J/MNRAS/485/4311 Light element discontinuities in NGC 6402 (Johnson+, 2019)
Light element discontinuities suggest an early termination of star formation in
the globular cluster NGC 6402 (M14).
Johnson C.I., Caldwell N., Rich R.M., Mateo M., Bailey J.I.
<Mon. Not. R. Astron. Soc., 485, 4311-4329 (2019)>
=2019MNRAS.485.4311J 2019MNRAS.485.4311J (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, giant ; Spectra, optical ;
Abundances ; Magnitudes ; Effective temperatures ;
Radial velocities
Keywords: galaxies: star clusters: individual: NGC 6402 (M14)
Abstract:
NGC 6402 is among the most massive globular clusters in the Galaxy,
but little is known about its detailed chemical composition.
Therefore, we obtained radial velocities and/or chemical abundances of
11 elements for 41 red giant branch stars using high resolution
spectra obtained with the Magellan-M2FS instrument. We find NGC 6402
to be only moderately metal-poor with <[Fe/H]≥-1.13dex
(σ=0.05 dex) and to have a mean heliocentric radial velocity of
-61.1km/s (σ=8.5km/s). In general, NGC 6402 exhibits mean
composition properties that are similar to other inner Galaxy
clusters, such as [α/Fe]~+0.3dex, [Cr,Ni/Fe]∼0.0dex, and
<[La/Eu]≥-0.08dex. Similarly, we find large star-to-star abundance
variations for O, Na, Mg, Al, and Si that are indicative of gas that
experienced high temperature proton-capture burning. Interestingly, we
not only detect three distinct populations but also find large gaps in
the [O/Fe], [Na/Fe], and [Al/Fe] distributions that may provide the
first direct evidence of delayed formation for intermediate
composition stars. A qualitative enrichment model is discussed where
clusters form stars through an early (~<5-10Myr) phase, which results
in first generation and 'extreme' composition stars, and a delayed
phase (≳40Myr), which results in the dilution of processed and
pristine gas and the formation of intermediate composition stars. For
NGC 6402, the missing intermediate composition stars suggest the
delayed phase terminated prematurely, and as a result the cluster may
uniquely preserve details of the chemical enrichment process.
Description:
The spectra for this project were obtained using the Michigan-Magellan
Fiber System (M2FS; Mateo et al. 2012SPIE.8446E..4YM) and MSpec
spectrograph on the Magellan-Clay 6.5m telescope at Las Campanas
Observatory. The total wavelength coverage of all six orders ranged
from ∼6140-6720Å. The spectra were obtained under clear but
moderately humid conditions with reasonable seeing (∼1.2arcsec) on
2017 September 11, 12, and 15. The integration time totalled 18000s
(5h) and was distributed over ten 1800s exposures. Signal-to-noise
ratios (S/N) for individual exposures were approximately 25-50 per
reduced pixel.
Targets and coordinates were obtained using the Two Micron All Sky
Survey (2MASS; Skrutskie et al. 2006AJ....131.1163S 2006AJ....131.1163S, Cat. VII/233),
and membership probabilities were estimated using a fiducial sequence
derived from 2MASS CMDs that only included stars within 1arcmin of the
cluster core. The brightest RGB-tip stars were not included in order
to avoid targets with effective temperatures (Teff) lower than
∼4100K.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 93 42 Star identifiers, sky coordinates, photometry,
radial velocities, and model atmosphere
parameters for all stars
table23.dat 147 41 Abundance ratios and population designations
for all member stars
