Substellar-Mass Companions to the K-Dwarf Bd+14 4559 and the K-Giants Hd 240210 and Bd+20 2457

Abstract

We present the discovery of substellar-mass companions to three stars by the ongoing Penn State -Toruń 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 K2giant, BD +20 2457, whose estimated mass is 2.8±1.5 M ⊙ , 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.

Hipparcos preliminary astrometric masses for the two close-in companions to HD 131664 and HD 43848

“…A quick look at literature data allows us to speculate on the possibility that the brown dwarf desert may not be very "dry" when it comes to close substellar companions to intermediatemass stars, in light of a handful of systems containing at least one companion with minimum mass in the brown dwarf regime (e.g., Omiya et al 2009, and references therein). In particular, the recently announced system of brown dwarfs around BD+20 2457 (Niedzielski et al 2009) has an architecture very similar to that of HD 168443, with a solar-type primary. It is reminiscent of an origin in a massive circumstellar disk, further suggesting a scenario in which more massive substellar companions are found around more massive stellar hosts (and their frequency also increases with increasing primary mass).…”

A radial-velocity survey of Ap stars with HARPS

“…However, some recent programs have been monitoring also more massive stars, such as evolved subgiants and giants (e.g., Hatzes et al 2006;Döllinger et al 2009;Niedzielski et al 2009;Johnson et al 2011;Sato et al 2013) as well as A-F-type mainsequence stars (e.g., Galland et al 2005;Guenther et al 2009;Hartmann et al 2010;Borgniet et al 2014). One of our targets was the roAp star HD 42659.…”

The Pennsylvania-Toruń search for planets around evolved stars with HET

“…This offers an excellent opportunity to improve our understanding of the population of planets around stars that are significantly more massive than the Sun, without which it would be difficult to produce abroad, integrated picture of planet formation and evolution. Since 2001, about 30 such objects have been identified, including our five published HET detections (Niedzielski et al 2007;Niedzielski et al 2009a;Niedzielski et al 2009b). Our work has produced the tightest orbit of a planet orbiting a K-giant identified so far (0.6 AU), and the first convincing evidence for a multiplanet system around such as star (Niedzielski et al 2009a).…”

“…Our work has produced the tightest orbit of a planet orbiting a K-giant identified so far (0.6 AU), and the first convincing evidence for a multiplanet system around such as star (Niedzielski et al 2009a). Our most recent discoveries (Niedzielski et al 2009b) have identified new multiplanet systems, including a very intriguing one of two brown dwarf-mass bodies orbiting a 2.8M , K2 giant. This particular detection challenges the standard interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars.…”