Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω...

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Annalisa Calamida (INAF-OAR) Annalisa Calamida (INAF-OAR) Deep optical and Near- Deep optical and Near- Infrared photometry of Infrared photometry of the globular cluster the globular cluster ω ω Cen Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G. Iannicola, L. Pulone, M. Monelli, F. Caputo, V. Castellani (INAF-OAR) S. D’Odorico, E. Marchetti, P. Amico (ESO) S. Degl’Innocenti, P. Prada Moroni (Pisa University) M. Nonino (INAF-OAT) P. B. Stetson (DAO, Victoria, Canada) Summary Star counts and evolutionary lifetimes in ω Cen White Dwarfs in ω Cen Conclusions

Transcript of Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω...

Page 1: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Annalisa Calamida (INAF-OAR)Annalisa Calamida (INAF-OAR)

Deep optical and Near-Infrared Deep optical and Near-Infrared photometry of the globular cluster photometry of the globular cluster

ωω Cen Cen

G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G. Iannicola, L. Pulone, M. Monelli, F. Caputo, V. Castellani (INAF-OAR)S. D’Odorico, E. Marchetti, P. Amico (ESO)S. Degl’Innocenti, P. Prada Moroni (Pisa University)M. Nonino (INAF-OAT)P. B. Stetson (DAO, Victoria, Canada)

Summary

Star counts and evolutionary lifetimes in ω Cen

White Dwarfs in ω Cen

Conclusions

Page 2: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Why ω Cen?• Most luminous (MV~ -10) and most massive (M ~ 5·106M⊙) galactic globular cluster

• Retrograde orbit (zmax= 1 Kpc; Ra = 6 Kpc)

Metallicity dispersion: -2.2 < [Fe/H] < -0.5

Overabundance α-elements (O, Mg, Si, Ca)

Overabundance s -elements (Ba, Mo, La, Zi)

Evidence of primordial chemical self-enrichment in short time scales (1-3 Gyr)

Relic of a dwarf galaxy accreted on the Milky Way

“Merging” of two stellar systems

Properties GCs ω Cen dSphs

Magnitude (MV) < -9 -10 -8/-13

Mass (M⊙) ~ 105 ~106 106-108

Metallicity spread, Δ [Fe/H] (dex) < 0.1 ~1 0.2-1.4

Page 3: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Many different RGBs:

– Metal-poor (ω1)

– Metal-intermediate (ω2)

– Metal-rich (ω3)

U, V photometry from WFI@2-2m

– Main peak at [Fe/H] ~ -1.7

– Secondary peak at [Fe/H] ~ -1.2

– Tail up to [Fe/H] ~ -0.5

Gratton et al. (2005)

Pancino et al. (2000)

Page 4: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Blue & Red MS

(Bedin et al. 2004)

Super-metal-poor population ([Fe/H] <<-2.0) -> 30% of ω Cen stars!!! Helium enhanced population (ΔY ~ 0.15)

Population of stars located behind ω Cen

HST

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Spectra of 17 stars (Piotto et al. 2005):

rMS: [M/H] = -1.57 dex, bMS: [M/H] = -1.26 dex

bMS is ~ 0.3 dex more metal-rich than the rMS

CMD:Isochrone best fit

[M/H] = -1.26

Y ~ 0.35

ΔY/ΔZ > 70 !!

Page 6: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Quest for Quest for complete star countscomplete star counts of of HB, RG & MS stars in HB, RG & MS stars in ωω Cen Cen

B, R, Hα ACS/HST (108 frames), FOV~ 9’9’

U, B, V, I WFI/2.2m (125 frames), FOV~ 45’45’

ACS

WFI

Page 7: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Simultaneous reduction of all space & ground-based data:

DAOPHOTII/ALLFRAME (Stetson 1994)

ACS@HST 1.3 Million starsWFI-2.2m ESO/MPI 0.6 Million stars

ωω CenCen

FINAL CATALOGUE: 1.7 million stars!!!FINAL CATALOGUE: 1.7 million stars!!!

BS

WDs

EHB

SGB-a

AGB

Page 8: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Setting the “theoretical clock”M/M⊙ = 0.80Age = 12 Gyr

Castellani et al. 2007, ApJ, 663, 1021

Pisa Evolutionary CodeCariulo et al. (2004)

Canonical scenario (Y=0.23):

Arrival rate of stars onto the HB

r(HB) = NHB/tHB compared to

r(RG) = NRG/tRG and to

r(MS) = NMS/tMS

Discrepancy

between theory &

observations:

~30-40% for HB/RG

and ~ 43% for

HB/MS

Excess of HB stars

Page 9: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

He-mixed scenario:

70% canonical +

30% He-enriched (Red and

Blue-MS)

Castellani et al. 2007, ApJ, 663, 1021

HB rate ~ 24% (Y=0.42) HB rate ~ 24% (Y=0.42) and and ~~30% (Y=33) larger 30% (Y=33) larger

than MS rate !than MS rate !

