Kerr, Ronan; Paolino, Facundo P茅rez; Tan, Jonathan C.; Speagle, Joshua S.; Kraus, Adam L.; Fern谩ndez-Trincado, Jos茅 G.; Stassun, Keivan G.; Chanam茅, Julio (2025).听.听Astrophysical Journal, 995(2), 217.听
Recent surveys using data from the聽Gaia space telescope聽have uncovered many small, faint groups of young stars that were previously too sparse to detect. These groups, called聽stellar associations聽(loose collections of stars that formed together), are still poorly understood, especially because their isolated locations may preserve clues about how they formed without being heavily disturbed by gravity from nearby objects. In this study, researchers examined 15 of these newly identified associations for the first time by combining Gaia data鈥攚hich provides precise measurements of star positions and brightness鈥攚ith additional聽spectroscopy聽(analysis of starlight to determine motion and composition).
They confirmed which stars belong to each group, looked for internal structure, estimated their total mass, and determined their ages. Some of these associations are extremely small, containing less than 20 times the mass of the Sun, making them the smallest known groups of this kind. In a few cases, the researchers found smaller subgroups within the larger associations, including a newly identified one that appears to have a different origin than its neighbors. Using models of how stars evolve over time (called聽isochrones) and other age indicators like聽lithium depletion聽(a method based on how stars burn lithium as they age), they estimated ages ranging from about 7 million to 43 million years.
Overall, this work provides the first detailed look at a previously overlooked population of young star groups. Studying these small and relatively undisturbed systems could help scientists better understand how stars form and evolve in our region of the galaxy.
Figure 1.聽Fits to the background contamination for all 15 associations included in this paper, which provide false-positive rates, or the rate at which field stars are incorrectly assigned to the association. For populations where a Gaussian fit was used to fit the background, the fit is shown in dark blue, while the RV histogram of all stars is shown in light blue. The shaded region is masked, as that is the RV range occupied by the association. For populations with features that make a fit difficult, we take the mean and standard deviation of a set of probable nonmembers, which are indicated by the red bins. A curve representing the field model in these cases is shown in dark red. In TOR1, we show聽Pfp聽results separately for the two components discussed in Section聽.