# The metallicity variations along the chromosome maps: The Globular Cluster
47 Tucanae111Based on observations collected at the European Organisation for
Astronomical Research in the Southern Hemisphere under ESO programme 105.20NB,
and on observations with the NASA/ESA Hubble Space Telescope, obtained at the
Space Telescope Science Institute, which is operated by AURA, Inc., under NASA
contract NAS 5-26555.

A. F. Marino  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di
Padova, Vicolo dell’Osservatorio 5, Padova, IT-35122  Istituto Nazionale di
Astrofisica - Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi, 5,
Firenze, IT-50125  A. P. Milone  Dipartimento di Fisica e Astronomia “Galileo
Galilei” - Univ. di Padova, Vicolo dell’Osservatorio 3, Padova, IT-35122
Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Padova, Vicolo
dell’Osservatorio 5, Padova, IT-35122  E. Dondoglio  Dipartimento di Fisica e
Astronomia “Galileo Galilei” - Univ. di Padova, Vicolo dell’Osservatorio 3,
Padova, IT-35122  A. Renzini  Istituto Nazionale di Astrofisica - Osservatorio
Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova, IT-35122  G.
Cordoni  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di
Padova, Vicolo dell’Osservatorio 5, Padova, IT-35122  H. Jerjen  Research
School of Astronomy & Astrophysics, Australian National University, Canberra,
ACT 2611, Australia  A. Karakas  School of Physics and Astronomy, Monash
University, VIC 3800, Australia  Centre of Excellence for Astrophysics in
Three Dimensions (ASTRO-3D), Melbourne, Victoria, Australia  E. P. Lagioia
South-Western Institute for Astronomy Research, Yunnan University, Kunming,
650500 P.R. China  Dipartimento di Fisica e Astronomia “Galileo Galilei” -
Univ. di Padova, Vicolo dell’Osservatorio 3, Padova, IT-35122  M. V. Legnardi
Dipartimento di Fisica e Astronomia “Galileo Galilei” - Univ. di Padova,
Vicolo dell’Osservatorio 3, Padova, IT-35122  M. McKenzie  Research School of
Astronomy & Astrophysics, Australian National University, Canberra, ACT 2611,
Australia  A. Mohandasan  Dipartimento di Fisica e Astronomia “Galileo
Galilei” - Univ. di Padova, Vicolo dell’Osservatorio 3, Padova, IT-35122  M.
Tailo  Dipartimento di Fisica e Astronomia Augusto Righi, Università degli
Studi di Bologna, Via Gobetti 93/2, I-40129, Bologna, Italy  D. Yong  Research
School of Astronomy & Astrophysics, Australian National University, Canberra,
ACT 2611, Australia  T. Ziliotto  Dipartimento di Fisica e Astronomia “Galileo
Galilei” - Univ. di Padova, Vicolo dell’Osservatorio 3, Padova, IT-35122 A. F.
Marino<EMAIL_ADDRESS>
(Received 19-Jul-2023; Accepted 21-Sep-2023)

###### Abstract

The ”chromosome maps” (ChMs) of globular clusters (GCs) have revealed that
these ancient structures are not homogeneous in metallicity in various ways,
and in different natures. The Type II GCs, generally display larger
variations, sometimes coupled with slow neutron capture ($s$) element
enrichment on the ChMs redder sequences, which has been interpreted as due to
multiple generations of stars. On the other hand, most GCs have inhomogeneous
first populations (1P) in the form of large ranges in the
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values, pointing towards a not fully
mixed pristine molecular cloud. We analyse the chemical composition the GC 47
Tucanae, which shows both inhomogeneous 1P stars and, although not formally a
Type II GC, hosts a small number of stars distributed on a red side of the
main stream of ChM stars. Our results suggest that 1P stars are not
homogeneous in the overall metallicity, with variations of the order of
$\sim$0.10 dex in all the chemical species. The anomalous stars distributed on
a redder sequence of the ChM, are further enriched in metals, but without any
evidence for a significant enrichment in the $s$ elements. Our three second
population stars located on the normal component of the map, have
metallicities similar to those of the metal-richer 1P group, suggesting that
this population formed from these stars. Although three stars is a too-small
sample to draw strong conclusions, the low spread in metals of these objects
might point towards a formation in a fully mixed medium, possibly after a
cooling flow phase.

globular clusters: individual (NGC 104) — chemical abundances – Population II
– Hertzsprung-Russell diagram

††journal: ApJ

##  1 Introduction

The existence of multiple stellar populations in virtually all globular
clusters (GCs) of the Milky Way is a well-established fact (see Gratton et
al., 2012; Bastian & Lardo, 2015; Milone & Marino, 2022, for reviews). Yet,
the mechanisms responsible for this phenomenon continue to be debated (e.g.
Renzini et al., 2015).

The most effective tool to isolate the different populations of stars hosted
in a GC is offered by a combination of four bands from the Hubble Space
Telescope ($HST$), namely F275W, F336W, F438W and F814W, allowing the
construction of multiple pseudo-color plots now known as “Chromosome Maps”
(ChMs, Milone et al., 2015). In these diagrams the position of stars is
especially sensitive to the abundance of C, N and O elements via the molecules
that they form as well as to the helium and iron abundance (e.g. Marino et
al., 2008; Milone et al., 2017; Marino et al., 2019a). The ChMs have
revolutionized the traditional picture of GCs, and have revealed unexpected
features of the multiple population pattern.

On the basis of the ChM shape, GCs have been subdivided into two main groups,
namely Type I and Type II. The majority ($\sim$83%) of Milky Way GCs belongs
to the Type I class, with the ChM displaying a first population (1P) and
different numbers of second population (2P) groups, but following a single
“sequence” along the map. ChMs of Type II clusters are more complex. In
addition to the common 1P and 2P stars, a second sequence (hereafter
anomalous) appears on the red side of their maps (Milone et al., 2017). A
large number of spectroscopic studies have demonstrated that stars on the
anomalous sequence are metal richer than the normal ones and, in most cases,
they also are enriched in the elements produced by the slow neutron capture
reactions ($s$ elements) (e.g. Yong & Grundahl, 2008; Marino et al., 2009,
2015, 2021; Johnson et al., 2017; McKenzie et al., 2022).

Perhaps the most shocking discovery from the ChMs was the apparent chemical
inhomogeneity of even the 1P, with elemental ratios similar to that of halo
field stars. Indeed, in most GCs, the 1P stars themselves do not look as a
chemically homogeneous group as they show a large spread in the $m_{\rm
F275W}-m_{\rm F814W}$ color, the $x$ axis of the ChMs. This was first noticed
by Milone et al. (2015) who hinted at a variation of helium among 1P stars to
account for the spread. However, none of the several plausible physical
mechanisms considered by Milone et al. (2018) was able to account for an
helium enrichment without a concomitant conversion of C and O into N. Thus,
either a totally new, unknown process was at work producing a spread in helium
among 1P stars, or helium was not the culprit and some other element was
driving it.

To shed light on the apparent chemical inhomogeneity of 1P stars, once
associated to one single stellar population (the primordial one),
spectroscopic tagging in GCs with more pronounced spreads along the 1P on the
ChM has promptly followed the photometric findings. The first spectroscopic
evidence of metallicity variations among 1P stars has been shown in the GC NGC
3201 ([Fe/H]=$-$1.59 dex), where a small spread of the order of $\sim$0.10 dex
has been detected, at constant [O/Fe] and [Na/Fe] (Marino et al., 2019b).
These findings suggest indeed that the overall metallicity, rather than
helium, is the main factor for the 1P spread along the ChM. Later on,
photometric support for internal variations in metallicity among the 1P stars
has been reported for several analysed GCs (see Legnardi et al., 2022).

The possibility that 1P stars themselves have an internal spread in the
overall metallicity suggests that either the molecular cloud out of which 1P
stars formed was not chemically homogeneous, i.e., was not fully mixed
following its original chemical enrichment, or while 1P stars were forming
some Type Ia supernova from previous generations may have polluted the intra-
cluster medium. These options can provide us with new hints to understand the
process of GC formation, its time-scale, and help to identify the class of
stars responsible for the further enrichment of the interstellar medium (ISM)
to form the 2P stars in GCs. In this context, it is noteworthy that
hydrodynamical simulations have predicted that metal abundance spreads within
GC forming giant molecular clouds can influence the iron abundances of future
cluster members (McKenzie & Bekki, 2021).

It is clear now that the chemical enrichment in metallicity, though small,
might be a quite common property of Milky Way GCs. The phenomenon seems to be
linked to different mechanisms, depending on whether the GC is Type I, and
metallicity variations could account for the 1P spread in the $m_{\rm
F275W}-m_{\rm F814W}$ color along the ChMs, or Type II where the enrichment of
the redder anomalous component could be larger, sometimes associated with
further enhancements in the [$s$/Fe] and C+N+O abundances (e.g. Marino et al.,
2011a; Yong et al., 2015). In this context, we note that, when spectra of
excellent quality are used, very small variations in metals, of the order of a
few hundredths of dex are found in both globular and open clusters (e.g. Yong
et al., 2013; Liu et al., 2016; Monty et al., 2023; Lardo et al., 2023).

In this work we analyse the chemical pattern of 1P stars in the relatively
metal rich GC NGC 104 (47 Tucanae, [Fe/H]=$-$0.72 dex) (Harris, 2010). This
bright cluster offers the opportunity to analyse the different metal-
enrichment events that these systems can experience. Indeed, 47 Tucanae,
besides displaying a well-elongated 1P, shows a very broad ChM sequence of 1P
and 2P stars, rather than a clearly split ChM as in Type II clusters. Its
broad ChM suggests that it can include metal enriched stars like the anomalous
stars in Type II clusters. Thus, 47 Tucanae has not been formally classified
as a Type II GC by Milone et al. (2017), but represents an ideal target for an
in-depth investigation of both the chemical abundance pattern within 1P stars
and other metal enrichment channels associated with its candidate anomalous
stars which can the progeny of a faint sub giant branch populated by about 10%
of the stars (Anderson et al., 2009).

The layout of this paper is as follows: Section 2 presents the photometric and
spectroscopic data; Section 3 describes how we derive atmospheric parameters
and the chemical abundance analysis; Section 4 presents our results, that are
discussed and summarised in Sections 5-6.

