GeminiFocus July 2018 - Page 14

Figure 2. Magnitude differences for real and simulated detections of stellar companions plotted as a function of separation in AU. The cyan points are the 21 K2 exoplanet hosts at known distances that have stellar companions discovered by DSSI on Gemini. Open black circles represent a random sampling of simulated stellar systems with bound components that would be detectable by Gemini/DSSI, while filled gray circles represent detectable line-of-sight companions from the same simulations. The dashed gray line at 50 AU marks the semi-major axis within which a previous study had concluded that stellar companions are suppressed among Kepler exoplanet hosts. (Figure adapted from Matsen et al., 2018.) 12 mission has observed a series of fields along the ecliptic plane, each one for 80 days, and has detected more than 500 exoplanet can- didates. The different observing strategy results in differences in the distributions of mass and orbital properties as compared to the original Kepler sample. The team observed 206 unique K2 planet hosts with DSSI and detected a total of 29 stellar companions, including 23 compan- ions to the 102 stars observed at Gemini. In order to assess the intrinsic binarity, the team compared their detections to expectations from simulations of both the Gemini and WIYN DSSI samples. Figure 2 compares the distributions in magnitude difference and separation of the simulated and actual Gem- ini observations. Assuming the field binarity fraction of 40-50%, the simulations predict 26 ± 6% of the exoplanet hosts should have companions detectable by DSSI on Gemini, consistent with the observations. Thus, the fraction of binary stars among K2 exoplanet hosts is consistent with that found among the general population of nearby stars of similar mass. GeminiFocus “While we have known that about 50% of all stars are binary, to confirm a similar ratio in exoplanet host stars helps set some impor- tant constraints on the formation of poten- tial exoplanets seen by Kepler,” said Rachel Matson of NASA’s Ames Research Center, the study’s lead author. “In our sample we did not find evidence that the proximity of a companion star suppresses the formation of exoplanets, even at distances as small as 50 astronomical units.” The paper is accepted for publication in The Astrophysical Journal, and a preprint is available online. AO Constraints on Psyche’s Shape, Density, and Polar Axis The Main Belt asteroid 16 Psyche is one of the defining members of the metallic M- class asteroids. The classification is based on its high radar albedo, which suggests that Psyche’s surface is about 90% nickel- iron metal. This could indicate that Psyche is the remnant core of a larger differenti- ated body. Although its mean diameter of about 225 km places it 35th among Main Belt asteroids, it ranks 11th in terms of mass. July 2018