J/AJ/157/70 Search for sodium-rich stars among metal-poor stars (Pereira+, 2019)
Search for sodium-rich stars among metal-poor stars.
Pereira C.B., Holanda N., Drake N.A., Roig F.
<Astron. J., 157, 70-70 (2019)>
=2019AJ....157...70P 2019AJ....157...70P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Spectroscopy ; Effective temperatures ;
Abundances, [Fe/H]
Keywords: stars: abundances - stars: AGB and post-AGB -
stars: chemically peculiar - stars: evolution -
stars: fundamental parameters
Abstract:
Sodium-rich stars are often found in globular clusters giants. However,
some sodium-rich stars have been found among field metal-poor stars.
These stars are considered as evaporated from globular clusters. Identified
such kind of stars among the field stars in the Galaxy may provide insights
of which mechanism was responsible for the ejection from a globular cluster
and may reveal some chemical peculiarity. Therefore, we started a search,
using high-resolution spectroscopy, among metal-poor stars from several
sources of the literature to find a sodium-rich star. Here we present
the results for the temperature, gravity, metallicity, and sodium
abundances for the stars of our sample. For many of them we determined
the temperature, gravity, metallicity, and sodium abundances for the first
time. As a result of our search we found one star, CD-23°16310, which
has a [Na/Fe] ratio of +1.09. We also show that CD-23°16310 is not
a carbon-enhanced metal-poor (CEMP) star since carbon is not enriched but
is nitrogen-rich. We did not detect any variation of the radial velocity
that would support the hypothesis of mass transfer. Thus, the high sodium
and nitrogen abundance could be due to a strong internal mixing process,
suggesting that CD-23°16310 is an early asymptotic giant branch star.
Description:
The stars were selected from Bidelman & MacConnell (1973, Cat. III/46),
Bidelman (1981, Cat. 1981AJ.....86..553B 1981AJ.....86..553B), Osborn & MacConnell
(1987PASP...99.1317O 1987PASP...99.1317O), and Beers et al. (2002AJ....124..931B 2002AJ....124..931B). We did not
observe all of the stars of each sample for three main reasons: (1) some
stars have a visual magnitude around 12.0; this requires exposure times
around one hour for a 2.2 m telescope (see Section 3), where this survey
was done; (2) lack of telescope time (there were many stars to be observed,
even if only considering the brightest ones); and (3) because we were
mainly interested in giant stars rather than dwarfs. Therefore besides
the original sources we also considered other investigations that used
photometric calibrations and other spectroscopic surveys that separated
giants from dwarfs, for example, such as the studies of Norris et al.
(1985ApJS...58..463N 1985ApJS...58..463N) and Beers et al. (2014, J/ApJ/794/58) that
investigated the sample of Bidelman & MacConnell (1973, Cat. III/46). Since
most of our observations were done before 2014, we extensively used the
work of Norris et al. (1985ApJS...58..463N 1985ApJS...58..463N) to select the stars. With a new
set of observations done in 2016 we also used the work of Beers et al.
(2014, J/ApJ/794/58).
The high-resolution spectra of the metal-poor stars analyzed in this work
were obtained with the Fiberfed Extended Range Optical Spectrograph (FEROS),
installed at the 1.52 m telescope and later at 2.2 m telescope of European
Southern Observatory (ESO) at La Silla (Chile). FEROS has a charge-coupled
device (CCD) with an array of 2048x4096 with a pixel size of 15 µm.
The wavelength range obtained with FEROS covers the spectral region between
3900 Å and 9200 Å with a resolving power of
λ/Δλ=48000 (Kaufer et al. 1999Msngr..95....8K 1999Msngr..95....8K). The
spectra were reduced following the standard procedure, including bias
subtraction, flat-fielding, order extraction, and wavelength calibration
with the MIDAS pipeline reduction package. The signal-to-noise (S/N) ratio
of the spectra was generally in the range between 80 and 170.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 41 49 Log of the observations, V magnitude of
the stars, and the source from where the stars
were selected
table2.dat 59 41 Adopted atmospheric parameters
--------------------------------------------------------------------------------
See also:
III/46 : Ap and Am Stars (Bertaud+ 1974; Bidelman+ 1973)
J/PASP/107/846 : LSE stars, extension of Case-Hamburg surveys. (Drilling+ 1995)
J/A+A/356/238 : Atmospheric parameters in metal-poor stars. III.
(Carretta+ 2000)
J/AN/331/474 : Abundances of metal-poor stars (Frebel, 2010)
J/ApJ/771/67 : Detailed abundances for 97 metal-poor stars. II.
(Ishigaki+, 2013)
J/ApJ/794/58 : Metal-poor stars in the thick disk of the Galaxy
(Beers+, 2014)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Star Star identifier
17 A1 --- r_Star [abcd] Original source from which the star was
selected (G1)
19- 29 A11 "date" Date Date of observation
31- 36 A6 s Texp Exposure time
38- 41 F4.1 mag Vmag [7.6/11.8]? Visual magnitude
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Star Star identifier
17 A1 --- r_Star [abcd] Original source from which the star
was selected (G1)
19- 22 I4 K Teff [4250/6000] Effective temperature
24- 26 F3.1 [cm/s2] logg [0.2/2.8] Surface gravity
28- 32 F5.2 [-] [FeI/H] [-2.88/-0.98] Abundance of Fe I
34- 37 F4.2 [-] e_[FeI/H] [0.06/0.12] Uncertainty in [FeI/H]
39- 41 I3 --- o_FeI [39/113] Number of Fe I absorption lines used
for the determination of atmospheric
parameters
43- 47 F5.2 [-] [FeII/H] [-2.87/-0.97] Abundance of Fe II
49- 52 F4.2 [-] e_[FeII/H] [0.05/0.14] Uncertainty in [FeII/H]
54- 55 I2 --- o_FeII [6/17] Number of Fe II absorption lines used
for the determination of atmospheric
parameters
57- 59 F3.1 km/s xi [1.2/2.8] Microturbulence ξ
--------------------------------------------------------------------------------
Global notes:
Note (G1): And also the source of a previous photometric and/or spectroscopic
survey in which metallicity and/or evolutionary status of the star were
determined:
a = Osborn & MacConnell (1987PASP...99.1317O 1987PASP...99.1317O);
b = Bidelman & MacConnell (1973, Cat. III/46), Norris et al.
(1985ApJS...58..463N 1985ApJS...58..463N), Beers et al. (2014, J/ApJ/794/58);
c = Bidelman (1981AJ.....86..553B 1981AJ.....86..553B);
d = Drilling & Bergeron (1995, J/PASP/107/846),
Beers et al. (2002AJ....124..931B 2002AJ....124..931B).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 24-May-2019