J/ApJS/240/31 M-subdwarf research. I. LAMOST DR4 spectra obs. (Zhang+, 2019)
M-subdwarf research.
I. Identification, modified classification system, and sample construction.
Zhang S., Luo A.-L., Comte G., Gizis J.E., Wang R., Li Y., Qin Li, Kong X.,
Bai Y., Yi Z.
<Astrophys. J. Suppl. Ser., 240, 31 (2019)>
=2019ApJS..240...31Z 2019ApJS..240...31Z
ADC_Keywords: Radial velocities; Spectra, optical; Stars, M-type;
Photometry, ugriz; Proper motions; Parallaxes, trigonometric;
Stars, late-type
Keywords: stars: late-type ; stars: low-mass ; stars: statistics ; subdwarfs
Abstract:
We propose a revision of the system developed by Lepine+
(2007ApJ...669.1235L 2007ApJ...669.1235L) for spectroscopic M-subdwarf classification.
Based on an analysis of subdwarf spectra and templates from Savcheva+
(2014ApJ...794..145S 2014ApJ...794..145S), we show that the CaH1 feature originally
proposed by Gizis (1997, J/AJ/113/806) is important in selecting
reliable cool subdwarf spectra. This index should be used in
combination with the [TiO5, CaH2+CaH3] relation provided by Lepine+ to
avoid misclassification results. In the new system, the dwarf-subdwarf
separators are first derived from a sample of more than 80000 M dwarfs
and a "labeled" subdwarf subsample, and these objects are all visually
identified from their optical spectra. Based on these two samples, we
refit the initial [TiO5, CaH1] relation and propose a new [CaOH, CaH1]
relation supplementing the [TiO5, CaH1] relation to reduce the impact
of uncertainty in flux calibration on classification accuracy. In
addition, we recalibrate the ζTiO/CaH parameter defined in
Lepine+ to enable its successful application to Large Sky Area
Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. Using
this new system, we select candidates from LAMOST Data Release 4 and
finally identify a set of 2791 new M-subdwarf stars, covering the
spectral sequence from type M0 to M7. This sample contains a large
number of objects located at low Galactic latitudes, especially in the
Galactic anti-center direction, expanding beyond previously published
halo- and thick disk-dominated samples. Besides, we detect magnetic
activity in 141 objects. We present a catalog for this M-subdwarf
sample, including radial velocities, spectral indices and errors, and
activity flags, with a compilation of external data (photometric and
Gaia Data Release 2 astrometric parameters).
Description:
The DR4 of the LAMOST regular survey contains 7620612 spectra,
covering the entire optical band (∼3700-9000Å) at resolution
R∼1800, including 6944971 stellar spectra, 153348 extragalactic
spectra (galaxies and quasi-stellar objects (QSO)), and 522293 spectra
classified as unknown (most of the latter because of insufficient
signal to noise).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 545 2791 The subdwarf catalog
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See also:
III/198 : Palomar/MSU nearby star spectroscopic survey (Hawley+ 1997)
I/298 : LSPM-North Catalog (Lepine+ 2005)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/146 : LAMOST DR1 catalogs (Luo+, 2015)
V/153 : LAMOST DR4 catalogs (Luo+, 2018)
J/AJ/113/806 : M-Subdwarfs (Gizis 1997)
J/AJ/125/1598 : New high PM stars in the northern sky (Lepine+, 2003)
J/AJ/128/426 : Subdwarfs in the SDSS (West+, 2004)
J/AJ/134/2398 : Stellar SEDs in SDSS and 2MASS filters (Covey+, 2007)
J/AJ/141/97 : SDSS DR7 M dwarfs (West+, 2011)
J/AJ/143/67 : SLoWPoKES. II. Wide, low-mass binaries (Dhital+, 2012)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/AJ/145/102 : Spectrosc. of bright M dwarfs in northern sky (Lepine+, 2013)
J/A+A/556/A15 : Effective temperature scale of M dwarfs (Rajpurohit+, 2013)
J/ApJ/783/122 : AllWISE motion survey (Kirkpatrick+, 2014)
J/other/RAA/16.G7 : Nearby M subdwarfs from LAMOST DR2 (Bai+, 2016)
J/ApJS/224/36 : The AllWISE motion survey (AllWISE2) (Kirkpatrick+, 2016)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- LAMOST Target identifier (JHHMMSS.ss+DDMMSS.s)
21- 60 A40 --- FITS LAMOST FITS spectrum name
62- 66 I5 d MJD [55859/57541] Modified Julian Date of
LAMOST observation
68- 87 A20 --- Plan LAMOST Plan name
89- 90 I2 --- SpID [1/16] LAMOST Spectrograph identifier
92- 94 I3 --- Fiber [1/250] LAMOST Fiber identifier
96-105 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
107-115 F9.6 deg DEdeg Declination in decimal degrees (J2000)
117-129 F13.9 deg GLON Galactic longitude
131-143 F13.9 deg GLAT Galactic latitude
145-149 F5.1 --- SNRr [0.4/360] Average spectrum SNR in
LAMOST r band
