Know the Star, Know the Planet. V. Characterization of the Stellar Companion to the Exoplanet Host HD 177830

Lewis C. Roberts Jr. Rebecca Oppenheimer, Justin R. Crepp, Christoph Baranec, Charles Beichman, Douglas Brenner, Rick Burruss, Eric Cady, Statia Luszcz-Cook, Richard Dekany, Lynne Hillenbrand, Sasha Hinkley, David King, Thomas G. Lockhart, Ricky Nilsson, Ian R. Parry, Laurent Pueyo, Anand Sivaramakrishnan, Remi Soummer, Emily L. Rice, Aaron Veicht, Gautam Vasisht, Chengxing Zhai, Neil T. Zimmerman

Published 2015-07-28Version 1

HD 177830 is an evolved K0IV star with two known exoplanets. In addition to the planetary companions it has a late-type stellar companion discovered with adaptive optics imagery. We observed the binary star system with the PHARO near-IR camera and the Project 1640 coronagraph. Using the Project 1640 coronagraph and integral field spectrograph we extracted a spectrum of the stellar companion. This allowed us to determine that the spectral type of the stellar companion is a M4$\pm$1V. We used both instruments to measure the astrometry of the binary system. Combining these data with published data, we determined that the binary star has a likely period of approximately 800 years with a semi-major axis of 100-200 AU. This implies that the stellar companion has had little or no impact on the dynamics of the exoplanets. The astrometry of the system should continue to be monitored, but due to the slow nature of the system, observations can be made once every 5-10 years.