DanceDance ofof thethe Stars:Stars: AnAn AnalysisAnalysis ofof thethe SpatialSpatial EvolutionEvolution ofof TwoTwo ClustersClusters Anne Buckner (University of Leeds) & the SFM Collaboration Image Credit: Wikimedia Commons TalkTalk OutlineOutline Stellar Association INDICATE A B C Carina Nebula D Upper Scorpius StellarStellar AssociationAssociation ● Point processes – intensity – correlation – spatial distribution StellarStellar AssociationAssociation ● Point processes – intensity – correlation – spatial distribution Q. How “clustered” are stars? WhyWhy isis studyingstudying stellarstellar associationassociation important?important? WhyWhy isis studyingstudying stellarstellar associationassociation important?important? ● Define the distribution and clustering of stars ● Trace morphological features → variation in degree of clustering of stars in regions (as a function of e.g. age, mass, position) ● Discriminate between different modes of Massive SF MeasuringMeasuring StellarStellar AssociationAssociation MeasuringMeasuring StellarStellar AssociationAssociation 1. Global measures MeasuringMeasuring StellarStellar AssociationAssociation 1. Global measures – 2-point correlation function – Hopkins Statistic == xx MeasuringMeasuring StellarStellar AssociationAssociation 1. Global measures – 2-point correlation function – Hopkins Statistic 2. Local measures MeasuringMeasuring StellarStellar AssociationAssociation 1. Global measures X X 6 7 X – 2-point correlation function 8 – X X Hopkins Statistic X 5 9 X X 4 2 3 X X 10 11 X X X 18 12 1 X 19 X X 2. Local measures 17 X 13 X 14 16 X – INDICATE 15 INDICATE INdex to Define Inherent Clustering And TEndencies INDICATE INdex to Define Inherent Clustering And TEndencies ● Local measure of degree of stellar association ● Any parameter space ● 2+D INDICATE INdex to Define Inherent Clustering And TEndencies ● Local measure of degree of stellar association ● Any parameter space ● 2+D ● Assigns a clustering index to each star ● Comparison of number of nearest neighbours with an evenly spaced control field ● Meaningful index values → calibrated against random distributions INDICATE INdex to Define Inherent Clustering And TEndencies I = 20/5 = 4 I = 3/5 = 0.6 Carina Nebula Typical A ~ 0.5-3 mag v (< 10 mag) Age < 6 Myr D ~ 2.3 kpc M > 105 M . 130+ OB Stars Image Credit: Wikipedia/ Harel Boren Carina Nebula Khun et al. (2014) Buckner et al. 2018 (in review) Carina Nebula Sig level: I > I random + 3σ 5 5 Buckner et al. 2018 (in review) OB Stars Sig level: I > I random + 3σ 5 5 Buckner et al. 2018 (in review) OB Stars: self-clustering Sig level: I > I random + 3σ 5 5 Buckner et al. 2018 (in review) OB Stars OB Stars OB Stars Buckner et al. 2018 (in review) Upper Scorpius Age ~5-10 Myr D ~ 145 pc OB association ~1300 candidate members Image Credit: WIkipedia Galli et al. 2018 5 I Buckner et al. 2018 (in prep) Members clustered above random 90 80 70 60 Column B 50 40 30 20 % star's significantly %star's clustered 10 0 All G<12 mag G>12 mag Index ranges All G<12 mag G>12 mag 0 5 10 15 20 25 30 35 40 45 Buckner et al. 2018 (in prep) I 5 Self-clustering 90 80 70 60 Column B 50 40 30 % star's significantly star's % clustered 20 10 0 G<12 mag G>12 mag Buckner et al. 2018 (in prep) Summary INDICATE → powerful local measure of degree of “clustering” of stars 2+D, any parameter space Trace morphological features in SF regions Buckner et al. (2018, A&A, in review) Image from Pixabay.com Summary INDICATE → powerful local measure of degree of “clustering” of stars 2+D, any parameter space Trace morphological features in SF regions Buckner et al. (2018, A&A, in review) Clustering tendencies in NW and SE regions of Carina different More pronounced for OB stars No mass segregation in SE region Image from Pixabay.com Summary INDICATE → powerful local measure of degree of “clustering” of stars 2+D, any parameter space Trace morphological features in SF regions Buckner et al. (2018, A&A, in review) Clustering tendencies in NW and SE regions of Carina different More pronounced for OB stars No mass segregation in SE region Upper Scorpius is centrally concentrated Higher mass population more spatially dispersed than lower mass Signature of SF history Image from Pixabay.com.