Rediscovering star clusters with CSS-OS Jing Zhong ng (SHAO) AO) - - PowerPoint PPT Presentation

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 ?

Star Star cluster Galaxy Universe

Star clusters play the role of bridge between star and galaxy

Distance Age Metallicity

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 Galactic structure and evolution

▲ Star clusters ▲ Stellar distribution ▲ Gas distribution

• 1. Globular clusters 

Galactic halo

• 2. Open clusters 

Galactic disk

Two major tracers ➢ Spatial distribution ➢ Dynamical properties ➢ Chemical / age tagging ➢ Mass function Star clusters

 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 (106 － 109 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 Importance of open clusters observation to the Galaxy

Massive / Supermassive globular clusters provide…

Testbeds – stellar evolution Unique hosts for exotic objects: LMXRBs, IMBH, blue stragglers Testbeds -- dynamics of dense stellar systems (N ~ 106) Internal dynamics and mass profile of galaxy halo Relics of the pre-galactic clouds at the beginning of hierarchical merging Testbeds -- starburst, merger events, evolution histories of galaxies

Galactic halo mass

Kravtsov et al. 2014

M(stellar) strongly nonlinear function of M(halo)

Harris et al. 2015

Total mass in all globular clusters Halo mass from weak lensing

➢ M(GCs) ~ initial M(gas) ~ M(halo) ➢ GCs formation is largely immune to feedback

A stellar population that forms in direct proportion to halo mass

Galaxy formation and evolution

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

Li et al. 2016

 Accretion history  Binary evolution  Formation history  … Multiple- population in GCs

Harris catalog:~156 GCs (2010) Kharchenko catalog: ~3006 star clusters (2013)

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)

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)

• WIYN open cluster study

➢ 31 (photometry) , 10 (spectroscopy)

The great advantage of CSS-OS

High spatial resolution ~ 0.074”(pixel size) Proper motion accuracy ~0.05 -0.6 mas/yr (magnitude dependent) High precision PMs catalog

• Membership identification in OCs
• Internal Kinematics/Dynamics in GCs

High detection sensibility R~26 mag Stellar mass function ~0.09 Mʘ within 500 pc ~0.16Mʘ within 3kpc

Heliocentric distance (kpc)

~100 d<10kpc ~20 d<5kpc

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 σv ~ 5-10 km/s
• For GCs with dist=10 kpc 

σμ ~ 0.1-0.2 mas/yr (r~23mag)

• For GCs in LMC/SMC dist~50kpc, σv ~ 30km/s  σμ ~ 0.1 mas/yr (r~21mag)

➢ Intrinsic rotation & velocity dispersion  Dynamical mass ➢ Distribution of velocity dispersion  Spatial mass segregation ➢ Tidal stream ➢ …

Open Clusters：

✓ Membership Identification : High precision proper motion r=24mag: CSST ( 0.6 mas/yr ) > LSST ( 1.0 mas/yr) σμ=0.2 mas/yr: CSST ( 23mag ) > Gaia ( 19 mag ) OCs with dist =2 kpc :

➢ cluster members : ~10km/s  σμ ~ 1.0 mas/yr ➢ intrinsic σv (dynamics) : ~ 1km/s  σμ ~ 0.1 mas/yr Gaia LSST

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  High precision photometry

Multi-epoch observations in cluster region