Globular clusters as galaxy building blocks
Our recent study of Galactic globular clusters using ground-based Ca & Stromgren by photometry has shown that many globular clusters have multiple red giant branch populations with distinct calcium abundances. This suggests that these globular clusters, like omega Cen, are most likely the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy. We seek to perform a pilot program to obtain main-sequence photometry for a carefully selected sample of five globular clusters with mutiple red giant populations, and one control cluster with a simple stellar population using the WFC3/UVIS and F395N, F467M, and F547M filters to investigate the presence of subtle differences in heavy elemental abundances between multiple main-sequence populations. This will play a crucial role to test our idea on the origin of globular clusters. Our proposed observations will provide unique opportunity to explore fundamental aspects of stellar evolution, the star formation and chemical enrichment histories of globular clusters, and furthermore, the formation of the Milky Way Galaxy in the Lambda CDM hierarchical merging paradigm.
We plan to image the central regions of six globular clusters (GCs) using the WFC3/UVIS in the F395N, the F467M and the F547M passbands. Our aim is to detect the main-sequence (MS) splits in the hk index [= (F395N-F467M) - (F467M - F547M)] to investigate differences in primordial calcium abundances between multiple stellar populations. With our designated exposure times, we expect to secure precision photometry at about 2 magnitude below the MS turn-off. Each GC is observed using a two-point dither pattern (POS TARG 1.446, 2.926) in each filter to improve the PSF, minimize detector defects, fill the gap between two CCDs in the WFC3 and remove cosmic ray events.
Our field locations for the primary observations with the WFC3/UVIS are chosen to match the existing HST archival photometry using the ACS/WFC (PID-10775) from which we can obtain auxiliary photometric and astrometric information.
In addition to WFC3/UVIS imaging, we will employ coordinated parallel observations with the ACS/WFC in the F606W and the F814W passbands. Our field locations for coordinated parallels with the ACS/WFC are also chosen to match the existing HST archives which will significantly improve photometric and astrometric measurements.
RESOLVED STELLAR POPULATIONS
12
false
0.0
0.0
false
false
false
false
false
false
SUPPORTED
STELLAR CLUSTER
GLOBULAR CLUSTER
J2000
00 52 44.6700
-26 34 43.10
J2000
STELLAR CLUSTER
GLOBULAR CLUSTER
J2000
13 26 46.0700
-47 28 28.70
J2000
STELLAR CLUSTER
GLOBULAR CLUSTER
J2000
16 23 35.1100
-26 31 24.30
J2000
STELLAR CLUSTER
GLOBULAR CLUSTER
J2000
17 40 41.3000
-53 40 15.00
J2000
STELLAR CLUSTER
GLOBULAR CLUSTER
J2000
18 36 23.7200
-23 54 6.70
J2000
STELLAR CLUSTER
GLOBULAR CLUSTER
J2000
19 10 51.6500
-59 58 56.90
J2000
WFC3/UVIS
Imaging
No
No
F395N
WFC3/UVIS
Imaging
No
No
F467M
WFC3/UVIS
Imaging
No
No
F547M
WFC3/UVIS
Imaging
No
No
F395N
WFC3/UVIS
Imaging
No
No
F467M
WFC3/UVIS
Imaging
No
No
F547M
WFC3/UVIS
Imaging
No
No
F395N
WFC3/UVIS
Imaging
No
No
F467M
WFC3/UVIS
Imaging
No
No
F547M
WFC3/UVIS
Imaging
No
No
F395N
WFC3/UVIS
Imaging
No
No
F467M
WFC3/UVIS
Imaging
No
No
F547M
WFC3/UVIS
Imaging
No
No
F395N
WFC3/UVIS
Imaging
No
No
F467M
WFC3/UVIS
Imaging
No
No
F547M
WFC3/UVIS
Imaging
No
No
F395N
WFC3/UVIS
Imaging
No
No
F467M
WFC3/UVIS
Imaging
No
No
F547M
The scheduling data was generated by CASM 18.3.1.
CASM was run in Phase II mode.
This visit is for the WFC3 imaging of NGC 288. Two orbits are required to complete this visit. Visit 01 is devoted to obtain deep imaging of NGC 288 using the WFC3/UVIS. With no previous observations in the outer field of the cluster, our field location for coordinated parallel observations with the ACS/WFC is chosen to avoid bright stars.
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