Table 1: Coordinates, Photometric Information (including the location on the ChM), Radial Velocities, with associated rms from the # (number) exposures and maximum time between observations (Time interval) for our 29 spectroscopic targets observed with UVES. The anomalous candidate stars have been highlighted in the last column. ID | RA | DEC | $V$ | $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ | $\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ | RV | rmsRV | # | Time interval | anomalous
---|---|---|---|---|---|---|---|---|---|---
| [J2000] | [J2000] | [mag] | [mag] | [mag] | [km s-1] | [km s-1] |  | [months] |
8672 | 00:24:20.5 |  $-$72:06:00.19 | 14.97 |  $-$0.2192 |  $+$0.0446 |  $-$13.99 | 0.93 | 9 | 14 | no
116624 | 00:23:52.9 |  $-$72:04:18.59 | 13.81 |  $-$0.1252 |  $+$0.3932 |  $-$17.56 | 0.27 | 9 | 14 | yes
11746 | 00:24:15.6 |  $-$72:06:04.31 | 14.06 |  $-$0.0514 |  $+$0.0653 |  $+$3.58 | 0.29 | 9 | 14 | no
44780 | 00:24:16.1 |  $-$72:05:32.89 | 13.64 |  $-$0.1588 |  $+$0.0013 |  $-$36.37 | 0.26 | 9 | 14 | no
68444 | 00:23:58.0 |  $-$72:05:03.00 | 14.90 |  $-$0.1876 |  $+$0.0951 |  $-$12.37 | 0.35 | 9 | 14 | no
71504 | 00:23:54.8 |  $-$72:05:32.58 | 14.54 |  $-$0.0861 |  $+$0.0603 |  $-$27.26 | 0.27 | 9 | 14 | no
92267 | 00:24:12.6 |  $-$72:04:23.67 | 13.43 |  $-$0.3425 |  $+$0.3754 |  $-$13.04 | 0.27 | 11 | 14 | no
115804 | 00:23:53.6 |  $-$72:04:48.31 | 14.00 |  $-$0.1349 |  $+$0.0846 |  $-$28.39 | 0.08 | 2 | 2 | no
22386 | 00:24:02.7 |  $-$72:05:46.67 | 14.00 |  $+$0.0107 |  $+$0.2369 |  $-$19.00 | 0.06 | 2 | 2 | yes
28653 | 00:23:54.6 |  $-$72:05:46.67 | 14.53 |  $-$0.0891 |  $+$0.0871 |  $-$16.39 | 0.25 | 10 | 5 | no
41968 | 00:24:19.0 |  $-$72:05:13.88 | 14.33 |  $-$0.0929 |  $+$0.1460 |  $-$27.99 | 0.10 | 2 | 2 | no
61006 | 00:24:03.6 |  $-$72:05:06.60 | 14.52 |  $-$0.1427 |  $+$0.0568 |  $-$19.85 | 0.10 | 2 | 2 | no
73063 | 00:23:53.2 |  $-$72:05:25.31 | 14.44 |  $-$0.2656 |  $+$0.4352 |  $-$5.87 | 0.06 | 2 | 2 | yes
84553 | 00:24:21.0 |  $-$72:04:49.08 | 14.45 |  $-$0.1813 |  $+$0.1326 |  $-$33.42 | 0.13 | 2 | 2 | no
10619 | 00:24:17.1 |  $-$72:06:10.60 | 13.47 |  $-$0.0842 |  $-$0.0339 |  $+$1.33 | 0.22 | 9 | 13 | no
112499 | 00:23:57.2 |  $-$72:04:17.30 | 14.13 |  $-$0.2180 |  $+$0.0792 |  $+$10.52 | 0.28 | 9 | 13 | no
143175 | 00:23:59.8 |  $-$72:03:53.10 | 14.58 |  $-$0.1573 |  $+$0.0434 |  $-$31.93 | 0.28 | 9 | 13 | no
22746 | 00:24:01.9 |  $-$72:06:05.41 | 13.46 |  $+$0.0110 |  $-$0.0008 |  $-$22.62 | 0.21 | 9 | 13 | no
70896 | 00:23:55.5 |  $-$72:05:00.48 | 13.77 |  $-$0.0069 |  $+$0.0662 |  $-$1.59 | 6.72 | 9 | 13 | no
83377 | 00:24:22.9 |  $-$72:04:31.58 | 14.44 |  $-$0.0451 |  $-$0.0195 |  $-$26.26 | 0.21 | 9 | 13 | no
86528 | 00:24:18.5 |  $-$72:04:16.09 | 14.82 |  $-$0.0041 |  $+$0.0420 |  $+$4.21 | 0.31 | 9 | 13 | no
90842 | 00:24:14.0 |  $-$72:04:14.20 | 14.53 |  $+$0.0042 |  $+$0.0076 |  $+$4.39 | 0.25 | 5 | 13 | no
146316 | 00:23:55.4 |  $-$72:04:00.79 | 14.67 |  $-$0.1399 |  $+$0.0973 |  $-$24.38 | 0.24 | 3 | 5 | no
15613 | 00:24:10.4 |  $-$72:05:58.37 | 13.81 |  $-$0.1329 |  $+$0.0712 |  $-$9.06 | 0.34 | 8 | 5 | no
69465 | 00:23:56.8 |  $-$72:05:09.60 | 13.88 |  $-$0.1467 |  $+$0.1009 |  $+$12.42 | 0.29 | 8 | 5 | no
86281 | 00:24:18.9 |  $-$72:04:35.89 | 13.64 |  $-$0.0327 |  $+$0.0670 |  $+$4.75 | 0.24 | 8 | 5 | no
91298 | 00:24:13.5 |  $-$72:04:31.50 | 14.36 |  $-$0.2290 |  $+$0.3097 |  $-$19.00 | 0.33 | 8 | 5 | no
9946 | 00:24:18.2 |  $-$72:06:03.79 | 14.80 |  $-$0.0361 |  $-$0.0199 |  $-$14.92 | 0.24 | 8 | 5 | no
100719 | 00:24:06.2 |  $-$72:04:48.78 | 13.69 |  $-$0.2126 |  $+$0.0517 |  $-$17.87 | 0.23 | 7 | 12 | no

##  2 Data

###  2.1 The chromosome map of 47 Tucanae

Milone et al. (2017) analysed the ChMs of 57 GCs, including 47 Tucanae, whose
ChM is shown in Figure 1. As noticed by Milone et al. (2017), clearly, the ChM
of this cluster covers a large range along the
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ axis, which is not consistent with the
1P stars being chemically homogeneous.

In this work we analyse high-resolution spectra for the targets shown in
Figure 1, and couple our spectroscopic data (see Section 2.2) with high-
precision photometry from the $HST$. The photometric data come from the $HST$
UV Legacy Survey that is designed to investigate multiple stellar populations
in GCs (GO-13297, Piotto et al., 2015). Details on the images and on the data
reduction can be found in Piotto et al. (2015) and Milone et al. (2017). Our
photometry has been corrected for differential reddening effects as in Milone
et al. (2012a, b).

Figure 1: The chromosome map of 47 Tucanae from Milone et al. (2017). Grey
dots represent the complete sample of RGB stars used to construct the map. Our
spectroscopic targets observed with UVES are highlighted with large coloured
symbols. Specifically, green circles are 1P stars, magenta squares are normal
2P stars, while magenta triangles represent candidate anomalous stars. The
locations of two RV binaries are indicated by black crosses.

###  2.2 The spectroscopic dataset

Our spectroscopic data have been acquired using the FLAMES Ultraviolet and
Visual Echelle Spectrograph (FLAMES-UVES, Pasquini et al., 2000) on the
European Southern Observatory’s (ESO) Very Large Telescope (VLT), through the
programme 105.20NB. The observations were taken in the standard RED580 setup,
which has a wavelength coverage 4726-6835 Å and a resolution of $R\sim$47,000
(Dekker et al., 2000). Each target has been selected to pass the isolation
criteria, namely no neighbors brighter than 1.5 mag within two fiber radii.

The stars were chosen to span a range in
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ as large as possible, and a quite
narrow range in $\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$. Indeed, our
primary goal was to observe red giants associated to the 1P on the ChM. As
shown in Figure 1, most of our targets lie on the 1P, spanning a range of
$\sim$0.20 in $\Delta_{\tiny{\mathrm{F275W,F814W}}}$. Because of the limited
sample of isolated targets located within the inner $\sim$3′$\times$3′ field,
where the ChM has been constructed, not all the UVES fibers could be fed with
1P stars avoiding fiber collisions. Hence, we had the opportunity to observe a
few targets on the 2P as well, namely three stars on the blue and three other
stars on the red edge of the ChM as indicated in Figure 1. The red targets
might be associated with stars that have an enhanced heavy element composition
in Type II GCs (e.g. Milone et al., 2017; Marino et al., 2019a, 2021).

Spectra are based on a number of multiple 2775s exposures, which varies from a
minimum of 2 to a maximum of 11, depending both on the brightness and priority
of each target. Individual exposures have been taken a few months apart to
allow us to detect variations in radial velocities (RVs), and identify
possible binaries in our sample. Data were reduced using the FLAMES-UVES
pipelines within the EsoReflex
interface222https://www.eso.org/sci/software/esoreflex/ (Ballester et al.,
2000), including bias subtraction, flat-field correction, wavelength
calibration, sky subtraction and spectral rectification. As an example, Figure
2 shows two portions of our final spectra.

RVs were derived using the iraf@FXCOR task, which cross-correlates the object
spectrum with a template. For the template we used a synthetic spectrum
obtained through MOOG333http://www.as.utexas.edu/ chris/moog.html (version
June 2014, Sneden, 1973), computed with a model stellar atmosphere
interpolated from the Castelli & Kurucz (2004) grid, adopting parameters
(effective temperature/surface gravity/microturbulence/metallicity) =
(Teff/log g/$\xi_{\rm t}$/[A/H]) = (4500 K/2.0/2.0 km s-1/$-0.70$
dex). Each spectrum was corrected to the restframe system, and observed RVs
were then corrected to the heliocentric system. Table 1 lists the observed
targets, together with their coordinates, photometric information, RVs, number
of exposures and time interval between the observations.

We notice that two stars in our sample, namely #8672 and #70896, have larger
root mean square deviations (rms) in their RV values obtained from different
exposures (rmsRV), hence we treat these two objects as probable binaries, and
highlight their location in the figures with black crosses. However, we warn
the reader that we cannot rule out the presence of other binaries with no
sizeable differences in the RV values in our sample.

The final mean heliocentric RV for our 47 Tucanae giants, excluding the two
binary candidates, is $\langle$RV$\rangle$=$-14.2\pm 2.8$ km s-1
($\sigma$=14.1 km s-1), which lies within $\sim$1 $\sigma$ of the value listed
in Baumgardt & Hilker (2018) of $\langle$RV$\rangle$=$-17.2\pm 0.1$ km
s-1$\sigma$=11.50 km s-1 within an average distance of 18.02 arcsec from the
cluster centre).

Finally, the individual exposures for each star have been co-added. The
signal-to-noise (S/N) ratio for the combined spectra around $\lambda$6300 Å
ranges from S/N$\sim$60 to $\sim$200, depending on the brightness of the star
and the number of exposures.

Figure 2: Examples of two portions of FLAMES@UVES spectra including some
analyzed Fe and Ca spectral features, plus the Ba line 6496.9 Å. The displayed
spectra are relative to stars #11746 and #112499 which have similar
atmospheric parameters but different $\Delta_{\tiny{\mathrm{F275W,F814W}}}$
values. Overall, the spectral features of star #11746 (with higher
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$) are deeper.

##  3 Chemical abundance analysis

The UVES spectra have a spectral coverage high enough to allow us a fully-
spectroscopical estimate of the stellar parameters, Teff, log g, [A/H] and
$\xi_{\rm t}$. Indeed the number of measured Fe I and Fe II lines for each
star is typically 120 and 12, respectively. Briefly, Teff and log g were
inferred by imposing the excitation potential (E.P.) equilibrium of the Fe I
lines and the ionization equilibrium between Fe I and Fe II spectral features,
respectively. For log g we further imposed Fe II abundances 0.05-0.07 dex
higher than the Fe I ones to adjust for non-local thermodynamic equilibrium
(non-LTE) effects (Bergemann et al., 2012; Lind et al., 2012). $\xi_{\rm t}$
was set to minimize any dependence of Fe I abundances as a function of
equivalent width (EW). The adopted atmospheric parameters are listed in Table
2.

As our sample of stars is composed of giants with information on the ChM
obtained from $HST$ filters, our targets are located in the 2.7′$\times$2.7′
innermost region of 47 Tucanae. Hence, we have only star #69465 in common with
Carretta et al. (2009a). For this target, our inferred atmospheric parameters
are in excellent agreement with those of Carretta and collaborators. Indeed,
we obtain differences (Carretta minus this work) of $\Delta\mbox{T${}_{\rm
eff}$}=+27$ K, $\Delta\mbox{log~{}{\it g}}=-0.01$, and $\Delta\mbox{$\xi_{\rm
t}$}=-0.02$ km s-1. The larger difference we obtain is in the Fe abundance,
$\Delta$[Fe/H]=$+0.13$ dex, which could be likely explained with the different
lines used in the two studies, as we exploit UVES data with a larger
wavelength coverage and a higher resolution than the GIRAFFE spectra analyzed
by Carretta et al. (2009a).

