J/ApJ/781/40 Metal-poor stars from HES survey. II. Spectroscopy (Placco+, 2014)
Metal-poor stars observed with the Magellan telescope.
II. Discovery of four stars with [Fe/H] ≤ -3.5.
Placco V.M., Frebel A., Beers T.C., Christlieb N., Lee Y.S., Kennedy C.R.,
Rossi S., Santucci R.M.
<Astrophys. J., 781, 40 (2014)>
=2014ApJ...781...40P 2014ApJ...781...40P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Stars, halo ; Stars, metal-deficient ;
Abundances ; Equivalent widths
Keywords: Galaxy: halo - stars: abundances - stars: atmospheres -
stars: Population II - techniques: spectroscopic
Abstract:
We report on the discovery of seven low-metallicity stars selected
from the Hamburg/ESO Survey, six of which are extremely metal-poor
(EMP, [Fe/H]≤-3.0), with four having [Fe/H]≤-3.5. Chemical
abundances or upper limits are derived for these stars based on
high-resolution (R∼35000) Magellan/MIKE spectroscopy, and are in
general agreement with those of other very and extremely metal-poor
stars reported in the literature. Accurate metallicities and abundance
patterns for stars in this metallicity range are of particular
importance for studies of the shape of the metallicity distribution
function of the Milky Way's halo system, in particular for probing the
nature of its low-metallicity tail. In addition, taking into account
suggested evolutionary mixing effects, we find that six of the program
stars (with [Fe/H]≤-3.35) possess atmospheres that were likely
originally enriched in carbon, relative to iron, during their
main-sequence phases. These stars do not exhibit overabundances of
their s-process elements, and hence may be, within the error bars,
additional examples of the so-called CEMP-no class of objects.
Description:
We report on the discovery of seven low-metallicity stars selected
from the Hamburg/ESO Survey, six of which are extremely metal-poor
(EMP, [Fe/H]≤-3.0), with four having [Fe/H]≤-3.5.
Our program stars were originally selected according to the strength
of their Ca II K lines in low-resolution (R∼300) objective-prism
spectra, in comparison with their broadband de-reddened (J-K)0
colors. Medium-resolution (R∼2000) spectroscopic observations were
then carried out in order to determine first-pass estimates of their
stellar atmospheric parameters. Finally, high-resolution (R∼35000)
spectra were gathered, in order to determine elemental abundances (or
upper limits) for as many elements as possible.
Medium-resolution spectroscopic follow-up was carried out along with
observations of the sample of Carbon-Enhanced Metal-Poor (CEMP)
candidates described by Placco et al. 2011 (cat. J/AJ/142/188), using
the 4.1m SOAR Telescope (HE2141-3741, HE2157-3404, and HE2323-6549 on
2011-08-03) and the 3.5m ESO New Technology Telescope (NTT;
HE0048-6408, HE0139-2826, and HE2233-4724, HE2318-1621 on 2011-10-17).
Most of the observations were carried out in semester 2011B, using the
Goodman Spectrograph on the SOAR telescope, with the 600l/mm grating,
the blue setting, a 1.03'' slit, and covering the wavelength range
3550-5500Å. This combination yielded a resolving power of R∼1500,
and S/N∼30/pixel at 4000Å. NTT/EFOSC-2 data were also gathered in
semester 2011B with a similar setup, using Grism7 (600gr/mm) with a
1.00'' slit, covering the wavelength range of 3400-5100Å. The
resolving power (R∼2000) and signal-to-noise ratios S/N∼40 per pixel
at 4000Å, were similar to the SOAR data.
