J/AJ/147/4 HST photometry of 5 globular clusters (Ross+, 2014)
Measuring metallicities with Hubble Space Telescope/Wide-Field Camera 3
photometry.
Ross T.L., Holtzman J.A., Anthony-Twarog B.J., Bond H.E., Twarog B.,
Saha A., Walker A.
<Astron. J., 147, 4 (2014)>
=2014AJ....147....4R 2014AJ....147....4R
ADC_Keywords: Clusters, globular ; Clusters, open ; Photometry, HST ;
Keywords: globular clusters: individual (M92,NGC 6752,NGC 104,NGC 5927,
NGC 6791) - Hertzsprung-Russell and C-M diagrams
Abstract:
We quantified and calibrated the metallicity and temperature
sensitivities of colors derived from nine Wide-Field Camera 3 filters
on board the Hubble Space Telescope using Dartmouth isochrones and
Kurucz atmosphere models. The theoretical isochrone colors were tested
and calibrated against observations of five well studied galactic
clusters, M92, NGC 6752, NGC 104, NGC 5927, and NGC 6791, all of which
have spectroscopically determined metallicities spanning
-2.30<[Fe/H]<+0.4. We found empirical corrections to the Dartmouth
isochrone grid for each of the following color-magnitude diagrams
(CMDs): (F555W-F814W, F814W), (F336W-F555W, F814W), (F390M-F555W,
F814W), and (F390W-F555W, F814W). Using empirical corrections, we
tested the accuracy and spread of the photometric metallicities
assigned from CMDs and color-color diagrams (which are necessary to
break the age-metallicity degeneracy). Testing three color-color
diagrams [(F336W-F555W),(F390M-F555W),(F390W-F555W), versus
(F555W-F814W)], we found the colors (F390M-F555W) and (F390W-F555W) to
be the best suited to measure photometric metallicities. The color
(F390W-F555W) requires much less integration time, but generally
produces wider metallicity distributions and, at very low metallicity,
the metallicity distribution function (MDF) from (F390W-F555W) is ∼60%
wider than that from (F390M-F555W). Using the calibrated isochrones,
we recovered the overall cluster metallicity to within ∼0.1dex in
[Fe/H] when using CMDs (i.e., when the distance, reddening, and ages
are approximately known). The measured MDF from color-color diagrams
shows that this method measures metallicities of stellar clusters of
unknown age and metallicity with an accuracy of ∼0.2-0.5dex using
F336W-F555W, ∼0.15-0.25dex using F390M-F555W, and ∼0.2-0.4dex with
F390W-F555W, with the larger uncertainty pertaining to the lowest
metallicity range.
Description:
Hubble Space Telescope/Wide-Field Camera 3 (HST/WFC3) observations
were obtained in the following filters: F336W (u, Stromgren), F390M
(CaII continuum), F390W (C, Washington), F395N (CaII, 3933/3968),
F410M (v, Stromgren), F467M (b, Stromgren), F547M (y, Stromgren),
F555W (WFPC2 V), F814W (WFPC2 Wide I), F110W (Wide YJ), and F160W
(WFC3 H).
WFC3 images were obtained of five clusters during cycle 17 as part of
the calibration program 11729, (PI Holtzman). Additional images of the
five clusters come from the calibration portion of the program 11664
(PI Brown).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table7.dat 78 5 Cluster data
table10.dat 34 715 Corrected isochrone sequence in color-color
diagrams
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/AJ/143/50 : White dwarfs in 47 Tuc (NGC 104) with HST (Woodley+, 2012)
J/A+A/543/A106 : UBVRI photometry in NGC6791 (Brogaard+, 2012)
J/A+A/492/171 : VIc light curves of NGC 6791 V20 (Grundahl+, 2008)
J/AJ/130/1693 : HST-ACS observations of 5 globular clusters (Brown+, 2005)
J/A+A/440/901 : Reddening and metallicity of NGC 6752 (Gratton, 2005)
Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Galactic cluster name
10- 11 I2 h RAh Hour of Right Ascension (J2000)
13- 14 I2 min RAm Minute of Right Ascension (J2000)
16- 20 F5.2 s RAs Second of Right Ascension (J2000)
22 A1 --- DE- Sign of the Declination (J2000)
23- 24 I2 deg DEd Degree of Declination (J2000)
26- 27 I2 arcmin DEm Arcminute of Declination (J2000)
29- 32 F4.1 arcsec DEs Arcsecond of Declination (J2000)
34- 38 F5.3 mag E(B-V) Reddening
40- 44 F5.2 mag m-M Distance modulus (m-M)v (1)
46- 50 F5.2 [Sun] [Fe/H]0 Lower value of spectroscopic metallicity
range (from literature)
52- 56 F5.2 [Sun] [Fe/H]1 Upper value of spectroscopic metallicity
range (from literature)
58- 62 F5.2 [Sun] [Fe/H] Isochrone metallicity adopted
64- 68 F5.2 [Sun] [a/Fe]l ? α enhancement [α/Fe]
(from literature)
70- 73 F4.1 [Sun] [a/Fe] α enhancement [α/Fe] adopted
75- 78 F4.1 Gyr Age Estimated age
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Note (1): Adjusted to self consistently fit the MSTO and subgiant branches for
each cluster to the adopted isochrones. See Section 3.3 for more details.
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Byte-by-byte Description of file: table10.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 F5.2 [Sun] [Fe/H] [-2.3/0.4] Metallicity (5 values:
-2.30, -1.45, -0.70, -0.40, +0.40)
7- 12 F6.4 mag V-I HST/WFC3 F555W-F814W corrected color index (1)
14- 20 F7.4 mag u-V HST/WFC3 F336W-F555W corrected color index (1)
22- 27 F6.4 mag CaII-V HST/WFC3 F390M-F555W corrected color index (1)
29- 34 F6.4 mag U-V HST/WFC3 F390W-F555W corrected color index (1)
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Note (1): Dartmouth isochrone colors empirically corrected to match the observed
Wide-Field Camera 3 (WFC3) colors of 5 Galactic clusters. Galactic clusters
span a range of metallicities: M92, [Fe/H]=-2.30; NGC 6752, [Fe/H]=-1.45;
NGC 104, [Fe/H]=-0.70; NGC 5927, [Fe/H]=-0.40; NGC 6791, [Fe/H]=0.40.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 26-Aug-2014