table4a.dat 61 3 Mean abundance ratios for the P1, P2, and E
populations
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See also:
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- Name Star name (2MHHMMSSSS+DDMMSSS)
20 A1 --- f_Name Flag on Name (1)
22- 31 F10.6 deg RAdeg Right ascension (J2000)
33- 41 F9.6 deg DEdeg Declination (J2000)
43- 48 F6.3 mag Jmag J-band magnitude from 2MASS
50- 55 F6.3 mag Hmag H-band magnitude from 2MASS
57- 62 F6.3 mag Ksmag Ks-band magnitude from 2MASS
64- 68 F5.1 km/s RV Heliocentric radial velocity
70- 72 F3.1 km/s e_RV Error on RV
74- 77 I4 K Teff ? Effective temperature
79- 82 F4.2 [cm/s2] logg ? Surface gravity
84- 88 F5.2 [-] [Fe/H] ? Iron to hydrogen abundance ratio
90- 93 F4.2 km/s vt ? Microturbulence velocity
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Note (1): Flag as follows:
* = Non-member star
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Byte-by-byte Description of file: table23.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- Name Star name (2MHHMMSSSS+DDMMSSS)
20- 21 A2 --- Pop Population designation (G1)
23- 27 F5.2 [-] [FeI/H] ? FeI to hydrogen abundance ratio
29- 33 F5.2 [-] [FeII/H] ? FeII to hydrogen abundance ratio
35- 39 F5.2 [-] [OI/Fe] ? OI to iron abundance ratio
41- 45 F5.2 [-] [NaI/Fe] ? NaI to iron abundance ratio
47- 50 F4.2 [-] [MgI/Fe] ? MgI to iron abundance ratio
52- 55 F4.2 [-] [AlI/Fe] ? AlI to iron abundance ratio
57- 60 F4.2 [-] [SiI/Fe] ? SiI to iron abundance ratio
62- 65 F4.2 [-] [CaI/Fe] ? CaI to iron abundance ratio
67- 71 F5.2 [-] [CrI/Fe] ? CrI to iron abundance ratio
73- 77 F5.2 [-] [NiI/Fe] ? NiI to iron abundance ratio
79- 82 F4.2 [-] [LaII/Fe] ? LaII to iron abundance ratio
84- 87 F4.2 [-] [EuII/Fe] ? EuII to iron abundance ratio
89- 92 F4.2 [-] e_[FeI/H] ? Error on [FeI/H]
94- 97 F4.2 [-] e_[FeII/H] ? Error on [FeII/H]
99-102 F4.2 [-] e_[OI/Fe] ? Error on [OI/Fe]
104-107 F4.2 [-] e_[NaI/Fe] ? Error on [NaI/Fe]
109-112 F4.2 [-] e_[MgI/Fe] ? Error on [MgI/Fe]
114-117 F4.2 [-] e_[AlI/Fe] ? Error on [AlI/Fe]
119-122 F4.2 [-] e_[SiI/Fe] ? Error on [SiI/Fe]
124-127 F4.2 [-] e_[CaI/Fe] ? Error on [CaI/Fe]
129-132 F4.2 [-] e_[CrI/Fe] ? Error on [CrI/Fe]
134-137 F4.2 [-] e_[NiI/Fe] ? Error on [NiI/Fe]
139-142 F4.2 [-] e_[LaII/Fe] ? Error on [LaII/Fe]
144-147 F4.2 [-] e_[EuII/Fe] ? Error on [EuII/Fe]
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Byte-by-byte Description of file: table4a.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Pop Population designation (G1)
4- 8 F5.2 [-] [Fe/H] Mean Fe to hydrogen abundance ratio
10- 14 F5.2 [-] [O/Fe] Mean O to iron abundance ratio
16- 20 F5.2 [-] [Na/Fe] Mean Na to iron abundance ratio
22- 25 F4.2 [-] [Mg/Fe] Mean Mg to iron abundance ratio
27- 30 F4.2 [-] [Al/Fe] Mean Al to iron abundance ratio
32- 35 F4.2 [-] [Si/Fe] Mean Si to iron abundance ratio
37- 40 F4.2 [-] [Ca/Fe] Mean Ca to iron abundance ratio
42- 45 F4.2 [-] [Cr/Fe] Mean Cr to iron abundance ratio
47- 51 F5.2 [-] [Ni/Fe] Mean Ni to iron abundance ratio
53- 56 F4.2 [-] [La/Fe] Mean La to iron abundance ratio
58- 61 F4.2 [-] [Eu/Fe] Mean Eu to iron abundance ratio
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Global Notes:
Note (G1): Population as follows:
P1 = First generation stars, 'halo-like' (12/35)
P2 = Intermediate second generation stars, diluted (14/35)
E = Extreme second generation stars, polluted material (9/35)
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 29-Sep-2022