Following our previous work based on data with similar quality, we here adopt
typical internal uncertainties in the atmospheric parameters of 50 K for Teff,
0.20 dex for log g, 0.20 km s-1 for $\xi_{\rm t}$, and 0.10 dex for
metallicity (see Marino et al., 2019b). We also emphasize that systematic
errors might be larger.

Table 2: Adopted atmospheric parameters. ID | Teff | log g | [Fe/H] | $\xi_{\rm t}$
---|---|---|---|---
| (K) | (cgs) | dex | (km s-1)
8672 | 4600 | 2.20 |  $-$0.87 | 1.10
116624 | 4580 | 2.20 |  $-$0.70 | 1.30
11746 | 4640 | 2.30 |  $-$0.76 | 1.27
44780 | 4550 | 2.15 |  $-$0.83 | 1.33
68444 | 4970 | 3.05 |  $-$0.83 | 0.65
71504 | 4800 | 2.70 |  $-$0.80 | 0.78
92267 | 4530 | 2.07 |  $-$0.82 | 1.19
115804 | 4660 | 2.33 |  $-$0.76 | 1.26
22386 | 4660 | 2.35 |  $-$0.65 | 1.33
28653 | 4830 | 2.75 |  $-$0.72 | 1.12
41968 | 4780 | 2.60 |  $-$0.74 | 1.17
61006 | 4900 | 3.00 |  $-$0.79 | 0.81
73063 | 4880 | 2.80 |  $-$0.66 | 1.15
84553 | 4700 | 2.30 |  $-$0.95 | 1.12
10619 | 4470 | 1.95 |  $-$0.85 | 1.47
112499 | 4700 | 2.47 |  $-$0.88 | 0.90
143175 | 4830 | 2.80 |  $-$0.79 | 1.10
22746 | 4450 | 1.97 |  $-$0.79 | 1.47
70896 | 4550 | 2.15 |  $-$0.77 | 1.30
83377 | 4780 | 2.60 |  $-$0.74 | 1.18
86528 | 4880 | 2.90 |  $-$0.74 | 0.84
90842 | 4760 | 2.60 |  $-$0.75 | 0.95
146316 | 4920 | 2.95 |  $-$0.68 | 0.90
15613 | 4600 | 2.20 |  $-$0.82 | 1.41
69465 | 4550 | 2.12 |  $-$0.87 | 1.15
86281 | 4500 | 2.10 |  $-$0.82 | 1.40
91298 | 4870 | 3.02 |  $-$0.73 | 1.07
9946 | 4900 | 2.85 |  $-$0.67 | 1.12
100719 | 4650 | 2.30 |  $-$0.97 | 0.93

Chemical abundances have been inferred for 22 elements, namely Na, Mg, Al, Si,
Ca, Sc (ii), Ti (i and ii), V, Cr (i and ii), Mn, Fe (i and ii), Co, Ni, Cu,
Zn, Y (ii), Zr (ii), Ba (ii), La (ii), Pr (ii), Nd (ii), Eu (ii). The
abundance analysis has been performed by employing the MOOG code (Sneden,
1973) with the alpha-enhanced Kurucz model atmospheres of Castelli & Kurucz
(2004). Chemical abundances have been inferred by using an EW-based analysis;
when this was not possible because of blends or hyperfine/isotopic splitting
we performed spectral synthesis. We now comment on some of the transitions
that we used.

Proton-capture elements: Sodium abundances were determined from the EWs of the
Na i doublets at $\sim$5680 Å and $\sim$6150 Å, aluminum from the synthesis of
the doublet at $\sim$6667 Å, and magnesium from the EWs of the transitions at
$\sim$5528, 5711 Å. Because of the low radial velocity of the cluster, no
reliable abundances could be inferred for oxygen, as the [O I] line was masked
by much stronger telluric features.

Manganese: Spectral lines around 5399, 5420, 5433, 6014, 6022 Å have been
analyzed to infer chemical abundances for Mn. In our synthesis we assume
f(${\phantom{}}^{55}$Mn)=1.00 and hyperfine splitting from Lawler et al.
(2001a, b) and Kurucz (2009).

Copper: For Cu, we synthesised the spectral feature at $\sim$5105 Å, with both
hyperfine and isotopic splitting from Kurucz (2009). Solar-system isotopic
fractions of f(${\phantom{}}^{63}$Cu)=0.69 and f(${\phantom{}}^{65}$Cu)=0.31
have been assumed.

Neutron-capture elements: We inferred abundances for Y, Zr, Ba, La, Pr, Nd,
and Eu. A spectral synthesis analysis has been employed for Zr ($\lambda$5112
Å), Ba ($\lambda$5854, 6497 Å), La ($\lambda$4921, 5115, 5291, 5302, 5303,
6262, 5936, 6390, 6774 Å), Pr ($\lambda$5323 Å), and Eu ($\lambda$6645 Å),
affected by hyperfine and/or isotopic splitting and/or blending features.
Barium abundances were computed assuming the McWilliam (1998) $r$-process
isotopic composition and hyperfine splitting.

Table 3: Analyzed Chemical Abundances from Na to Sc. Average values for 1P and 2P stars are given for each element at the bottom of the table. STAR | [Na/Fe] | $\sigma$ | # | [Mg/Fe] | $\sigma$ | # | [Al/Fe] | $\sigma$ | # | [Si/Fe] | $\sigma$ | # | [Ca/Fe] | $\sigma$ | # | [Sc/Fe] | $\sigma$ | #
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---
8672 | 0.37 | 0.07 | 3 | 0.25 | 0.00 | 1 | 0.43 | 0.05 | 2 | 0.43 | 0.12 | 8 | 0.40 | 0.27 | 18 | 0.13 | 0.25 | 3
116624 | 0.64 | 0.06 | 4 | 0.35 | 0.00 | 1 | 0.47 | 0.12 | 2 | 0.49 | 0.08 | 8 | 0.32 | 0.20 | 17 | 0.22 | 0.14 | 6
11746 | 0.38 | 0.09 | 4 | 0.45 | 0.00 | 1 | 0.21 | 0.04 | 2 | 0.44 | 0.05 | 7 | 0.30 | 0.15 | 20 | 0.24 | 0.14 | 6
44780 | 0.24 | 0.10 | 4 | 0.46 | 0.00 | 1 | 0.21 | 0.06 | 2 | 0.44 | 0.06 | 7 | 0.30 | 0.17 | 19 | 0.23 | 0.12 | 6
68444 | 0.23 | 0.05 | 4 | 0.26 | 0.00 | 1 | 0.06 | 0.10 | 2 | 0.34 | 0.09 | 7 | 0.28 | 0.14 | 17 | 0.18 | 0.11 | 6
71504 | 0.18 | 0.06 | 4 | 0.29 | 0.00 | 1 | 0.15 | 0.05 | 2 | 0.35 | 0.02 | 6 | 0.26 | 0.13 | 19 | 0.23 | 0.15 | 6
92267 | 0.75 | 0.06 | 4 | 0.43 | 0.00 | 1 | 0.32 | 0.03 | 2 | 0.44 | 0.06 | 7 | 0.32 | 0.19 | 17 | 0.27 | 0.15 | 6
115804 | 0.18 | 0.13 | 4 | 0.41 | 0.00 | 1 | 0.16 | 0.04 | 2 | 0.41 | 0.07 | 8 | 0.30 | 0.16 | 19 | 0.20 | 0.13 | 6
22386 | 0.62 | 0.13 | 4 | 0.51 | 0.00 | 1 | 0.28 | 0.01 | 2 | 0.41 | 0.09 | 8 | 0.33 | 0.17 | 18 | 0.23 | 0.09 | 6
28653 | 0.26 | 0.12 | 4 | 0.41 | 0.00 | 1 | 0.12 | 0.05 | 2 | 0.37 | 0.07 | 7 | 0.26 | 0.13 | 20 | 0.24 | 0.15 | 6
41968 | 0.36 | 0.06 | 4 | 0.41 | 0.00 | 1 | 0.15 | 0.02 | 2 | 0.38 | 0.10 | 8 | 0.24 | 0.13 | 18 | 0.22 | 0.11 | 6
61006 | 0.20 | 0.05 | 4 | 0.28 | 0.00 | 1 | 0.07 | 0.06 | 2 | 0.39 | 0.10 | 6 | 0.22 | 0.12 | 16 | 0.26 | 0.21 | 5
73063 | 0.50 | 0.05 | 4 | 0.37 | 0.00 | 1 | 0.23 | 0.10 | 2 | 0.35 | 0.09 | 7 | 0.25 | 0.17 | 19 | 0.30 | 0.13 | 6
84553 | 0.47 | 0.14 | 3 | 0.40 | 0.00 | 1 | 0.21 | 0.07 | 2 | 0.39 | 0.09 | 7 | 0.30 | 0.09 | 10 | 0.12 | 0.13 | 6
10619 | 0.29 | 0.12 | 4 | 0.51 | 0.00 | 1 | 0.24 | 0.08 | 2 | 0.45 | 0.04 | 8 | 0.28 | 0.16 | 17 | 0.22 | 0.11 | 6
112499 | 0.20 | 0.04 | 4 | 0.35 | 0.00 | 1 | 0.10 | 0.04 | 2 | 0.38 | 0.06 | 6 | 0.23 | 0.12 | 16 | 0.26 | 0.15 | 6
143175 | 0.20 | 0.11 | 4 | 0.38 | 0.00 | 1 | 0.11 | 0.05 | 2 | 0.39 | 0.06 | 8 | 0.26 | 0.15 | 18 | 0.28 | 0.12 | 6
22746 | 0.30 | 0.14 | 4 | 0.47 | 0.00 | 1 | 0.20 | 0.06 | 2 | 0.45 | 0.04 | 8 | 0.28 | 0.17 | 19 | 0.22 | 0.11 | 6
70896 | 0.27 | 0.09 | 4 | 0.45 | 0.00 | 1 | 0.14 | 0.02 | 2 | 0.43 | 0.02 | 7 | 0.31 | 0.15 | 17 | 0.22 | 0.12 | 6
83377 | 0.25 | 0.12 | 4 | 0.46 | 0.00 | 1 | 0.16 | 0.04 | 2 | 0.37 | 0.03 | 7 | 0.28 | 0.14 | 19 | 0.22 | 0.12 | 6
86528 | 0.19 | 0.07 | 4 | 0.34 | 0.00 | 1 | 0.18 | 0.05 | 2 | 0.39 | 0.07 | 8 | 0.27 | 0.19 | 16 | 0.28 | 0.13 | 6
90842 | 0.18 | 0.06 | 4 | 0.40 | 0.00 | 1 | 0.12 | 0.03 | 2 | 0.37 | 0.17 | 7 | 0.30 | 0.17 | 18 | 0.28 | 0.18 | 5
146316 | 0.18 | 0.06 | 4 | 0.16 | 0.20 | 2 | 0.06 | 0.12 | 2 | 0.28 | 0.21 | 7 | 0.26 | 0.15 | 18 | 0.30 | 0.08 | 5
15613 | 0.38 | 0.10 | 4 | 0.48 | 0.00 | 1 | 0.18 | 0.04 | 2 | 0.46 | 0.07 | 8 | 0.29 | 0.15 | 17 | 0.22 | 0.12 | 6
69465 | 0.28 | 0.08 | 4 | 0.39 | 0.00 | 1 | 0.14 | 0.02 | 2 | 0.46 | 0.08 | 7 | 0.30 | 0.16 | 19 | 0.24 | 0.14 | 6
86281 | 0.38 | 0.11 | 4 | 0.46 | 0.00 | 1 | 0.18 | 0.07 | 2 | 0.49 | 0.05 | 7 | 0.28 | 0.16 | 18 | 0.26 | 0.11 | 6
91298 | 0.56 | 0.04 | 4 | 0.31 | 0.00 | 1 | 0.19 | 0.12 | 2 | 0.42 | 0.07 | 7 | 0.27 | 0.15 | 15 | 0.31 | 0.15 | 6
9946 | 0.17 | 0.12 | 4 | 0.37 | 0.00 | 1 | 0.14 | 0.03 | 2 | 0.32 | 0.06 | 8 | 0.26 | 0.12 | 18 | 0.25 | 0.08 | 6
100719 | 0.30 | 0.08 | 4 | 0.37 | 0.00 | 1 | 0.15 | 0.05 | 2 | 0.39 | 0.11 | 8 | 0.34 | 0.17 | 16 | 0.15 | 0.15 | 6
$<$[X/Fe]$>_{\rm 1P}$ | 0.26 |  |  | 0.38 |  |  | 0.16 |  |  | 0.40 |  |  | 0.28 |  |  | 0.23 |  |
$\pm$ | 0.02 |  |  | 0.02 |  |  | 0.02 |  |  | 0.01 |  |  | 0.01 |  |  | 0.01 |  |
$\sigma$ | 0.08 |  |  | 0.09 |  |  | 0.08 |  |  | 0.05 |  |  | 0.04 |  |  | 0.04 |  |
$<$[X/Fe]$>_{\rm 2P}$ | 0.57 |  |  | 0.40 |  |  | 0.27 |  |  | 0.41 |  |  | 0.29 |  |  | 0.24 |  |
$\pm$ | 0.06 |  |  | 0.03 |  |  | 0.05 |  |  | 0.02 |  |  | 0.01 |  |  | 0.03 |  |
$\sigma$ | 0.13 |  |  | 0.07 |  |  | 0.11 |  |  | 0.05 |  |  | 0.04 |  |  | 0.06 |  |

