J/A+A/669/A115 Galactic Bulge GC stars CaT and RV (Geisler+, 2023)
Ca triplet metallicities and velocities for 12 globular clusters towards
the Galactic Bulge.
Geisler D., Parisi M.C., Dias B., Villanova S., Mauro F., Saviane I.,
Cohen R.E., Moni Bidin C., Minniti D.
<Astron. Astrophys. 669, A115 (2023)>
=2023A&A...669A.115G 2023A&A...669A.115G (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Radial velocities ;
Equivalent widths ; Abundances, [Fe/H] ; Optical
Keywords: Galaxy: abundances - Galaxy: bulge - galaxies: clusters: general
Abstract:
Globular clusters (GCs) are excellent tracers of the formation and
early evolution of the Milky Way. The bulge GCs (BGCs)
are particularly important because they can reveal vital information
about the oldest, in-situ component of the Milky Way.
We aim at deriving mean metallicities and radial velocities for 13 GCs
that lie towards the bulge and are generally associated with this
component. This region is observationally challenging because of high
extinction and stellar density, hampering optical studies of these and
similar BGCs, making most previous determinations of these parameters
quite uncertain.
We use near infrared low resolution spectroscopy with the FORS2
instrument on the VLT to measure the wavelengths and equivalent widths
of the CaII triplet (CaT) lines for a number of stars per cluster. We
derive radial velocities, ascertain membership and apply known
calibrations to determine metallicities for cluster members, for a
mean of 11 members per cluster. Unfortunately, one of our targets,
VVV-GC002, which is the closest GC to the Galactic center, turned out
not to have any members in our sample.
We derive mean cluster RV values to 3km/s, and mean metallicities to
0.05dex. We find generally good agreement with previous determinations
for both metallicity and velocity. On average, our metallicities are
0.07dex more metal-rich than Harris (2010,
https://physics.mcmaster.ca/%7Eharris/mwgc.dat), with a standard
deviation of the difference of 0.25dex. Our sample has metallicities
lying between -0.21 and -1.64 and is distributed between the
traditional metal-rich BGC peak near [Fe/H]~-0.5 and a more metal-poor
peak around [Fe/H]~-1.1, which has recently been identified. These
latter are candidates for the oldest GCs in the Galaxy, if blue
horizontal branches are present, and include BH261, NGC6401, NGC6540,
NGC6642, and Terzan 9. Finally, Terzan 10 is even more metal-poor.
However, dynamically, Terzan 10 is likely an intruder from the halo,
possibly associated with the Gaia-Enceladus or Kraken accretion
events. Terzan 10 is also confirmed as an Oosterho type II GC based on
our results.
The CaT technique is an excellent method for deriving mean
metallicities and velocities for heavily obscured GCs. Our sample
provides reliable mean values for both of these key properties for an
important sample of previously poorly-studied BGCs from spectroscopy
of a significant number of members per cluster. We emphasize that the
more metal-poor GCs are excellent candidates for being ancient relics
of bulge formation. The lone halo intruder in our sample, Terzan 10,
is conspicuous for also having by far the lowest metallicity, and
casts doubt on the possibility of any bonafide BGCs at metallicities
below about ~-1.5.
Description:
We have obtained low resolution spectra of the CaT lines in a total of
about 540 red giants in the vicinity of 13 bulge GCs using the FORS2
instrument on the Very Large Telescope. The targeted clusters were
those which did not have spectra of individual stars at the time of
our observations because of high reddening and therefore had rather
poor existing estimates of RVs and especially metallicities. We
measured the wavelengths and equivalent widths of the CaT lines and
derived RVs and metallicities using standard procedures. An extensive
membership assessment involving position in the cluster and CMD, RV,
metallicity and proper motion insured very high membership
probabilities for our final sample. Unfortunately, one of our
clusters, VVV CL002, turned out to not to have any members among our
observed stars. We derive mean cluster RV values with a mean standard
error of the mean of 3km/s, and mean metallicities to 0.05dex for an
average of 11 members per cluster for the remaining sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 13 Observed Bulge globular clusters
table2.dat 84 130 Measured values for member stars
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See also:
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Cluster Cluster name
10 A1 --- n_Cluster [*] *: for VVVCL002, no data in table2
12- 13 I2 h RAh Cluster right ascension (J2000)
15- 16 I2 min RAm Cluster right ascension (J2000)
18- 21 F4.1 s RAs Cluster right ascension (J2000)
23 A1 --- DE- Cluster declination sign (J2000)
24- 25 I2 deg DEd Cluster declination (J2000)
27- 28 I2 arcmin DEm Cluster declination (J2000)
30- 31 I2 arcsec DEs Cluster declination (J2000)
33- 37 F5.2 mag Ksmag Cluster Ks magnitude at the horizontal branch
(HB) level
39- 42 F4.2 mag e_Ksmag Cluster Ks magnitude at the horizontal branch
(HB) level error
44- 47 F4.2 mag E(B-V) Extinction from Harris (2010, 1012.3224,
https://physics.mcmaster.ca/%7Eharris/mwgc.dat)
49- 95 A47 --- ANames Alternative names
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Cluster Cluster name
11- 19 I9 --- ID ID from photometry
21 A1 --- CCD [MS] CCD chip (M: master, S: secondary)
23- 24 I2 --- ap Aperture number
26- 32 F7.4 h RAhour Right ascension in decimal hours (J2000)
34- 41 F8.4 deg DEdeg Declination in decimal degrees (J2000)
43- 48 F6.1 km/s RV Heliocentric radial velocity
50- 52 F3.1 km/s e_RV The 1σ error in RV
54- 58 F5.2 mag K-KHB Brightness difference between star and
cluster's horizontal branch
60- 63 F4.2 mag e_K-KHB Error in K-KHB
65- 68 F4.2 0.1nm SigmaW Summed CaII equivalent width (1)
70- 73 F4.2 0.1nm e_SigmaW The 1σ error in SigmaW
75- 79 F5.2 --- [Fe/H] Metallicity
81- 84 F4.2 --- e_[Fe/H] The error in Metallicity
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Note (1): Where SigmaW = EW(8542) + EW(8662).
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Acknowledgements:
Celeste Parisi, cparisi(at)unc.edu.ar
(End) Patricia Vannier [CDS] 11-Oct-2022