Rediscovering star clusters with CSS-OS Jing Zhong ng (SHAO) AO) Li Chen (SHAO), Chao Liu (NAOC) , Zhou Fan (NAOC), Xiangxiang Xue (NAOC), Haining Li (NAOC ), Jian Gao (BNU), Zhengyi Shao (SHAO), Jinliang Hou (SHAO), et al.
Why star clusters ? Distance Universe Galaxy Age Star cluster Star Metallicity Star clusters play the role of bridge between star and galaxy
Cluster study & stellar formation and evolution Binary fraction & evolution ✓ Blue straggler, Red straggler, … Special evolution stage ✓ BHB, Be, RC, TP- AGB,… Stellar initial mass function Stellar populations Stellar rotation, mass ratio (Q value) …
Cluster study & Galactic structure and evolution ▲ Star clusters Galactic structure and ▲ Stellar distribution evolution ▲ Gas distribution ➢ Spatial distribution ➢ Dynamical properties Star clusters ➢ Chemical / age tagging ➢ Mass function 1. Globular clusters Galactic halo Two major tracers 2. Open clusters Galactic disk
Importance of open clusters observation to the Galaxy Open Clusters (-- GMC) where most of (thin) disk stars born Main characteristics of Galactic OC system ： • spatial distribution (4 – 20 kpc) ； reliable distance tracer of disk structure • wide range of age (10 6 － 10 9 yr) & mass evolution effects ； IMF, … • [M/H]: -0.8 ~ +0.7, coeval, more reliable chemical evolution of disk ， AMR ， … OCs great tracer of the structure and evolution of Galactic disk
Massive / Supermassive globular clusters provide… Testbeds – stellar evolution Unique hosts for exotic objects: LMXRBs, IMBH, blue stragglers Testbeds -- dynamics of Internal dynamics and dense stellar systems (N mass profile of galaxy ~ 10 6 ) halo Testbeds -- starburst, merger Relics of the pre-galactic events, evolution histories of clouds at the beginning of galaxies hierarchical merging
Galactic halo mass A stellar population that forms in direct proportion M(stellar) strongly nonlinear function of M(halo) to halo mass Total mass in all globular clusters Halo mass from weak lensing Kravtsov et al. 2014 Harris et al. 2015 ➢ M(GCs) ~ initial M(gas) ~ M(halo) Galaxy formation and evolution ➢ GCs formation is largely immune to feedback
Studies on Globular clusters Tidal tails on Palomar 5 ➢ How do they form? ➢ How do they evolve with time? ➢ How do they trace the galactic evolution? Odenkirchen et al. 2003
Studies on Globular clusters Multiple- population in GCs Accretion history Binary evolution Formation history … Li et al. 2016
The database for Galactic star clusters Globular Clusters: • Harris catalog(1996,2010) ➢ Positions, Integrated magnitudes, metallicites, Radial velcocities, structural parameters • The HST Proper Motion Collaboration ➢ 22 GCs ( Bellini et al. 2014) Harris catalog:~156 GCs (2010) Open Clusters : • Photometric ➢ Pan-STARRS (r~23mag), 2MASS(J~15.8mag), LSST(r~27.5mag) ,… • Kinematical ➢ proper motion ： <1-2kpc ( PPMXL, UCAC5, Gaia) ➢ radial velocity ： low data-density (LAMOST) Kharchenko catalog: • WIYN open cluster study ~3006 star clusters (2013) ➢ 31 (photometry) , 10 (spectroscopy)
The great advantage of CSS-OS Proper motion accuracy High spatial resolution ~0.05 -0.6 mas/yr ~ 0.074”(pixel size) (magnitude dependent) • Membership identification in OCs High precision PMs catalog • Internal Kinematics/Dynamics in GCs Stellar mass function High detection sensibility ~0.09 Mʘ within 500 pc R~26 mag ~0.16Mʘ within 3kpc
Globular Clusters ： ✓ 1 degree FOV ： Astrometric standard stars in Gaia Absolute proper motions + proper motion in HST high precision proper motion • The intrinsic velocity dispersion σ v ~ 5-10 km/s • For GCs with dist=10 kpc σ μ ~ 0.1-0.2 mas/yr (r~23mag) • For GCs in LMC/SMC dist~50kpc, σ v ~ 30km/s σ μ ~ 0.1 mas/yr (r~21mag) ➢ Intrinsic rotation & velocity dispersion ~100 d<10kpc Dynamical mass ~20 d<5kpc ➢ Distribution of velocity dispersion Spatial mass segregation ➢ Tidal stream ➢ … Heliocentric distance (kpc)
Open Clusters ： LSST Gaia ✓ Membership Identification : High precision proper motion r=24mag: CSST ( 0.6 mas/yr ) > LSST ( 1.0 mas/yr) σ μ =0.2 mas/yr: CSST ( 23mag ) > Gaia ( 19 mag ) OCs with dist =2 kpc : ➢ cluster members : ~10km/s σ μ ~ 1.0 mas/yr ➢ intrinsic σ v (dynamics) : ~ 1km/s σ μ ~ 0.1 mas/yr Membership identification and kinematical analysis for low mass stars
Survey suggestion for CSS-OS Multi-epoch observations Proper Motions ✓ > 2 epochs ✓ 2 epoch + HST (GCs) Deep observations High precision photometry, Mass function ✓ r limit > 26mag ~ 100 GCs in MW, dist < 10 kpc ~ 100 OCs in MW, with different age, metallicity and mass ~ GCs in LMC / SMC / M31 or other local group galaxies 230 square degree field, 20 hours exposure time
Summary Star clusters in MW: ✓ Stellar properties, Population, Mass function, Binary evolution, … ✓ Multiple-population, Internal dynamics ,Tidal tails, Fundamental plane,… Star clusters in other nearby galaxies: ✓ Dynamical evolution , formation environment, mass profile of galaxy halo, evolution histories of galaxies,… High precision proper motion Multi-epoch observations in cluster region High precision photometry
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