J/AJ/133/1658 ACS survey of galactic globular clusters (Sarajedini+, 2007)
The ACS survey of galactic globular clusters.
I. Overview and clusters without previous Hubble Space Telescope photometry.
Sarajedini A., Bedin L.R., Chaboyer B., Dotter A., Siegel M., Anderson J.,
Aparicio A., King I., Majewski S., Marin-Franch A., Piotto G., Reid I.N.,
Rosenberg A.
<Astron. J., 133, 1658-1672 (2007)>
=2007AJ....133.1658S 2007AJ....133.1658S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Photometry, HST
Keywords: globular clusters: individual (E3, Lynga 7, NGC 5053, NGC 5466,
NGC 6144, NGC 6366, NGC 6779, Palomar 1, Palomar 2) -
Hertzsprung-Russell Diagram
Abstract:
We present the first results of a large Advanced Camera for Surveys
(ACS) survey of Galactic globular clusters. This Hubble Space
Telescope (HST) Treasury project is designed to obtain photometry with
S/N (signal-to-noise ratio) ≳10 for main-sequence stars with masses
≳0.2M☉ in a sample of globulars using the ACS Wide Field
Channel. Here we focus on clusters without previous HST imaging data.
These include NGC 5466, NGC 6779, NGC 5053, NGC 6144, Palomar 2, E3,
Lynga 7, Palomar 1, and NGC 6366. Our color-magnitude diagrams (CMDs)
extend reliably from the horizontal branch to as much as 7 mag fainter
than the main-sequence turnoff and represent the deepest CMDs
published to date for these clusters. Using fiducial sequences for
three standard clusters (M92, NGC 6752, and 47 Tuc) with well-known
metallicities and distances, we perform main-sequence fitting on the
target clusters in order to obtain estimates of their distances and
reddenings. These comparisons, along with fitting the cluster main
sequences to theoretical isochrones, yield ages for the target
clusters. We find that the majority of the clusters have ages that are
consistent with the standard clusters at their metallicities. The
exceptions are E3, which appears ∼2Gyr younger than 47 Tuc, and Pal 1,
which could be as much as 8Gyr younger than 47 Tuc.
Description:
The stars x,y positions in the *.dat file are converted to RA and Dec
using the F606W fits image.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
clusters.dat 19 65 Cluster list
acssggc.dat 189 6332017 Catalog for the 65 clusters
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See also:
https://users.astro.ufl.edu/~ata/public_hstgc : ACS SGGC Home Page
Byte-by-byte Description of file: clusters.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Cluster Cluster name
14- 19 I6 --- Nstars Number of stars for this cluster
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Byte-by-byte Description of file: acssggc.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Cluster Cluster
12- 17 I6 --- Seq Sequential number, within the cluster
19- 26 F8.3 pix Xpos X position
28- 35 F8.3 pix Ypos Y position
38- 44 F7.3 mag Vmag ?=100.021 V magnitude (Vega)
47- 53 F7.4 mag e_Vmag ?=99.9990 rms uncertainty on Vmag (1)
56- 62 F7.3 mag V-I V-I colour index (V-I)
65- 71 F7.4 mag e_V-I ?=99.9990 rms uncertainty on V-I (1)
74- 80 F7.3 mag Imag ?=100.034 I magnitude (Vega)
83- 89 F7.4 mag e_Imag ?=99.9990 rms uncertainty on Imag (1)
93- 98 F6.3 mag Vground ?=99.999 Ground V magnitude
102-107 F6.3 mag Iground ?=99.999 Ground I magnitude
109-110 I2 --- o_Vmag Number of observations in Vmag
112-113 I2 --- o_Imag Number of observations in Imag
116 I1 --- wV [1/4] where did the V mag come from
(1=deep unsat, 2=short unsat)
119 I1 --- wI [1/4] where did the I mag come from
(3=short sat, 4=deep sat)
122-126 F5.3 --- xsig RMS of x positions (2)
129-133 F5.3 --- ysig RMS of y positions (2)
136-140 F5.3 --- othv fraction of F606W light from other stars
143-147 F5.3 --- othi fraction of F814W light from other stars
150-154 F5.3 --- qfitV quality of the V fit (smaller is better)
157-161 F5.3 --- qfitI quality of the I fit (smaller is better)
165-175 F11.7 deg RAdeg Rigth ascension (J2000)
179-189 F11.7 deg DEdeg Declination (J2000)
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Note (1): When n (the number of observations, i.e. o_Vmag aor o_Imag) is >2,
the "error" gives the rms residual of the individual measurements.
When n=2, they are the difference between the two measurements, which is twice
the rms residual.
When n=1, they are error estimates calculated from the number of counts in
the star image; these tend to be underestimates of the real error,
by a factor of ∼3-4.
Note (2): Note that xsig and ysig are not astrometric error estimates; instead
xsig is the difference between the X positions in the V and I images, and
correspondingly for ysig. The positions are not of high astrometric accuracy,
and xsig and ysig should be used only as an additional flag of the photometric
accuracy (since stars with poor photometry tend also to have poor astrometry).
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History:
Copied at https://users.astro.ufl.edu/~ata/public_hstgc/databases.html
(End) Patricia Vannier [CDS] 26-Sep-2019