High-resolution data were obtained, during semesters 2011B
(HE2141-3741, HE2157-3404, and HE2323-6549 on 2011-11-03), 2012B
(HE0048-6408, HE0139-2826, and HE2233-4724 on 2012 09 09), and 2013B
(HE2318-1621 on 2013-10-26), using the Magellan Inamori Kyocera
Echelle spectrograph (MIKE) on the Magellan-Clay Telescope at Las
Campanas Observatory. The observing setup included a 0.7'' and a 1.0''
slits with 2*2 on-chip binning, which yielded a resolving power of
R∼35000 in the blue spectral range and R∼28000 in the red spectral
range, with an average S/N∼85 per pixel at 5200Å. MIKE spectra have
nearly full optical wavelength coverage from ∼3500-9000Å.
Measurements of atomic absorption lines were based on a line list
assembled from the compilations of Aoki et al. (2002ApJ...567.1166A 2002ApJ...567.1166A)
and Barklem et al. 2005 (cat. J/A+A/439/129), as well as from a
collection retrieved from the VALD database (Kupka et al.,
1999A&AS..138..119K 1999A&AS..138..119K). References for the atomic gf values can be found
in these references. Equivalent-width measurements were obtained by
fitting Gaussian profiles to the observed atomic lines. Table2 lists
the lines used in this work, their measured equivalent widths, and the
derived abundances from each line.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 117 406 Equivalent-width measurements
table3.dat 82 7 Derived stellar parameters
table4.dat 42 168 Abundances for individual species
--------------------------------------------------------------------------------
See also:
J/ApJ/778/56 : Hamburg/ESO Survey extremely metal-poor stars (Cohen+, 2013)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/762/26 : Most metal-poor stars. II. Galactic halo stars (Yong+, 2013)
J/ApJ/762/25 : The most metal-poor stars in HES and SDSS. I. (Norris+, 2013)
J/AJ/142/188 : Metal-poor stars from the HES using CH G-band (Placco+, 2011)
J/AJ/139/1051 : Carbon-enhanced metal-poor stars in the Galaxy (Placco+, 2010)
J/A+A/484/721 : HES survey. IV. Candidate metal-poor stars (Christlieb+, 2008)
J/ApJ/652/1585 : Bright metal-poor stars from HES survey (Frebel+, 2006)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/A+A/375/366 : Carbon stars from the Hamburg/ESO survey (Christlieb+ 2001)
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/AJ/90/2089 : Stars of very low metal abundance. I (Beers+, 1985)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Ion Ion designation
7- 13 F7.2 0.1nm lambda Wavelength λ (in Å)
15- 18 F4.2 eV EP ? Excitation potential χ
20- 24 F5.2 [-] loggf ? Log of the oscillation strength
26- 30 F5.1 0.1pm EW0048 ? Equivalent width in HE 0048-6408
(in mÅ)
32 A1 --- f_EW0048 [sa] Flag on EW0048 (a=upper limit;
s=derived from spectral synthesis)
34- 37 F4.1 [-] Abd0048 ? Log number abundance in HE 0048-6408
(log ε)
39- 43 F5.1 0.1pm EW0139 ? Equivalent width in HE 0139-2826
(in mÅ)
45 A1 --- f_EW0139 [sa] Flag on EW0139 (a=upper limit;
s=derived from spectral synthesis)
47- 50 F4.1 [-] Abd0139 ? Log number abundance in HE 0139-2826
(log ε)
52- 56 F5.1 0.1pm EW2141 ? Equivalent width in HE 2141-3741
(in mÅ)
58 A1 --- f_EW2141 [sa] Flag on EW2141 (a=upper limit;
s=derived from spectral synthesis)
60- 63 F4.1 [-] Abd2141 ? Log number abundance in HE 2141-3741
(log ε)
