The VAST survey - IV. A wide brown dwarf companion to the A3V star ζ Delphini

R. J. De Rosa, Jennifer Patience, K. Ward-Duong, A. Vigan, C. Marois, I. Song, B. Macintosh, J. R. Graham, R. Doyon, M. S. Bessel, O. Lai, D. W. McCarthy, C. Kulesa

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


We report the discovery of a wide comoving substellar companion to the nearby (D = 67.5 ± 1.1 pc) A3V star ζ Delphini based on imaging and follow-up spectroscopic observations obtained during the course of our Volume-limited A-Star (VAST) multiplicity survey. ζ Del was observed over a five-year baseline with adaptive optics, revealing the presence of a previously unresolved companion with a proper motion consistent with that of the A-type primary. The age of the ζ Del system was estimated as 525 ± 125 Myr based on the position of the primary on the colour-magnitude and temperature-luminosity diagrams. Using intermediate-resolution near-infrared spectroscopy, the spectrum of ζ Del B is shown to be consistent with a mid-L dwarf (L5 ± 2), at a temperature of 1650 ± 200 K. Combining the measured near-infrared magnitude of ζ Del B with the estimated temperature leads to a modeldependent mass estimate of 50 ± 15MJup, corresponding to a mass ratio of q = 0.019 ± 0.006. At a projected separation of 910 ± 14 au, ζ Del B is among the most widely separated and extreme-mass ratio substellar companions to a main-sequence star resolved to date, providing a rare empirical constraint of the formation of low-mass ratio companions at extremely wide separations.

Original languageEnglish (US)
Pages (from-to)3694-3705
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Sep 29 2014


  • Binaries: visual
  • Brown dwarfs
  • Stars: early-type
  • Stars:individual: ζ Del
  • Techniques: high angular resolution
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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