Observations of Binaries in Globular Clusters

Observations of Binaries in Globular Clusters

Adrienne Cool San Francisco State University

Observations of ^ Binaries in Globular Clusters

Adrienne Cool San Francisco State University

Primordial

OUTLINE

• Why bother?

• What do we want to know?

• How can we find out?

• What’s new?

• What’s next?

Why bother?

• Binary fraction is a fundamental parameter

• Primordial binaries play a key role in cluster dynamics

• Primordial binaries are implicated in the formation of many more exotic populations

What do we want to know?

• What fraction of globular cluster stars are binaries? • Do clusters have different binary fractions (fb)? Any correlation with particular cluster parameters?

• Are there signs of dynamical evolution of binaries?

• How are the binaries distributed in…• period (Porb)• eccentricity (e)• mass ratio (q m2/m1)• primary mass

How can we find out?

radial velocity variables

photometric variables

outliers incolor-magnitude diagrams

3 methods used so far…

Pryor / Hut et al. 1992 Kaluzny et al. 1999 Rubenstein & Bailyn 1997

Method 1: Radial velocity variables

• ground-based spectroscopy• samples of ~30-300 giants• ~2-4 velocities per star• accuracies ~0.6–3 km/s• baselines ~ 1-20 years

Cote et al. 1996 – M22

sensitive to binaries withPorb ~ days – years

fb estimates depend oneccentricity distribution

cluster MV c bin/total fb Porb reference47 Tuc, M2, M3

M12, M13, M71–9.4 –

–5.6

2.03 –

1.15

6 / 393 ~ 5 % (circ)

~ 12 % (therm)

0.2 – 20 yr Pryor et al.

1989

NGC 3201 –7.5 1.30 2 / 276 6 – 10 % (circ)

15 – 18 % (therm)

0.1 – 10 yr Cote et al.

1994

NGC 5053 –6.7 0.84 6 / 66 ~ 20 – 30% 3 day – 10 yr Yan & Cohen

1996

M71 –5.6 1.15 12 / 121 10 – 30 % (circ)

15 – 40 % (therm)

3 day – 10 yr Barden et al.

1996

M22 –8.5 1.31 0–1 / 109 1+10–1 % (circ)

3+16–3 % (therm)

0.2 – 40 yr Cote et al.

1996

M4 –7.2 1.59 0 – 2 / 33 15 15% @ > 4 rc 2 day – 3 yr Cote & Fischer 1996

Cen –10.3 1.61 ? / 310 3 – 4% 0.5 – 10 yr Mayor et al.

1996

Pal 5 –5.2 0.70 -- / 17 40 20%

(68% conf)

a < 50 A.U. Odenkirchen et al. 2002

searches for radial velocity variables

Method 2: photometric variables

Albrow et al. 2001 – 47 Tuc

• HST & ground-based imaging• ~ 2000 – 40,000 stars sampled• 250 – 1300 images• baselines ~ 1 week – 1 month

sensitive to binaries withPorb ~ 0.1 day – few days

fb estimates depend on assumedPorb, e, q distributions

cluster MV c bin/total fb Porb reference

M71 –5.6 1.15 5 / 5300

~ 0.09 %

4 contact

10 – 72 %

Porb < 800 yr

0 – 5 rc

hours - days Yan & Mateo 1994

M5 –8.8 1.83 6 / 3600

~ 0.17 %

5 contact

22 – 39 %

2.5 day – 550 yr

4 – 8 rc

hours - days Yan & Reid 1996

47 Tuc –9.4 2.03 26 / 46,422

~ 0.06 %

11 detached

16 contact

13 6 %

(5 w/Porb> 4 day)

0 – 4 rc

0.3 hr – 15 day Albrow et al. 2001

47 Tuc –9.4 2.03 28 / 43,067

~ 0.07 %

7 detached

21 contact

--

15 rc – 0.6 rt

2 hr – 60 day Weldrake et al. 2004

M4 –7.2 1.59 0 – 1 / 2102

0.05 %

--

@ 6 rc

4 hr – 6 day Ferdman et al. 2004

searches for eclipsing binaries – selected results

Method 3: Outliers in color-magnitude diagrams

Cool & Bolton 2002 – NGC 6397

• HST & gnd-based imaging• 100s – 1000s of stars• 2 filters is enough• no repeat measure required• high photometric accuracy

sensitive to binaries with… any Porb, e, inclination!

fb estimates depend on assumed q distribution, F(q)

cluster MV c fb note ref.

