Internal motions in star clusters

Internal motions in star clusters

Gordon DrukierDept. of Astronomy, Yale University

Yale Astrometry Workshop — 21 July 2005

Gordon DrukierDept. of Astronomy, Yale University

Yale Astrometry Workshop — 21 July 2005

Why?Why?

Kinematics:

Velocity structure of the cluster

Mass distribution

Distance

Dynamics

Kinematics:

Velocity structure of the cluster

Mass distribution

Distance

Dynamics

Planning the observationsPlanning the observations

e: proper motion error (km/s)a: centering accuracy (pixels)r: plate scale (mas/pixel)d: distance (kpc)t: time baseline (years)N: Number of frame pairs

e: proper motion error (km/s)a: centering accuracy (pixels)r: plate scale (mas/pixel)d: distance (kpc)t: time baseline (years)N: Number of frame pairs

e=4.74√2 ard/t√N e=4.74√2 ard/t√N

Example:ACS/HRC a=0.03 r=27 mas/pixel, N=20e=σ0/3

NGC 6752d=4kpc, σ0 =12 km/s

t=1.2 years

NGC 6388d=10kpc, σ0 =19 km/s

t=2 years

M71d=4kpc, σ0 =2 km/s

t=7 years

Example:ACS/HRC a=0.03 r=27 mas/pixel, N=20e=σ0/3

NGC 6752d=4kpc, σ0 =12 km/s

t=1.2 years

NGC 6388d=10kpc, σ0 =19 km/s

t=2 years

M71d=4kpc, σ0 =2 km/s

t=7 years

Now, assuming you have some proper motions, what can you do with them?

Now, assuming you have some proper motions, what can you do with them?

[King et al. (1998)][King et al. (1998)]

NGC 6397: HST/WFPC2 32 mo. baseline NGC 6397: HST/WFPC2 32 mo. baseline

MembersMembers Non-membersNon-members

[Richer et al. (2004)][Richer et al. (2004)]

M4: HST/WFPC2 6 year baselineM4: HST/WFPC2 6 year baseline

White dwarf sequence!White dwarf sequence!

Bottom of the main sequenceBottom of the main sequence

M4: HST/WFPC2, 5 yearsM4: HST/WFPC2, 5 years

[Bedin et al. (2003)][Bedin et al. (2003)]

M4M4

Galactic bulgeGalactic bulge

QSOQSO

Absolute proper motion & Galactic rotation constantAbsolute proper motion & Galactic rotation constant

[Bedin et al. (2003)][Bedin et al. (2003)]

A - B = V0/R0 = 27.6 ± 1.7 km s-1 kpc-1

[Anderson & King (2003)][Anderson & King (2003)]

47 Tuc: HST/WFPC2 5 yr baseline47 Tuc: HST/WFPC2 5 yr baseline

SMCSMC

[Anderson & King (2003)][Anderson & King (2003)]

SMC motion with respect to 47 TucSMC motion with respect to 47 Tuc

[Anderson & King (2003)][Anderson & King (2003)]

core radiuscore radius

SMC with respect to 47 Tuc

Relative motion in RA, -4.716 ± 0.035 mas yr-1;

Relative motion in declination, -1.357 ± 0.021 mas yr-1;

Absolute motion in RA, 5.64 ± 0.20 mas yr-1;

Absolute motion in declination, -2.05 ± 0.20 mas yr-1;

Rotational proper motion, 0.233 ± 0.055 mas yr-1.

SMC with respect to 47 Tuc

Relative motion in RA, -4.716 ± 0.035 mas yr-1;

Relative motion in declination, -1.357 ± 0.021 mas yr-1;

Absolute motion in RA, 5.64 ± 0.20 mas yr-1;

Absolute motion in declination, -2.05 ± 0.20 mas yr-1;

Rotational proper motion, 0.233 ± 0.055 mas yr-1.

[van Leeuwen et al. (2000)][van Leeuwen et al. (2000)]

ω Cen: Yale-Columbia 26”, 239 year effective baselineω Cen: Yale-Columbia 26”, 239 year effective baseline

μr

μr

μt

μt

Radial & Tangential proper motion profileRadial & Tangential proper motion profile

Velocity Dispersion ProfileVelocity Dispersion Profile

Velocity Dispersion ProfileVelocity Dispersion Profile

Anisotropy?Anisotropy?

[McNamara et al. (2003)] [McNamara et al. (2003)]

M15: HST/WFPC2 8 year baselineM15: HST/WFPC2 8 year baselineLines are at ± 1mas/yearLines are at ± 1mas/year

M15M15

[Gerrsen et al. (2003)][Gerrsen et al. (2003)]

[McNamara et al. (2003)][McNamara et al. (2003)]

M15M15

[Gerrsen et al. (2003)][Gerrsen et al. (2003)]

[McNamara et al. (2003)][McNamara et al. (2003)]

[Drukier et al. (2003)][Drukier et al. (2003)]

NGC 6752: HST/WFPC2 5 yr baselineNGC 6752: HST/WFPC2 5 yr baseline

Error Median:0.31 mas/yr Mode: 0.17 mas/yrError Median:0.31 mas/yr Mode: 0.17 mas/yr

[Drukier et al. (2003)][Drukier et al. (2003)]

NGC 6752: HST/WFPC2 5 year baselineNGC 6752: HST/WFPC2 5 year baseline

Velocity Dispersion ProfileVelocity Dispersion Profile

C.f. 3.5 to 6.3 km/s central radial velocity dispersion from the integrated spectrum [Dubath et al. (1997)]

⇒ (M/L)V ~ 9(M/L)☉

C.f. 3.5 to 6.3 km/s central radial velocity dispersion from the integrated spectrum [Dubath et al. (1997)]

⇒ (M/L)V ~ 9(M/L)☉

Have a good evening.Have a good evening.