J/MNRAS/482/1275 WAGGS Globular Cluster Ca Triplet Metallicities (Usher+, 2019)
The WAGGS project - II. The reliability of the calcium triplet as a metallicity
indicator in integrated stellar light.
Usher C., Beckwith T., Bellstedt S., Alabi A., Chevalier L., Pastorello N.,
Cerulo P., Dalgleish H.S., Fraser-McKelvie A., Kamann S., Penny S.,
Foster C., McDermid R., Schiavon R.P., Villaume A.
<Mon. Not. R. Astron. Soc., 482, 1275-1303 (2019)>
=2019MNRAS.482.1275U 2019MNRAS.482.1275U (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Clusters, globular ; Galaxies ; Optical
Keywords: stars: abundances - globular clusters: general -
galaxies: abundances - galaxies: star clusters: general -
galaxies: stellar content
Abstract:
Using data from the WiFeS Atlas of Galactic Globular cluster Spectra,
we study the behaviour of the calcium triplet (CaT), a popular
metallicity indicator in extragalactic stellar population studies. A
major caveat of these studies is that the potential sensitivity to
other stellar population parameters such as age, calcium abundance,
and the initial mass function has not yet been empirically evaluated.
Here, we present measurements of the strength of the CaT feature for
113 globular clusters in the Milky Way and its satellite galaxies. We
derive empirical calibrations between the CaT index and both the iron
abundance ([Fe/H]) and calcium abundance ([Ca/H]), finding a tighter
relationship for [Ca/H] than for [Fe/H]. For stellar populations, 3Gyr
and older the CaT can be used to reliably measure [Ca/H] at the 0.1dex
level but becomes less reliable for ages of ∼2Gyr and younger. We find
that the CaT is relatively insensitive to the horizontal branch
morphology. The stellar mass function however affects the CaT
strengths significantly only at low metallicities. Using our newly
derived empirical calibration, we convert our measured CaT indices
into [Ca/H] values for the globular clusters in our sample.
Description:
We use an expanded version of the WAGGS sample presented in Usher et
al. (2017MNRAS.468.3828U 2017MNRAS.468.3828U). As detailed in that paper, the sample
consists of GCs in the MW, the LMC, the SMC, and the Fornax dSph
observable from the Siding Spring Observatory with central surface
brightness brighter than µV∼20mag/arcsec2. We favoured GCs with
high-quality HST photometry (e.g. Sarajedini et al.
2007AJ....133.1658S 2007AJ....133.1658S, Cat. J/AJ/133/1658) and GCs with abundances from
high-resolution spectroscopy. Additions from the previously presented
sample in Usher et al. (2017) are 11 GCs in the LMC and SMC and 16 GCs
in the MW.
As described in Usher et al. (2017MNRAS.468.3828U 2017MNRAS.468.3828U), we used the WiFeS
instrument (Dopita et al. 2007Ap&SS.310..255D 2007Ap&SS.310..255D, 2010Ap&SS.327..245D 2010Ap&SS.327..245D) on
the Australian National University 2.3m telescope at the Siding Spring
Observatory. WiFeS is a dual-arm, 38x25arcsec image slicer integral
field spectrograph. For this work, we only used data observed with the
RT615 beam splitter and I7 000 grating. This setup covers
6800-9050Å with 0.57Å/pixel and provides a spectral resolution
of δλ/λ∼6800 in the region of the CaT.
Our observations span nights from 2015 January to 2017 July. In
addition to the observations presented in Usher et al. (2017), we
utilized a series of observations of NGC 104 from our 2016 September
29 to October 3 observing run. We also utilized observations from our
2017 April 3 to April 6 run and our 2017 June 29 to July 2 run.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 144 113 Sample properties
table2.dat 171 75 Adopted high-resolution abundances
table5.dat 72 113 CaT measurements
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See also:
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Globular cluster designation
10- 15 A6 --- Galaxy Host galaxy (1)
17- 21 F5.2 --- [Fe/H] Literature metallicity
23- 28 F6.3 Gyr Age ? Literature age
30- 35 F6.2 arcsec Rc Core radius
37- 42 F6.2 arcsec Rh ? Half-light radius
44- 48 F5.2 mag/arcsec2 muV Central surface brightness in V band
50- 53 F4.2 mag AV V band extinction
55- 58 F4.2 [Msun] Mass Stellar mass
60- 63 F4.2 [Msun] MassIn Stellar mass in observed field-of-view
65- 83 A19 --- r_[Fe/H] Reference for metallicity (2)
85-103 A19 --- r_Age Reference for age (2)
105-144 A40 --- refstr References for structural
parameters (2)
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Note (1): Host galaxy as follows:
MW = Milky Way
LMC = Large Magellanic Cloud
SMC = Small Magellanic Cloud
Fornax = Fornax Dwarf Spheroidal
Note (2): List of ADS bibcodes. Harris10 refers to the 2010 edition of the
Harris (2006) catalogue 1996AJ....112.1487H 1996AJ....112.1487H, Cat. VII/195
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Globular cluster designation
10- 14 F5.2 --- [Fe/H] Iron abundance
16- 19 F4.2 --- e_[Fe/H] Error on [Fe/H]
21- 25 F5.2 --- [Ca/Fe] ? Calcium to Iron ratio
27- 30 F4.2 --- e_[Ca/Fe] ? Error on [Ca/Fe]
32-171 A140 --- Ref List of ADS bibcodes for abundance references
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Globular cluster designation
10- 17 F8.3 km/s RV Radial velocity
19- 24 F6.3 km/s e_RV Lower error on RV
26- 30 F5.3 km/s E_RV Upper error on RV
32- 37 F6.3 0.1nm CaT Calcium triplet strength
39- 43 F5.3 0.1nm e_CaT Lower error on CaT
45- 49 F5.3 0.1nm E_CaT Upper error on CaT
51- 56 F6.3 --- [Ca/H] Calcium triplet based Ca abundance
58- 62 F5.3 --- e_[Ca/H] Lower error on [Ca/H]
64- 68 F5.3 --- E_[Ca/H] Upper error on [Ca/H]
70 I1 --- AgeFlag [0,1] Age flag (0: ok, 1: Ca measurement less
reliable due to age <3Gyr)
72 I1 --- MassFlag [0,1] Mass flag (0: ok, 1: Ca measurement
less reliable due to Mass<5x103M☉ in
observed field-of-view)
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History:
From electronic version of the journal
References:
Usher et al., Paper I 2017MNRAS.468.3828U 2017MNRAS.468.3828U
Dalgleish et al., Paper III 2020MNRAS.492.3859D 2020MNRAS.492.3859D
(End) Ana Fiallos [CDS] 27-Jun-2022