M92 –8.2 1.81 < 9 % @ 10 – 30 rc all q Romani & Weinberg 1991

M30 –7.3 2.50

pcc

< 4 % @ 25 – 65 rc all q Romani & Weinberg 1991

NGC 288 –6.7 0.96 ~ 10 % @ 0 – 6 rc lower limit

q 0.7

Bolte

1992

E 3 –2.8 0.75 29 9 % @ 0 – 2 rc

lower limit?

q 0.7 ?

Veronesi et al.

1996

NGC 2808 –9.4 1.77 24 4 % @ 24 rc lower limit

q 0.8 ?

Ferraro et al.

1998

M30 –7.3 2.50

pcc

5 2 % @ 100 rc lower limit

q 0.7-0.8 ?

Alcaino et al.

1998

searches in color-magnitude diagrams – selected early results


NGC 6752 –7.7 2.50

pcc

15 – 38 % [99.7% conf.] @ < 1 rc

< 16 % [99.7 % conf.] @ > 1 rc

Monte-Carlo

various F(q)

Rubenstein & Bailyn 1997

NGC 6397 –6.6 2.50

pcc

3 % (q 0.45) @ 0 – 18 rc

5 – 7 % (all q) @ 0 – 18 rc

flat F(q)

extrapolated

Cool & Bolton

2002

NGC 288 –6.7 0.96 10–20 % [8–38% @ 99.9%] @ < 1 rh

0 – 10 % [<10% @ 99.9%] @ 1-2 rh

Monte-Carlo

various F(q)

Bellazzini et al. 2002

Pal 5 –5.2 0.70 9 1 % @ < 1 rc (Poisson errors)

9 8 % @ 2 – 3 rc

lower limit

(high q only)

Koch et al.

2004

Pal 13 –3.7 1.31 30 4 % (Poisson errors) @ 0-18 rc

lower limit

(high q only)

Clark et al. 2004

M4 –7.2 1.59 ~ 2 % @ < 1 rc

~ 1 % @ > 1 rc

lower limit

(high q only)

Richer et al.

2004

M3 –8.9 1.84 6 – 22 % [3–35% @95%] @ < 1 rc

1 – 3 % [0–22% @ 95%] @ 1-2 rc

Monte-Carlo

various F(q)

Zhao & Bailyn

2005

searches in color-magnitude diagrams -- more recent results

What fraction fb of globular cluster stars are binaries?

Does fb differ among clusters? Range?

Do any clusters have fb = 0% ? 100% ??

cluster MV c bin/total fb Porb fb (3 decades)

Cen –10.3 1.61 ? / 310 3 – 4% 0.5 – 10 yr 7 – 9 %

M22 –8.5 1.31 0–1 / 109 1+10–1 % (circ)

3+16–3 % (therm)

0.2 – 40 yr 1.3+13–1.3 % (circ)

4+21–4 % (therm)

NGC 3201 –7.5 1.30 2 / 276 6 – 10 % (circ)

15 – 18 % (therm)

0.1 – 10 yr 9 – 15 % (circ)

23 –27 % (therm)

M4 –7.2 1.59 0 – 2 / 33 15 15% @ > 4 rc 2 day – 3 yr 16 16% @ > 4 rc

NGC 5053 –6.7 0.84 6 / 66 ~ 20 – 30% 3 day – 10 yr ~ 20 – 30%

M71 –5.6 1.15 12 / 121 10 – 30 % (circ)

