J/ApJ/948/38 Extremely metal-poor stars with GRACES. I. (Jeong+, 2023)
Search for extremely metal-poor stars with Gemini-N/GRACES.
I. Chemical-abundance analysis.
Jeong M., Lee Y.S., Beers T.C., Placco V.M., Kim Y.K., Koo J.-R.,
Lee H.-G., Yang S.-C.
<Astrophys. J., 948, 38 (2023)>
=2023ApJ...948...38J 2023ApJ...948...38J
ADC_Keywords: Abundances; Spectra, optical; Stars, metal-deficient;
Effective temperatures
Keywords: Chemical abundances ; Galaxy chemical evolution ; Milky Way Galaxy ;
Interstellar abundances ; Galaxy stellar content
Abstract:
We present stellar parameters and abundances of 13 elements for
18 very metal-poor (VMP; [Fe/H]<-2.0) stars, selected as extremely
metal-poor (EMP; [Fe/H]<-3.0) candidates from the Sloan Digital Sky
Survey (SDSS) and Large sky Area Multi-Object Fiber Spectroscopic
Telescope (LAMOST) survey. High-resolution spectroscopic observations
were performed using GEMINI-N/GRACES. We find 10 EMP stars among our
candidates, and we newly identify three carbon-enhanced metal-poor
stars with [Ba/Fe]<0. Although chemical abundances of our VMP/EMP
stars generally follow the overall trend of other Galactic halo stars,
there are a few exceptions. One Na-rich star ([Na/Fe]=+1.14) with low
[Mg/Fe] suggests a possible chemical connection with second-generation
stars in a globular cluster. The progenitor of an extremely Na-poor
star ([Na/Fe]=-1.02) with high K- and Ni-abundance ratios may have
undergone a distinct nucleosynthesis episode, associated with
core-collapse supernovae (SNe) having a high explosion energy. We have
also found a Mg-rich star ([Mg/Fe]=+0.73) with slightly enhanced Na
and extremely low [Ba/Fe], indicating that its origin is not
associated with neutron-capture events. On the other hand, the origin
of the lowest Mg abundance ([Mg/Fe]=-0.61) star could be explained by
accretion from a dwarf galaxy, or formation in a gas cloud largely
polluted by SNe Ia. We have also explored the progenitor masses of our
EMP stars by comparing their chemical-abundance patterns with those
predicted by Population III SNe models, and find a mass range of
10-26M☉, suggesting that such stars were primarily responsible
for the chemical enrichment of the early Milky Way.
Description:
We selected extremely metal-poor (EMP) candidates from the
low-resolution (R∼1800) spectroscopic surveys of SDSS and LAMOST for
follow-up observations with high-resolution spectroscopy.
We carried out high-resolution spectroscopic observations for 20 stars
(18 EMP candidates and two reference stars), making use of Gemini
Remote Access to the CFHT ESPaDOnS Spectrograph (GRACES; R∼45000 in
the spectral range of 4000-10000Å) on the 8m Gemini-North telescope
during the 2016A (GN-2016A-Q-17), 2018B (GN-2018B-Q-122), and 2019B
(GN-2019B-Q-115, Q-219, and Q-310) semesters.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 134 20 Observation details of our program stars
table6.dat 23 205 Line lists
table8.dat 56 240 *Detailed chemical abundances for each object
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Note on table8.dat: The Li and Ba abundance ratios are derived from
the spectral synthesis.
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
V/156 : LAMOST DR7 catalogs (Luo+, 2019)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/90/2089 : Stars of very low metal abundance. I (Beers+, 1985)
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/AJ/107/1577 : Halo red giants reddening (Anthony-Twarog+, 1994)
J/AJ/119/2866 : Proper motions of metal-poor stars (Beers+, 2000)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/ApJ/652/1585 : Bright metal-poor stars from HES survey (Frebel+, 2006)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/ApJ/658/367 : Abundances of carbon stars in Galactic halo (Komiya+, 2007)
J/AJ/136/2070 : SEGUE stellar parameter pipeline. III. (Allende Prieto+, 2008)
J/A+A/484/721 : HES survey. IV. Candidate metal-poor stars (Christlieb+, 2008)
J/AJ/136/2050 : SEGUE stellar parameter pipeline. II. (Lee+, 2008)
J/A+A/497/497 : Physical parameters from JHK flux (Gonzalez-Hernandez+, 2009)
J/A+A/503/545 : Equivalent widths of Li, Na, Fe, Ca in NGC 6397 (Lind+, 2009)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/A+A/512/A54 : Teff and Fbol from Infrared Flux Method (Casagrande+, 2010)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/A+A/509/A93 : Carbon-enhanced metal-poor stars (Masseron+, 2010)
J/A+A/522/A26 : Fe Abundances in metal-poor stars (Sbordone+ 2010)
J/AJ/141/90 : SEGUE stellar parameter pipeline. V. (Lee+, 2011)
J/A+A/534/A136 : Halo red giants from the SEGUE survey (Martell+, 2011)
