Compact Multiple Paper Published in ApJ

Our latest paper on small stars with small planets has been published in The Astrophysical Journal:

In late 2013, Dr. Andrew Mann and I were chatting about collaborating on a project.  For the past few years we had each published papers on small planets orbiting small stars, Andrew focusing on statistics while I was focusing on individual systems.  We decided to do both in this recent paper.

In it, we confirm and characterize two new exoplanetary systems orbiting mid-M dwarf stars: Kepler-445 and Kepler-446.  Mid-M dwarf stars are special in that they are small, less than 30% the mass and diameter of the Sun, numerous, outnumbering all other types of stars in the Universe, and physically complex, with surfaces and interiors that are difficult to model.

When combined with GJ 1214 and Kepler-42, we now know of four mid-M dwarfs with transiting planets.   Four might not sounds like a lot, given the 1000s of planets Kepler has discovered, but these represent the smallest stars with confirmed transiting planets.  Unlike the GJ 1214 system, the Kepler-42, Kepler-445 and Kepler-446 systems are so-called compact multiples.  They host multiple planets all with periods of less than 10 days:

With three confirmed compact multiple systems, we calculated their occurrence and found that roughly one-in-five mid-Ms host compact multiples.  The prevalence of such systems is especially interesting as they may represent a link between the formation of planets in the Solar System and the formation of moons around gas-giant planets (see Jupiter and the Galilean moons above for comparison).  We won’t know for sure until we find compact multiples orbiting even smaller “stars": the brown dwarfs.  Speaking of the next project…

-Phil Muirhead