J/MNRAS/549/G853 A new Gaia census of OB associations (Quintana+, 2026)
A new Gaia census of OB associations within 1 kpc.
Quintana A.L, Wright N.J, Kormann L.A., Alves J., Katz D., Casamiquela L.,
Di Matteo P., Haywood M., Laporte C.
<Mon. Not. R. Astron. Soc. 549, G853 (2026)>
=2026MNRAS.549g.853Q 2026MNRAS.549g.853Q (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Associations, stellar ; Stars, OB ;
Fundamental catalog ; Optical
Keywords: stars: kinematics and dynamics - stars: early-type - stars: massive -
open clusters and associations: general -
Galaxy: solar neighbourhood - Galaxy: structure
Abstract:
OB associations are primordial tracers of star formation and Galactic
structure. Originally defined about 80 years ago, their historical
membership lists have been superseded thanks to the precise astrometry
from ESA's Gaia's satellite. Recent studies have however been mostly
focused on individual OB associations or limited by the coverage of
spectroscopic surveys. In this paper, we exploit a complete census of
∼25000 O- and B-type stars within 1kpc of the Sun to produce a
highly-reliable catalogue of 56 OB associations using the HDBSCAN
clustering algorithm, increasing the number of known OB associations
by a factor of two within this volume. We assess the validity of this
catalogue by crossmatching our OB association members with other
catalogues of OB associations, star clusters and young stellar groups,
confirming the high-confidence of our census of OB associations. We
characterize these OB associations physically (total initial stellar
mass, number of OB stars, ...) and kinematically (velocity dispersion,
linear expansion ages, ...). The majority of the OB associations (38
out of 56) exhibit a significant expansion pattern in at least one
direction, including 12 in both plane-of-the-sky directions, though
differences in expansion velocity suggest anisotropical expansion
patterns. We compare the locations of these OB associations with
superclouds and features in the local Milky Way such as the Radcliffe
Wave and discuss the implications for star formation in the solar
neighbourhood.
Description:
We have exploited a complete census of 25000 O- and B-type stars
within 1 kpc, to which we have applied a clustering algorithm to their
3D positions and 2D velocities. In doing so we have identified 56
highly confident OB associations.
We present three tables.
table1.dat lists the properties of the 56 OB associations
members.dat contains all the identified OB members of these 56 OB
associations.
rejected.dat correspond to the members of the groups initially
identified by HDBSCAN, but ultimately rejected in the final analysis.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 559 56 Main catalogue
members.dat 298 2551 OB members of the OB associations
rejected.dat 257 1308 Members of the rejected candidate OB associations
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/160/279 : Untangling the Galaxy. II. Structure within 3kpc
(Kounkel+, 2020)
J/A+A/686/A42 : Improving the open cluster census. III. (Hunt+, 2024)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name Assigned OB association name (Name)
15- 23 A9 --- AName Alternative name for the OB association
(Alternative name)
25- 26 I2 --- ID ID assigned to the OB association,
ordered by increasing median line (ID)
