PRIN 2001: Summary of the activities of the Research Unit at the

Dipartimento di Astronomia dell’Università di Padova

Giampaolo Piotto (Local PI)Sergio Ortolani

Luigi Bedin Francesca De Angeli

Yazan Momany Alejandra Recio Blanco

Contributions of: Christian Bidin, Giorgia Busso, Marco Riello, Manuela Zoccali

Theoretical Support: Giuseppe Bono, Santi Cassisi, Fiorella Castelli

Wide Field Photometric Survey of Galactic Globular Clusters

• Developed the photometric and astrometric pipeline for WFI data reduction;

• About 80 objects observed in with the WFI at the 2.2m in at least 2 photometric bands;

• About 20 objects with UBV photometry;

• Calibrated photometric catalog for 21 objects;

• Photometric and astrometric catalog for 14 objects

Wide Field Photometric Survey: Results

•The final stellar catalogs satisfy the astrometric, photometric and field coverage requirements for FLAMES follow-up

•The second U-jump;

•The post-HB sampling in BHB clusters;

•The BHB “red incursion”;

•Field WDs.

AstrometricCapabilities

The second U-jump

There are clearly two jumps:

The first one, at T=11.600K,corresponds to the Grundahl et al (1999) jump.

The second one, at T=23.000 K is a new discovered feature.

Momany, Piotto, Recio-Blanco, Bedin, Cassisi, Bono, 2002, ApJL, 576, L65

NGC 6752

NGC 5139

Momany et al. 2003, in prep.

The second U-jump isAn ubiquitous feature

The second U-jump has beenIdentifird in at least other Four globular clusters

Is it an evolutionary effect?

30+3 stars

14 stars

Clearly there must be an evolutionary effect, but:

1. We expect a ratio of 0.80 between the stars in the lower and the upper box, while we observe 0.44+-0.20.

2. For T>23.000K the mass distribution of the HB stars in NGC 6752 must be sharply peaked around 0.505 solar masses, with all the stars within 0.006 solar masses.

0.5040.505

0.510

Also diffusion may be partially responsible of the second jump

The first jump is the consequence of the onset of radiative levitation and diffusion after the disappearence of the envelope convective layers across the H and HeI ionization regions at T=10.000-11.000K.

Canonical models predict that the HeII convective region approaches the stellar surface in the ZAHB structures at T=23.000. In addition, mass loss, which is a competing process to diffusion increases with effective temperature. As a result, radiative levitation is less and less effective in the temperature range 11.000-23.000K (supported by observational evidences).For stars with T>23.000K, as a consequence of the larger surface gravity and longer central He burning lifetime, one expects that atomic diffusion becomes more and more efficent in decreasing the envelope He abundance, implying the quenching of the HeII convection. At the same time, larger effective temperatures should enhance radiative levitation, producing a change in the surface composition.It is tempting to associate the second jump with this chemical discontinuity.

Momany et al. 2002 Post-HB starsIn the field covered by our data there are 13 post-HB stars.

A comparison with the models shows that 11 of these should be classified as AGB-manquè. 84 HB stars are hot enough to evolve in AGB-manquè

The ratio between the two populations is 0.13+-0.05, consistent, within the uncertainties, with the predicted value of 0.09, thus solving the discrepancy pointed out by Landsman et al. (1996).

HBs with EBTs in far-UV

NGC 6388, Busso, Piotto, Cassisi 2003, Piotto et al. 2003, in prep.

4 clusters with EBTs observed with WFPC2In F255W, F336W,F439W, F555W

(GO8718, PI Piotto)

HBs with EBTs in far-UV

The HB of NGC 6388extends beyond Te=31.500K

There is a clear presenceof late helium flasher(blue hook) stars, forthe first time identifiedin such metal rich clusters

NGC 6388

HBs with EBTs in far-UVIt is not possible to simultaneuslyfit the red and the blue part of theHB: the tilt of the HB is present also in the FUV CMDs.

The HB tilt is not a reddeningeffect.

The redincursion!

Momany et al.,2003, A&A,in press

To make things clearer:

Problem:

HB stars have hotter effective temp. than RGB stars with the same metallicity

In a CMD the RGB corresponds to the Hayashi track: in stars in hydrostatic

equilibrium and having convection, the Hayashi line separates between a

permitted regionpermitted region (on its left) from a forbidden oneforbidden one (on its right).

To make things more complicated:

BHB red-incursion is not present in all BHB clusters (metallicity effect?)

Moreover, some clusters show different HB morphology …. at different telescopes!