J/AJ/141/89 : SEGUE stellar parameter pipeline. IV. (Smolinski+, 2011)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
J/ApJ/760/86 : Equivalent widths for 13 NGC2419 RGB stars (Cohen+, 2012)
J/AJ/145/13 : Metal-poor stars from SDSS/SEGUE. I. Abundances (Aoki+, 2013)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/773/33 : Analysis of the metal-poor subgiant BD+44 493 (Ito+, 2013)
J/ApJ/762/26 : Most metal-poor stars. II. Galactic halo stars (Yong+, 2013)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/A+A/571/A40 : Abundances in 2 extremely metal-poor stars (Spite+, 2014)
J/ApJ/807/171 : SkyMapper Survey metal-poor star spec. (Jacobson+, 2015)
J/AJ/150/187 : Abundances and stellar parameters of LAMOST stars (Lee+, 2015)
J/ApJ/812/109 : HST & Keck spectroscopy of bright CEMP-s stars (Placco+, 2015)
J/A+A/586/A158 : Binary properties of CH and CEMP stars (Jorissen+, 2016)
J/ApJS/222/19 : KPNO spectroscopy of G & K dwarfs HIP stars (Kim+, 2016)
J/ApJ/833/20 : Carbon-enhanced metal-poor (CEMP) star abund. (Yoon+, 2016)
J/AJ/154/52 : Metal-poor stars from SDSS/SEGUE. I. (Matsuno+, 2017)
J/A+A/601/A112 : GES iDR4 Mg-Al anticorrelation in GCs (Pancino+, 2017)
J/A+A/608/A46 : Constraining cosmic scatter (Reggiani+, 2017)
J/A+A/618/A133 : Non standard s-process in massive rot. stars (Choplin+, 2018)
J/ApJ/857/46 : Modelled vs observed abundances of EMP stars (Ishigaki+, 2018)
J/ApJ/897/78 : RAVE J183013.5-455510 equivalent-widths (Placco+, 2020)
J/ApJ/905/20 : Metal-poor stars observed with SALT/HRS (Rasmussen+, 2020)
J/A+A/654/A170 : Abundances of metal-poor stars (Matas Pinto+, 2021)
J/MNRAS/507/43 : Study of the Spite plateau with GALAH DR3 (Simpson+, 2021)
J/ApJ/931/147 : Very metal-poor stars with LAMOST & Subaru. II. (Li+, 2022)
J/ApJS/262/8 : Sp. follow-up of low-metallicity S-PLUS stars (Placco+, 2022)
J/ApJS/259/60 : SEGUE-2 updated stellar parameter pipeline (Rockosi+, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 38 A38 --- ProgID Gemini program identifier
40- 65 A26 --- Name Star name
67- 71 A5 --- ID Abbreviated identifier
73 A1 --- f_ID [c] c = reference star (1)
75- 84 A10 "Y/M/D" Date Date of observation (UT)
86- 87 I2 h RAh Hour of right ascension (J2000)
89- 90 I2 min RAm Minute of right ascension (J2000)
92- 96 F5.2 s RAs Second of right ascension (J2000)
98 A1 --- DE- Sign of declination (J2000)
99-100 I2 deg DEd Degree of declination (J2000)
102-103 I2 arcmin DEm Arcminute of declination (J2000)
105-108 F4.1 arcsec DEs Arcsecond of declination (J2000)
110-113 F4.1 mag gmag [9.1/16.5] g-band magnitude
115 A1 --- n_gmag [a] a = V magnitude
117-122 A6 s Exp Exposure time
123 A1 --- f_Exp [b] Flag on exposure time (1)
125-126 I2 pix-1 S/N [31/93] Signal-to-noise ratio; average value
around 5500Å
128-134 F7.2 km/s HRV [-379/145] Heliocentric radial velocity
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Note (1): Flag as follows:
b = Even though we obtained multiple exposures, we used the spectrum obtained
with 20s exposure in our analysis to validate the abundance analysis of
our program stars, which have the spectrum with the similar S/N to this
object.
c = The reference stars, J0226 and J1522, studied by Ito+ (2013, J/ApJ/773/33)
and Matsuno+ (2017, J/AJ/154/52), respectively.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.1 --- Species [11.0/56.1] Species code identifier (1)
6- 12 F7.2 0.1nm lambda [4702.99/7698.96] Wavelength; Angstroms
14- 17 F4.2 eV ExPot [0/4.55] Excitation potential
19- 23 F5.2 [-] log(gf) [-5.46/0.65] log oscillator strength
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Note (1): In X.Y format where X is the element number and
Y is the ionization state.
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Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- ID Short object identifier; see Table 1
7- 11 A5 --- Species Species identifier
13- 15 I3 --- N [1/121]? Number of lines
17 A1 --- l_loge(X) Upper limit flag on loge(X)
19- 23 F5.2 [-] loge(X) [-2.9/5.9]? Log abundance of Species
25 A1 --- l_[X/Fe] Upper limit flag on [X/Fe]
27- 31 F5.2 [Sun] [X/Fe] [-2.1/4.3]? Log Species number abundance
relative to Fe
33- 36 F4.2 [Sun] SE [0.02/0.8]? Standard error in the mean of
[X/Fe]
38- 41 F4.2 [Sun] DelTeff [0/0.2]? Uncertainty in [X/Fe] due to ±100
in Teff
43- 46 F4.2 [Sun] Dellogg [0/0.1]? Uncertainty in [X/Fe] due to
±0.2dex in log (g)
48- 51 F4.2 [Sun] DelVt [0/0.1]? Uncertainty in [X/Fe] due to
±0.2km/s in Vturb
53- 56 F4.2 [Sun] TE [0.02/0.4]? Total error in [X/Fe] (1)
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Note (1): calculated by quadrature sum of SE and errors caused by deviation
of the other errors.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 25-Apr-2025