J/ApJS/280/28 OB associations from LAMOST DR7 & Gaia DR3 (Liu+, 2025)
Identification of OB associations using the LAMOST-Gaia OB star sample.
Liu Z., Wang X.-L., Cui W., Shi J., Liu C., Xue X.-X., Fang M., Huang Y.,
Hu G., Zhao G.
<Astrophys. J. Suppl. Ser., 280, 28 (2025)>
=2025ApJS..280...28L 2025ApJS..280...28L
ADC_Keywords: Associations, stellar; Stars, OB; Stars, distances;
Spectral types ; Proper motions; Radial velocities;
Space velocities; Surveys; Optical
Keywords: Early-type stars ; OB associations ; Open star clusters ;
Stellar kinematics ; Dynamical evolution
Abstract:
OB associations, as an intermediate stage between Galactic clusters
and field stars, play an important role in understanding the star
formation process, early stellar evolution, and Galactic evolution. In
this work, we construct a large sample of OB stars with
six-dimensional (6D) phase space parameters (l, b, d, Vlos, pmra,
pmdec) by combining the distances from Bailer-Jones+ (I/352), radial
velocities derived from low-resolution spectra of the Large Sky Area
Multi-Object Fiber Spectroscopic Telescope (LAMOST), and proper
motions from Gaia Data Release 3 (DR3). This sample includes 19,933 OB
stars, most of which are located within 6 kpc of the Sun. Using 6D
phase-space parameters and a friends-of-friends clustering algorithm,
we identify 67 OB associations and 112 OB association candidates;
among these, 49 OB associations and 107 OB association candidates are
newly identified. The Galactic rotation curve derived using 67 OB
association members is relatively flat in the range of Galactocentric
distances 7<R<13kpc. The angular rotation velocity at a solar
Galactocentric distance of R☉=8.34kpc is
Ω0=29.05±0.55km/s/kpc. The spatial distribution of the 67 OB
associations indicates that they are mainly located at low Galactic
latitudes and near spiral arms of the Milky Way. Additionally, we
estimate the velocity dispersions and sizes of these 67 OB
associations. Our results show that the velocity dispersions decrease
as Galactocentric distances increase, while their sizes increase as
Galactocentric distances increase.
Description:
In this work, we use the OB stars selected by Liu+ 2024, J/ApJS/275/24
from LAMOST DR7 to identify OB associations. In addition, we include
137 OB stars that are missed due to their low signal-to-noise ratios
of the low-resolution spectra. Thus, the final OB star sample consists
of 27,780 stars. After crossmatching with Gaia DR3 and the distance
catalog of Bailer-Jones+ (2021, I/352) with a matching radius of 3",
we obtained the parallaxes, proper motions, RUWE, and the photometric
distances.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 179 The parameters of 67 OB associations and 112 OB
association candidates
table2.dat 205 3707 The 3707 OB members for 67 OB associations and 112
OB association candidates
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See also:
V/156 : LAMOST DR7 catalogs (Luo+, 2019)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
V/162 : LAMOST DR11 catalogs (Luo+, 2026)
J/A+A/278/36 : M 31 new OB associations (Magnier+ 1993)
J/AJ/117/354 : OB associations from Hipparcos (de Zeeuw+, 1999)
J/AJ/126/1916 : JHK phot. of young clusters near the Sun (Porras+, 2003)
J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)
J/MNRAS/400/518 : Velocity & proper motion of OB associations (Melnik+, 2009)
J/MNRAS/411/2596 : High Galactic latitude runaway stars (Silva+, 2011)
J/A+A/563/A94 : Kinematics of the Gamma Vel cluster (Jeffries+, 2014)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/ApJ/816/80 : The SEGUE K giant survey. III. Galactic halo (Janesh+, 2016)
J/MNRAS/472/3887 : Kinematic data for stars in OB-associations (Melnik+, 2017)
J/AJ/156/90 : APOGEE radial velocity standard stars (Huang+, 2018)
