J/MNRAS/485/2167 M-type stars in LAMOST DR5 unclassified spectra (Guo+, 2019)
Recognition of M-type stars in the unclassified spectra of LAMOST DR5 using a
hash-learning method.
Guo Y.-X., Luo A.-L., Zhang S., Du B., Wang Y.-F., Chen J.-J., Zuo F.,
Kong X., Hou Y.-H.
<Mon. Not. R. Astron. Soc., 485, 2167-2178 (2019)>
=2019MNRAS.485.2167G 2019MNRAS.485.2167G (SIMBAD/NED BibCode)
ADC_Keywords: Spectroscopy ; Stars, M-type ; Stars, late-type ; Optical
Keywords: techniques: spectroscopic - stars: late-type - stars: low-mass
Abstract:
Our study aims to recognize M-type stars which are classified as
'UNKNOWN' due to poor quality in the Large sky Area Multi-Object fiber
Spectroscopic Telescope (LAMOST) DR5 V1. A binary nonlinear hashing
algorithm based on Multi-Layer Pseudo-Inverse Learning (ML-PIL) is
proposed to effectively learn spectral features for M-type-star
detection, which can overcome the bad fitting problem of template
matching, particularly for low S/N spectra. The key steps and the
performance of the search scheme are presented. A positive data set is
obtained by clustering the existing M-type spectra to train the ML-PIL
networks. By employing this new method, we find 11410 M-type spectra
out of 642178 'UNKNOWN' spectra, and provide a supplemental catalogue.
Both the supplemental objects and released M-type stars in DR5 V1 are
composed of a whole M-type sample, which will be released in the
official DR5 to the public in June 2019. All the M-type stars in the
data set are classified as giants and dwarfs by two suggested
separators: (1) a colour diagram of H versus J-K from 2MASS, (2) line
indices CaOH versus CaH1, and the separation is validated with the
Hertzsprung-Russell diagram (HRD) derived from Gaia DR2. The magnetic
activities and kinematics of M dwarfs are also provided with the
equivalent width (EW) of the Hα emission line and the
astrometric data from Gaia DR2 respectively.
Description:
LAMOST is a 4-m reflecting Schmidt telescope with a large field of
view (FoV) of 5 degrees in diameter. It has 4000 fibres mounted on its
focal plane and 16 spectrographs with 32 CCD cameras, so that it can
simultaneously observe up to 4000 objects (Cui et al.
2012RAA....12.1197C 2012RAA....12.1197C). The raw CCD data are reduced and analyzed by the
LAMOST data pipelines, which consist of a 2D pipeline and a 1D
pipeline. The primary functions of the 2D pipeline include bias
calibration, flat-field correction, spectral extraction, sky
subtraction, wavelength calibration, flux calibration, and
sub-exposures combination. The calibrated spectra from the 2D pipeline
are then fed to the 1D pipeline which performs spectral classification
and parameter determination based on template matching and chi-square
criteria (Luo et al. 2015RAA....15.1095L 2015RAA....15.1095L, Cat. V/146).
By July 2017, LAMOST had completed its five-year regular survey. The
LAMOST DR5 V1 includes 9017844 spectra of stars, galaxies, quasars,
and unrecognized objects. These spectra cover the wavelength range
from 3690 to 9100Å with a resolution of R∼1800 at the wavelength
5500Å.
Among the 9 million spectra in LAMOST DR5 V1, 642178 unrecognized
spectra were labelled 'UNKNOWN'. During the classification process of
the 1D pipeline, a spectrum is classified as 'UNKNOWN' if the
confidence of the classification result is lower than a given
threshold value. In this study we build a multilayer Pseudo-Inverse
Learning (ML-PIL) to fulfil the hash-learning process, so as to search
M-type stars in the 'UNKNOWN' spectra of LAMOST DR5 V1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 388 11410 Supplemental catalogue of 11410 recognized
M-type stars
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See also:
V/164 : LAMOST DR5 catalogs (Luo+, 2019)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- ID LAMOST object ID (JHHMMSS.ss+DDMMSS.s)
21- 30 A10 "Y:M:D" ObsDate LAMOST Target observation date
32- 36 I5 d MJD Modified Julian Day
38- 57 A20 --- PlanId LAMOST Plan Name
59- 60 I2 --- specId LAMOST unique spectra ID
62- 64 I3 --- FiberId LAMOST Fiber ID
66- 76 F11.7 deg RAdeg Right ascension (J2000)
78- 87 F10.7 deg DEdeg Declination (J2000)
89- 94 F6.2 --- SNR Signal to noise ratio of r filter
96- 97 A2 --- subClass Stellar Sub-Class
99-106 F8.2 km/s HRV Heliocentric radial velocity
108-114 F7.2 --- EWHa ? Equivalent width of Hα line
116-123 F8.3 --- e_EWHa ? Error on EWHa
125-129 F5.2 --- TiO5 ? Spectral index of TiO5
131-135 F5.2 --- CaH2 ? Spectral index of CaH2
137-141 F5.2 --- CaH3 ? Spectral index of CaH3
143-147 F5.2 --- TiO1 ? Spectral index of TiO1
149-153 F5.2 --- TiO2 ? Spectral index of TiO2
155-159 F5.2 --- TiO3 ? Spectral index of TiO3
161-166 F6.2 --- TiO4 ? Spectral index of TiO4
168-172 F5.2 --- CaH1 ? Spectral index of CaH1
174-179 F6.2 --- CaOH ? Spectral index of CaOH
181-186 F6.3 --- e_TiO5 ? Error on TiO5
188-193 F6.3 --- e_CaH2 ? Error on CaH2
195-200 F6.3 --- e_CaH3 ? Error on CaH3
202-207 F6.3 --- e_TiO1 ? Error on TiO1
209-214 F6.3 --- e_TiO2 ? Error on TiO2
216-221 F6.3 --- e_TiO3 ? Error on TiO3
223-228 F6.3 --- e_TiO4 ? Error on TiO4
230-235 F6.3 --- e_CaH1 ? Error on CaH1
237-242 F6.3 --- e_CaOH ? Error on CaOH
244-251 F8.2 --- Na ? Line index of Na line
253-258 F6.2 --- zeta ? Metal-sensitive parameter
(Yi et al. 2014AJ....147...33Y 2014AJ....147...33Y;
Guo et al. 2015RAA....15.1182G 2015RAA....15.1182G,
Cat. J/other/RAA/15.1182)
260-266 F7.3 --- e_zeta ? Error on zeta
268 I1 --- Giant Luminosity class (0 for dwarfs,
1 for giants)
270-277 F8.5 mas plx ? Parallax
279-284 F6.4 mas e_plx ? Error on plx
286-293 F8.3 mas/yr pmRA ? Proper motion in right ascension
295-299 F5.3 mas/yr e_pmRA ? Error on pmRA
301-308 F8.3 mas/yr pmDE ? Proper motion in declination
310-314 F5.3 mas/yr e_pmDE ? Error on pmDE
316-327 F12.2 pc Dist ? Distance in parsecs from the sun
329-336 F8.2 km/s U ? Galactic space velocity, the direction
towards the center of the galaxy is
positive
338-346 F9.2 km/s V ? Galactic space velocity, the direction
towards the Milky Way's rotation is
positive
348-355 F8.2 km/s W ? Galactic space velocity, the direction
towards the North Pole of the Milky Way
is positive
357-366 F10.2 pc zgal ? Verticle Distance from the plane
368-377 F10.6 deg GLON ? Galactic Longtitude of the object
379-388 F10.6 deg GLAT ? Galactic Latitude of the object
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 19-Sep-2022