J/ApJ/961/227 Red giant branch stars in M30 and M92 (Lee, 2024)
A comparative study between M30 and M92: M92 is a merger remnant with a large
helium enhancement.
Lee J.-W.
<Astrophys. J., 961, 227 (2024)>
=2024ApJ...961..227L 2024ApJ...961..227L
ADC_Keywords: Clusters, globular; Stars, giant; Photometry; Optical; Abundances;
Stars, population II
Keywords: Stellar populations ; Population II stars ;
Hertzsprung Russell diagram ; Globular star clusters ;
Chemical abundances ; Stellar evolution ; Red giant branch ;
Red giant bump ; Horizontal branch
Abstract:
We perform a comparative study of the ex situ second-parameter pair
globular clusters (GCs) M30 and M92, having similar metallicities but
different horizontal branch morphologies. We obtain similar mean
primordial carbon abundances for both clusters. However, M92 shows a
large dispersion in carbon due to a more extended C-N anticorrelation,
while M30 exhibits a higher primordial nitrogen abundance, suggesting
that they have different chemical enrichment histories. Our new
results confirm our previous result that M92 is a metal-complex GC
showing a bimodal metallicity distribution. We also find that the
metal-rich group of stars in M92 shows a helium enhancement as large
as ΔY∼0.05 from the red giant branch bump V magnitudes, which
can also be supported by (i) a lack of bright red giant branch stars,
(ii) synthetic evolutionary horizontal branch population models and
(iii) the more extended spatial distribution due to different degree
of the diffusion process from their lower masses. We reinterpret the
[Eu/Fe] measurements by others, finding that the two metallicity
groups of stars in M92 have significantly different [Eu/Fe] abundances
with small scatters. This strongly suggests that they formed
independently out of well-mixed interstellar media in different
environments. We suggest that M92 is a more complex system than a
normal GC, most likely a merger remnant of two GCs or an even more
complex system. In the Appendix, we address the problems with the
recently developed color-temperature relations and the usage of
broadband photometry in the populational taggings.
Description:
The journal of observations for M92 is given in
Lee J.-W. (2023ApJ...948L..16L 2023ApJ...948L..16L). Briefly, observations for M92 were
carried out in 15 nights, five of which were photometric, in five runs
from 2017 April to 2019 July using the KPNO 0.9m telescope. The total
integration times of Stromgren y, b, CaJWL, JWL39, JWL43, and JWL34
for the M92 science field were 3160s, 6930s, 20700s, 11400s, 11600s,
and 21800s, respectively.
Observations for M30 were made in 33 nights in 13 runs from 2007 July
to 2019 September using the CTIO 1.0m and KPNO 0.9m telescopes.
Until 2010, we used the filters that were provided by the CTIO.
We used our own filters since 2011, both in the CTIO and KPNO, and our
work presented here will rely on photometric data using our own
filters (Lee 2017ApJ...844...77L 2017ApJ...844...77L ; 2019ApJ...872...41L 2019ApJ...872...41L ;
2019ApJ...883..166L 2019ApJ...883..166L; Lee & Sneden 2021ApJ...909..167L 2021ApJ...909..167L). The total
integration times for M30 using our own filters were 6680, 13160,
27400, 12500, 9600, 7600s for Stromgren y, b, CaJWL, JWL39, JWL43,
