HD 166191

HD 166191 is a young late-F or early G-type star in the constellation Sagittarius. It is surrounded by a large amount of dust. In 2019 it was reported in the Astronomer's Telegram that the star had brightened in the infrared, as was seen from Spitzer observations. A study was published in 2022, reporting on the result of a follow-up campaign. This study showed that a dust cloud as large as the star did transit in front of it. This cloud was produced from a giant collision between two planetesimals.

In early works the age of the system was not certain and ranged between 10-100 Myrs. The large amount of dust was interpreted as being produced by a recent collision of planetary embryos or by massive ongoing collisional grinding. A later work did determine a younger age. The star was observed with ground-based spectroscopy and with Herschel. The researchers did find that the star is surrounded by a protoplanetary disk with a hole in the center. The silicate feature was also determined to be similar to primordial object. This would make the disk a so-called transitional disk, meaning it lies in between protoplanetary and debris disk. Observations with the Submillimeter Array did however find a high amount of dust and only little amount of gas, indicating that the disk is a debris disk. Another work determined that the disk is made up of two debris belts. An inner belt at ~0.27 AU with a temperature of about 760 Kelvin (K) and an outer belt at ~5 AU with a temperature of about 175 K.

It was suggested that HD 166191 co-moves with HD 163296. This was questioned in a later work.