HD 219828 is an 8th magnitude star approximately 265 light years away in the constellation of Pegasus. It is a yellow subgiant, meaning that hydrogen fusion has ceased in its core.
In 2007, a Neptune-mass planet was found orbiting the star by Melo. According to the author, assuming an Earth-like rocky composition, the planet could yield a radius 2.2 times that of Earth. This could be furtherly proved if transit were observed, though, as authors state, it is a difficult task. Moreover a best fit orbital solution hints the presence of an additional planetary companion (so far unconfirmed) with 70% of Jupiter's mass, likely orbital separation of 0.68 Astronomical units and eccentric orbit (e=0.3).
* HD 159868
1. ^ Valencia et al.; Oconnell, R; Sasselov, D (2006). "Internal structure of massive terrestrial planets". Icarus 181 (2): 545–554. doi:10.1016/j.icarus.2005.11.021. Bibcode: 2006Icar..181..545V. http://arxiv.org/abs/astro-ph/0511150.
* "HD 219828". The Extrasolar Planets Encyclopaedia. http://exoplanet.eu/star.php?st=HD+219828.