An international team of astronomers reports the discovery of a new planetary system by observing star HD 18599, (or TOI-179). This star appears to be orbited by a Neptune-mass exoplanet and a massive sub-stellar object. The discovery was detailed in a paper published on the arXiv pre-print server on October 14.
TESS is surveying approximately 200,000 of the brightest stars near the sun in search of transiting exoplanets. It has identified nearly 6,000 candidate exoplanets (TESS Objects of Interest, or TOI), with 266 confirmed.
Now, another TOI monitored by TESS has been confirmed by a group of astronomers led by Silvano Desidera of the Astronomical Observatory of Padova. They report finding a transit signal in the light curve of a bright K-dwarf star—TOI-179 (other designations HD 18599 and HIP 13754). Follow-up observations with the High Accuracy Radial velocity Planet Searcher (HARPS) and Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instruments confirmed the planetary nature of this signal.
“As part of ongoing efforts to validate and characterise young transiting exoplanets identified by TESS,” the researchers wrote in the paper, “we present in this paper our analysis for the system observed around the star HD 18599 = HIP 13754, a bright (V=8.99 mag) and active K dwarf, also known as TESS Object of Interest (TOI)-179.”
TOI-179 b, the newly discovered alien world, is approximately 2.62 times larger than Earth and 24 times more massive than our planet, resulting in a relatively high mean density of 7.4 g/cm3. The exoplanet orbits its host every 4.14 days at a distance of 0.048 AU on a highly eccentric orbit.
Furthermore, SPHERE observations revealed the existence of another object in the TOI-179 system with an estimated mass of about 83 Jupiter masses, placing it at the boundary between brown dwarfs and very low-mass stars. The object, designated HD 18599 B, has a relatively close projected separation from the parent star—about 3.3 AU.
The host star TOI-179 has the spectral type K2V, a radius of approximately 0.76 solar radii, and a mass of 0.83 solar masses. The star is thought to be 400 million years old, with an effective temperature of 5,145 K.
In summarizing the findings, the study’s authors emphasized the uniqueness of the TOI-179 system when considering the properties of its components.
“The TOI-179 system represents a high-quality laboratory for our understanding of the physical evolution of planets and other low-mass objects, as well as how planet properties are affected by dynamical effects and interactions with the parent star,” the researchers concluded.