Globular cluster candidates in the Galactic bulge: Gaia and VVV view of the latest discoveries. (arXiv:1904.10872v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Gran_F/0/1/0/all/0/1">F. Gran</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zoccali_M/0/1/0/all/0/1">M. Zoccali</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ramos_R/0/1/0/all/0/1">R. Contreras Ramos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Valenti_E/0/1/0/all/0/1">E. Valenti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rojas_Arriagada_A/0/1/0/all/0/1">A. Rojas-Arriagada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carballo_Bello_J/0/1/0/all/0/1">J. A. Carballo-Bello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alonso_Garcia_J/0/1/0/all/0/1">J. Alonso-García</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Minniti_D/0/1/0/all/0/1">D. Minniti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rejkuba_M/0/1/0/all/0/1">M. Rejkuba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Surot_F/0/1/0/all/0/1">F. Surot</a>
Thanks to the recent wide-area photometric surveys, the number of star Thanks to the recent wide-area photometric surveys, the number of star http://arxiv.org/icons/sfx.gif
cluster candidates have risen exponentially in the last few years. Most
detections, however, are based only on the presence of an overdensity of stars
in a given region, or an overdensity of variable stars, regardless of their
distance. As candidates, their detection has not been dynamically confirmed.
Therefore, it is currently unknown how many, and which ones, of the published
candidates, are true clusters, and which ones are chance alignments. We present
a method to detect and confirm star clusters based on the spatial distribution,
coherence in motion and appearance on the color-magnitude diagram. We explain
and apply it to one new star cluster, and several candidate star clusters
published in the literature. The presented method is based on data from the
Second Data Release of Gaia complemented with data from the VISTA Variables in
the V’ia L’actea survey for the innermost bulge regions. It consists of a
nearest neighbors algorithm applied simultaneously over spatial coordinates,
star color, and proper motions, in order to detect groups of stars that are
close in the sky, move coherently and define narrow sequences in the
color-magnitude diagram, such as a young main sequence or a red giant branch.
When tested in the bulge area ($-10
cluster candidates have risen exponentially in the last few years. Most
detections, however, are based only on the presence of an overdensity of stars
in a given region, or an overdensity of variable stars, regardless of their
distance. As candidates, their detection has not been dynamically confirmed.
Therefore, it is currently unknown how many, and which ones, of the published
candidates, are true clusters, and which ones are chance alignments. We present
a method to detect and confirm star clusters based on the spatial distribution,
coherence in motion and appearance on the color-magnitude diagram. We explain
and apply it to one new star cluster, and several candidate star clusters
published in the literature. The presented method is based on data from the
Second Data Release of Gaia complemented with data from the VISTA Variables in
the V’ia L’actea survey for the innermost bulge regions. It consists of a
nearest neighbors algorithm applied simultaneously over spatial coordinates,
star color, and proper motions, in order to detect groups of stars that are
close in the sky, move coherently and define narrow sequences in the
color-magnitude diagram, such as a young main sequence or a red giant branch.
When tested in the bulge area ($-10<ell {rm (deg)}<+10$; $-10<b {rm
(deg)}<+10$) the method successfully recovered several known young and old star
clusters. We report here the detection of one new, likely old star cluster,
while deferring the others to a forthcoming paper. Additionally, the code has
been applied to the position of 93 candidate star clusters published in the
literature. As a result, only two of them are confirmed as coherently moving
groups of stars at their nominal positions.
