J/A+A/585/A86 Fornax dSph H4 globular cluster stars (Hendricks+, 2016)
Evidence for a chemical enrichment coupling of globular clusters and field stars
in the Fornax dSph.
Hendricks B., Boeche C., Johnson C.I., Frank M.J., Koch A., Mateo M.,
Bailey III J.I.
<Astron. Astrophys., 585, A86-86 (2016)>
=2016A&A...585A..86H 2016A&A...585A..86H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Abundances
Keywords: galaxies: clusters: individual: Fornax -
globular clusters: individual: H4 - galaxies: abundances -
galaxies: evolution - galaxies: dwarf - stars: abundances
Abstract:
The globular cluster H4, located in the center of the Fornax dwarf
spheroidal galaxy, is crucial for understanding the formation and
chemical evolution of star clusters in low-mass galactic environments.
H4 is peculiar because the cluster is significantly more metal-rich
than the galaxy's other clusters, is located near the galaxy center,
and may also be the youngest cluster in the galaxy. In this study, we
present detailed chemical abundances derived from high-resolution
(R∼28000) spectroscopy of an isolated H4 member star for comparison
with a sample of 22 nearby Fornax field stars. We find the H4 member
to be depleted in the alpha-elements Si, Ca, and Ti with
[Si/Fe]=-0.35±0.34, [Ca/Fe]=+0.05±0.08, and [Ti/Fe]=-0.27±0.23,
resulting in an average [α/Fe]=-0.19±0.14. If this result is
representative of the average cluster properties, H4 is the only known
system with a low [α/Fe] ratio and a moderately low metallicity
embedded in an intact birth environment. For the field stars we find a
clear sequence, seen as an early depletion in [α/Fe] at low
metallicities, in good agreement with previous measurements. H4 falls
on top of the observed field star [α/Fe] sequence and clearly
disagrees with the properties of Milky Way halo stars. We therefore
conclude that within a galaxy, the chemical enrichment of globular
clusters may be closely linked to the enrichment pattern of the field
star population. The low [α/Fe] ratios of H4 and similar
metallicity field stars in Fornax give evidence that slow chemical
enrichment environments, such as dwarf galaxies, may be the original
hosts of alpha-depleted clusters in the halos of the Milky Way and
M31.
Description:
For this project, we used the Michigan/Magellan Fiber System (M2FS)
and MSpec spectrograph, a fiber-fed spectrograph mounted on the
Nasmyth-east port of the Magellan-Clay 6.5 m telescope at Las Campanas
Observatory. For M2FS, we used the Bulge_GC1 setup and 125m slit,
which allows a simultaneous observation of up to 48 targets at a
resolving power of R~=28000 and a continuous wavelength coverage from
6140 to 6720Å. The observations have been carried out during three
consecutive nights in December 2014. With 8 individual exposures, a
total of 6.7h have been observed on target with typical seeing
conditions around 0.8".
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 75 30 Basic parameters - positions, photometry, and
quality of the spectra
tablea2.dat 72 30 Chemical abundances - [Fe/H], and alpha-elements
tablea3.dat 79 30 Chemical abundances - iron-peak elements
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Star Star designation
7 A1 --- n_Star [*] Note on Star (G1)
9 I1 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 18 F5.2 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 31 F5.2 arcsec DEs Declination (J2000)
33 A1 --- Group [AB] Group (2)
35- 40 F6.3 mag Vmag V magnitude
42- 46 F5.3 mag e_Vmag ?=- rms uncertainty on Vmag
48- 52 F5.3 mag V-I V-I colour index
54- 58 F5.3 mag e_V-I ?=- rms uncertainty on V-I
60- 64 F5.2 --- msep ?=- Separation index (3)
66- 69 F4.1 --- S/N Signal-to-noise ratio (4)
71- 75 F5.1 0.1nm Dleff Effective wavelength range
Δλeff (5)
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Note (2): "Group" indicates whether the star has been selected within the tidal
radius of H4 (A), or whether it is a field star from the central part of
Fornax (B).
Note (3): For stars of category A, the separation index msep is an indicator
for the flux contamination of a spectrum, as described in Sect. 2.2.1 of the
main article.
Note (4): The S/N is per pixel of the degraded spectra as they are supplied to
SP_Ace.
Note (5): The effective wavelength range {lambdal}eff gives the final wavelength
range which is used in the chemical analysis after critical regions flagged in
various pixel masks have been removed.
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Star Star designation
7 A1 --- n_Star [*] Note on Star (G1)
9- 13 F5.2 km/s v Velocity
15- 18 F4.2 km/s e_v rms uncertainty on v
20- 24 F5.2 [-] [Fe/H] Abundance [Fe/H]
26- 30 F5.2 [-] b_[Fe/H] ?=- Lower value of [Fe/H] interval
32- 36 F5.2 [-] B_[Fe/H] ?=- Upper value of [Fe/H] interval
38- 42 F5.2 [-] [Ca/H] ?=- Abundance [Ca/H]
44- 48 F5.2 [-] b_[Ca/H] ?=- Lower value of [Ca/H] interval
50- 54 F5.2 [-] B_[Ca/H] ?=- Upper value of [Ca/H] interval
56- 60 F5.2 [-] [Ti/H] ?=- Abundance [Ti/H]
62- 66 F5.2 [-] b_[Ti/H] ?=- Lower value of [Ti/H] interval
68- 72 F5.2 [-] B_[Ti/H] ?=- Upper value of [Ti/H] interval
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Star Star designation
7 A1 --- n_Star [*] Note on Star (G1)
9- 13 F5.2 [-] [V/H] ?=- Abundance [V/H]
15- 19 F5.2 [-] b_[V/H] ?=- Lower value of [V/H] interval
21- 25 F5.2 [-] B_[V/H] ?=- Upper value of [V/H] interval
27- 31 F5.2 [-] [Cr/H] ?=- Abundance [Cr/H]
33- 37 F5.2 [-] b_[Cr/H] ?=- Lower value of [Cr/H] interval
39- 43 F5.2 [-] B_[Cr/H] ?=- Upper value of [Cr/H] interval
45- 49 F5.2 [-] [Co/H] ?=- Abundance [Co/H]
51- 55 F5.2 [-] b_[Co/H] ?=- Lower value of [Co/H] interval
57- 61 F5.2 [-] B_[Co/H] ?=- Upper value of [Co/H] interval
63- 67 F5.2 [-] [Ni/H] ?=- Abundance [Ni/H]
69- 73 F5.2 [-] b_[Ni/H] ?=- Lower value of [Ni/H] interval
75- 79 F5.2 [-] B_[Ni/H] ?=- Upper value of [Ni/H] interval
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Global notes:
Note (G1): *: The star with ID r_0010 is the target with 99.2% H4 membership
probability.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 10-Mar-2016