The VAST Survey - IV. A wide brown dwarf companion to the A3V star ζ Delphini
Abstract
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 model-dependent mass estimate of 50 ± 15 MJup, 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2014
- DOI:
- 10.1093/mnras/stu2018
- arXiv:
- arXiv:1410.0005
- Bibcode:
- 2014MNRAS.445.3694D
- Keywords:
-
- techniques: high angular resolution;
- techniques: spectroscopic;
- binaries: visual;
- brown dwarfs;
- stars: early-type;
- stars: individual: ζ Del;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 12 pages, 11 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Society, 2014 September 25. Revised to incorporate typographical errors noted during the proofing process