HB/RG: smaller discrepancy but still high for Y = 0.33 (15-25%) & Y = 0.42 (15-20%)

New theoretical clocksat fixed cluster age

Page 10: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Current findings indicate that a mix of stellar populations made

with 70% canonical He (Y=0.23) and 30% He-enhanced (Y=0.33

or Y=0.42) only partially account for the observed excess of HB stars in ω Cen

Working hypothesis:

Hot He-flashers

Huge mass-loss (binarity) before He-core flash, Castellani & Castellani 1993, D’Cruz et al. (1996), Sweigart (1997), Castellani et al. (2006) )

He-core WDsHe-core WDs

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DM0=13.700.10 (Del Principe et al. 2006)

E(B-V)=0.110.02 (Calamida et al. 2005)

WDs in WDs in ωω Cen: theoryCen: theory

WD cooling sequences by

Althaus & Benvenuto (1998)

and atmosphere models by

Bergeron et al. (1995):

1. CO core + H envelope

2. CO core + He envelope

Preliminary evidence of He core WDs in ω

Cen

Models by Serenelli et al. (2002)Calamida et al. 2008

Page 12: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

8 ACS fields 6500 WDs !! (Individually double-

checked with ROMAFOT)

EHB

WDs

WDs in WDs in ωω Cen: star countsCen: star counts

65125

118934

204745

MS stars

18.775≤F435W≤19.025:

25133160B=24

B=24.5

B=25

N(WDs)/N(MS)

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Star counts & evolutionary lifetimes

N(WDs)/N(MS) t(WDs)/t(MS)

B ≲ 24 mag 0.052±0.002 0.021±0.003 (~2.5)

B 24.5 mag≲ 0.095±0.002 0.048±0.007 (~2)

B 25 mag≲ 0.163±0.004 0.12 ±0.02 (~1.5)

Similar discrepancy for CO core + He envelope

An increase in the WDs mass increases the discrepancy

Completeness problems go in the direction of Completeness problems go in the direction of

increasing the discrepancyincreasing the discrepancy

Canonical scenario: M = 0.5Mʘ and CO core + H envelope Observations Theory

Page 14: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

He-mixed scenario: 70% canonical + 30% He-enriched

Y = 0.42 N(WDs)/N(MS) t(WDs)/t(MS)

B 24 mag≲ 0.052±0.002 0.024±0.003

B 24.5 mag≲ 0.095±0.002 0.057±0.008

B 25 mag≲ 0.163±0.004 0.11±0.02

Smaller discrepancy but still high!!!

A decrease in cluster age, t =10 Gyr, does not remove

the discrepancy

A change in the distance modulus of 0.2mag affects the

lifetime ratios for MWD=0.5M⊙ of ~18%

Page 15: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Helium-core WDs (M = 0.3MHelium-core WDs (M = 0.3Mʘʘ): ):

N(WDs)/N(MS) t(WDs)/t(MS)

B ≲ 24 mag 0.052±0.002 0.07±0.01

B 24.5 mag≲ 0.095±0.002 0.18±0.03

B 25 mag≲ 0.163±0.004 0.33±0.05

A fraction ≥10% of ω Cen WDs could

be He-core WDs (0.3Mʘ)

This fraction decreases if we

account for a smaller WD mass

(lower limit 0.17-0.2M⊙ )

He-core WDs have already been identified in

NGC6397 (Taylor et al. 2001), 47 Tuc

(Edmonds et al. 2001), NGC6791 (Kalirai et

al. 2007)….

X-ray/Hα excess, variability, suggesting

their binarity

Page 16: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

MADMAD: Multi-Conjugate Adaptive Optics Demonstrator (ESO/VLT)

Wide field of View (~ 1”1”) adaptive optics correction in the J/K bands

CAMCAO: 2k2k IR camera, 0.028”/pixel

Two nights:

03/04/2007 5K (524s), 3J (524s)

04/04/2007 3K (1024s), 3J (1024s)

Dimm seeing: ~ 0.6-1”

Image Seeing:

K: ~ 0.1" & J : ~ 0.25"K~20.5 & J~20 with SNR =10

Candidate WDs in the Near-Candidate WDs in the Near-IRIR

Selected in separation &Sharpness < 0.5

Page 17: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

ISAAC@VLT:FWHM ~ 0.6”

MAD@VLT FWHM ≤ 0.1”

Multi-Conjugate Adaptive Optics (MCAO)

Page 18: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

SOFI@NTT ISAAC@VLT

MAD@VLT

Page 19: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Candidate WDs in the IRCandidate WDs in the IR

First time in a globular cluster!

NIR excess: 4-5 mag in K!

Page 20: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

HHαα excess!! excess!!

