J/A+A/700/A213 C and N abund. and isochrone fitting in 47 Tuc (Villanova+, 2025)
C and N abundances in globular clusters. I. The case of 47 Tuc (NGC 104) and the
effect of the first dredge-up: Implications for the isochrone fitting.
Villanova S., Monaco L., Momany Y., Ordenes I., Harbeck D., Plotnikova A.
<Astron. Astrophys. 700, A213 (2025)>
=2025A&A...700A.213V 2025A&A...700A.213V (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Abundances ; Isochrones
Keywords: Galaxy: abundances - globular clusters: individual: NGC 104
Abstract:
Globular clusters exhibit star-to-star chemical variations, traceable
through both photometric and spectroscopic data. While UV photometry
and light-element abundances (e.g., Na and O) are commonly used, the
optical V vs. (V-I) color-magnitude diagram (CMD) is often assumed to
be relatively unaffected by such inhomogeneities and is typically used
to derive basic cluster parameters. On the other hand, C and N would
be the best chemical tracers of these variations but are challenging
to measure due to their spectral features lying in the blue/UV or IR
regions.
In this study, we investigate chemical variations in the globular
cluster NGC104 (47Tucanae), aiming to trace multiple stellar
populations across evolutionary phases and examine how the C/N
anti-correlation evolves from the main sequence (MS) to the asymptotic
giant branch (AGB). We also assess the impact of these populations on
the interpretation of the V vs. V-I diagram.
Using spectra spanning all evolutionary stages, we derive [C/Fe] and
[N/Fe] abundances for a large stellar sample. These abundance
measurements are inferred from the CN and the CH features, while
atmospheric parameters are homogeneously derived from photometry. The
inferred abundances allow us to disentangle multiple populations along
the CMD and refine cluster parameters.
We find that MS stars are more C- and N-rich than their red giant
branch, horizontal branch, and AGB counterparts. The C/N
anti-correlation shifts during the sub-giant branch phase, coinciding
with the first dredge-up: C decreases by 0.15-0.20dex, N by ∼0.1dex,
while Fe remains unchanged. Interestingly, stars with different C and
N abundances occupy distinct regions of the V vs V-I diagram--a
pattern not attributable to differential reddening. Proper CMD fitting
requires two isochrones with differing helium content, metallicity,
and possibly age.
Description:
We have analyzed the V vs V-I CMD of the globular cluster NGC 104 in
the inner part and out to 25' from the center. We also analyzed a
sample of low, medium, and high resolution spectra covering CH and CN
blue and UV bands in order to obtain [C/Fe] and [N/Fe] abundances for
a sample of targets covering all the evolutionary phases, from the MS
to the AGB.
Table 3: ID, RA and DEC are in degrees, V and I magnitudes, proper
motions in mas/yr, temperature in K, gravity, and microturbulence in
km/s. Phase indicates the evolutionary phase of the target and Gen
indicates if the target belong to the FG or to the FG. The last two
columns give [C/Fe] and [N/Fe]
Objects:
---------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------
00 24 05.35 -72 04 53.1 47 Tuc = NGC 104
---------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 100 202 Parameters and [C/Fe] and [N/Fe] abundances
for our targets
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See also:
J/AJ/125/197 : CN abundances of the 47 Tuc main sequence (Harbeck+, 2003)
J/AJ/127/1588 : 47 Tuc main-sequence star abundances (Briley+, 2004)
J/AJ/135/1551 : Abundances of stars in 47 Tuc (Koch+, 2008)
J/A+A/537/A2 : 8.6um imaging of 47 Tuc (Momany+, 2012)
J/A+A/549/A41 : Horizontal branch stars in 47 Tuc and M5 (Gratton+, 2013)
J/A+A/550/A34 : Abundances of red giants in M4 and 47 Tuc (Carretta+, 2013)
J/A+A/572/A108 : 47 Tuc red giants chemical composition (Thygesen+, 2014)
J/ApJ/780/94 : Abundances of red giants in 47 Tuc (Cordero+, 2014)
J/ApJ/797/124 : AGB and RGB stars in 47 Tuc (Lapenna+, 2014)
J/MNRAS/459/610 : 47 Tuc sub-giant branch chemical abundances (Marino+, 2016)
J/A+A/661/A35 : eROSITA study of 47 Tuc globular cluster (Saeedi+, 2022)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- ID Identififier
17- 26 F10.8 deg RAdeg Right ascension (J2000.0)
28- 39 F12.8 deg DEdeg Declination (J2000.0)
41- 46 F6.3 mag Vmag Johnson V magnitude
48- 53 F6.3 mag Imag Johnson I magnitude
55- 59 F5.3 mas/yr pmRA Proper motion along right ascension
61- 66 F6.3 mas/yr pmDE Proper motion along declination
68- 71 I4 K Teff Effective temperature
73- 76 F4.2 [cm/s2] logg Logarithm of the surface gravity
78- 81 F4.2 km/s vt Microtubulente
83- 85 A3 --- Phase Evolutionary phase (MS, SGB, RGB, HB or AGB)
87- 88 A2 --- Gen [FG SG] Generation the target belongs to (1)
90- 94 F5.2 [-] [C/Fe] C abundance
96-100 F5.2 [-] [N/Fe] N abundance
--------------------------------------------------------------------------------
Note (1): Generation the target belongs to as follows:
FG = first generation
SG = second generation
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History:
From Sandro Villanova, svillanova(at)astro-udec.cl
Acknowledgements:
S.V. gratefully acknowledges the support provided by Fondecyt Regular
n. 1220264 and by the ANID BASAL project FB210003. L.M. gratefully
acknowledges support from ANID-FONDECYT Regular Project n. 1251809.
The authors acknowledge the anonymous referee for the constructive
report. This work has made use of data from the European Space Agency
(ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the
Gaia Data Processing and Analysis Consortium (DPAC,
https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the
DPAC has been provided by national institutions, in particular the
institutions participating in the Gaia Multilateral Agreement.
(End) Patricia Vannier [CDS] 23-Jul-2025