28- 30 I3 --- N Number of identified members (N)
32- 37 F6.2 deg RAdeg Median right ascension (ICRS) at Ep=2016.0
(RA_ICRS)
39- 44 F6.2 deg DEdeg Median declination (ICRS) at Ep=2016.0
(DE_ICRS)
46- 51 F6.2 deg GLON Median Galactic longitude (GLON)
53- 58 F6.2 deg GLAT Median Galactic latitude (GLAT)
60- 62 F3.1 mag AV Median extinction in the V-band (AV)
64- 69 F6.2 pc d Median SED-fitted line-of-sight distance (d)
71- 77 F7.2 pc X Median X coordinate in heliocentric
Cartesian Galactic coordinates (X)
79- 82 F4.1 pc s_X Intrinsic dispersion in the X direction
(Sigma_X)
84- 90 F7.2 pc Y Median Y coordinate in heliocentric
Cartesian Galactic coordinates (Y)
92- 95 F4.1 pc s_Y Intrinsic dispersion in the Y direction
(Sigma_Y)
97-103 F7.2 pc Z Median Z coordinate in heliocentric
Cartesian Galactic coordinates (Z)
105-108 F4.1 pc s_Z Intrinsic dispersion in the Z direction
(Sigma_Z)
110-115 F6.2 km/s Vl Median transverse velocity in
Galactic longitude (V_l)
117-119 F3.1 km/s s_Vl Intrinsic dispersion in transverse velocity
in Galactic longitude (Sigma_Vl)
121-126 F6.2 km/s Vb Median transverse velocity in
Galactic latitude (V_b)
128-130 F3.1 km/s s_Vb Intrinsic dispersion in transverse velocity
in Galactic latitude (Sigma_Vb)
132-137 F6.3 km/s/pc kappal Linear velocity gradient in
Galactic longitude (Kappa_l)
139-143 F5.3 km/s/pc e_kappal Error on linear velocity gradient in
Galactic longitude (Errkappal)
145-148 F4.1 Myr Agekinl ?=- Linear kinematic age in
Galactic longitude (Age_kin,l)
150-153 F4.1 Myr e_Agekinl ?=- Error on linear kinematic age in
Galactic longitude (ErrAgekin,l)
155-160 F6.3 km/s/pc kappab Linear velocity gradient in
Galactic latitude (Kappa_b)
162-166 F5.3 km/s/pc e_kappab Error on linear velocity gradient in
Galactic latitude (ErrKappab)
168-171 F4.1 Myr Agekinb ?=- Linear kinematic age in
Galactic latitude (Age_kin,b)
173-176 F4.1 Myr e_Agekinb ?=- Error on linear kinematic age in
Galactic latitude (ErrAgekin,b)
178-181 F4.1 --- NO Estimated median number of systems
containing a O-type star in the O (N_O)
183-184 I2 --- e_NO Lower error on NO, 16th percentile (NOP16)
186-187 I2 --- E_NO Upper error on NO, 84th percentile (NOP84)
189-193 F5.1 --- NB Estimated median number of systems
containing a B-type star in the O (N_B)
195-197 I3 --- e_NB Lower error on NBP, 16th percentile
(NBP16)
199-201 I3 --- E_NB Upper error on NBP, 84th percentile
(NBP84)
203-209 F7.1 Msun Mtot Estimated median total stellar initial mass
(M_tot)
211-214 I4 Msun e_Mtot Lower error on Mtot, 16th percentile
(MtotP16)
216-220 I5 Msun E_Mtot Upper error on Mtot, 84th percentile
(MtotP84)
222-226 F5.1 Myr Agemax Estimated maximum isochronal age from the
hottest member (Age_max)
228-229 I2 --- NC Number of crossmatched members with the OCs
from Hunt & Reffert (2024,
Cat. J/A+A/686/A42 (N_OC)
231-301 A71 Myr RelOCsAge Age range of the overlapping OCs from
Hunt & Reffert (2024, Cat. J/A+A/686/A42)
(Related OCs age)
303-435 A133 --- RelOCs Crossmatched OCs from Hunt & Reffert
(2024, Cat. J/A+A/686/A42) (Related OCs)
437-439 I3 --- NG Number of crossmatched members with the
stellar groups from Kounkel (N_G)
441-476 A36 Myr RelGrAge Age range of the overlapping stellar groups
from Kounkel et al. (2020,
Cat. J/AJ/160/279) (Related groups age)
478-544 A67 --- RelGr Crossmatched groups from Kounkel et al.
