J/AJ/158/163 Li abundance values for stars in NGC 6819 (Deliyannis+, 2019)
Li evolution and the open cluster NGC 6819: a correlation between Li depletion
and spindown in dwarfs more massive than the F-dwarf Li-dip.
Deliyannis C.P., Anthony-Twarog B.J., Lee-Brown D.B., Twarog B.A.
<Astron. J., 158, 163 (2019)>
=2019AJ....158..163D 2019AJ....158..163D (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, double and multiple ;
Effective temperatures ; Abundances
Keywords: open clusters and associations: general -
open clusters and associations: individual (NGC 6819) -
stars: abundances
Abstract:
Spectroscopy of 333 NGC 6819 stars and Gaia astrometry are used to map Li
evolution from the giant branch tip to 0.5 mag below the Li dip. Isochrone
comparison with [Fe/H]=-0.04, based upon neural network spectroscopic
analysis, produces an age of 2.25 (2.4) Gyr for E(B-V)=0.16 (0.14) and
(m-M)=12.40 (12.29). Despite originating outside the Li dip, only 10% of
single subgiants/giants have measurable Li. Above the Li dip, the limiting
A(Li) for single stars is 3.2±0.1 but the lower range is comparable
to that found within the dip. The F-dwarf Li dip profile agrees with
the Hyades/Praesepe, evolved forward. The Li level among stars populating
the plateau fainter than the Li dip is A(Li)=2.83±0.16; the dispersion
is larger than expected from spectroscopic error alone. Comparison of Li
and VROT distributions among turnoff stars in NGC 7789, NGC 2506,
NGC 3680, and NGC 6819 indicates that rotational spindown from the main
sequence is critical in defining the boundaries of the Li dip. For
higher-mass dwarfs, spindown is likewise correlated with Li depletion,
creating a second dip, but at higher mass and on a longer timescale.
The Li distribution among evolved stars of NGC 6819 is more representative
of the older M67, where subgiant and giant stars emerge from within the
Li dip, than the younger NGC 7789, where a broad range in VROT among
the turnoff stars likely produces a range in mass among the giants.
Description:
Table 1 contains parameters, and in particular Lithium abundance values,
for 333 stars in the open cluster NGC 6819. The initial spectroscopic
sample of probable cluster members was constructed using the
radial-velocity survey of NGC 6819 by Hole et al. (2009, J/AJ/138/159).
All stars brighter than V∼16.75 with radial-velocity membership
probabilities greater than 50% were identified as spectroscopic candidates,
while stars classed as double-lined spectroscopic binaries were eliminated.
Single-lined systems were retained since the existence of the companion
would have minimal impact on spectral line measurement. Spectroscopic data
were obtained using the WIYN 3.5 m telescope and the Hydra multi-object
spectrograph over 13 nights from 2010 September and October, 2011 June
and 2013 February. Six configurations were designed to position fibers
on the stars.
Objects:
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RA (ICRS) DE Designation(s)
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19 41 18 +40 11.2 NGC 6819 = Cl Melotte 223
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 42 333 Li abundance values for stars in NGC 6819
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/138/159 : NGC 6819 stellar radial-velocity and photometry (Hole+, 2009)
J/AJ/146/43 : WIYN open cluster study. LV. NGC 6819 (Platais+, 2013)
J/AJ/148/38 : WIYN open cluster study. LX. RV survey of NGC 6819
(Milliman+, 2014)
J/AJ/148/51 : WIYN Open Cluster. LXI. NGC 6819 photometry
(Anthony-Twarog+, 2014)
J/AJ/149/121 : WOCS. LXV. Abundances in NGC 6819 (Lee-Brown+, 2015)
J/A+A/618/A93 : Gaia DR2 open clusters in the Milky Way (Cantat-Gaudin+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- WOCS [1002/80025] WIYN Open Cluster Study (WOCS)
identification
7 A1 --- PMga [Y-N] Membership designation based on Gaia
proper motion
9 A1 --- PARga [Y-N] Membership designation based on Gaia
parallax
11- 13 A3 --- Bin [N SB1] Binary indication
15 A1 --- Mem [Y-N] Membership designation
17- 19 I3 --- S/N [19/323]? Signal-to-noise ratio
21- 24 I4 K Teff [3967/6859]? Effective temperature based on ANNA
code (1)
26- 30 F5.2 [-] [Fe/H] [-0.33/0.17]? Metal abundance [Fe/H] (1)
32 A1 --- l_A(Li) [<] Limit flag on A(Li)
33- 37 F5.2 [-] A(Li) [-1.5/3.5]? Lithium abundance A(Li)
39- 42 F4.2 [-] e_A(Li) [0.01/0.21]? Uncertainty in A(Li)
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Note (1): As an alternative to our EW-based spectroscopic [Fe/H] estimates and
our photometric Teff values, we have attempted to derive [Fe/H] and Teff
for each cluster member in our sample using ANNA (Lee-Brown 2017, Artificial
Neural Network Abundances (ANNA) v0.1.0, Zenodo, doi:10.5281/zenodo.1043585;
2018PhDT........48L 2018PhDT........48L; Lee-Brown et al. 2018AAS...23121305L 2018AAS...23121305L), a new, flexible,
Python-based code for automated stellar parameterization. See Section 4.1 for
more details.
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History:
From electronic version of the journal
References:
Anthony-Twarog et al. Paper I. 2014AJ....148...51A 2014AJ....148...51A, Cat. J/AJ/148/51
Lee-brown et al. Paper II. 2015AJ....149..121L 2015AJ....149..121L, Cat. J/AJ/149/121
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 07-Nov-2019