J/A+A/631/A166 Members of 5 cluster in Ori OB1a association (Kos+, 2019)
Discovery of a 21 Myr old stellar population in the Orion complex.
Kos J., Bland-Hawthorn J., Asplund M., Buder S., Lewis G.F., Lin J.,
Martell S.L., Ness M.K., Sharma S., De Silva G.M., Simpson J.D.,
Zucker D.B., Zwitter T., Cotar K., Spina L.
<Astron. Astrophys. 631, A166 (2019)>
=2019A&A...631A.166K 2019A&A...631A.166K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Proper motions ; Parallaxes, trigonometric ;
Radial velocities
Keywords: surveys - parallaxes - proper motions - stars: early type -
open clusters and associations: individual: Ori OB1a -
Hertzsprung-Russell and C-M diagrams
Abstract:
The Orion complex is arguably the most studied star-forming region in
the Galaxy. While stars are still being born in the Orion nebula, the
oldest part was believed to be no more than 13Myr old.
In order to study the full hierarchy of star formation across the
Orion complex, we perform a clustering analysis of the Ori OB1a region
using new stellar surveys and derive robust ages for each identified
stellar aggregate.
We use Gaia DR2 parameters supplemented with radial velocities from
the GALAH and APOGEE surveys to perform clustering of the Ori OB1a
association. Five overdensities are resolved in a six-dimensional
parameter space (positions, distance, proper motions, and radial
velocity). Most correspond to previously known structures (ASCC 16,
25 Orionis, ASCC 20, ASCC 21). We use Gaia DR2, Pan-STARRS1 and 2MASS
photometry to fit isochrones to the colour-magnitude diagrams of the
identified clusters. The ages of the clusters can thus be measured
with 10% precision.
While four of the clusters have ages between 11 and 13Myr, the
ASCC 20 cluster stands out at an age of 21±3Myr. This is
significantly greater than the age of any previously known component
of the Orion complex. To some degree, all clusters overlap in at least
one of the six phase-space dimensions.
We argue that the formation history of the Orion complex, and its
relation to the Gould belt, must be reconsidered. A significant
challenge in reconstructing the history of the Ori OB1a association is
to understand the impact of the newly discovered 21Myr old population
on the younger parts of the complex, including their formation.
Description:
The Gaia DR2 parameters supplemented with radial velocities from the
GALAH and APOGEE surveys are used to perform clustering of the Ori
OB1a association.
Table 1 contains the properties of 5 identified clusters clusters,
including ages (derived using Gaia DR2, Pan-STARRS1 and 2MASS
photometry to fit isochrones to their colour-magnitude diagrams).
Tableb 1 - tableb 5 contain the identified members of the different
clusters.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 72 5 Parameters used in the final step of the
clustering algorithm
tableb1.dat 87 644 Members of ASCC 16
tableb2.dat 87 254 Members of ASCC 21
tableb3.dat 87 264 Members of ASCC 21a
tableb4.dat 87 218 Members of ASCC 20
tableb5.dat 87 141 Members of ASCC 18
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Cluster Cluster name
10- 15 F6.3 deg RAdeg Right ascension (ICRS) at Ep=2015.5
17- 21 F5.3 deg DEdeg Declination (ICRS) at Ep=2015.5
23- 26 F4.2 deg r Radius enclosing 50% of the stars
28- 32 F5.2 mas/yr pmRA* Proper motion along RA, pmnRA*cosDE
34- 38 F5.2 mas/yr pmDE Proper motion along DE
40- 43 F4.2 mas Plx Absolute parallax
45- 49 F5.2 km/s RV Radial velocity
51- 54 F4.2 km/s sigma Velocity dispersion
56- 60 F5.2 Myr Age Age
62- 65 F4.2 Myr e_Age rms uncertainty on Age
67- 69 I3 --- Nstar Number of stars
71- 72 I2 --- NstarRV Number of stars with known radial velocities
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Byte-by-byte Description of file: tableb?.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- Gaia Gaia DR2 id (source_id)
21- 28 F8.5 deg RAdeg Right ascension (ICRS) at Ep=2015.5
30- 37 F8.5 deg DEdeg Declination (ICRS) at Ep=2015.5
39- 44 F6.3 mas/yr pmRA* Proper motion along RA, pmnRA*cosDE
46- 50 F5.3 mas/yr e_pmRA* rms uncertainty on pmRA*
52- 57 F6.3 mas/yr pmDE Proper motion along DE
59- 63 F5.3 mas/yr e_pmDE rms uncertainty on pmDE
65- 69 F5.3 mas Plx Absolute parallax
71- 75 F5.3 mas e_Plx rms uncertainty on Plx
77- 81 F5.2 km/s RV ? Radial velocity GALAH and APOGEE surveys
83- 87 F5.2 km/s e_RV ? rms uncertainty on RV
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Acknowledgements:
Janez Kos, janez.kos(at)fmf.uni-lj.si
(End) Patricia Vannier [CDS] 22-Oct-2019