Table 4: Analyzed Chemical Abundances from Ti to Ni. Average values for 1P and 2P stars are given for each element at the bottom of the table. STAR | [Ti/Fe]i | $\sigma$ | # | [Ti/Fe]ii | $\sigma$ | # | [V/Fe] | $\sigma$ | # | [Cr/Fe]i | $\sigma$ | # | [Cr/Fe]ii | $\sigma$ | # | [Mn/Fe] | $\sigma$ | # | [Co/Fe] | $\sigma$ | # | [Ni/Fe] | $\sigma$ | #
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---
8672 | 0.35 | 0.23 | 14 | 0.30 | 0.20 | 3 | 0.22 | 0.16 | 11 |  $-$0.31 | 0.07 | 4 |  $-$0.15 | 0.24 | 2 |  $-$0.55 | 0.17 | 5 |  $-$0.18 | 0.06 | 2 | 0.13 | 0.23 | 24
116624 | 0.33 | 0.15 | 21 | 0.25 | 0.06 | 4 | 0.34 | 0.13 | 12 |  $-$0.15 | 0.10 | 4 |  $+$0.05 | 0.01 | 2 |  $-$0.26 | 0.02 | 5 |  $+$0.07 | 0.10 | 2 | 0.10 | 0.16 | 22
11746 | 0.33 | 0.10 | 23 | 0.31 | 0.05 | 4 | 0.33 | 0.21 | 14 |  $-$0.10 | 0.06 | 4 |  $+$0.20 | 0.05 | 2 |  $-$0.23 | 0.04 | 5 |  $+$0.08 | 0.12 | 2 | 0.11 | 0.15 | 24
44780 | 0.33 | 0.14 | 23 | 0.38 | 0.07 | 6 | 0.45 | 0.25 | 16 |  $-$0.07 | 0.06 | 5 |  $+$0.10 | 0.07 | 2 |  $-$0.24 | 0.02 | 5 |  $+$0.10 | 0.14 | 2 | 0.11 | 0.14 | 27
68444 | 0.31 | 0.10 | 22 | 0.34 | 0.07 | 4 | 0.25 | 0.12 | 13 |  $-$0.10 | 0.13 | 4 |  $+$0.08 | 0.07 | 2 |  $-$0.31 | 0.05 | 5 |  $-$0.04 | 0.10 | 2 | 0.10 | 0.13 | 25
71504 | 0.31 | 0.11 | 22 | 0.28 | 0.06 | 4 | 0.26 | 0.14 | 13 |  $-$0.06 | 0.10 | 4 |  $+$0.01 | 0.05 | 2 |  $-$0.33 | 0.04 | 5 |  $-$0.01 | 0.11 | 2 | 0.10 | 0.15 | 25
92267 | 0.33 | 0.14 | 23 | 0.29 | 0.09 | 4 | 0.39 | 0.22 | 14 |  $-$0.12 | 0.10 | 4 |  $+$0.05 | 0.03 | 2 |  $-$0.31 | 0.03 | 5 |  $+$0.05 | 0.17 | 2 | 0.11 | 0.15 | 24
115804 | 0.30 | 0.11 | 22 | 0.27 | 0.03 | 4 | 0.30 | 0.22 | 13 |  $-$0.10 | 0.12 | 4 |  $+$0.06 | 0.01 | 2 |  $-$0.32 | 0.03 | 5 |  $+$0.06 | 0.13 | 2 | 0.08 | 0.14 | 25
22386 | 0.35 | 0.12 | 21 | 0.27 | 0.09 | 4 | 0.46 | 0.21 | 13 |  $-$0.06 | 0.10 | 4 |  $+$0.05 | 0.28 | 2 |  $-$0.27 | 0.04 | 5 |  $+$0.12 | 0.20 | 2 | 0.06 | 0.15 | 23
28653 | 0.31 | 0.14 | 23 | 0.31 | 0.04 | 4 | 0.26 | 0.15 | 14 |  $-$0.04 | 0.10 | 3 |  $+$0.09 | 0.15 | 2 |  $-$0.27 | 0.03 | 5 |  $+$0.08 | 0.06 | 2 | 0.11 | 0.12 | 23
41968 | 0.35 | 0.11 | 23 | 0.28 | 0.08 | 4 | 0.31 | 0.16 | 13 |  $-$0.06 | 0.11 | 4 |  $+$0.07 | 0.02 | 2 |  $-$0.29 | 0.03 | 5 |  $+$0.07 | 0.15 | 2 | 0.09 | 0.14 | 23
61006 | 0.30 | 0.13 | 20 | 0.30 | 0.14 | 4 | 0.22 | 0.14 | 13 |  $-$0.07 | 0.20 | 4 |  $+$0.17 | 0.15 | 2 |  $-$0.38 | 0.08 | 5 |  $+$0.15 | 0.06 | 2 | 0.08 | 0.14 | 23
73063 | 0.33 | 0.12 | 22 | 0.34 | 0.03 | 4 | 0.38 | 0.25 | 12 |  $-$0.13 | 0.19 | 4 |  $+$0.14 | 0.18 | 2 |  $-$0.25 | 0.03 | 5 |  $+$0.08 | 0.07 | 2 | 0.13 | 0.13 | 23
84553 | 0.44 | 0.17 | 9 | 0.31 | 0.04 | 3 | 0.61 | 0.44 | 5 |  $+$0.16 | 0.18 | 3 | – | – | 0 |  $-$0.32 | 0.10 | 5 |  $+$0.16 | 0.08 | 2 | 0.09 | 0.16 | 20
10619 | 0.36 | 0.10 | 19 | 0.29 | 0.03 | 3 | 0.39 | 0.26 | 14 |  $-$0.13 | 0.06 | 4 |  $+$0.12 | 0.05 | 2 |  $-$0.23 | 0.02 | 5 |  $+$0.15 | 0.13 | 2 | 0.10 | 0.12 | 25
112499 | 0.31 | 0.07 | 20 | 0.41 | 0.19 | 3 | 0.26 | 0.15 | 13 |  $-$0.02 | 0.11 | 4 |  $+$0.02 | 0.02 | 2 |  $-$0.35 | 0.05 | 5 |  $-$0.02 | 0.08 | 2 | 0.13 | 0.17 | 25
143175 | 0.29 | 0.10 | 23 | 0.35 | 0.05 | 4 | 0.23 | 0.14 | 13 |  $-$0.11 | 0.10 | 4 |  $+$0.10 | 0.06 | 2 |  $-$0.28 | 0.04 | 5 |  $+$0.03 | 0.11 | 2 | 0.11 | 0.12 | 25
22746 | 0.35 | 0.13 | 22 | 0.30 | 0.04 | 4 | 0.46 | 0.26 | 12 |  $-$0.10 | 0.08 | 4 |  $+$0.13 | 0.09 | 2 |  $-$0.18 | 0.05 | 5 |  $+$0.19 | 0.21 | 2 | 0.11 | 0.13 | 25
70896 | 0.34 | 0.14 | 19 | 0.28 | 0.09 | 3 | 0.40 | 0.23 | 13 |  $-$0.12 | 0.09 | 4 |  $+$0.07 | 0.08 | 2 |  $-$0.34 | 0.07 | 5 |  $+$0.19 | 0.19 | 2 | 0.12 | 0.14 | 25
83377 | 0.31 | 0.10 | 23 | 0.26 | 0.02 | 4 | 0.25 | 0.14 | 13 |  $-$0.04 | 0.10 | 4 |  $+$0.12 | 0.14 | 2 |  $-$0.25 | 0.03 | 5 |  $+$0.05 | 0.13 | 2 | 0.09 | 0.13 | 25
86528 | 0.31 | 0.12 | 18 | 0.34 | 0.17 | 2 | 0.22 | 0.17 | 12 |  $-$0.16 | 0.15 | 3 |  $-$0.06 | 0.01 | 2 |  $-$0.27 | 0.05 | 5 |  $+$0.07 | 0.07 | 2 | 0.14 | 0.17 | 24
90842 | 0.28 | 0.11 | 22 | 0.30 | 0.06 | 4 | 0.24 | 0.17 | 12 |  $-$0.11 | 0.14 | 4 |  $+$0.05 | 0.02 | 2 |  $-$0.31 | 0.04 | 5 |  $+$0.09 | 0.14 | 2 | 0.11 | 0.18 | 25
146316 | 0.29 | 0.16 | 23 | 0.30 | 0.04 | 3 | 0.28 | 0.17 | 15 |  $-$0.10 | 0.22 | 4 |  $+$0.22 | 0.26 | 2 |  $-$0.28 | 0.05 | 5 |  $+$0.15 | 0.21 | 2 | 0.14 | 0.16 | 23
15613 | 0.36 | 0.09 | 21 | 0.33 | 0.07 | 4 | 0.35 | 0.19 | 13 |  $-$0.10 | 0.08 | 3 |  $+$0.10 | 0.05 | 2 |  $-$0.21 | 0.05 | 5 |  $+$0.09 | 0.10 | 2 | 0.10 | 0.13 | 24
69465 | 0.28 | 0.10 | 23 | 0.37 | 0.08 | 4 | 0.27 | 0.18 | 13 |  $-$0.12 | 0.09 | 4 |  $+$0.05 | 0.07 | 2 |  $-$0.30 | 0.02 | 5 |  $+$0.05 | 0.11 | 2 | 0.11 | 0.15 | 25
86281 | 0.35 | 0.11 | 20 | 0.33 | 0.04 | 3 | 0.41 | 0.25 | 11 |  $-$0.09 | 0.06 | 4 |  $+$0.10 | 0.11 | 2 |  $-$0.21 | 0.03 | 5 |  $+$0.14 | 0.16 | 2 | 0.14 | 0.16 | 23
91298 | 0.35 | 0.12 | 23 | 0.35 | 0.10 | 4 | 0.30 | 0.14 | 13 |  $-$0.10 | 0.08 | 4 |  $+$0.16 | 0.02 | 2 |  $-$0.25 | 0.04 | 5 |  $+$0.10 | 0.10 | 2 | 0.14 | 0.14 | 24
9946 | 0.33 | 0.15 | 23 | 0.28 | 0.06 | 4 | 0.27 | 0.20 | 13 |  $+$0.02 | 0.11 | 3 |  $+$0.11 | 0.08 | 2 |  $-$0.25 | 0.01 | 5 |  $+$0.09 | 0.05 | 2 | 0.10 | 0.13 | 24
100719 | 0.32 | 0.15 | 22 | 0.26 | 0.05 | 3 | 0.28 | 0.12 | 13 |  $-$0.10 | 0.08 | 4 |  $-$0.03 | 0.02 | 2 |  $-$0.38 | 0.09 | 5 |  $+$0.01 | 0.07 | 2 | 0.10 | 0.13 | 26
$<$[X/Fe]$>_{\rm 1P}$ | 0.32 |  |  | 0.31 |  |  | 0.30 |  |  |  $-$0.10 |  |  | 0.08 |  |  |  $-$0.29 |  |  | 0.07 |  |  | 0.11 |  |
$\pm$ | 0.01 |  |  | 0.01 |  |  | 0.02 |  |  | 0.01 |  |  | 0.02 |  |  | 0.02 |  |  | 0.02 |  |  | 0.00 |  |
$\sigma$ | 0.02 |  |  | 0.04 |  |  | 0.08 |  |  | 0.06 |  |  | 0.08 |  |  | 0.08 |  |  | 0.08 |  |  | 0.02 |  |
$<$[X/Fe]$>_{\rm 2P}$ | 0.35 |  |  | 0.30 |  |  | 0.40 |  |  |  $-$0.07 |  |  | 0.09 |  |  |  $-$0.28 |  |  | 0.09 |  |  | 0.10 |  |
$\pm$ | 0.02 |  |  | 0.01 |  |  | 0.04 |  |  | 0.04 |  |  | 0.02 |  |  | 0.01 |  |  | 0.02 |  |  | 0.01 |  |
$\sigma$ | 0.04 |  |  | 0.04 |  |  | 0.11 |  |  | 0.11 |  |  | 0.05 |  |  | 0.03 |  |  | 0.04 |  |  | 0.03 |  |

