Star Cluster searches
Detecting new star clusters in the contemporary
era
Methods to detect star clusters
●
Usually utilized in conjunction
●
Visual → searching for stellar overdensities or ‘seeds’
●
Star-counting (dividing the sky into bins and searching
for enhancements in star count)
●
Radial number density profiles (RDPs) and radial
velocities
●
Color-magnitude diagrams comparisons
●
Parallaxes (distances), proper motions, radial velocities
‘Seeds’
●
Massive stars or massive star formation indications
(YSOs, masers, etc.) → all or almost all massive
stars form in star clusters (beware of the wording!)
●
Various type of nebulae (HII regions, mid-infrared
nebulae, supernova remnants?)
●
Catalog ‘seeds’ → cataloged compact extended
sources from older and/or lower resolution surveys
(2MASS, WISE), possible misclassified galaxies in
the Galactic plane
M 103 (credit: APOD)
??
Cas A
Barba+ (2015)
Survey exploitation
ra207.9981 (preliminary)
Froebrich (2017)
Ryu & Lee (2018)
OCs toward the inner Galaxy
Credit: Ryu & Lee (2018)
Methods to detect star clusters
●
Usually utilized in conjunction
●
Visual → searching for stellar overdensities or ‘seeds’
●
Star-counting (dividing the sky into bins and searching
for enhancements in star count)
●
Radial number density profiles (RDPs) and radial
velocities
●
Color-magnitude diagrams comparisons
●
Parallaxes (distances), proper motions, radial velocities
Gaia 1 (star-counting)
Koposov+ (2017)
Methods to detect star clusters
●
Usually utilized in conjunction
●
Visual → searching for stellar overdensities or ‘seeds’
●
Star-counting (dividing the sky into bins and searching
for enhancements in star count)
●
Radial number density profiles (RDPs) and radial
velocities
●
Color-magnitude diagrams comparisons
●
Parallaxes (distances), proper motions, radial velocities
Radial density profiles
Piatti (2017)
Radial velocities
Bravi+ (2018)
Methods to detect star clusters
●
Usually utilized in conjunction
●
Visual → searching for stellar overdensities or ‘seeds’
●
Star-counting (dividing the sky into bins and searching
for enhancements in star count)
●
Radial number density profiles (RDPs) and radial
velocities
●
Color-magnitude diagrams comparisons
●
Parallaxes (distances), proper motions, radial velocities
Color-magnitude diagram analysis
Navarrete+ (2017)
Gaia 2
Koposov+ (2017)
Methods to detect star clusters
●
Usually utilized in conjunction
●
Visual → searching for stellar overdensities or ‘seeds’
●
Star-counting (dividing the sky into bins and searching
for enhancements in star count)
●
Radial number density profiles (RDPs) and radial
velocities
●
Color-magnitude diagrams comparisons
●
Parallaxes (distances), proper motions, radial velocities
Clustering
Which one is the most appropriate algorithm?
K-means
Image credit: Michael Jordan
Cantat-Gaudin+ (2018)
DBSCAN
Credit: Castro-Ginard+ (2018)
Two parameters:
Radius of the hypersphere ε
minimum number of sources
(minPts, in this minPts=3)