and JWL34, respectively.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
21 40 22.11 -23 10 47.4 M30 = NGC 7099
17 17 07.38 +43 08 09.3 M92 = NGC 6341
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 98 863 Photometric data of red giant branch (RGB) stars
in M30 and M92
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See also:
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/ApJ/518/262 : CCD VIc Photometry of M30 Stars (Sandquist+, 1999)
J/A+A/505/117 : Abund. of red giants in 15 globular clusters (Carretta+, 2009)
J/AJ/142/22 : Heavy-element dispersion in M92 (Roederer+, 2011)
J/ApJ/786/14 : He abundances in M30 and NGC 6397 (Mucciarelli+, 2014)
J/ApJS/219/7 : Ca,by photometry in globular clusters. I. M22 (Lee, 2015)
J/MNRAS/478/1520 : Milky Way globular clusters data (Baumgardt+, 2018)
J/MNRAS/485/3042 : UBVRI photometry in 48 globular clusters (Stetson+, 2019)
J/ApJ/958/45 : Keck/HIRES spectroscopy obs. of stars in M92 (Kirby+, 2023)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Cluster Cluster Name ("M30": 271 occurrences or
"M92": 592 occurrences)
5- 8 I4 --- ID [18/9624] Star number within Cluster
10- 15 F6.3 mag Vmag [12.12/17.1] V-band magnitude
17- 21 F5.3 mag b-y [0.43/0.91] Color, Stromgren b-y
23- 28 F6.3 --- cnJWL [-0.15/-0.012] Photometric index,
CNλ3883 (1)
30- 35 F6.3 --- chJWL [-0.71/-0.52] Photometric index,
CHλ4250 (1)
37- 42 F6.3 --- nhJWL [-1.24/0.41] Photometric index,
NHλ3360 (1)
44- 48 F5.3 --- hkJWL [0.23/0.91] Photometric index, CaII H&K (1)
50- 56 F7.4 --- [Fe/H]hk [-2.6/-2.1] Photometric iron abundance
(metallicity) from hkJWL (2)
58- 64 F7.4 --- [C/Fe]ch [-0.84/0.36] Photometric carbon abundance
from chJWL (2)
66- 72 F7.4 --- [N/Fe]nh [-0.4/1.8] Photometric nitrogen abundance
from nhJWL (2)
74- 85 F12.8 deg RAdeg [259.1/325.3] Right Ascension (J2000)
87- 98 F12.8 deg DEdeg [-23.3/43.3] Declination (J2000)
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Note (1): Photometric indices defined in Anthony-Twarog+ 1991AJ....101.1902A 1991AJ....101.1902A ;
Lee (2015ApJS..219....7L 2015ApJS..219....7L ; 2017ApJ...844...77L 2017ApJ...844...77L; 2019ApJ...883..166L 2019ApJ...883..166L), and
Lee & Sneden 2021ApJ...909..167L 2021ApJ...909..167L and described in detail as:
hkJWL = ((CaJWL-b)-(b-y)) [1991AJ....101.1902A 1991AJ....101.1902A, using
CaJWL in place of the original CaAT or CaCTIO filters];
cnJWL = (JWL39-CaJWL) [2017ApJ...844..77L, Table 1];
chJWL = ((JWL43-b)-(b-y)) [2019ApJ...883..166L 2019ApJ...883..166L, Equation 7];
nhJWL = ((JWL34-b)-(b-y)) [2021ApJ...909..167L 2021ApJ...909..167L, Equation 2];
where b,y are standard Stromgren filters and the JWL filters are
defined as follows:
CaJWL = λc∼395nm, FWHM∼9nm, Lee 2015ApJS..219....7L 2015ApJS..219....7L
JWL39 = λc∼390nm, FWHM∼18nm, Lee 2017ApJ...844...77L 2017ApJ...844...77L
JWL34 = λc∼337nm, FWHM∼20.5nm Lee & Sneden 2021ApJ...909..167L 2021ApJ...909..167L
JWL43 = λc∼430nm, FWHM∼5nm Lee 2019ApJ...883..166L 2019ApJ...883..166L
Note (2): Abundances derived, equations as:
[Fe/H]hk∼f1(hkJWL,Y,[C,N,O/Fe],MV) = Equation 1, this work;
[C/Fe]ch∼f2(chJWL,[Fe/H]hk,Y,[N,O/Fe],MV) = Equation 3, this work;
[N/Fe]nh∼f3(nhJWL,[Fe/H]hk,Y,[C,O/Fe],MV) = Equation 4, this work.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Apr-2026