J/AJ/117/2244 HST color-magnitude diagrams of the LMC (Olsen, 1999)
Star formation histories from Hubble space telescope color-magnitude diagrams
of six fields of the Large Magellanic Cloud
Olsen K.A.G.
<Astron. J. 117, 2244 (1999)>
=1999AJ....117.2244O 1999AJ....117.2244O
ADC_Keywords: Clusters, globular ; HR diagrams ; Magellanic Clouds ; Photometry
Mission_Name: HST
Keywords: galaxies: evolution - galaxies: stellar content - Magellanic
Clouds - stars: formation
Abstract:
We present results on the analysis of background field stars found in
Hubble Space Telescope Wide Field Planetary Camera 2 observations of
six of the old globular clusters of the Large Magellanic Cloud.
Treated as contaminants by the globular cluster analysts, we produce
(V-I, V) color-magnitude diagrams (CMDs) of the field stars and use
them to explore the LMC's star formation history. The photometry
approaches V ∼ 26, well below the turnoff of an ancient (∼ 14 Gyr)
LMC population of stars. The field star CMDs are generally
characterized by an upper main sequence broadened by stellar
evolution, an old red giant branch, a prominent red clump, and an
unevolved lower main sequence. The CMDs also contain a few visual
differences, the most obvious of which is the smeared appearance of
the NGC 1916 field caused by heavy differential reddening. More
subtly, the base of the subgiant branch near the old turnoff appears
extended in V, and the red giant branch appears broad in V-I in four
of the fields but not in the NGC 1754 field.
Description:
Observations of the six LMC globular clusters NGC 1754, 1835, 1898,
1916, 2005, and 2019 were taken during Cycle 5 of HST using the Wide
Field Planetary Camera 2 (WFPC2) and the F555W and F814W filters. By
taking both long and short exposures through each filter, we were
ensured reliable photometry of the brightest stars in the fields while
still reaching V ≥ 25. We centered the clusters on the Planetary
Camera leaving the Wide Field (WF) chips containing primarily field
stars.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
04 54 17 -70 26.5 NGC 1754
05 05 11 -69 24.5 NGC 1835
05 16 43 -69 39.9 NGC 1898
05 18 39 -69 24.9 NGC 1916
05 30 15 -69 45.5 NGC 2005
05 32 02 -70 09.9 NGC 2019
-----------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1a.dat 75 10787 NGC 1754 Wide Field Camera photometry
table1b.dat 75 27047 NGC 1835 Wide Field Camera photometry
table1c.dat 75 28568 NGC 1898 Wide Field Camera photometry
table1d.dat 71 29144 NGC 1916 Wide Field Camera photometry
table1e.dat 75 29156 NGC 2005 Wide Field Camera photometry
table1f.dat 75 29144 NGC 2019 Wide Field Camera photometry
--------------------------------------------------------------------------------
See also:
J/MNRAS/300/665 : HST VI Photometry of Six LMC Old Globular Clusters
(Olsen+ 1998)
Byte-by-byte Description of file: table1*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- Star Star number
8- 13 F6.2 pix Xpix X pixel value in the V band image
16- 21 F6.2 pix Ypix Y pixel value in the V band image
25- 31 F7.4 mag Vmag Johnson V band magnitude
36- 41 F6.4 mag e_Vmag Uncertainty in Vmag from DaoPHOT
45- 51 F7.4 mag Imag Cousins I band magnitude
56- 61 F6.4 mag e_Imag Uncertainty in Imag from DaoPHOT
65- 66 I2 --- VType DaoPHOT object type (1)
70- 71 I2 --- IType DaoPHOT object type (1)
75 A1 --- f_Star [y] Stars removed by cluster-star
cleaning procedure
--------------------------------------------------------------------------------
Note (1): The DaoPHOT object type is:
1 = perfect star
2 = galaxy
3 = member of overlapping stellar group
7 = faint but measurable object
Where the short-exposure photometry was used, the DoPHOT object type
has been multiplied by 10.
--------------------------------------------------------------------------------
History:
From AJ electronic edition
(End) Greg Schwarz [AAS] 11-Apr-2000