Page 21: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

The discrepancy between star counts and evolutionary

lifetimes suggests that a fraction of at least 10% (0.3Mʘ)

of ω Cen WDs are He-core WDs, thus supporting results

based on the evolved component (HB) hot He-flashers (Calamida et al. 2008)

We identified for the first time in a globular cluster 9 WD

candidates with NIR excess (6 of them show also Hα

excess)

We identified ~30 HB stars with Hα excess, ~50 with NIR

excess and 13 with both of them

ConclusionsConclusions

Page 22: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.
Page 23: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Many thanks to:

G. Bono, R. Buonanno, S. Degl’Innocenti, G. Bono, R. Buonanno, S. Degl’Innocenti,

P. Prada Moroni, E. Marchetti, P. Prada Moroni, E. Marchetti,

S. D’Odorico, P. Amico,S. D’Odorico, P. Amico,

C. E. Corsi, I. Ferraro, M. MonelliC. E. Corsi, I. Ferraro, M. Monelli

Page 24: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

To refer the Johnson B mag to the F435W mag :B = F435W + 0.03(0026) - 0.0015( 0.001)F435W

And V and I mag to the F625W mag:

F625W = V0.544 + I0.455

Page 25: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Star counts & Theoretical predictions

Discrepancy

between theory & observations

≈ 30-40%

Arrival rate of stars onto the HB:

r (HB) = NHB/tHB

Arrival rate of stars onto the RGB:

r(RG) = NRG/tRG

B, B-F658N & B, U-V

B, B-F625N & B, B-V

RG/MSCastellani et al. 2007, ApJ, 663, 1021

Page 26: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Total rates:

r(HB) ~ 39 stars/ Myr & r(MS) ~ 26 stars/Myr

HB rate HB rate ~ ~ 43% larger than MS rate43% larger than MS rate

Excess of HB stars

Discrepancy marginally affected by the assumed metal

abundance and field star contamination.

Hot HB stars are systematically hotter than field stars and the selected MS stars cover a very narrow magnitude range.

Page 27: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

r(HB)/r(RG):

Smaller discrepancy but

still high for:

Y = 0.33 (15-25%)

Y = 0.42 (15-20%)

HB rate HB rate ~ 24%~ 24% (Y=0.42) and (Y=0.42) and ~~30%30% (Y=33) larger than MS (Y=33) larger than MS raterate

RG/MSCastellani et al. 2007, ApJ, 663, 1021

Page 28: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Best fit with 2 isochrones:

Δμ = 0.2 mag

ΔE(B-V) = 0.03mag

-1.1 < [Fe/H] < -0.8

Coeval to bulk of stars

- ω3-branch might be a chunk of

stars located 500pc beyond the

bulk of cluster

- Difference in distance is 10% in

agreement with distance density

maxima of tidal tails in Palomar5

(Freyhammer et al. 2005)

Page 29: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

(Capuzzo Dolcetta 2005)

ρ = volume mass density

Clumps

Page 30: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Binary frequency: ~ 3-4% (Mayor et al. 1996) ~ 3-4·104 binaries

• Central density, log ρC 3.12 LV/Mº

• Concentration,c (log rt /rc ) 1.24 (Trager et al. 1995)

• Half-mass relaxation time, trh 2·1011 Gyrs > cluster age

Presence of primordial binaries among the giants with periods

200 P 4000 days

Cluster AgeS Experiment (6/2004): ~ 30 eclipsing binaries &

~ 30 contact binaries (mostly short period, P < 1day)

Collision rate (prob. that a star centrally located exp. a collision in 1 year) is one order of magnitude smaller in ω Cen than in NGC2808

Page 31: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Origin of EHB stars:

1) coalescence of two low-mass He-core WDs -> + HBs

2) extreme mass loss episodes before the He flash:

a. stars above the limit for He ignition -> + HBs

b. below the limit -> + He-core WDs

Page 32: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

The ‘separation index’ quantifies the degree of

crowding (Stetson et al. 2003)

The current sep value (sep > 3) corresponds to stars that

have required a correction of less than 6% for light

contributed by known neighbours.

Page 33: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

Explain origin of EHB stars in

NGC2808 and in ω Cen

Working hypothesis:He-enriched population

EHB

EHB

HB morphology:

HB becomes systematically bluer (hotter)

NGC2808 -> Helium overabundance? (D’Antona et al. 2005)

Helium enhancement?Lee et al. (2005)

Page 34: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

bMS: Metal-intermediate population with ΔY ~ 0.10-0.15

Requires: ΔY/ ΔZ > 70 (canonical value ~ 3)

Y produced from:

SNe with M > 20M⊙

Winds of low Z rotating massive stars

Gas ejected from field stellar pop. that sorrounded ω Cen

AGB intermediate-mass stars ->ΔY is not enough

Problems with the IMF (chemical evol. models by

Romano et al. 2007)

Page 35: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

The discrepancy ranges from 10% to 15% from brighter to fainter RG stars

NRG/NMS vs B

18.65<BMS<19.15

Page 36: Annalisa Calamida (INAF-OAR) Deep optical and Near-Infrared photometry of the globular cluster ω Cen G. Bono, R. Buonanno, C. E. Corsi, I. Ferraro, G.

NRG/NMS vs B

Marginally dependent on He content