J/ApJ/923/183 Metallicities of very low metal-poor stars (Li, 2021)
Fuzzy Cluster Analysis: application to determining metallicities for very
metal-poor stars.
Li H.
<Astrophys. J., 923, 183 (2021)>
=2021ApJ...923..183L 2021ApJ...923..183L
ADC_Keywords: Abundances, [Fe/H]; Stars, metal-deficient; Spectra, optical
Keywords: Population II stars
Abstract:
This work presents a first attempt to apply fuzzy cluster analysis
(FCA) to analyzing stellar spectra. FCA is adopted to categorize line
indices measured from LAMOST low-resolution spectra, and automatically
remove the least metallicity-sensitive indices. The FCA-processed
indices are then transferred to the artificial neural network (ANN) to
derive metallicities for 147 very metal-poor (VMP) stars that have
been analyzed by high-resolution spectroscopy. The FCA-ANN method
could derive robust metallicities for VMP stars, with a precision of
∼0.2dex compared with high-resolution analysis. The recommended FCA
threshold value λ for this test is between 0.9965 and 0.9975.
After reducing the dimension of the line indices through FCA, the
derived metallicities are still robust, with no loss of accuracy, and
the FCA-ANN method performs stably for different spectral quality from
[Fe/H]∼1.8 down to -3.5. Compared with traditional classification
methods, FCA considers ambiguity in groupings and noncontinuity of
data, and is thus more suitable for observational data analysis.
Though this early test uses FCA to analyze low-resolution spectra, and
feeds the input to the ANN method to derive metallicities, FCA should
be able to, in the large data era, also analyze slitless spectroscopy
and multiband photometry, and prepare the input for methods not
limited to ANN, in the field of stellar physics for other studies,
e.g., stellar classification, identification of peculiar objects. The
literature-collected high-resolution sample can help improve pipelines
to derive stellar metallicities, and systematic offsets in
metallicities for VMP stars for three published LAMOST catalogs have
been discussed.
Description:
The analysis of this paper is based on spectra obtained through LAMOST
DR5 (V/164), which was released in 2019 July. The selected LAMOST
targets have been cross-matched with very metal-poor (VMP) stars
confirmed by high-resolution spectroscopy from SAGA database
(Suda+ 2011, J/MNRAS/412/843) and JINAbase
(Abohalima & Frebel 2018ApJS..238...36A 2018ApJS..238...36A).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 299 147 List of the very metal-poor (VMP) stars used
refs.dat 54 58 References
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/164 : LAMOST DR5 catalogs (Luo+, 2019)
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/AJ/117/981 : Estimation of stellar metal abundance. II. (Beers+, 1999)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/A+A/442/961 : Lithium content of the Gal. Halo stars (Charbonnel+, 2005)
J/AJ/132/137 : Abund. of extremely metal-poor carbon stars (Cohen+, 2006)
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/A+A/484/721 : HES survey. IV. Cand. metal-poor stars (Christlieb+, 2008)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/A+A/501/519 : Extremely metal-poor turnoff stars abund. (Bonifacio+, 2009)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/ApJ/743/140 : Abund. (Be,α) in metal-poor stars (Boesgaard+, 2011)
J/ApJ/742/54 : CASH project II. Extremely metal-poor stars (Hollek+, 2011)
J/MNRAS/412/843 : SAGA extremely metal-poor stars (Suda+, 2011)
J/A+A/548/A34 : Abundances of carbon-enhanced metal-poor stars (Allen+, 2012)
J/AJ/145/13 : Metal-poor stars from SDSS/SEGUE. I. Abundances (Aoki+, 2013)
J/ApJ/778/56 : Hamburg/ESO Survey extremely metal-poor stars (Cohen+, 2013)
J/ApJ/771/67 : Abundances for 97 metal-poor stars. II. (Ishigaki+, 2013)
J/ApJ/762/26 : Most metal-poor stars. II. Galactic halo stars (Yong+, 2013)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/ApJ/797/13 : Abundances of bright metal-poor stars (Schlaufman+, 2014)
J/ApJ/807/171 : SkyMapper Survey metal-poor star sp. (Jacobson+, 2015)
J/ApJ/798/110 : Equivalent widths of LAMOST metal-poor stars (Li+, 2015)
