Juan Casado

We define an open supercluster (OSC) as a cluster of at least six open clusters (OCs) born from the same giant molecular cloud (GMC). We surveyed the recent catalogs of OCs based on Gaia data and relevant literature to find 17 OSCs of the third Galactic quadrant, along with 190 likely members of them. OSCs are frequent enough to be considered an extra class of objects in the hierarchy of star formation. Some of these supersystems are new and most of them contain more members than previously thought. The detailed study of some OSCs lead to the discovery of four new young OCs that are members of them, named Casado-Hendy 2–5. In certain instances, subgroups with distinct proper motions (PMs) or 3D positions have been found within an OSC, suggesting the presence of multiple generations of stars formed from several bursts of star formation within the same GMC. OSCs are typically unbound and tend to disintegrate on timescales of ∼0.1 Gyr. The present results confirm that young OCs tend to form primordial groups and suggest that globular clusters (GCs) are not formed from the accretion of OSCs, that is, at least in the local Universe at late times.

An open supercluster (OSC) is defined as a cluster of at least six open clusters (OCs) born from the same giant molecular cloud (GMC). We survey the recent catalogs of OCs based on Gaia data and relevant literature to find 17 OSCs of the third galactic quadrant, along with 190 likely members of them. OSCs are frequent enough to be considered an extra class of objects in the hierarchy of star formation. Some of these supersystems are new and most of them contain more members than previously thought. The detailed study of some OSCs has leaded to the discovery of four new young clusters that are members of them, named Casado-Hendy 2 to 5. In certain instances, subgroups with distinct PMs or 3D positions have been found within an OSC, suggesting the presence of multiple generations of stars formed from several bursts of star formation within the same GMC. OSCs are typically unbound and tend to disintegrate on timescales of 0.1 Gyr. The present results support the Primordial Group hypothesis (Casado 2022) and suggest that globular clusters are not formed from the accretion of open superclusters, at least in the local Universe at late times.

Advanced oxidation processes (AOPs) such as Fenton's reagent, which generates highly reactive oxygen species, are efficient in removing biorefractory organic pollutants from wastewater. However, Fenton's reagent has drawbacks such as the generation of iron sludge, high consumption of H₂O₂, and the need for pH control. To address these issues, Electro-Fenton (EF) and heterogeneous Electro-Fenton (HEF) have been developed. HEF, which uses solid catalysts, has gained increasing attention, and this review focuses on the use of mineral catalysts in HEF and derived processes. The reviewed studies highlight the advantages of using mineral catalysts, such as efficiency, stability, affordability, and environmental friendliness. However, obstacles to overcome include the agglomeration of unsupported nanoparticles and the complex preparation techniques and poor stability of some catalyst-containing cathodes. The review also discusses the optimal pH range and dosage of the heterogeneous catalysts and compares the performance of iron sulfides versus iron oxides. Although natural minerals appear to be the best choice for effluents at pH>4, no scale-up reports have been found. The need for further development in this field and the importance of considering the environmental impact of trace toxic metals or catalytic nanoparticles in the treated water on the receiving ecosystem is emphasized. Finally, the article acknowledges the high energy consumption of HEF processes at the lab scale and calls for their performance development to achieve environmentally friendly and cost-effective results using real wastewaters on a pilot scale.

A primordial group of open clusters containing NGC 6871 is confirmed and described through Gaia DR3 data and the previous literature. It is a star-forming complex containing at least six young open clusters (OCs), including Teutsch 8, FSR 198, and Biurakan 2. Two nearby OCs (Casado 82 and Casado-Hendy 1) are newly identified and studied in detail and found to be also members of the cited group. The parameters of the components are sufficiently similar to postulate the case of at least six clusters born from a single giant molecular cloud. None of the cluster pairs of the group seems to be an authentic binary cluster, with the possible exception of the candidate pair Teutsch 8/FSR 198. Instead, NGC 6871 seems to be disintegrating, and the primordial group members appear to be dispersing out rapidly. Searching for new open clusters in the vicinity of young or grouped OCs using Gaia data is an efficient strategy to find new associated OCs forming primordial groups.

A primordial group of open clusters containing NGC 6871 is confirmed and described through Gaia DR3 data and the previous literature. It is a star-forming complex containing at least six young OCs, including Teutsch 8, FSR 198 and Biurakan 2. Two nearby OCs (Casado 82 and Casado-Hendy 1) are newly identified and studied in detail and found to be also members of the cited group. The parameters of the components are sufficiently similar to postulate the case of at least six clusters born from a single GMC. None of the cluster pairs of the group seems to be an authentic binary cluster, with the possible exception of the candidate pair Teutsch 8/FSR 198. Instead, NGC 6871 seems to be disintegrating, and the primordial group members appear to be dispersing out rapidly. Searching for new open clusters in the vicinity of young or grouped OCs using Gaia data is an efficient strategy to find new associated OCs forming primordial groups.

The title study lacks practical feasibility since it mostly ignores O ₂ released with CO ₂ ; underestimates the impact of vapour, SOx, and NOx on the system; anodes are unstable vs O ₂ evolution, and the total voltage does not match the quoted voltage.

In the present study, we continue testing the Primordial Group hypothesis (Casado 2022), which postulates that only sufficiently young open clusters can be binary or multiple, and old clusters are essentially single. To this end, we revisit all the remaining binary cluster candidates in the Galaxy having at least one cluster older than 100 Myr through Gaia data and careful revision of the literature. We found no convincing case for an old binary system among the 120 pairs/groups revised. Most of the pairs are optical pairs or flyby encounters. However, we found three dubious pairs that could falsify the title hypothesis upon further research. We also found two possible primordial pairs older than expected. Our results confirm that the vast majority of binary/multiple OCs in the Galaxy, if not all, are of primordial origin and are not stable for a long time. This finding is in line with similar studies of the Magellanic Clouds and theoretical N-body simulations in the Galaxy. The pairs of OCs in these groups are generally not binary systems since they are not gravitationally bound. We also point out some inconsistencies in previous works and databases, such as false open clusters and duplicities.

The open star cluster NGC 1605 has recently been reported to in fact consist of two clusters (one intermediate-aged and one old) that merged via a flyby capture. Here we show that Gaia data do not support this scenario. We also report the serendipitous discovery of a new open cluster, Can Batlló 1, with a similar age and distance.

The Primordial Group hypothesis states that only sufficiently young open clusters (OCs) can be multiple, and old OCs are essentially isolated. We tested this postulate through four different studies using a manual search of Gaia EDR3 and extensive literature. First, we revisited the work of de La Fuente Marcos and de La Fuente Marcos (2009), which states that only ca. 40% of OC pairs are of primordial origin. However, no plausible binary system among their proposed OC pairs having at least one member older than 0.1 Gyr was found. Second, we researched the OCs < 0.01 Gyr old in Tarricq et al. (2021) and found that ca. 71% of them remain in their primordial groups. Third, a similar study of the oldest OCs (age > 4 Gyr) showed that they are essentially alone. Forth, the well-known case of the double cluster in Perseus and some other binary systems described in the literature were also shown to accommodate the title hypothesis. A simplified bimodal model allows for retrieval of the overall fraction of related OCs (approximately 12–16%) from our results, assuming that young clusters remain associated at ~0.04 Gyr. The obtained results further support that OCs are born in groups (Casado 2021).