15 – 40 % (therm)

3 day – 10 yr 10 – 30 % (circ)

15 – 40 % (therm)

radial velocity variables – global binary fractions

• typical fb ~ 15% (~5% per decade)

• trend toward lower fb for massive clusters (high , low Pcrit)

disruption of soft binaries? Cote et al. 1996

Odenkirchen et al. 2002 – Pal 5

• MV = –5.2

• c = 0.70

• single epoch, VLT

• 17 cluster stars

• accuracy ~ 0.15 km/s

broad pedestal under narrow peak = binaries?

fb = 40 20 %

Pal 5

photometric variables – global binary fractions

cluster MV c bin/total Porb fb Porb assumed ref

47 Tuc –9.4 2.03 26 / 46,422

~ 0.06 %

11 detached

16 contact

0.1 hr –

15 day

13 6 %

(5 w/Porb> 4 day)

0 – 4 rc

2.5 d – 50 yr A01

M5 –8.8 1.83 6 / 3600

~ 0.17 %

5 contact

hours –

days

22 – 39 %

4 – 8 rc

2.5 day – 550 yr YR96

M71 –5.6 1.15 5 / 5300

~ 0.09 %

4 contact

hours –

days

10 – 72 %

0 – 5 rc

< 800 yr YM94

47 Tuc: fb ~ 2 – 5 % per decade for hard binaries

consistent with vrad results


CMD outliers – binary fractions – “all q” subset


M3 –8.9 1.84 6 – 22 % [3–35% @ 95%] @ < 1 rc

1 – 3 % [0–22% @ 95%] @ 1-2 rc

Monte-Carlo

various F(q)

Zhao & Bailyn

2005

M92 –8.2 1.81 < 9 % @ 10 – 30 rc max likelihood

Romani & Weinberg 1991

NGC 288 –6.7 0.96 10–20 % [8–38% @ 99.9%] @ < 1 rh

0 – 10 % [<10% @ 99.9%] @ 1-2 rh

Monte-Carlo

various F(q)


NGC 6752 –7.7 2.50

pcc

15 – 38 % [99.7% conf.] @ < 1 rc

< 16 % [99.7 % conf.] @ > 1 rc

Monte-Carlo

various F(q)


M30 –7.3 2.50

pcc

< 4 % @ 25 – 65 rc max likelihood

Romani & Weinberg 1991

NGC 6397 –6.6 2.50

pcc

3 % (q 0.45) @ 0 – 18 rc

5 – 7 % (all q) @ 0 – 18 rc

flat F(q)

extrapolated

Cool & Bolton

2002

Zhao & Bailyn 2005 – M3



q = 1

more high q

~ flat

more low q

mass ratiodistribution F(q)

core 1 – 2 rc

CMD outliers – binary fractions – “all q” subset


M3 –8.9 1.84 6 – 22 % [3–35% @ 95%] @ < 1 rc

1 – 3 % [0–22% @ 95%] @ 1-2 rc

Monte-Carlo

various F(q)

Zhao & Bailyn 2005

NGC 288 –6.7 0.96 10–20 % [8–38% @ 99.9%] @ < 1 rh

0 – 10 % [<10% @ 99.9%] @ 1-2 rh

Monte-Carlo

various F(q)


NGC 6397 –6.6 2.50

pcc

3 % (q 0.45) @ 0 – 18 rc

5 – 7 % (all q) @ 0 – 18 rc

flat F(q)

extrapolated

Cool & Bolton 2002

NGC 6752 –7.7 2.50

pcc

15 – 38 % [99.7% conf.] @ < 1 rc

< 16 % [99.7 % conf.] @ > 1 rc

Monte-Carlo

various F(q)


• all Porb, all e, any inclination… 4 - 5 decades in Porb

why not higher fb ?

• maybe M3 is okay, but NGC 288?

• how come a post-collapse cluster has such a high fb??