(2020, Cat. J/AJ/160/279) (Related groups)
546-559 A14 --- AssSCL Spatially related supercloud from Kormann
et al. (2026A&A...706A.161K 2026A&A...706A.161K)
(Associated supercloud)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: members.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name Assigned OB association name (Name)
15- 16 I2 --- ID ID assigned to the OB association,
ordered by increasing median line (ID)
18- 36 I19 --- GaiaDR3 ?=0 Gaia DR3 source ID (0 if not in Gaia)
(GaiaDR3)
38- 46 A9 --- HD Henry Draper Number (HD)
48- 59 F12.8 deg RAdeg Right ascension of star (ICRS) at Ep=2016.0
(RA_ICRS)
61- 70 F10.8 deg e_RAdeg Standard error on right ascension (eRAICRS)
72- 83 F12.8 deg DEdeg Declination of star (ICRS) at Ep=2016.0
(DE_ICRS)
85- 94 F10.8 deg e_DEdeg Standard error on declination (eDEICRS)
96-107 F12.8 deg GLON Galactic longitude (GLON)
109-120 F12.8 deg GLAT Galactic latitude (GLAT)
122-134 F13.8 pc X X coordinate in heliocentric Cartesian
Galactic coordinates (X)
136-148 F13.8 pc Y Y coordinate in heliocentric Cartesian
Galactic coordinates (Y)
150-162 F13.8 pc Z Z coordinate in heliocentric Cartesian
Galactic coordinates (Z)
164-174 F11.8 mas plx Corrected parallax (parallax)
176-185 F10.8 mas e_plx Standard error on corrected parallax
(parallax_error)
187-197 F11.7 mas/yr pmRA Mean proper motion in right ascension
multiplied by cos(dec) (pmra)
199-207 F9.7 mas/yr e_pmRA Standard error of pmra (pmra_error)
209-219 F11.7 mas/yr pmDE Mean proper motion in declination (pmdec)
221-229 F9.7 mas/yr e_pmDE Standard error of pml (pmdec_error)
231-241 F11.7 mas/yr pml Mean proper motion in Galactic longitude
multiplied by cos(b) (pml)
243-251 F9.7 mas/yr e_pml Standard error of pml (pml_error)
253-263 F11.7 mas/yr pmb Mean proper motion in Galactic latitude (pmb)
265-273 F9.7 mas/yr e_pmb Standard error of pmb (pmb_error)
275-284 F10.8 mag AV Median extinction in the V-band (AV)
286 A1 --- Marker Marker used to plot the OB association
members in the paper (marker)
288-298 A11 --- Colour Colour used to plot the OB association
members in the paper (colour)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: rejected.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- ID ID assigned to the OB association, ordered
from increasing median line-of-sight
distance (ID)
4- 22 I19 --- GaiaDR3 ?=0 Gaia DR3 source ID (0 if not in Gaia)
(GaiaDR3)
24- 31 A8 --- HD Henry Draper Number (HD)
33- 44 F12.8 deg RAdeg Right ascension of star (ICRS) at Ep=2016.0
(RA_ICRS)
46- 55 F10.8 deg e_RAdeg Standard error on right ascension (eRAICRS)
57- 68 F12.8 deg DEdeg Declination of star (ICRS) at Ep=2016.0
(DE_ICRS)
70- 79 F10.8 deg e_DEdeg Standard error on declination (eDEICRS)
81- 92 F12.8 deg GLON Galactic longitude (GLON)
94-105 E12.4 deg GLAT Galactic latitude (GLAT)
107-119 F13.8 pc X X coordinate in heliocentric Cartesian
Galactic coordinates (X)
121-133 F13.8 pc Y Y coordinate in heliocentric Cartesian
Galactic coordinates (Y)
135-147 F13.8 pc Z Z coordinate in heliocentric Cartesian
Galactic coordinates (Z)
149-158 F10.8 mas plx Corrected parallax (parallax)
160-169 F10.8 mas e_plx Standard error on corrected parallax
(parallax_error)
171-181 F11.7 mas/yr pmRA Mean proper motion in right ascension
multiplied by cos(dec) (pmra)
183-191 F9.7 mas/yr e_pmRA Standard error of pmra (pmra_error)
193-203 F11.7 mas/yr pmDE Mean proper motion in declination (pmdec)
205-213 F9.7 mas/yr e_pmDE Standard error of pml (pmdec_error)
215-225 F11.7 mas/yr pml Mean proper motion in Galactic longitude
multiplied by cos(b) (pml)
227-235 F9.7 mas/yr e_pml Standard error of pml (pml_error)
237-247 F11.7 mas/yr pmb Mean proper motion in Galactic latitude (pmb)
249-257 F9.7 mas/yr e_pmb Standard error of pmb (pmb_error)
--------------------------------------------------------------------------------
Acknowledgements:
Alexis Quintana, alexis.quintana(at)obspm.fr
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 05-Jun-2026