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arXiv · 1410.0005

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

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

We report the discovery of a wide co-moving substellar companion to the nearby ($D=67.5\pm1.1$ 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 $525\pm125$ 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 (L$5\pm2$), at a temperature of $1650\pm200$ K. Combining the measured near-infrared magnitude of $ζ$ Del B with the estimated temperature leads to a model-dependent mass estimate of $50\pm15$ M$_{\rm Jup}$, corresponding to a mass ratio of $q=0.019\pm0.006$. At a projected separation of $910\pm14$ 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.

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R. J. De Rosa, J. Patience, K. Ward-Duong, A. Vigan, C. Marois, I. Song, B. Macintosh, J. R. Graham, R. Doyon, M. S. Bessell, O. Lai, D. W. McCarthy, C. Kulesa. 2014-10-13. The VAST Survey - IV. A wide brown dwarf companion to the A3V star $ζ$ Delphini. https://doi.org/10.1093/mnras%2Fstu2018

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