Additional planets to K-type stars

BD+20 2457 seems to have two brown dwarfs.

Substellar-mass companions to the K-dwarf BD +14 4559 and the K-giants HD 240210 and BD +20 2457
http://arxiv.org/abs/0906.1804

Abstract wrote:

We present the discovery of substellar-mass companions to three stars by the ongoing Penn State - Toru\' n Planet Search (PTPS) conducted with the 9.2-m Hobby-Eberly Telescope. The K2-dwarf, BD +14 4559, has a 1.5 M$_{J}$ companion with the orbital period of 269 days and shows a non-linear, long-term radial velocity trend, which indicates a possible presence of another planet-mass body in the system. The K3-giant, HD 240210, exhibits radial velocity variations that require modeling with multiple orbits, but the available data are not yet sufficient to do it unambiguously. A tentative, one-planet model calls for a 6.9 M$_J$ planet in a 502-day orbit around the star. The most massive of the three stars, the K2-giant, BD +20 2457, whose estimated mass is 2.8$\pm$1.5 M$_\odot$, has two companions with the respective minimum masses of 21.4 M$_J$ and 12.5 M$_J$ and orbital periods of 380 and 622 days. Depending on the unknown inclinations of the orbits, the currently very uncertain mass of the star, and the dynamical properties of the system, it may represent the first detection of two brown dwarf-mass companions orbiting a giant. The existence of such objects will have consequences for the interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars.

Good good

More evidence that some planets go through a stage of their evolution where they fuse deuterium in their cores. Just as VB 10b and 2M1207b show that some brown dwarfs don't.

Lazarus wrote:

More evidence that some planets go through a stage of their evolution
where they fuse deuterium in their cores. Just as VB 10b and 2M1207b
show that some brown dwarfs don't.

I'm not sure I follow. Can you elabourate on that?

BD+20 2457 has a planet-like orbital configuration, yet the two objects exceed 13 Jupiter masses. Looks like they formed like planets, and apparently such objects can fuse deuterium at the core/mantle interface. (Similarly the HW Vir system, where one of the companions exceeds the brown dwarf limit, and possibly Iota Aurigae with 2 brown dwarf-mass objects in a 2:1 resonance, though information on that system is somewhat lacking at present)

On the other hand VB 10b and 2M1207b have primary/secondary mass ratios in the stellar domain: accretion processes would require ludicrously massive discs relative to the primary to form these. So they may perhaps better be regarded as brown dwarfs.

A Dynamical Investigation of the Proposed BD +20 2457 System
http://arxiv.org/abs/1401.2793

Quote :

We present a detailed dynamical analysis of the orbital stability of the BD +20 2457 system, which features planets or brown dwarfs moving on relatively eccentric orbits. We find that the system exhibits strong dynamical instability on astronomically short timescales across a wide range of plausible orbital eccentricities, semi-major axes, and inclinations. If the system truly hosts massive planets or brown dwarfs, our results suggest that they must move on orbits significantly different to those proposed in the discovery work. If that is indeed the case, then it is likely that the best-fit orbital solutions for the proposed companions will change markedly as future observations are made. Such observations may result in the solution shifting to a more dynamically-stable regime, potentially one where stability is ensured by mutually resonant motion.

Oh well, at least Nu Ophiuchi's still there...