The Evanescent Protoplanetary Disks Of Dolidze 25 (Planetary Science)

The dispersion times of protoplanetary disks, and in general the times available to form planets, are faster in low metallicity environments. This is what emerges from a study, led by Mario Guarcello of INAF of Palermo, conducted on archival data in optical and infrared bands and on X-ray observations obtained with NASA’s Chandra satellite.

The protoplanetary disks are hard structures from which planetary systems form, and featuring low-mass stars typically younger than 10 million years, these stars of pre-sequence . In recent years, the scientific community has paid great attention to the study of the evolution and dispersion of protoplanetary disks. This is thanks to instruments such as Alma which, thanks to an unprecedented angular resolution, have made it possible to observe many protoplanetary disks with great spatial detail, and also thanks to the evidence – obtained in recent years of research on exoplanets – that the presence of planets is a common feature among the stars in our galaxy.

In recent decades, several authors have estimated the number of stars with protoplanetary disks associated with star clusters with different ages. Thanks to these studies, we know that discs disperse rapidly: in star clusters of 5 million years the fraction of stars with discs is typically very low. This obviously places an important upper limit on the times a star can form a planetary system. In addition, some studies have also shown that in certain star formation environments, disks can disperse even more rapidly, so much so that planets cannot be formed. These are mainly environments characterized by intense local fields of ultraviolet radiation, emitted by rich populations of massive stars, or by high stellar densities.Ngc 6611 (the star cluster in the Eagle Nebula) and more populated OB associations , such as Cygnus OB2 .

Mario Giuseppe Guarcello, researcher at INAF in Palermo, first author of the study on the Dolidze 25 cluster published on A&A © INAF

The dispersion times of protoplanetary disks may also depend on the metallicity of the environment in which they were formed, that is, on the abundance of chemical elements heavier than hydrogen and helium. In fact, various properties of the discs depend on the abundance of heavy elements, such as the amount of dust present and the opacity of the material in the disc, i.e. the ability to absorb external radiation, properties that can be important in determining the dispersion times. discs. However, these environments are typically distant, and therefore difficult to study.

An exception to this rule is the young star cluster (about one million years) Dolidze 25 , at a distance of about 15 thousand light years from us, characterized by a low metallicity. By studying archival data in optical and infrared band and X-ray observations obtained with the NASA Chandra satellite, a team led by astrophysicist Mario Giuseppe GuarcelloINAF in Palermo has identified 1091 stars associated with the star cluster, determining their stellar parameters and calculating that about 34 percent of the stars of Dolidze 25 still have a protoplanetary disk. When compared with star clusters of the same age, this fraction is significantly low, and comparable to those star-forming regions where disks are dispersed more rapidly due to the properties of the surrounding environment.

“This result therefore indicates that the dispersion times of protoplanetary disks, and in general the times available to form planets, are faster in low metallic environments: an important result if we consider that the metallicity of the galaxy depends on both the distance from the center galactic that from the time considered ».

Featured image: Fraction of stars associated with 58 star clusters of various ages that still hosts a protoplanetary disk, depending on the age of the cluster. Clusters within 3,300 light years of the Sun are marked with black circles, clusters with a rich population of massive stars with red circles, low metallicity environments with green circles. The village of Dolidze 25 is marked with a star symbol. Credits: M. Guarcello et al., A&A, 2021


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