Table 5: Analyzed Chemical Abundances from Cu to Eu. Average values for 1P and 2P stars are given for each element at the bottom of the table. STAR | [Cu/Fe] | [Zn/Fe] | $\sigma$ | # | [Y/Fe] | $\sigma$ | # | [Zr/Fe] | [Ba/Fe] | $\sigma$ | # | [La/Fe] | $\sigma$ | # | [Pr/Fe] | [Nd/Fe] | $\sigma$ | # | [Eu/Fe]
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---
8672 |  $-$0.63 |  $+$0.03 | 0.00 | 1 |  $-$0.14 | 0.26 | 2 | 0.20 |  $+$0.40 | 0.04 | 2 | 0.17 | 0.19 | 7 | 0.22 | 0.18 | – | 1 | 0.40
116624 |  $-$0.05 | – | – | 0 |  $+$0.15 | 0.27 | 3 | 0.33 |  $+$0.33 | 0.05 | 2 | 0.16 | 0.18 | 9 | 0.12 | 0.30 | 0.15 | 2 | 0.46
11746 |  $-$0.06 |  $+$0.09 | 0.00 | 1 |  $+$0.09 | 0.11 | 3 | 0.19 |  $+$0.22 | 0.13 | 2 | 0.19 | 0.13 | 9 | 0.29 | 0.30 | 0.16 | 2 | 0.50
44780 |  $-$0.09 |  $+$0.28 | 0.01 | 2 |  $+$0.06 | 0.26 | 3 | 0.25 |  $+$0.24 | 0.05 | 2 | 0.21 | 0.18 | 9 | 0.27 | 0.38 | 0.15 | 2 | 0.54
68444 |  $-$0.35 |  $+$0.12 | 0.00 | 1 |  $+$0.04 | 0.15 | 3 | 0.22 |  $+$0.31 | 0.01 | 2 | 0.29 | 0.14 | 7 | 0.30 | 0.33 | 0.20 | 2 | 0.62
71504 |  $-$0.26 |  $+$0.22 | 0.00 | 1 |  $+$0.06 | 0.18 | 3 | 0.30 |  $+$0.34 | 0.02 | 2 | 0.33 | 0.17 | 8 | 0.33 | 0.41 | 0.16 | 2 | 0.56
92267 |  $-$0.22 |  $+$0.14 | 0.00 | 1 |  $+$0.05 | 0.18 | 3 | 0.18 |  $+$0.16 | 0.03 | 2 | 0.17 | 0.16 | 9 | 0.23 | 0.36 | 0.13 | 2 | 0.44
115804 |  $-$0.10 | – | – | 0 |  $+$0.14 | 0.24 | 3 | 0.20 |  $+$0.23 | 0.05 | 2 | 0.23 | 0.12 | 9 | 0.15 | 0.47 | – | 1 | 0.48
22386 |  $+$0.00 |  $+$0.15 | 0.00 | 1 |  $+$0.16 | 0.31 | 3 | 0.32 |  $+$0.30 | 0.08 | 2 | 0.34 | 0.06 | 8 | 0.34 | 0.51 | – | 1 | 0.55
28653 |  $-$0.23 |  $+$0.20 | 0.00 | 1 |  $+$0.09 | 0.14 | 3 | 0.23 |  $+$0.32 | 0.11 | 2 | 0.31 | 0.10 | 8 | 0.35 | 0.42 | 0.03 | 2 | 0.65
41968 |  $+$0.13 |  $+$0.25 | 0.00 | 1 |  $+$0.15 | 0.31 | 3 | 0.40 |  $+$0.15 | 0.21 | 2 | 0.30 | 0.09 | 8 | 0.38 | 0.53 | 0.14 | 2 | 0.60
61006 |  $-$0.43 |  $+$0.24 | 0.00 | 1 |  $+$0.09 | 0.13 | 3 | 0.32 |  $+$0.24 | 0.19 | 2 | 0.44 | 0.07 | 4 | 0.35 | 0.53 | 0.00 | 2 | 9999
73063 |  $-$0.05 |  $+$0.31 | 0.00 | 1 |  $+$0.19 | 0.15 | 3 | 0.26 |  $+$0.28 | 0.13 | 2 | 0.27 | 0.14 | 6 | 0.30 | 0.45 | 0.05 | 2 | 0.50
84553 |  $-$0.31 |  $-$0.09 | 0.00 | 1 |  $+$0.40 | 0.24 | 3 | 0.24 |  $+$0.23 | 0.54 | 2 | 0.41 | 0.38 | 5 | 0.33 | 0.22 | – | 1 | 9999
10619 |  $-$0.01 |  $+$0.13 | 0.00 | 1 |  $+$0.04 | 0.24 | 3 | 0.23 |  $+$0.16 | 0.02 | 2 | 0.19 | 0.20 | 9 | 0.27 | 0.50 | – | 1 | 0.56
112499 |  $-$0.36 |  $+$0.23 | 0.00 | 1 |  $+$0.06 | 0.25 | 3 | 0.22 |  $+$0.30 | 0.13 | 2 | 0.24 | 0.15 | 8 | 0.28 | 0.35 | 0.18 | 2 | 0.58
143175 |  $+$0.03 | – | – | 0 |  $+$0.17 | 0.11 | 3 | 0.20 |  $+$0.31 | 0.18 | 2 | 0.30 | 0.18 | 8 | 0.37 | 0.33 | 0.18 | 2 | 0.59
22746 |  $+$0.02 | – | – | 0 |  $+$0.09 | 0.23 | 3 | 0.21 |  $+$0.16 | 0.00 | 2 | 0.24 | 0.18 | 9 | 0.26 | 0.62 | – | 1 | 0.53
70896 |  $-$0.42 |  $+$0.02 | 0.00 | 1 |  $-$0.09 | 0.29 | 2 | 0.20 |  $-$0.05 | 0.05 | 2 | 0.16 | 0.16 | 9 | 0.25 | 0.39 | 0.17 | 2 | 0.54
83377 |  $-$0.11 |  $+$0.06 | 0.00 | 1 |  $+$0.04 | 0.17 | 3 | 0.19 |  $+$0.23 | 0.10 | 2 | 0.24 | 0.14 | 9 | 0.20 | 0.35 | 0.20 | 2 | 0.65
86528 |  $-$0.50 |  $-$0.21 | 0.00 | 1 |  $-$0.04 | 0.09 | 3 | 0.35 |  $+$0.38 | 0.10 | 2 | 0.31 | 0.17 | 7 | 0.32 | 0.23 | 0.02 | 2 | 0.68
90842 |  $-$0.29 |  $-$0.05 | 0.00 | 1 |  $+$0.05 | 0.13 | 3 | 0.23 |  $+$0.24 | 0.16 | 2 | 0.22 | 0.09 | 9 | 0.26 | 0.44 | 0.18 | 2 | 0.63
146316 |  $-$0.30 |  $+$0.01 | 0.00 | 1 |  $+$0.10 | 0.18 | 3 | 0.30 |  $+$0.28 | 0.28 | 2 | 0.35 | 0.12 | 6 | 0.34 | 0.46 | 0.12 | 2 | 9999
15613 |  $-$0.04 |  $+$0.17 | 0.00 | 1 |  $+$0.05 | 0.18 | 3 | 0.20 |  $+$0.16 | 0.06 | 2 | 0.22 | 0.20 | 9 | 0.29 | 0.32 | 0.18 | 2 | 0.55
69465 |  $-$0.42 |  $+$0.21 | 0.00 | 1 |  $+$0.01 | 0.21 | 3 | 0.19 |  $+$0.27 | 0.07 | 2 | 0.15 | 0.14 | 9 | 0.15 | 0.35 | 0.14 | 2 | 0.51
86281 |  $-$0.21 |  $+$0.07 | 0.00 | 1 |  $+$0.06 | 0.33 | 3 | 0.21 |  $+$0.17 | 0.01 | 2 | 0.20 | 0.16 | 9 | 0.28 | 0.41 | 0.16 | 2 | 0.55
91298 |  $-$0.20 |  $+$0.07 | 0.00 | 1 |  $+$0.24 | 0.11 | 3 | 0.30 |  $+$0.37 | 0.03 | 2 | 0.39 | 0.10 | 7 | 0.42 | 0.53 | 0.22 | 2 | 0.60
9946 |  $+$0.00 |  $+$0.29 | 0.00 | 1 |  $+$0.16 | 0.14 | 3 | 0.17 |  $+$0.32 | 0.12 | 2 | 0.28 | 0.11 | 7 | 0.30 | 0.48 | – | 1 | 0.62
100719 |  $-$0.70 |  $-$0.05 | 0.00 | 1 |  $+$0.01 | 0.16 | 3 | 0.18 |  $+$0.14 | 0.07 | 2 | 0.23 | 0.13 | 9 | 0.19 | 0.25 | 0.08 | 2 | 0.59
$<$[X/Fe]$>_{\rm 1P}$ |  $-$0.25 | 0.11 |  |  | 0.05 |  |  | 0.23 | 0.24 |  |  | 0.25 |  |  | 0.27 | 0.39 |  |  | 0.57
$\pm$ | 0.05 | 0.03 |  |  | 0.02 |  |  | 0.01 | 0.02 |  |  | 0.02 |  |  | 0.01 | 0.02 |  |  | 0.02
$\sigma$ | 0.21 | 0.13 |  |  | 0.07 |  |  | 0.05 | 0.10 |  |  | 0.07 |  |  | 0.06 | 0.10 |  |  | 0.07
$<$[X/Fe]$>_{\rm 2P}$ |  $-$0.10 | 0.14 |  |  | 0.19 |  |  | 0.29 | 0.26 |  |  | 0.29 |  |  | 0.30 | 0.41 |  |  | 0.53
$\pm$ | 0.06 | 0.06 |  |  | 0.04 |  |  | 0.03 | 0.03 |  |  | 0.04 |  |  | 0.04 | 0.05 |  |  | 0.03
$\sigma$ | 0.15 | 0.14 |  |  | 0.11 |  |  | 0.07 | 0.08 |  |  | 0.10 |  |  | 0.10 | 0.12 |  |  | 0.07

The inferred chemical abundances are listed in Tables 3-4-5. Internal
uncertainties to these abundances introduced by errors in the atmospheric
parameters were estimated by varying the stellar parameters, one at a time, by
Teff/log g/[A/H]/$\xi_{\rm t}$=$\pm$50 K/$\pm$0.20 cgs/$\pm$0.10 dex/$\pm$0.20
km s-1. The contribution due to the limits of our spectra, e.g. the finite S/N
that affects the measurements of EWs and the spectral synthesis ($\sigma_{\rm
S/N}$), was estimated as the average rms listed in Tables 3-4-5 divided by the
square root of the typical number of the analysed spectral features. For those
elements with only one line available, a larger error of 0.15 dex has been
adopted. Our error budget is listed in Table 6. The total uncertainty
$\sigma_{\rm total}$ is the quadratic sum of the errors introduced by the
individual contributions.