CMD outliers – binary fractions – high q subset


NGC 2808 –9.4 1.77 24 4 % @ 24 rc q 0.8 ? Ferraro et al. 1998

M30 –7.3 2.50 5 2 % @ 100 rc q 0.7-0.8 ? Alcaino et al. 1998

M4 –7.2 1.59 ~ 1 – 2 % 0 – 4 rc high q Richer et al. 2004

NGC 288 –6.7 0.96 ~ 10 % @ 0 – 6 rc q 0.7 Bolte 1992

Pal 5 –5.2 0.70 ~ 9 % @ 0 – 3 rc high q Koch et al. 2004

Pal 13 –3.7 1.31 30 4 % @ 0 – 18 rc high q Clark et al. 2004

E 3 –2.8 0.75 29 9 % @ 0 – 2 rc q 0.7 ? Veronesi et al. 1996

• 3 cases with fb ~ 25 – 30 % … extrapolate to all q (×3??) 75 – 90 % ?!

• NGC 2808 so high even far outside core ?

• Pal 5 with tidal stripping… why not higher?

• M4… why so low?

Koch et al. 2004

Odenkirchen et al. 2002

Pal 5 – compare 2 methods

CMDs: fb ~ 9 1% vrad: fb ~ 40 20 %

Richer et al. 2004

M4 – compare 3 methods

CMDs: fb ~ 1–2 % (high q)

vrad: fb ~ 15 15 % Cote et al. 1996

variables: fb (observed) < 0.05%

(similar to 47 Tuc w/fb ~ 13%)

Ferdman et al. 2004

Hut et al. 1992

effect of photometric errors on perceived binary fraction in CMDs

fb = 10%

Primordial binary fraction in globular clusters

• all GCs studied have at least some binaries

• not all GCs have same binary fraction… at present low end: < 5 – 7 % ? (NGC 6397) high end: ~ 30% ~ 90% for all q ?? (E3, Pal 13)

• fb = 100% is not ruled out for some poor clusters

• fb = 0% is possible in outskirts of some clusters

• trend toward higher fb for poorer clusters, with exceptions

Cool & Bolton 2002 – NGC 6397Clark et al. 2004 – Pal 13

effect of photometric errors on perceived binary fraction in CMDs

fb = 100%

Hut et al. 1992

Are there signs of dynamical evolution of binaries?

Are there signs of dynamical evolution of binaries?

• trends toward lower fb for higher mass clusters consistent with destruction of binaries beyond hard/soft boundary

… or are fb values in loose clusters justenhanced by tidal stripping?

• low fb in NGC 6397 and M30 destruction in collapsed cores?

… but what about NGC 6752??

Bellazzini et al. 2002 – NGC 288



mass segregation in NGC 288


mass segregation of binaries in 47 Tuc

71 BY Dra stars in 47 Tuc! an untapped resource

Weldrake et al. 2004 – 47 Tuc

period segregation of eclipsing binaries in 47 Tuc

contact all stars detached

• segregation of binaries by mass is observed

• 47 Tuc: shorter period binaries are more centrally concentrated than long period binaries

mass effect?? binary hardening?

More signs of dynamical evolution…

What about binary parameters?

• Radial velocities can give Porb, e and more… long-term tracking of candidates required

• Eclipsing binaries beginning to give information on Porb

• CMDs in principle can give information on q = m1/m2



What’s next?

• better constraints on binary fraction and distribution

* vrad – need larger samples! Fabry-Perot underway

* eclipsing – large samples are proven to work

* CMDs – exploit highest possible photometric accuracy

– look for MS-WD pairs too?

• contraints on binary parameters? track candidates!

* vrad – already done for some

* CMDs – spectroscopy on MS-MS binaries? – BY Dra stars: more complete sample?? • HST very valuable, especially in crowded cluster cores• ground-based work equally powerful in sparse clusters (e.g. Pal 13) or outskirts (e.g. 47 Tuc)

How many “primordial” binaries are really primordial??

Documents

Observations of Binaries in Globular Clusters