Astronomers using NASA’s Transiting Exoplanets Survey Satellite (TESS) have discovered a compact three-planet system around the sixth-magnitude star HR 858.
An artist’s conception of the HR 858 planetary system. Image credit: Sci-News.com.
The newly-discovered planets orbit HR 858, a slightly-evolved F-type star, which is also a member of a visual binary system.
Also known as HD 17926, HIP 13363, TIC 178155732 and TOI 396, the star lies in the constellation of Fornax, approximately 104.4 light-years from Earth.
It has a radius 30% larger than the Sun, a mass 1.15 times solar, and a temperature of about 10,700 degrees Fahrenheit (5,928 degrees Celsius).
“We analyzed the TESS observations, using novel methods to model and remove instrumental systematic errors, and combined these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system,” said University of Texas at Austin astronomer Andrew Vanderburg and colleagues.
Named HR 858b, c and d, the new planets are all about twice the size of Earth and have periods of 3.6, 6 and 11.2 days, respectively.
“HR 858b and c orbit within 0.03% of the 3:5 period ratio, and may be in true mean motion resonance,” the astronomers said.
“This compact and near-resonant architecture harkens back to the systems of tightly packed inner planets discovered by Kepler, but HR 858 is hundreds to thousands of times brighter (V = 6.4) than the hosts of those Kepler systems.”
According to the team, HR 858 is one of the brightest stars known to host transiting exoplanets, trailing only HD 219134, pi Mensae, and 55 Cancri.
“Though the TESS prime mission survey is only about 25% complete, there may not be many new transiting planets around stars brighter than HR 858 left to discover,” Dr. Vanderburg and co-authors said.
“Pre-launch estimates of the TESS planet yield predicted a handful of planet discoveries around naked-eye stars, and so far only HR 858 and pi Mensae have fit this description.”
“HR 858 will thus likely retain its privileged position as one of the brightest transit hosts in the sky and most favorable systems for detailed study.”
A paper detailing the discovery will be published in a journal of the American Astronomical Society (AAS).
_____
Andrew Vanderburg et al. 2019. TESS Spots a Compact System of Super-Earths around the Naked-Eye Star HR 858. AAS Journals, in press; arXiv: 1905.05193