Table 6: Sensitivity of the derived abundances to the uncertainties in atmospheric parameters and uncertainties due to the limited S/N of our spectra. We reported the total internal uncertainty ($\sigma_{\rm total}$) associated to individual stars obtained by the quadratic sum of all the contributors to the error. |  $\Delta$Teff |  $\Delta$log g |  $\Delta$$\xi_{\rm t}$ |  $\Delta$[A/H] |  $\Delta$Teff | $\sigma_{\rm S/N}$ | $\sigma_{\rm total}$
---|---|---|---|---|---|---|---
|  $\pm$100 K |  $\pm$0.20 |  $\pm$0.20 km s-1 |  $\pm$0.10 dex |  $\pm$50 K |  |
$\rm{[Na/Fe]}$ |  $\pm$0.01 |  $\mp$0.03 |  $\pm$0.05 |  $\mp$0.01 |  $\pm$0.01 |  $\pm$0.05 |  $\pm$0.08
$\rm{[Mg/Fe]}$ |  $\mp$0.01 |  $\mp$0.03 |  $\pm$0.01 |  $\mp$0.01 |  $\mp$0.00 |  $\pm$0.15 |  $\pm$0.15
$\rm{[Al/Fe]}$ |  $\pm$0.06 |  $\mp$0.00 |  $\mp$0.01 |  $\mp$0.01 |  $\pm$0.03 |  $\pm$0.04 |  $\pm$0.05
$\rm{[Si/Fe]}$ |  $\mp$0.10 |  $\pm$0.03 |  $\pm$0.07 |  $\pm$0.01 |  $\mp$0.05 |  $\pm$0.03 |  $\pm$0.10
$\rm{[Ca/Fe]}$ |  $\pm$0.03 |  $\mp$0.04 |  $\mp$0.00 |  $\mp$0.01 |  $\pm$0.02 |  $\pm$0.04 |  $\pm$0.06
$\rm{[Sc/Fe]}$ ii |  $\pm$0.07 |  $\mp$0.01 |  $\mp$0.00 |  $\mp$0.01 |  $\pm$0.04 |  $\pm$0.06 |  $\pm$0.07
$\rm{[Ti/Fe]}$ i |  $\pm$0.08 |  $\mp$0.02 |  $\pm$0.01 |  $\mp$0.02 |  $\pm$0.04 |  $\pm$0.03 |  $\pm$0.06
$\rm{[Ti/Fe]}$ ii |  $\pm$0.05 |  $\mp$0.02 |  $\mp$0.01 |  $\mp$0.01 |  $\pm$0.03 |  $\pm$0.04 |  $\pm$0.06
$\rm{[V/Fe]}$ |  $\pm$0.09 |  $\mp$0.01 |  $\pm$0.00 |  $\mp$0.02 |  $\pm$0.05 |  $\pm$0.06 |  $\pm$0.08
$\rm{[Cr/Fe]}$ i |  $\pm$0.06 |  $\mp$0.02 |  $\mp$0.01 |  $\mp$0.01 |  $\pm$0.03 |  $\pm$0.06 |  $\pm$0.07
$\rm{[Cr/Fe]}$ ii |  $\pm$0.02 |  $\mp$0.01 |  $\pm$0.02 |  $\mp$0.01 |  $\pm$0.01 |  $\pm$0.06 |  $\pm$0.07
$\rm{[Mn/Fe]}$ |  $\pm$0.10 |  $\pm$0.02 |  $\mp$0.02 |  $\mp$0.01 |  $\pm$0.05 |  $\pm$0.02 |  $\pm$0.06
$\rm{[Fe/H]}$ i |  $\pm$0.07 |  $\pm$0.01 |  $\mp$0.09 |  $\pm$0.01 |  $\pm$0.03 |  $\pm$0.01 |  $\pm$0.10
$\rm{[Fe/H]}$ ii |  $\mp$0.09 |  $\pm$0.10 |  $\mp$0.05 |  $\pm$0.03 |  $\mp$0.05 |  $\pm$0.03 |  $\pm$0.13
$\rm{[Co/Fe]}$ |  $\mp$0.00 |  $\pm$0.02 |  $\pm$0.05 |  $\pm$0.00 |  $\pm$0.00 |  $\pm$0.08 |  $\pm$0.10
$\rm{[Ni/Fe]}$ |  $\mp$0.03 |  $\pm$0.03 |  $\pm$0.03 |  $\pm$0.01 |  $\mp$0.01 |  $\pm$0.03 |  $\pm$0.05
$\rm{[Cu/Fe]}$ |  $\pm$0.11 |  $\mp$0.00 |  $\mp$0.09 |  $\mp$0.03 |  $\pm$0.07 |  $\pm$0.15 |  $\pm$0.19
$\rm{[Zn/Fe]}$ |  $\mp$0.12 |  $\pm$0.04 |  $\mp$0.02 |  $\pm$0.02 |  $\mp$0.06 |  $\pm$0.15 |  $\pm$0.17
$\rm{[Y/Fe]}$ ii |  $\pm$0.08 |  $\mp$0.02 |  $\mp$0.04 |  $\mp$0.01 |  $\pm$0.04 |  $\pm$0.14 |  $\pm$0.15
$\rm{[Zr/Fe]}$ ii |  $\pm$0.03 |  $\pm$0.07 |  $\mp$0.02 |  $\pm$0.02 |  $\pm$0.02 |  $\pm$0.15 |  $\pm$0.17
$\rm{[Ba/Fe]}$ ii |  $\pm$0.01 |  $\pm$0.06 |  $\mp$0.16 |  $\pm$0.03 |  $\pm$0.00 |  $\pm$0.07 |  $\pm$0.19
$\rm{[La/Fe]}$ ii |  $\pm$0.03 |  $\pm$0.07 |  $\mp$0.02 |  $\pm$0.01 |  $\pm$0.01 |  $\pm$0.06 |  $\pm$0.10
$\rm{[Pr/Fe]}$ ii |  $\pm$0.00 |  $\pm$0.08 |  $\mp$0.01 |  $\pm$0.03 |  $\mp$0.00 |  $\pm$0.15 |  $\pm$0.17
$\rm{[Nd/Fe]}$ ii |  $\pm$0.12 |  $\mp$0.02 |  $\mp$0.02 |  $\mp$0.00 |  $\pm$0.06 |  $\pm$0.14 |  $\pm$0.15
$\rm{[Eu/Fe]}$ ii |  $\mp$0.01 |  $\pm$0.08 |  $\pm$0.00 |  $\pm$0.04 |  $\mp$0.01 |  $\pm$0.15 |  $\pm$0.17
Figure 3: Location of our spectroscopic targets along the ChM of 47 Tucanae from Milone et al. (2017). The color of each star is indicative of the inferred chemical abundances, as illustrated in the color bar. In these two plots we illustrate the chemical pattern of Na and Al abundances relative to Fe. Figure 4: As Figure 3, but for [Fe/H].  Figure 5: Chemical abundances ${\rm log}\epsilon$(X) as a function of $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ and $\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ values on the ChM of 47 Tucanae. The color code is indicative of the Spearman correlation coefficient ($r$). The coefficients and their associated significance are listed in Table 7.  Figure 6: From top to bottom, [Fe/H] and absolute chemical abundances for all the $\alpha$ and the $s$ elements as a function of $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values on the ChM of 47 Tucanae. Left and right panels represent 1P and 2P stars, respectively. The dashed line on the left panel at $\Delta_{\tiny{\mathrm{F275W,F814W}}}$=$-$0.10 separates the two groups of $\rm{1P_{a}}$ and $\rm{1P_{b}}$ stars (see text for details). The plotted error bars represent the dispersion of the values in each group divided by the square root of the number of stars. Symbols are as in Figure 1. Table 7: Spearman correlation coefficient ($r$), and associated significance, between chemical abundances log$\epsilon$(X) and the ChM $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values. Lower % reflects a more important correlation. Element | $r$ | Significance (%)
---|---|---
Fe | 0.62 | 1.0
Na | 0.47 | 1.7
Mg | 0.77 | 0.8
Al | 0.48 | 5.0
Si | 0.73 | 0.0
Ca | 0.58 | 4.8
Sc ii | 0.60 | 0.2
Ti i | 0.66 | 3.4
Ti ii | 0.44 | 6.2
V | 0.55 | 1.2
Cr i | 0.43 | 4.7
Cr ii | 0.49 | 0.3
Mn | 0.71 | 0.1
Co | 0.73 | 0.0
Ni | 0.62 | 0.1
Cu | 0.50 | 1.5
Zn | 0.17 | 26.9
Y ii | 0.29 | 19.0
Zr ii | 0.52 | 17.2
Ba ii | 0.15 | 35.9
La ii | 0.31 | 20.0
Pr ii | 0.46 | 17.1
Nd ii | 0.60 | 0.2
Eu ii | 0.62 | 12.2

##  4 Chemical abundances along the ChM of 47 Tucanae

Overall, for our 29 stars we obtain a mean iron abundance of
[Fe/H]=$-$0.78$\pm$0.02 dex (rms=0.08 dex), consistent with the value of
[Fe/H]=$-$0.72 dex listed in Harris (2010). As typical of Population II stars,
47 Tucanae stars are $\alpha$ enhanced in all the analysed $\alpha$ elements,
namely Mg, Si, Ca, and Ti.

In this section we analyse the chemical abundance pattern along the ChM of 47
Tucanae. First, we discuss on the 1P/2P chemical differences, and then the
abundances internal to the 1P.

###  4.1 Light elements

As shown in Figure 1, the ChM of 47 Tucanae clearly displays a sharp
separation between 1P and 2P stars occurring at
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$$\sim$0.1. Although our sample
was not specifically designed to analyse 2P stars, it includes six giants
belonging to this stellar population. From the average chemical abundances
listed in Tables 3-4-5, larger differences are observed in the elements
involved in the hot-H burning processes, namely Na and Al, as expected for 2P
stars in GCs. The six 2P stars are significantly enhanced in sodium by
$\Delta$[Na/Fe]2P-1P=0.31$\pm$0.06 and mildly enhanced in aluminum by
$\Delta$[Al/Fe]2P-1P=0.11$\pm$0.05.