65- 69 F5.1 0.1pm EW2157 ? Equivalent width in HE 2157-3404
(in mÅ)
71 A1 --- f_EW2157 [sa] Flag on EW2157 (a=upper limit;
s=derived from spectral synthesis)
73- 76 F4.1 [-] Abd2157 ? Log number abundance in HE 2157-3404
(log ε)
78- 82 F5.1 0.1pm EW2233 ? Equivalent width in HE 2233-4724
(in mÅ)
84 A1 --- f_EW2233 [sa] Flag on EW2233 (a=upper limit;
s=derived from spectral synthesis)
86- 89 F4.1 [-] Abd2233 ? Log number abundance in HE 2233-4724
(log {epsilon)}
91 A1 --- f_Abd2233 [a] Flag on Abd2233 (a=upper limit;
s=derived from spectral synthesis)
93- 97 F5.1 0.1pm EW2318 ? Equivalent width in HE 2318-1621
(in mÅ)
99 A1 --- f_EW2318 [sa] Flag on EW2318 (a=upper limit;
s=derived from spectral synthesis)
101-104 F4.1 [-] Abd2318 ? Log number abundance in HE 2318-1621
(log ε)
106-110 F5.1 0.1pm EW2323 ? Equivalent width in HE 2323-6549
(in mÅ)
112 A1 --- f_EW2323 [sa] Flag on EW2323 (a=upper limit;
s=derived from spectral synthesis)
114-117 F4.1 [-] Abd2323 ? Log number abundance in HE 2323-6549
(log ε)
--------------------------------------------------------------------------------
Byte-by-byte Description of file:table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [HE ]
4- 12 A9 --- HE Star name in Hamburg/ESO survey (HHMM-DDMM)
14- 17 I4 K Teff1 Effective temperature (1)
19- 21 I3 K e_Teff1 Uncertainty in Teff (1)
23- 26 F4.2 [cm/s2] logg1 Log of surface gravity (1)
28- 31 F4.2 [cm/s2] e_logg1 Uncertainty in logg (1)
33- 37 F5.2 [Sun] [Fe/H]1 Metallicity (1)
39- 42 F4.2 [Sun] e_[Fe/H]1 Metallicity (1)
44- 47 I4 K Teff2 Effective temperature (2)
49- 51 I3 K e_Teff2 Uncertainty in Teff2 (2)
53- 56 F4.2 [cm/s2] logg2 Log of surface gravity (2)
58- 61 F4.2 [cm/s2] e_logg2 Uncertainty in logg2 (2)
63- 66 F4.2 km/s Vt Microturbulent velocity ξ (2)
68- 71 F4.2 km/s e_Vt Uncertainty in Vt (2)
73- 77 F5.2 [Sun] [Fe/H]2 Metallicity (2)
79- 82 F4.2 [Sun] e_[Fe/H]2 Metallicity (2)
--------------------------------------------------------------------------------
Note (1): Estimates of the stellar atmospheric parameters from
medium-resolution 4.1m SOAR Telescope/3.5m ESO New Technology Telescope
(SOAR/NTT) spectra obtained using the n-SSPP, a modified version of the
SEGUE Stellar Parameter Pipeline (SSPP).
Note (2): From the Magellan Inamori Kyocera Echelle spectrograph (MIKE) on the
Magellan-Clay Telescope at Las Campanas Observatory.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [HE ]
4- 12 A9 --- HE Star name in Hamburg/ESO survey (HHMM-DDMM)
14- 18 A5 --- Ion Ion designation
20- 24 F5.2 [-] log(e) ? Log number abundance (log ε)
26 A1 --- l_[X/Fe] [<] Upper limit flag on [X/Fe]
27- 31 F5.2 [Sun] [X/Fe] ? Derived elemental abundance ratio (1)
33 A1 --- f_[X/Fe] [a] Indicates [FeI/H] and [FeII/H] values
35- 38 F4.2 [Sun] sigma ? Standard error of the mean (σ)
40- 42 I3 --- N ? NUmber of lines
--------------------------------------------------------------------------------
Note (1): Calculated taking solar abundances from Asplund et al.
(2009ARA&A..47..481A 2009ARA&A..47..481A).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Placco et al., Paper I. 2013ApJ...770..104P 2013ApJ...770..104P
Placco et al., Paper II. 2014ApJ...781...40P 2014ApJ...781...40P
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 02-Dec-2015