Download (Relative) Distances from the HST Snapshot Database

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.
Astrometric
Capabilities
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
The second U-jump is
An ubiquitous feature
Momany et al. 2003, in prep.
NGC 6752
The second U-jump has been
Identifird in at least other
Four globular clusters
NGC 5139
Is it an evolutionary effect?
0.504
0.505
0.510
30+3 stars
14 stars
Clearly there must be an evolutionary effect, but:
1.
2.
We expect a ratio of 0.80 between the stars in the lower and the upper
box, while we observe 0.44+-0.20.
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.
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 stars
In the field covered by
our data there are 13 postHB 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
4 clusters with
EBTs observed
with WFPC2
In F255W, F336W,
F439W, F555W
(GO8718, PI Piotto)
NGC 6388,
Busso, Piotto, Cassisi 2003, Piotto et al. 2003, in prep.
HBs with EBTs in far-UV
NGC 6388
The HB of NGC 6388
extends beyond
Te=31.500K
There is a clear presence
of late helium flasher
(blue hook) stars, for
the first time identified
in such metal rich
clusters
HBs with EBTs in far-UV
It is not possible to simultaneusly
fit the red and the blue part of the
HB: the tilt of the HB is present
also in the FUV CMDs.
The HB tilt is not a reddening
effect.
The red
incursion!
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 region (on its left) from a
forbidden 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
(Anderson and King 2002, 2003)
Just the random error
remains ~
0.02 pxl
which corresponds
to 1 mas (PC) on a single image
with
N:
N images:
~1
mas /sqrt(N)
(in the PC case)
Multi-epoch WFPC2/HST images allows accurate proper motion
(and proper motion dispersion) measurements for thousands of
stars, and…
…thanks to
Multifiber
High
Resolution
Spectrographs
(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: example
NGC2808: 1283 stars observed
1000 prop. accepted
(FLAMES@VLT)
In addition: NGC6121 (2500*)
NGC6752 (1500*)
Prop. 71.D-0205 PI: Piotto
(ongoing)
ABSOLUTE MOTIONS
…of M4:
(U,V,W)LSR =
( 53+- 3,
-202+-20,
0+- 4)Km/s
(P, Q, Z)LSR =
(
54+- 3,
16+-20,
0+- 4)Km/s
Once corrected
m l cos b and mb
for
the Sun peculiar
motion we can get
Bedin, Piotto, King, Anderson 2003, AJ, in press
Hunting the
bottom of the
Main Sequence
(Bedin, Anderson, King, Piotto 2001, ApJL, 560, L75)
Mass Functions down to the Hydrogen Burning Limit
Ongoing Projects:
47 Tuc and w Centauri
(HST Cyc. 11 and 13)
NGC6791
(HST Cyc. 12 and 14)
NGC6397
(King et al.1998 and
HST archive)
Example: M4, Bedin et al., in prep
(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
Templates
-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
(Relative) Distances from the HST Snapshot Database
The method. I.
for [Fe/H]<-1.0
In each group we
registered the HB of each
cluster to the
corresponding template
and therefore measured
the location of the
Mean 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
Piotto, Ortolani, Barbuy Bica, Saviane, 2003, A&A, submitted
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.
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.
Log
There is a
dependence of the
BSs relative
frequency on the
cluster total mass and
on the expected
collision rate
The enviroment
affects the
number of BSs.
Log
Field
Piotto et al. 2003
The total number
of BS stars
varies only by a
factor of about 10
while HB stars
varies by a factor of
about 100!
BS formation must
be affected by
the environment.
HOW?
Production of Blue Stragglers in GCs
Davies, Piotto, De Angeli 2003, A&A, in prep
Blue Stragglers Luminosity Function