Blue: measures the extent of the incursion (HB-RGB)

Red: measures (RGB-RGB[Z=0.0001])

Black: measures (HB-HB[Z=0.0001])

Field White Dwarfs

High Precision Astrometry on WFPC2/ACS HST Images

Just the random error remains ~ 0.02 pxl which corresponds to 1 mas (PC) on a single image

with N images:

N: ~1 mas /sqrt(N) (in the PC case)

(Anderson and King 2002, 2003)

Multi-epoch WFPC2/HST images allows accurate proper motion(and proper motion dispersion) measurements for thousands of stars, and…

…thanks to MultifiberHigh ResolutionSpectrographs(like FLAMES at VLT)we are obtaining radial velocities with uncertainties << 1km/s for thousands of stars/night

Combining the proper motion dispersion (an angular quantity) with the radial velocity dispersion (a linear quantity) we have:

DISTANCES (sampling error for 3000 stars: 1.3%!)

Ongoing projects on: NGC 2808, NGC 6121, NGC 6397, NGC 6752

Cluster modeling with Schwarzschild models (PhD thesis work of FDA, starting from Gebhardt code)

Suitable multi-epoch WFPC2/ACS HST images available for 13 globular cluster in total.

Ongoing work on proper motions: example

HST observations scheduled for Cycle 12

GO9899, PI: Piotto

Ongoing work on radial velocities: exampleNGC2808: 1283 stars observed 1000 prop. accepted(FLAMES@VLT)

In addition: NGC6121 (2500*) NGC6752 (1500*)Prop. 71.D-0205 PI: Piotto(ongoing)

ABSOLUTE MOTIONS

(U,V,W)LSR = ( 53+- 3, -202+-20, 0+- 4)Km/s, LSR = ( 54+- 3, 16+-20, 0+- 4)Km/s

…of M4:

Once corrected l cos b and b

for the Sun peculiar motion we can get

Bedin, Piotto, King, Anderson 2003, AJ, in press

(Bedin, Anderson, King, Piotto 2001, ApJL, 560, L75)

Hunting the bottom of the Main Sequence

Mass Functions down to the Hydrogen Burning Limit

Example: M4, Bedin et al., in prep

Ongoing Projects:

47 Tuc and Centauri(HST Cyc. 11 and 13)

NGC6791(HST Cyc. 12 and 14)

NGC6397(King et al.1998 and HST archive)

(Relative) Distances from the HST Snapshot Database

The method. I. for [Fe/H]<-1.0

a) The metal poor clusters have been divided in 5 bins (approx. 0.2 dex each)

b) To each bin we associated a cluster with accurate photometry, low reddening, and a sizable of RRLyrae sample

c) We identified the RRLyrae mean location on the (HST) CMD of the template clusters

-1.10 < [Fe/H] NGC 6362 Walker 2001, private communication

-1.28 < [Fe/H] < -1.10 NGC 1851 Walker 1998

-1.50 < [Fe/H] < -1.28 NGC 5904 Caputo et al. 1999

-1.80 < [Fe/H] < -1.50 NGC 1904 - NGC 5272 Buonanno et al. 1994

[Fe/H] < -1.80 NGC 4590 Walker 1994

TemplatesTemplates

(Relative) Distances from the HST Snapshot Database The method. I. for [Fe/H]<-1.0

In each group weregistered the HB of eachcluster to thecorresponding templateand therefore measuredthe location of theMean RRLyrae level.Then:

v_zahb = v_rr + 0.152 + 0.041 [M/H]

V_zahb = 0.9824 +

0.3008 [ M/H] + 0.0286 [ M/H]**2

NB: v = F555W

(Relative) Distances from the HST Snapshot Database

The method. II.for [Fe/H]>-1.0

v_zahb = v_le + 0.152 – 3 + 0.1 V_zahb = 0.9824

+ 0.3008

[ M/H] + 0.0286 [ M/H]**2

NB: v = F555W

(Relative) Distances from the HST Snapshot Database

Relative ages: new groundbased data

Plus 51 clusters from the HST snapshot database of Piotto et al. (2002)

Relative ages

51 clusters from HST

34 clusters from Rosenberg et al. (1999)

18 clusters from new groundbased data

CMDs for (relative) age determination: an example

TNG+OIG

Ages of single clusters: NGC6642

NGC 6642, a bulge cluster, is about 2 Gyr older than M5. As M5 is coeval with most of the Halo clusters (Rosenberg et al. 1999), NGC 6642 must have formed before most if not all the Halo globular clusters.

Piotto, Ortolani, Barbuy Bica, Saviane, 2003, A&A, submitted

Blue Stragglers from the snapshot catalog

•Blue stragglers (BS) are present in all of our 74 CMDs;•Almost 3000 BSs have been extracted from 62 GCs;•The location of BSs in the CMD depends on metallicity;•The brightest BSs have always a mass less than 1.6 solar masses;•In all GCs, BSs are significantly more concentrated than other cluster stars.

There is a dependence of the BSs relative frequency on the cluster total mass and on the expected collision rateThe enviroment affects the number of BSs.

Log

Log

Field

Piotto et al. 2003

The total numberof BS starsvaries only by a factor of about 10while HB stars varies by a factor ofabout 100!

BS formation mustbe affected bythe environment.

HOW?

Production of Blue Stragglers in GCs

Davies, Piotto, De Angeli 2003, A&A, in prep

Blue Stragglers Luminosity Function