J/AJ/156/84 : APOGEE-2 survey of Orion Complex. II. (Kounkel+, 2018)
J/MNRAS/475/5659 : OB association members (Ward+, 2018)
J/ApJS/241/32 : OB stars from the LAMOST DR5 spectra (Liu+, 2019)
J/ApJ/880/65 : LAMOST K giants in Galactic halo substructures (Yang+, 2019)
J/MNRAS/493/2339 : Internal motions in OB-associations (Melnik+, 2020)
J/MNRAS/495/663 : Gaia DR2 OB associations (Ward+, 2020)
J/ApJS/246/9 : Stellar parameters of LAMOST stars using SLAM (Zhang+, 2020)
J/MNRAS/508/2370 : Revisiting the Cygnus OB associations (Quintana+, 2021)
J/ApJS/256/14 : RVs from LAMOST MRS DR7 stellar spectra (Zhang+, 2021)
J/MNRAS/522/3124 : OB stars and associations in Auriga (Quintana+, 2023)
J/ApJS/275/24 : The value-added cat. of OB stars in LAMOST DR7 (Liu+, 2024)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/179] Cluster identifier in this work
5- 10 F6.2 deg GLON [64.72/212.22] Galactic longitude
12- 17 F6.2 deg GLAT [-13.37/7.27] Galactic latitude
19- 23 F5.2 mas/yr pmRA [-3.89/3.74] Average proper motion along RA
25- 29 F5.2 mas/yr pmDE [-8.41/0.63] Average proper motion along DE
31- 37 F7.2 km/s Vlos [-103.5/227.45] Average line-of-sight velocity
39- 43 F5.2 km/s e_Vlos [1.6/23.41] Uncertainty in Vlos
45- 51 F7.2 km/s Vl [-224.19/61.45] Average velocity along GLON
53- 57 F5.2 km/s e_Vl [0.31/11.97] Uncertainty in Vl
59- 64 F6.2 km/s Vb [-14.34/20.03] Average velocity along GLAT
66- 70 F5.2 km/s e_Vb [0.28/11.48] Uncertainty in Vb
72- 75 I4 pc Dsun [562/4657] Average heliocentric distance
77- 79 I3 pc e_Dsun [10/420] Uncertainty in dsun
81- 83 I3 --- GNum [5/545] Total number of OB stars in the group
85- 85 I1 --- ONum [0/9] Number of O-type stars in group
87- 89 I3 pc Size [0/307] Diameter of OB association
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/179] Cluster identifier in this work
5- 13 I9 --- ObsID [2403009/733515159] LAMOST DR7 object
identifier
15- 33 A19 --- LAMOST LAMOST DR7 object designation
(JHHMMSS.ss+DDMMSS.s)
35- 44 F10.6 deg RAdeg [8.29/353] LAMOST DR7 Right Ascension (J2000)
46- 54 F9.6 deg DEdeg [-4.72/61] LAMOST DR7 Declination (J2000)
56- 61 F6.2 km/s RVel [-97/67] Radial velocity from laspec algorithm
63- 67 F5.2 km/s e_RVel [0.5/18] Uncertainty in RVel
69- 87 I19 --- Gaia Gaia DR3 identifier
89- 94 F6.3 mas/yr pmRA [-4.2/3.91] Gaia DR3 proper motion along RA
96- 101 F6.3 mas/yr pmDE [-8.5/1.4] Gaia DR3 proper motion along DE
103- 106 F4.2 mas/yr e_pmRA [0.01/0.06] Uncertainty in pmRA
108- 111 F4.2 mas/yr e_pmDE [0.01/0.04] Uncertainty in pmDE
113- 122 F10.6 deg GLON [62.12/218.06] Galactic longitude
124- 133 F10.6 deg GLAT [-21.59/11.01] Galactic latitude
135- 141 F7.2 km/s Vlos [-125/235] Line-of-sight velocity in the
Galactic standard of rest
143- 149 F7.2 km/s Vl [-225/75] Velocity along GLON in the Galactic
standard of rest
151- 156 F6.2 km/s Vb [-35/26] Velocity along GLAT in the Galactic
standard of rest
158- 163 F6.2 kpc Xpos [-13/-7.6] Galactocentric coordinate in the
direction opposite the Sun
165- 169 F5.2 kpc Ypos [-1.7/3.1] Galactocentric coordinate in the
direction of Galactic rotation
171- 175 F5.2 kpc Zpos [-0.4/0.51] Galactocentric coordinate in the
direction north of Galactic pole
177- 183 F7.2 pc Rpgeo [489.9/5317.1] Median of the photogeometric
distance posterior from I/352
185- 191 F7.2 pc B_Rpgeo [497/5852] The 84th percentile of Rpgeo
193- 199 F7.2 pc b_Rpgeo [483/4781] The 16th percentile of Rpgeo
201 A1 --- SpT Spectral type (1)
203- 205 A3 --- Ver LAMOST release the star can be found in; DR3,
DR5 or DR7
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Note (1): The spectral types of O-type and B-type stars are obtained
from Liu+ 2024, J/ApJS/275/24
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Jun-2026