J/A+A/609/A13 Star cluster Gaia 1 stars equivalent widths (Koch+, 2018)
Detailed chemical abundance analysis of the thick disk star cluster Gaia 1.
Koch A., Hansen T., Kunder A.
<Astron. Astrophys. 609, A13 (2018)>
=2018A&A...609A..13K 2018A&A...609A..13K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Spectroscopy ; Equivalent widths
Keywords: stars: abundances - Galaxy: abundances - Galaxy: structure -
open clusters and associations: individual: Gaia 1 -
Galaxy: disk - globular clusters
Abstract:
Star clusters, particularly those objects in the disk-bulge-halo
interface are as yet poorly charted, despite the fact that they carry
important information about the formation and the structure of the
Milky Way. Here, we present a detailed chemical abundance study of the
recently discovered object Gaia 1. Photometry has previously suggested
it as an intermediate-age, moderately metal-rich system, although the
exact values for its age and metallicity remained ambiguous in the
literature. We measured detailed chemical abundances of 14 elements in
four red giant members, from high-resolution (R=25000) spectra that
firmly establish Gaia 1 as an object associated with the thick disk.
The resulting mean Fe abundance is -0.62±0.03(stat.)±0.10(sys.)
dex, which is more metal-poor than indicated by previous spectroscopy
from the literature, but it is fully in line with values from
isochrone fitting. We find that Gaia 1 is moderately enhanced in the
α-elements, which allowed us to consolidate its membership with
the thick disk via chemical tagging. The cluster's Fe-peak and
neutron-capture elements are similar to those found across the
metal-rich disks, where the latter indicate some level of s-process
activity. No significant spread in iron nor in other heavy elements
was detected, whereas we find evidence of light-element variations in
Na, Mg, and Al. Nonetheless, the traditional Na-O and Mg-Al
(anti-)correlations, typically seen in old globular clusters, are not
seen in our data. This confirms that Gaia 1 is rather a massive and
luminous open cluster than a low-mass globular cluster. Finally,
orbital computations of the target stars bolster our chemical findings
of Gaia 1's present-day membership with the thick disk, even though it
remains unclear which mechanisms put it in that place.
Description:
Observations of four candidate members were taken during four nights
in March 2017 using the Echelle spectrograph at the 2.5-m du Pont
telescope at the Las Campanas Observatory, Chile, with a seeing of
0.7"-1.0" throughout the nights. Our spectroscopic set-up included a
1.0" slit with 2x1 binning in spectral and spatial dimensions,
resulting in a resolving power of R∼25000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 4 Observing log and target properties
table2.dat 65 250 Line list
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See also:
J/A+A/565/A23 : Abundances of NGC5897 red giants (Koch+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 I1 --- Star Star sequential number
3- 4 I2 h RAh Rigth ascension (J2000.0)
6- 7 I2 min RAm Rigth ascension (J2000.0)
9- 13 F5.2 s RAs Rigth ascension (J2000.0)
15 A1 --- DE- Declination sign (J2000.0)
16- 17 I2 deg DEd Declination (J2000.0)
19- 20 I2 arcmin DEm Declination (J2000.0)
22- 26 F5.2 arcsec DEs Declination (J2000.0)
28- 33 F6.3 mag Jmag J magnitude
35- 40 F6.3 mag Hmag H magnitude
42- 47 F6.3 mag Kmag K magnitude
49- 59 A11 "date" Obs.Date Date of observation
61- 66 A6 s texp Exposure time
68- 69 I2 --- SN6550 Signal-to-noise ration measured at 6550Å
71- 72 I2 --- SN5500 Signal-to-noise ration measured at 5500Å
74- 75 I2 --- SN4500 Signal-to-noise ration measured at 4500Å
77- 80 F4.1 km/s HV Heliocentric velocity
82- 84 F3.1 km/s e_HV rms uncertainty on HV
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 F4.1 --- Ion Ion designation
8- 14 F7.2 0.1nm lambda Wavelength
19- 22 F4.2 eV EP Excitation potential
26- 32 F7.3 [-] loggf Oscillator strength
38- 40 I3 10-13m EW1 ? Equivalent width for Star 1 (1)
41 A1 --- n_EW1 [s] s for syn
46- 48 I3 10-13m EW2 ? Equivalent width for Star 2 (1)
49 A1 --- n_EW2 [s] s for syn
54- 56 I3 10-13m EW3 ? Equivalent width for Star 3 (1)
57 A1 --- n_EW3 [s] s for syn
62- 64 I3 10-13m EW4 ? Equivalent width for Star 4 (1)
65 A1 --- n_EW4 [s] s for syn
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Note (1): In milli-Angstroms.
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Acknowledgements:
Andreas Koch, a.koch1(at)lancaster.ac.uk
(End) Patricia Vannier [CDS] 25-Sep-2017