082
    Pages (from-to)L1-L5
    JournalMonthly Notices of the Royal Astronomical Society: Letters
    Issue number1
    Early online date1 Jun 2017
    Publication statusPublished - Oct 2017


    • AGB
    • Astrometry
    • Binaries: general
    • Circumstellar matter
    • stars: AGB and post
    • Stars: individual: CW Leo
    • stars: late-type


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