FAQ

Please contact me for any comments/suggestions or any other questions not listed here.

What is the UCC?

The acronym UCC stands for Unified Cluster Catalogue. It is the largest catalogue of open clusters in existence. It consists of comprehensive and homogeneous data for an ever expanding number of entries, taken from the latest published articles combined with data from the Gaia survey.

Catalogued OCs in the literature

What objects are included in the UCC?

The UCC lists any object that was catalogued as an open cluster in the literature. This object might be classified differently in other articles (e.g.: moving group, association, etc.) but it will remain listed in the UCC because at least one article at some point indicated that it was an open cluster.

The UCC is regularly updated to include new research. If your article is not listed in the database, you can contact me with the details and I will add it as soon as possible.

How are member stars selected?

Membership is obtained through the fastMP method described in Sect. 3 of Perren et al. (2023). The fastMP membership estimation method has been incorporated into the ASteCA package (see details here).

What is the C3 parameter?

The C3 parameter is the combined C1 and C2 classes, described in Sect. 4.3 of Perren et al. (2023) where the UCC was initially introduced.

The C1 and C2 classes can be described as:

C1: A density-based metric that quantifies the contrast between the spatial distribution of cluster member stars and that of the surrounding field stars within the five-dimensional parameter space defined by celestial coordinates, proper motions, and parallax.

C2: A photometric metric that estimates the likelihood that the observed stellar sequence of the candidate members is statistically indistinguishable from a sequence randomly drawn from the field star population.

Each one takes values [A, B, C, D] where A is best and D is worst.

Classification of OCs in the literature

What is the UTI parameter?

The UTI (UCC Trust Index) is a measure of the reliability of the cluster detection, ranging from 0 (worst) to 1 (best). It is calculated based on factors such as the number of members, stellar density, the C3 parameter, the presence of the object in the literature, and the probability of the object being a duplicate of a previous entry. It is estimated via the relation:

UTI = 0.2 * (C_N + C_dens + C_C3 + 2*C_lit) * C_dup

where the C factors have values in the [0, 1] range (1 is best) representing normalized estimates of:

  • C_N: number of members (1 = many members)
  • C_dens: stellar density in pc^2 (1 = dense object)
  • C_C3: C3 parameter (1 = AA class)
  • C_lit: presence in literature (1 = frequently mentioned in literature)
  • C_dup: probability of duplication (1 = not a duplicate)

UTI values for OCs in the literature

How can I cite the UCC?

If you found the UCC useful for your research, please reference its original article Perren et al. (2023). You can use a phrase such as the following:

“This research has made use of the Unified Cluster Catalogue (UCC)~\cite{Perren_2023}”

BibTeX entry for the original article:

@ARTICLE{Perren_2023,
       author = {{Perren}, Gabriel I. and {Pera}, Mar{\'\i}a S. and {Navone}, Hugo D. and {V{\'a}zquez}, Rub{\'e}n A.},
        title = "{The Unified Cluster Catalogue: towards a comprehensive and homogeneous data base of stellar clusters}",
      journal = {\mnras},
     keywords = {methods: data analysis, catalogues, open clusters and associations: general, Astrophysics - Astrophysics of Galaxies},
         year = 2023,
        month = dec,
       volume = {526},
       number = {3},
        pages = {4107-4119},
          doi = {10.1093/mnras/stad2826},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2023MNRAS.526.4107P}
}

Random cluster navigation

You can navigate to a random cluster page by searching the keyword “random” on the main search page, or directly accessing the random url.