No obvious variations are observed in neither [Mg/Fe] or [Si/Fe], being the
observed dispersions similar to those expected from observational errors (see
Table 6). Small rms values in these chemical species have been also reported
in Carretta et al. (2009b).

For both Na and Al, the observed spread in each population is larger for the
2P stars, consistent with the large range in
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ of these stars (see Marino et
al., 2019a). Looking at the distribution of Na and Al along the ChM, as
displayed in Figure 3, the most Na rich star (#92267) is located on the ChM
region associated with the most Na (and He)-enriched (O-depleted) stars. Our
2P star with the lowest $\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ value
(#41968) is also the less abundant in Na among the analysed 2P stars.

The observed variations in Al are smaller than those in Na (right panel of
Figure 3). We notice that one star located on the redder-anomalous sequence on
the ChM, namely #116624, has the highest Al abundance in our sample
([Al/Fe]=0.47 dex). Star #8672, which we treat as a binary, has also a
relatively high Al.

Among 1P stars we do not find significant variations in the [Na/Fe] and
[Al/Fe] abundance ratios. This is similar to what was previously found among
1P stars in NGC 3201, and rules out the possibility that the range in
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ of the 1P stars is due to internal
variations in He (see Marino et al., 2019b). We notice here that the ground
level of [Na/Fe] abundances in 47 Tucanae is relatively high, being
$<$[Na/Fe]$>_{\rm 1P}$=0.26$\pm$0.02 dex (with similar values also found in
previous analysis, e.g., Carretta et al., 2009a).

###  4.2 Chemical abundances along the 1P population

In this section, we consider stars with
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ values lower than $+$0.133
mag, a sample that includes 23 1P stars. The average Fe abundance ratios for
these stars is [Fe/H]1P=$-$0.80$\pm$0.02 dex (rms=0.08). The distribution of
1P stars along the x axis of the ChM is consistent with two main over-
densities, separated at $\Delta_{\tiny{\mathrm{F275W,F814W}}}$$\sim-$0.1. By
dividing the sample into two groups we obtain [Fe/H]1P=$-$0.84$\pm$0.02 dex
(rms=0.08, 12 stars), and [Fe/H]1P=$-$0.76$\pm$0.02 dex (rms=0.05, 11 stars),
for stars with $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ lower (hereafter 1Pa)
and higher (hereafter 1Pb) than $-$0.1, respectively. Hence, the mean
difference we get is $\Delta$[Fe/H]=0.08$\pm$0.03 dex, an almost 3 $\sigma$
difference.

From Figure 4, we note that the distribution of iron abundances looks less
homogeneous in the stars with lower $\Delta_{\tiny{\mathrm{F275W,F814W}}}$
values, questioning the possible presence of two separated groups rather than
a continuous distribution. Indeed, $\rm{1P_{a}}$ stars have a significantly
larger dispersion in Fe than $\rm{1P_{b}}$ ones, suggesting that this group
could be more heterogeneous. If we consider only stars with
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$$<-$0.17 we obtain
[Fe/H]1P=$-$0.90$\pm$0.03 dex (rms=0.06, 5 stars), and the difference in Fe of
0.14 dex with the 1Pb stars, which is at a $>3~{}\sigma$ level.

The observed differences in iron are smaller than those typically inferred for
the blue- and red-RGB stars in most Type II GCs (see Marino et al., 2019a),
and may be more difficult to detect. Our relatively high-S/N and high-
resolution UVES spectra allow us to detect such difference.

Within our uncertainties, chemical abundances relative to Fe ([X/Fe]) for all
elements are generally consistent with homogeneous content. By comparing the
observed rms associated to the mean average abundances, as listed in Tables
3-4-5, with the estimated errors, it appears that in most cases our expected
uncertainties are higher. This suggests that our estimated errors might be
overestimated, in particular for the $n$-capture elements.

Figure 5 shows a representation of the Spearman correlation for all the
analysed log$\epsilon$(X) abundances as a function of the ChM
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ and
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ values, for the 1P stars. The
correlation coefficients $r$ are listed in Table 7. With each $r$ value we
have associated a significance, which we obtained from a Monte Carlo
simulation of 1000 realizations of our dataset composed of 23 stars. In each
realization we have assumed the observed
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ and a uniform Fe abundance with the
associated error estimates of Table 6, and derived the slope. We have
calculated the fraction of realizations where the slope is higher than the
observed one, and assumed this value as the probability that the slope is due
to randomness.

From the significance values % listed in Table 7, we note that not all
correlations are significant, in particular larger uncertainties are
associated with the neutron-capture elements. However, all the absolute
abundances appear to be positively correlated with the
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values. The negative correlation with
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ is a reflection of the mild
negative correlation between $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ and
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ values for 1P stars. The
general correlation between each log$\epsilon$(X) abundance and the
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values supports the presence of a small
spread in the overall metallicity among the 1P stars.

In Figure 2 we show a portion spectrum from two 1P stars with similar
atmospheric parameters, and Fe abundances of [Fe/H]=$-$0.76 and [Fe/H]=$-$0.88
dex. Overall, the spectral features of the star at higher
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$, namely #11746, are more consistent
with higher metallicity than the spectrum of star #112499.

As discussed in Marino et al. (2019b) for NGC 3201, also in 47 Tucanae we
exclude a variation in the He content intrinsic to the 1P stars as responsible
for the $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ spread, which should be as high
as 0.054$\pm$0.006s in mass fraction (Milone et al., 2018), without any
corresponding enhancement in other chemical species, such as Na or Al. Another
effect to be considered is that a change in Y will affect the metal-to-
hydrogen ratio, Z/X, since X + Y + Z = 1. Hence, at constant Z, a He-rich star
will appear to be slightly more metal-rich than a He-normal star. Noting that
a pure He enhancement shifts stars towards lower
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values along the ChM (Milone et al.,
2015; Marino et al., 2019a), the possibility that increased metallicities are
the result of He enhancements can be ruled out, as the stars that should be
enhanced in He (at lower $\Delta_{\tiny{\mathrm{F275W,F814W}}}$), are metal-
poorer.

Marino et al. (2019b) also discussed the possibility that the presence of
binaries among 1P stars can translate in spurious lower metallicity abundances
for stars with lower $\Delta_{\tiny{\mathrm{F275W,F814W}}}$. Most of our stars
for 47 Tucanae have been observed spanning over a relatively large range in
time to spot for possible variations in the RVs values indicative of binarity
(see last column of Table 1). As already mentioned in Section 2.2, only two
stars have significantly larger dispersions in their RVs, but we cannot
exclude the presence of close binaries in our sample with lower (undetectable)
variations in the RVs. However, we enphasize here that Marino et al. (2019b)
pointed out that significant effects in the emerging spectra are present for
giant-giant pairs, which is unlikely to exist in such a large fraction to
account for the bluer 1P stars.

We conclude that the 1P of 47 Tucanae is not chemically homogeneous. A small
intrinsic variation in the overall metallicity is present among 1P stars of
this globular cluster.

###  4.3 Chemical abundances in second population and anomalous stars

In this section we investigate the overall chemical pattern, besides the light
elements, between the 1P and 2P stars, which include also three stars
associated with the anomalous component.

The first thing to note is that, by looking at the ChM in Figure 4, the
anomalous stars have somewhat higher Fe abundance, with the most Fe rich stars
being the anomalous stars #22386 and #73063, with [Fe/H]=$-$0.65 dex and
[Fe/H]=$-$0.66 dex, respectively. Comparing the average Fe abundance for the
three anomalous stars, namely [Fe/H]=$-$0.67$\pm$0.02 dex (rms=0.03 dex), with
that of the stars belonging to the blue normal component (26 stars), with
average abundance of [Fe/H]=$-$0.80$\pm$0.01 dex (rms=0.07 dex), it results
that the anomalous stars in 47 Tucanae are enhanced in iron. This is similar
to what is found in most Type II GCs.

However, the presence of internal variations in Fe among 1P stars imposes a
more careful analysis of possible Fe enhancements in anomalous stars. By
plotting the abundances as a function of the
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values of the ChM, we obtain the
chemical pattern displayed in Figure 6. In this figure we show the average
[Fe/H] abundances, as well as the average absolute abundances from all the
$\alpha$ and the $s$ elements, weighted for the corresponding observational
errors.

Compared with the 1P, we first notice some hints of chemical enrichment in 2P
stars. Translating into numbers, the mean chemical abundance differences
between 2P stars (all, normal, and anomalous) and 1P stars ($\rm{1P_{a}}$ and
$\rm{1P_{b}}$) are listed in Table 8. From these numbers the chemical
enrichment of anomalous stars is clearly confirmed for all the considered
chemical species above 3 $\sigma$ level, except for the $s$ elements, which
have, however, larger uncertainties.

When dividing 1P stars into $\rm{1P_{a}}$ and $\rm{1P_{b}}$, the abundances of
2P normal stars are closer to the abundances of the $\rm{1P_{b}}$ stars than
to those of the $\rm{1P_{a}}$ ones. This pattern is best illustrated by
considering the $\alpha$ elements, that have lower associated uncertainties.
Similar trends are observed for all the other considered chemical species.

Finally, we note that the dispersion in chemical abundances for 2P stars,
except for the elements involved in the hot-H burning, are smaller than those
associated with the 1P ones. As an example, the [Fe/H] abundance dispersion is
0.08 dex for the 26 1P and 0.06 dex for the six 2P stars. The difference is
larger if we divide the 2P population in normal and anomalous, with
dispersions of 0.05 and 0.03 dex, respectively.

Table 8: Differences in [Fe/H] and in the absolute abundances log$\epsilon$(X) for all the analysed elements, the $\alpha$ and $s$ elements between the stellar populations of 47 Tucanae. We have listed the differences between the 2P stars (all, normal, and anomalous) and 1P stars subdivided into $\Delta_{\tiny{\mathrm{F275W,F814W}}}$$<-0.10$ ($\rm{1P_{a}}$) and $>-0.10$ ($\rm{1P_{b}}$). | [Fe/H] |  $\Delta$log$\epsilon$(X)
---|---|---
|  | all elements |  $\alpha$ elements |  $s$ elements
2P (all) $-$ $\rm{1P_{a}}$ | 0.12$\pm$0.04 | 0.13$\pm$0.05 | 0.13$\pm$0.03 | 0.18$\pm$0.06
2P (all) $-$ $\rm{1P_{b}}$ | 0.05$\pm$0.03 | 0.07$\pm$0.04 | 0.05$\pm$0.03 | 0.10$\pm$0.05
2P (normal) $-$ $\rm{1P_{b}}$ | 0.00$\pm$0.04 | 0.02$\pm$0.04 | 0.01$\pm$0.03 | 0.06$\pm$0.09
2P (anomalous) $-$ $\rm{1P_{b}}$ | 0.09$\pm$0.02 | 0.11$\pm$0.02 | 0.10$\pm$0.02 | 0.14$\pm$0.05

##  5 Discussion

In this section we explore the chemical abundance pattern of 47 Tucanae in the
context of a plausible star formation history for its stellar populations. For
simplicity, this discussion follows the different populations that have been
detected through a list of subsections.

###  5.1 1P stars

1P stars themselves are not homogeneous in metallicity reflecting in a spread
along the the x axis of the ChM. We do not find any “indirect” evidence for
the presence of He variations within these stars. Indeed, the [Na/Fe] and
[Al/Fe] abundances are consistent with uniform composition, with no evidence
of chemical enrichment in none of these elements involved in the hot-H
burning. In addition, we can exclude the variation in metals to be a
consequence of a change in helium (Y) and, consequently to Z/X, as in this
case we would expect the opposite trend with the
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values.

