Astronomers discover a planetary system with the mass of Neptune and a massive quasi-stellar body

An international team of astronomers has reported the discovery of a new planetary system by observing a nearby star known as HD 18599 (or TOI-179). This star appears to orbit an exoplanet with the mass of Neptune and a massive quasi-stellar body. The discovery was detailed in a paper published October 14 on the arXiv server before printing.

TESS is surveying about 200,000 of the brightest stars near the Sun in search of transiting exoplanets. To date, it has identified nearly 6,000 candidate exoplanets (TESS Objects of Interest, or TOI), of which 266 have been confirmed so far.

Now, a group of astronomers led by Silvano Desidera of the Padua Astronomical Observatory recently confirmed another TOI spotted by TESS. They report that the transit signal has been identified in the light curve of a bright K dwarf star – TOI-179 (other designations HD 18599 and HIP 13754). The planetary nature of this signal was confirmed by follow-up observations using the High Resolution Radial Velocity Planetary Search (HARPS) and High Contrast Spectral Exoplanet Search (SPHERE) instruments.

“As part of the ongoing effort to validate and characterize the small transiting exoplanets identified by TESS, we present in this paper our analysis of 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,” the researchers wrote in the paper.

The newly discovered alien world, designated TOI-179 b, is about 2.62 times larger than Earth and 24 times larger than our planet, resulting in a relatively high average density of about 7.4 g/cm³. An exoplanet orbits its host every 4.14 days, at a distance of 0.048 AU from it, in a highly eccentric orbit.

Furthermore, Sphere observations have identified another object in the TOI-179 system with an estimated mass of about 83 Jupiter masses – thus, at the boundary between brown dwarfs and very low-mass stars. The object that received the designation HD 18599 B has a relatively small projection distance from the original star – about 3.3 AU.

The host star TOI-179 is of spectroscopic type K2V, has a radius of about 0.76 solar radii, while its mass has been measured at about 0.83 solar masses. The star is estimated to be about 400 million years old and has an effective temperature of 5,145 K.

Summing up the results, the authors of the study emphasized the uniqueness of the TOI-179 system taking into account the characteristics of its components.

The researchers conclude, “The TOI-179 system represents a high-quality laboratory for our understanding of the physical evolution of planets and other low-mass objects and how planet properties are affected by dynamical influences and interactions with the parent star.”

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