New star system discovered by the Kilo-Degree Survey

Astronomers have discovered a new star system on the outskirts of the Milky Way as part of the Kilo-Degree Survey (KiDS). The new system, named Sextans II, is most likely an ultra-faint dwarf galaxy. The discovery is reported in a paper published November 10 on the preprint server. arXiv.

KiDS is a large multi-band photometric survey using the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile. Since 2011, the survey has mapped 1,350 square degrees of the night sky with four broadband filters (u, g, r, i). Although KiDS focuses on assembling large-scale structures in the universe, it can also detect extragalactic star systems at low surface brightness.

That’s why a team of astronomers led by Massimiliano Gatto of the Capodimonte Astronomical Observatory in Naples, Italy, decided to conduct a large-scale search for faintly unknown star systems with KiDS. To this end, they looked for low-luminosity stellar overdensities in the latest KiDS data release (DR4), which yielded promising results.

“We report the discovery of a significant and compact overdensity of old, metal-poor stars in the KiDS survey (data 4),” the researchers wrote in the paper.

The team identified a very promising star overdensity in the Sextans constellation, with an absolute integrated magnitude of -3.9. Follow-up observations of this overdensity with the 8.2-meter Subaru Telescope confirmed that it is a star system located approximately 473,000 light years away.

Astronomers initially designated the new system KiDS-UFD-1 and dubbed it Sextans II. The data collected indicates that Sextans II is relatively small, with a half-light radius of approximately 629 light years, while its mass is estimated at 4,910 solar masses. The system has a metallicity of -1.5 dex, an ellipticity of 0.46, and is at least 10 billion years old.

According to the authors of the article, the results indicate that Sextans II is a weak, old and metal-poor system. Gatto’s team concluded that the newly detected star system is a faint spheroidal satellite of the Milky Way, most likely an ultra-faint dwarf (UFD) galaxy. In general, UFDs are the least luminous, most dark matter dominated, and least chemically evolved galaxies known.

However, the researchers do not rule out the possibility that Sextans II could be a disruptive globular cluster, adding that further investigation of this system is needed to confirm its true nature.

“The final word on the nature of the system can only be provided by appropriate spectroscopic tracking of a reasonable sample of member stars, which may prove difficult, given the magnitude range covered by candidate members of the RGB “, the scientists wrote.

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