As shown for another GC, namely NGC 3201, non-interacting binaries with mass
ratio q$\gtrsim$0.8 can produce a sizable shift towards low
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values (Marino et al., 2019b). Although
the presence of other binaries in our sample cannot be excluded, only two 1P
stars can be classified as binaries from RVs, with one of them displaying a
low $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ value. Simulated spectra of
giant–giant pairs are consistent with higher temperature and/or lower
metallicity (see the discussion in Marino et al. (2019b) for further details).
In such a case the stars with lower metallicity and low
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values would be binaries or blue
stragglers. Since no evidence exists supporting large fractions of such
binaries to account for the entire color spread of 1P stars in GCs (Milone et
al., 2012b), our analysis for 47 Tucanae corroborates the idea of a genuine
spread in the overall metallicity among these stars.

As photometrically shown by Legnardi et al. (2022), a spread in metals of
$0.087\pm 0.009$ dex among the 1P stars is sufficient to generate a $\sim 0.1$
mag spread in the $\rm{m_{F275W}-m_{F814W}}$ color of the RGB stars of 47
Tucanae. In this context, we note that the ChM of M-dwarfs constructed with
F606W filter of the UVIS/WFC3 camera on board HST and the F115W and F322W2 IR
filters from the James Webb Space Telescope also displays an elongated 1P
distribution, consistent with an internal variation in metals of $\sim$0.10
dex (Milone et al., 2023).

The evidence of metallicity variations among both the RGB 1P stars and the
unevolved low-mass MS stars, would suggest that the variation in metals
reflects the chemical composition of the cloud from which 1P stars formed.

###  5.2 2P normal stars

As expected, the 2P stars are enhanced in Na, at different degrees depending
on their $\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ value. The normal 2P
star with highest $\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ which also
displays the lowest $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ value in our
sample, is the most Na rich.

Although we warn about the small number of analysed stars, it is interesting
to note that chemical abundances of the 2P stars are overall more similar to
that of the 1P stars with higher $\Delta_{\tiny{\mathrm{F275W,F814W}}}$
values, namely what we have defined as the $\rm{1P_{b}}$ population. By
selecting only the 2P stars belonging to the normal component, the chemical
abundances (with the exception of Na and Al) are consistent with those of the
$\rm{1P_{b}}$ stars.

Furthermore, the 2P stars do not seem to show the same degree of inhomogeneity
as the 1P ones. This is more clear if we subdivide 2P stars in normal and
anomalous. However, we note that the available 2P targets are, at the moment,
a quite limited sample to draw strong conclusions on this issue.

###  5.3 Anomalous stars

The three candidate anomalous stars are enhanced in the overall metallicity.
Their [Fe/H] is higher by $\sim$0.10 dex than that of the mean [Fe/H]
abundance of $\rm{1P_{b}}$ and the normal 2P, and by $\sim$0.20 dex than the
$\rm{1P_{a}}$ stars. On the other hand, we do not find any evidence for a
significant enrichment in the $s$ elements for these stars, as observed for
many Type II GCs (see Table 10 in Marino et al., 2015). However, we cannot
exclude that, due to the larger observational errors associated with the
abundances of these elements, some enrichment could be present, possibly lower
than that observed in some Type II GCs, such as NGC 1851 and NGC 5286.

Furthermore, our anomalous stars are all enhanced in Na, in agreement with
their relatively-high values of
$\Delta_{\tiny{C~{}\mathrm{F275W,F336W,F438W}}}$ compared to the 1P stars.
This suggests that the anomalous population of 47 Tucanae could have entirely
formed from an ISM which was already enriched in the H-burning products.

It is interesting to note that our findings qualitatively agree with the
chemical pattern observed on the faint sub giant branch of 47 Tucanae by
Marino et al. (2016) who found higher N abundances for these stars.
Theoretical investigation has suggested that the faint sub giant branch stars,
the progeny of the anomalous red giants, could be enhanced in He and in C+N+O
(di Criscienzo et al., 2010). While the nitrogen abundances are consistent
with a possible enhancement in He of these faint sub-giants, no strong
evidence has been found for C+N+O enrichment. However, the predicted variation
is of the order of $\sim$0.10 dex, which is within the estimated observational
errors (Marino et al., 2016).

In the context of Type II GCs, a similar pattern has been shown, at different
degrees, for other clusters, including M 22 and $\omega$ Centauri. Both of
them host indeed anomalous stars with relatively-low Na that can be associated
with an anomalous 1P; however, the [Na/Fe]-ground level of anomalous 1P stars
is higher than that associated with the normal 1P (Johnson & Pilachowski,
2010; Marino et al., 2011a, b, 2019a). Other Type II GCs, such as NGC 1851,
have a more extreme pattern with a completely (or largely) missing anomalous
1P, and most, if not all, anomalous stars are consistent with being enhanced
in the H-burning products, such as Na. On the other hand, the Type II GC NGC
6934, besides a Na-rich anomalous population, hosts a Na-poor anomalous
component comparable with the normal 1P stars (Marino et al., 2021).

This discussion highlights a quite heterogeneous picture for the chemical
composition in light elements of anomalous stars in Type II GCs, suggesting
that each cluster might have experienced a different timing for the onset of
its anomalous population, and different nucleosynthetic processes contributing
to that population.

###  5.4 Interpreting the observations

This work outlines how complex is the chemical inventory of 47 Tucanae, which
however is not a one-off among Milky Way GCs. Already among the 1P we observe
internal variations in the overall metal content. If these small variations
are not associated to binarity, they can be interpreted either as the result
of inhomogeneity in the primordial cloud from which the GC formed, or from
intra-cluster chemical enrichment occurring in the first phase of the proto-
cluster evolution, before the medium is enriched in the products of the
H-burning. A similar spectroscopic pattern has been also observed in NGC 3201
by Marino et al. (2019b) and, from photometric diagrams, in a large sample of
Milky Way GCs analysed by Legnardi et al. (2022).

Since the idea of internal Fe enrichment starting from the metal-poorer stars
would dramatically exacerbate the mass budget problem, we favour the idea of
an intrinsic inhomogeneity in the primordial proto-cluster cloud, which is
theoretically supported by recent hydrodynamical simulations (McKenzie &
Bekki, 2021).

To understand how such a spread could have been established in the first
place, let us first quantify the iron spread in terms of supernova yields. The
1P of 47 Tucanae has a mass of $\sim 2\times 10^{5}\,\ {\rm M}_{\odot}$ and a
metallicity $\sim 0.2$ solar. For a solar iron abundance $Z_{\odot}^{\rm
Fe}=0.00124$ (Asplund et al., 2009), this gives $Z^{\rm Fe}=0.000248$. If half
of 1P is 0.1 dex richer in iron, this corresponds to $Z^{\rm Fe}=0.000312$,
hence the iron-rich half of 1P has $\sim 6.4\,{\rm M}_{\odot}$ of iron more
than the iron-poor half. This is fairly large amount, taking into account that
the average iron product of each core collapse (CC) or Type Ia supernova is
$\sim 0.07\,{\rm M}_{\odot}$ and $\sim 0.7\,{\rm M}_{\odot}$, respectively
(e.g., Renzini & Andreon, 2014, and references therein). Hence, these $\sim
6.4\,{\rm M}_{\odot}$ of iron would correspond to the yield of $\sim 100$ CC
supernovae or $\sim 10$ Type Ia supernovae, respectively. We conclude that it
is plausible that such number of Type Ia supernovae from previous populations
may have blown up inside the molecular cloud going to form the 1P of 47
Tucanae, and that there was not time enough for complete mixing of its iron
yield. It is also possible that the material going to form the 1P was
collected from ISM regions having experienced a different number of CC
supernovae, when considering that the full iron content of the 1P is $50\,{\rm
M_{\odot}}$, or the product of $\sim 700$ CC supernovae. A major intra-cluster
chemical enrichment in metals could have occurred at later times, responsible
for the formation of the anomalous component.

We notice here that Kirby et al. (2023) has recently detected an internal
variation in $r$-process elements affecting only 1P stars in the GC M 92. This
result further corroborates the occurrence of inhomogeneous chemical pollution
from SNe, which was internal to the 1P, before the formation of the 2P stars.

The onset of 2P stars associated with the normal component may have occurred
from the metal-richer 1P stars, the $\rm{1P_{b}}$. This would be in agreement
with the ChM morphology of 47 Tucanae, which shows the 2P main branch starting
from relatively-red $\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values, at the
location of the metal-richer 1P.

Noticeably, the dispersion of the 2P normal stars is smaller than that
observed in the 1P. Even though this result needs to be confirmed over a
larger sample of stars, a higher degree of homogeneity in the overall metal
content of these stars is remarkable. Understanding whether or not 2P stars
display the same level of inhomogeneity as the 1P stars is indeed crucial for
GC formation scenarios. If 2P normal stars are homogeneous in Fe, this will
strongly corroborate the idea that successive generations of stars formed in a
high-density environment, very likely the proto-clusters central regions after
a cooling flow process mixes and homogenizes the ISM. On the other hand, if 2P
normal stars will trace similar Fe variations as the 1P, the different stellar
populations would be hardly reconcilable with multiple bursts of star
formation. In this second case, the observations would support the early disc
accretion scenario, rather than the multiple generations one. Future
observational efforts will be certainly devoted to constrain metallicity
spreads also in 2P stars, and, hopefully, theoretical studies based on
hydrodynamical simulations of GC formation in the early Universe will need to
include the new observational results on this issue.

##  6 Summary

We have presented chemical abundances from UVES spectra of 29 red giant branch
stars in the GC 47 Tucanae. Our spectroscopic sample has been selected to
prioritize the observation of 1P stars that span a large range in
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$ values along the ChM. Hence, our target
sample consists of 23 1P stars, including two binary candidates, and six 2P
stars, including three stars distributed on the normal component of the ChM,
and other three on a possible anomalous one, as defined in Milone et al.
(2017).

Our analysis suggests that a variation in the overall metallicity of
$\sim$0.10 dex is responsible for the distribution of 1P stars along the ChM.
The average [Fe/H] abundance for 1P stars with
$\Delta_{\tiny{\mathrm{F275W,F814W}}}$$>-$0.10 is $\sim$0.10 dex higher than
that for 1P stars with lower values. The absolute abundances of all the other
analysed elements follow the same variation of Fe, keeping constant the
abundance ratios relative to Fe.

The abundances of the 2P stars, which include both normal and anomalous stars,
suggest that the bulk of 2P may have formed from 1P material with higher metal
content, and that the cluster experienced a further enrichment in metals,
which was responsible for the formation of the anomalous population. The small
number of 2P normal analyzed stars does not display a dispersion in metals as
large as that observed among 1P stars.

The complex chemical inventory of 47 Tucanae, as emerged from this work, not
confined to the commonly-observed light element patterns, further corroborates
the intricate interweaving of stellar populations in GCs. Clearly, these
objects, once considered the simplest examples of stellar systems, have
experienced the interplay of different processes which produced the observed
chemical diversity among GC stars.

The authors thank the anonymous referee for useful discussion. Based on
observations collected at the European Organisation for Astronomical Research
in the Southern Hemisphere under ESO programme 105.20NB. This work has
received funding from INAF Research GTO-Grant Normal RSN2-1.05.12.05.10 -
Understanding the formation of globular clusters with their multiple stellar
generations (ref. Anna F. Marino) of the ”Bando INAF per il Finanziamento
della Ricerca Fondamentale 2022”, from the European Union’s Horizon 2020
research and innovation programme under the Marie Skłodowska-Curie Grant
Agreement No. 101034319 and from the European Union – NextGenerationEU. MT
acknowledges support from the ERC Consolidator Grant funding scheme (project
ASTEROCHRONOMETRY, https://www.asterochronometry.eu, G.A. No. 772293).

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