J/ApJ/808/16 : The Cannon: a new approach to determine abund. (Ness+, 2015)
J/ApJ/819/110 : Extremely metal-poor gal. in SDSS II. (Sanchez Almeida+ 2016)
J/A+A/614/A68 : Carbon-enhanced metal-poor stars sample (Caffau+, 2018)
J/A+A/612/A98 : APOGEE full information on classes (Garcia-Dias+, 2018)
J/ApJ/858/92 : RPA Southern Pilot Search of 107 Stars (Hansen+, 2018)
J/ApJS/238/16 : LAMOST-DR3 very metal-poor star catalog (Li+, 2018)
J/ApJ/868/110 : R-Process Alliance: 1st release in Gal. halo (Sakari+, 2018)
J/ApJS/245/34 : Abundances for 6 million stars from LAMOST DR5 (Xiang+, 2019)
J/ApJ/891/39 : LAMOST very metal-poor stars of the Gal. halo (Yuan+, 2020)
http://www.lamost.org/ : LAMOST home page
http://jinabase.pythonanywhere.com/ : JINAbase - database for metal-poor stars
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 deg RAdeg Right Ascension (J2000)
12- 20 F9.6 deg DEdeg [-8.6/58.7] Declination (J2000)
22- 25 I4 K Teff [4210/6650]?=9999 Effective temperature
derived from high-resolution spectra
27- 30 F4.2 --- logg [0.01/5]?=9.99 Surface gravity derived
from high-resolution spectra
32- 36 F5.2 --- [Fe/H] [-4.8/-2] Metallicity derived from
high-resolution spectra
38- 43 F6.2 --- SNg [21.5/592] SNR at g-band of the LAMOST
spectra
45- 50 F6.2 --- SNr [23.8/913] SNR at r-band of the LAMOST
spectra
52- 56 F5.2 --- FeH-FCA865 [-4.3/-0.8] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9865
58- 62 F5.2 --- FeH-FCA885 [-5.3/0.8] Metallicity derived from LAMOST
spectra, FCA clustered, threshold=0.9885
64- 68 F5.2 --- FeH-FCA965 [-4.6/-1.9] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9965
70- 74 F5.2 --- FeH-FCA975 [-4.6/-1.9] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9975
76- 80 F5.2 --- FeH-FCA980 [-4.9/-1.4] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9980
82- 86 F5.2 --- FeH-FCA983 [-4.3/-1.2] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9983
88- 92 F5.2 --- FeH-FCA985 [-4.8/-1.7] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9985
94- 98 F5.2 --- FeH-FCA990 [-7.6/-1.5] Metallicity derived from
LAMOST spectra, FCA clustered,
threshold=0.9990
100- 105 F6.3 0.1nm CaHK [0/21.43] Line index CaHK
107- 112 F6.3 0.1nm K24 [0/11.34] Line index K24
114- 118 F5.3 0.1nm K12 [0/8.16] Line index K12
120- 124 F5.3 0.1nm K6 [0/4.92] Line index K6
126- 130 F5.3 0.1nm HeI4026 [0/0.9] Line index HeI4026
132- 137 F6.3 0.1nm HD24 [0/10.55] Line index HD24
139- 143 F5.3 0.1nm HD12 [0/6.57] Line index HD12
145- 150 F6.3 0.1nm CN1 [0/22] Line index CN1
152- 157 F6.3 0.1nm CN2 [0/22.95] Line index CN2
159- 163 F5.3 0.1nm Ca4227 [0/2.13] Line index Ca4227
165- 169 F5.3 0.1nm G4300 [0/8.93] Line index G4300
171- 175 F5.3 0.1nm G1 [0/8.34] Line index G1
177- 181 F5.3 0.1nm Fe4383 [0/4.45] Line index Fe4383
183- 187 F5.3 0.1nm Ca4455 [0/0.9] Line index Ca4455
189- 193 F5.3 0.1nm HeI4471 [0/0.82] Line index HeI4471
195- 199 F5.3 0.1nm Fe4531 [0/2.66] Line index Fe4531
201- 205 F5.3 0.1nm Hbeta [0.016/7.66] Line index Hbeta
207- 211 F5.3 0.1nm Fe5015 [0/3.4] Line index Fe5015
213- 218 F6.3 0.1nm Mg1 [0/29.87] Line index Mg1
220- 224 F5.3 0.1nm Mg2 [0.1/7.02] Line index Mg2
226- 230 F5.3 0.1nm Mgb [0/4.31] Line index Mgb
232- 236 F5.3 0.1nm Fe5270 [0/1.86] Line index Fe5270
238- 242 F5.3 0.1nm Fe5335 [0/1.74] Line index Fe5335
244- 248 F5.3 0.1nm Fe5406 [0/0.87] Line index Fe5406
250- 254 F5.3 0.1nm Fe5709 [0/0.6] Line index Fe5709
256- 260 F5.3 0.1nm Fe5782 [0/0.68] Line index Fe5782
262- 266 F5.3 0.1nm NaD [0/9.88] Line index NaD
268- 272 F5.2 --- FeH-DDPayne [-3.7/-0.9]?=-9.99 Metallicity derived
from LAMOST spectra, from DDPayne
274- 278 F5.2 --- FeH-DR5v3 [-2.5/-1.37]?=-9.99 Metallicity derived
from LAMOST spectra, from official DR5v3
280- 284 F5.2 --- FeH-GSN [-2.41/-1.39]?=-9.99 Metallicity derived
from LAMOST spectra, from generative
spectrum network (GSN)
286- 299 A14 --- r_[Fe/H] Reference of high-resolution analyses
(see refs.dat file)
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Ref Reference code
16- 34 A19 --- BibCode Bibcode of the reference
36- 54 A19 --- Comm Comment (Catalog's reference in VizieR)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 24-May-2023