151-155 F5.1 --- SNRi [1/815] Average spectrum SNR in LAMOST i band
157-160 I4 km/s HRV [-449/524] Heliocentric radial velocity;
this work
162-163 I2 km/s e_HRV [0/68] Standard error in HRV
165-170 F6.3 --- CaOH [-2.2/1.2] This work spectral index of
CaOH band
172-176 F5.3 --- e_CaOH [0.001/1.6]? Error in CaOH (1)
178-182 F5.3 --- CaH1 [0.04/1] This work spectral index of CaH1 band
184-188 F5.3 --- e_CaH1 [0.001/0.8]? Error in CaH1 (1)
190-194 F5.3 --- CaH2 [0.1/1] This work spectral index of CaH2 band
196-200 F5.3 --- e_CaH2 [0.001/0.3]? Error in CaH2 (1)
202-206 F5.3 --- CaH3 [0.3/1] This work spectral index of CaH3 band
208-212 F5.3 --- e_CaH3 [0.001/0.4]? Error in CaH3 (1)
214-218 F5.3 --- TiO5 [0.3/1.6] This work spectral index of TiO5 band
220-224 F5.3 --- e_TiO5 [0.001/0.4]? Error in TiO5 (1)
226-231 F6.3 --- Zeta [-2.3/0.9] Value of Ζ parameter
233 I1 --- SpT [0/7] Spectral subtype; this work (2)
235-239 I5 --- Act [-9999/1] Hα emission tag (3)
241 A1 --- Flag [*] Visual inspection of spectrum
quality flag (4)
243-249 F7.4 mas Plx [-2.5/42.6]? Gaia DR2 parallax
251-256 F6.4 mas e_Plx [0.01/1.2]? Standard error in Plx
258-265 F8.3 mas/yr pmRA [-405.1/343.3]? Gaia DR2 proper motion along RA
267-271 F5.3 mas/yr e_pmRA [0.01/2]? Standard error in pmRA
273-280 F8.3 mas/yr pmDE [-407.4/188]? Gaia DR2 proper motion along DE
282-286 F5.3 mas/yr e_pmDE [0.02/2.1]? Standard error in pmDE
288-296 F9.6 mag Gmag [9.7/20.4]? Mean Gaia DR2 G-band magnitude
298-306 F9.6 mag BPmag [11.8/21.5]? Mean Gaia DR2 BP magnitude
308-316 F9.6 mag RPmag [8.5/19.6]? Mean Gaia DR2 RP magnitude
318-325 F8.6 mag BP-RP [0.4/4.5]? Gaia DR2 (BP-RP) color index
327-339 F13.8 pc Dist [26.7/4173]? Estimated distance (5)
341-353 F13.8 pc b_Dist [26.7/3174]? Lower confidence interval
boundary on Dist
355-367 F13.8 pc B_Dist [26.8/5875]? Upper confidence interval
boundary on Dist
369-380 F12.7 pc rlen [335.4/1741]? Length scale used in the prior
for distance estimation
382-388 F7.4 mag gmag [12.3/22]? Mean Pan-STARRS1 g band PSF AB
magnitude
390-395 F6.4 mag e_gmag [0/0.3]? Error in gmag
397-403 F7.4 mag rmag [10.7/20.5]? Mean Pan-STARRS1 r band PSF AB
magnitude
405-410 F6.4 mag e_rmag [0/0.06]? Error in rmag
412-418 F7.4 mag imag [9/20]? Mean Pan-STARRS1 i band PSF AB magnitude
420-425 F6.4 mag e_imag [0/0.2]? Error in imag
427-433 F7.4 mag zmag [8/20]? Mean Pan-STARRS1 z band PSF AB
magnitude
435-440 F6.4 mag e_zmag [0/0.5]? Error in zmag
442-448 F7.4 mag ymag [7.6/19.7]? Mean Pan-STARRS1 y band PSF AB
magnitude
450-455 F6.4 mag e_ymag [0/0.2]? Error in ymag
457-462 F6.3 mag Jmag [5.9/17]? Default 2MASS J band magnitude
464-469 F6.3 mag Hmag [4.8/17.2]? Default 2MASS H band magnitude
471-476 F6.3 mag Ksmag [4.4/16.1]? Default 2MASS Ks band magnitude
478-482 F5.3 mag e_Jmag [0.01/0.3]? Photometric uncertainty in Jmag
484-488 F5.3 mag e_Hmag [0.01/0.3]? Photometric uncertainty in Hmag
490-494 F5.3 mag e_Ksmag [0.01/0.3]? Photometric uncertainty in Ksmag
496-501 F6.3 mag W1mag [4/17]? AllWISE W1 (3.4um) band standard
aperture magnitude
503-508 F6.3 mag W2mag [3.9/17]? AllWISE W2 (4.6um) band standard
aperture magnitude
510-515 F6.3 mag W3mag [3.6/13.4]? AllWISE W3 (12um) band standard
aperture magnitude
517-521 F5.3 mag W4mag [3.2/9.8]? AllWISE W4 (22um) band standard
aperture magnitude
523-527 F5.3 mag e_W1mag [0.02/0.4]? Uncertainty in W1mag
529-533 F5.3 mag e_W2mag [0.01/0.4]? Uncertainty in W2mag
535-539 F5.3 mag e_W3mag [0.01/0.6]? Uncertainty in W3mag
541-545 F5.3 mag e_W4mag [0.02/0.6]? Uncertainty in W4mag
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Note (1): A blank indicates an infinite value.
Note (2): The determination of spectral subtypes (SpT) for cool subdwarfs, in
this work, follows the definition in Lepine+ (2007ApJ...669.1235L 2007ApJ...669.1235L) in
which the "metallicity" subclass assignment is dependent on the
combined value of the CaH2 and CaH3 indices, given as (Equation (10)):
Sp=1.4x(CaH2+CaH3)2-10x(CaH2+CaH3)+12.4
The derived value of SpT is rounded up to the nearest integer, giving
the spectral subtype value from 0 for M0 to 7 for M7.
See section 4.4.
Note (3): Indicates the magnetic activity of the source as measured by
the Hα emission line.
-9999 = SNR<3 in r or i band (361 occurrences);
0 = no emission features;
1 = active object (141 occurrences).
Note (4):
* = A low quality spectrum or inaccurate flux calibration. The data on
this object should be used carefully.
Note (5): From Bailer-Jones et al. (2018, I/347), based on GAIA DR2.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-May-2019