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J/A+A/608/A148     Stellar populations towards Orion with Gaia DR1 (Zari+, 2017)

Mapping young stellar populations towards Orion with Gaia DR1. Zari E., Brown A.G.A., de Bruijne J., Manara C.F., de Zeeuw P.T. <Astron. Astrophys. 608, A148 (2017)> =2017A&A...608A.148Z (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Stars, pre-main sequence ; Photometry, infrared ; Parallaxes, trigonometric ; Proper motions Keywords: stars: distances - stars: formation - stars: pre-main sequence - stars: early-type Abstract: In this work we use the first data release of the Gaia mission to explore the three-dimensional arrangement and age ordering of the many stellar groups toward the Orion OB association, aiming at a new classification and characterization of the stellar population not embedded in the Orion A and B molecular clouds. We make use of the parallaxes and proper motions provided in the Tycho Gaia Astrometric Solution (TGAS) subset of the Gaia Data Release 1 (DR1) catalog and of the combination of Gaia DR1 and 2MASS photometry. In TGAS, we find evidence for the presence of a young population at a parallax ϖ∼2.65mas, which is loosely distributed around the following known clusters: 25 Ori, ε Ori, and σ Ori, and NGC 1980 (ι Ori) and the Orion Nebula Cluster (ONC). The low mass counterpart of this population is visible in the color magnitude diagrams constructed by combining Gaia DR1 G-band photometry and 2MASS. We study the density distribution of the young sources in the sky using a kernel density estimation (KDE). We find the same groups as in TGAS and also some other density enhancements that might be related to the recently discovered Orion X group, Orion dust ring, and λ Ori complex. The maps also suggest that the 25 Ori group presents a northern elongation.We estimated the ages of this population using a Bayesian isochronal fitting procedure assuming a unique parallax value for all the sources, and we inferred the presence of an age gradient going from 25 Ori (13-15Myr) to the ONC (1-2Myr). We confirmed this age ordering by repeating the Bayesian fit using the Pan-STARRS1 data. Intriguingly, the estimated ages toward the NGC 1980 cluster span a broad range of values. This can either be due to the presence of two populations coming from two different episodes of star formation or to a large spread along the line of sight of the same population. Some confusion might arise from the presence of unresolved binaries, which are not modeled in the fit, and usually mimic a younger population. Finally, we provisionally relate the stellar groups to the gas and dust features in Orion. Our results form the first step toward using Gaia data to unravel the complex star formation history of the Orion region in terms of the various star formation episodes, their duration, and their effects on the surrounding interstellar medium. Description: The files gaia.fits, XMatch_2MASS.fits and tgas.fits contain the data used in this work. The same data can be downloaded from the Gaia Archive using the queries reported in Appendix B. The data and some relevant ipython notebooks used in the preparation of this paper are available at https://github.com/eleonorazari/OrionDR1 File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file origaia.dat 156 9926756 Gaia DR1 sources in the Orion field x2mass.dat 124 5059068 Gaia DR1 sources cross-matched with the 2MASS catalogue, with separation < 1" oritgas.dat 162 34829 TGAS sources in the Orion field fits/* 0 3 Individual tables in fits
See also: I/337 : Gaia DR1 (Gaia Collaboration, 2016) II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) Byte-by-byte Description of file: origaia.dat
Bytes Format Units Label Explanations
1- 19 I19 --- Source Source ID (source_id) 21- 34 F14.10 deg RAdeg Gaia right ascension (ICRS) at epoch 2015.0 (ra) 36- 49 F14.10 deg DEdeg Gaia declination (ICRS) at epoch 2015.0 (dec) 51- 64 F14.10 deg GLON Gaia Galactic longitude at epoch 2015.0 (l) 66- 79 F14.10 deg GLAT Gaia Galactic latitude at epoch 2015.0 (b) 81- 86 F6.3 mag <Gmag> Gaia G-band mean magnitude (photgmean_mag) 88- 98 E11.5 e-/s <FG> Gaia G-band mean flux (photgmean_flux) 100-110 E11.5 e-/s e_<FG> Error on G-band mean flux (photgmeanfluxerror) 112-120 F9.3 mas/yr pmRA ?=- Gaia proper motion in right ascension direction (pmra) 122-130 F9.3 mas/yr pmDE ?=- Gaia proper motion in declination direction (pmdec) 132-137 F6.2 mas Plx ?=- Gaia Absolute barycentric stellar parallax (parallax) 139-144 F6.3 mas/yr e_pmRA ?=- Standard error of pmRA (pmra_error) 146-151 F6.3 mas/yr e_pmDE ?=- Standard error of pmDE (pmdec_error) 153-156 F4.2 mas e_Plx ?=- Standard error of Plx (parallax_error)
Byte-by-byte Description of file: x2mass.dat
Bytes Format Units Label Explanations
1- 19 I19 --- Source Gaia Source ID (source_id) 21- 34 F14.10 deg GLON Gaia Galactic longitude at epoch 2015.0 (l) 36- 49 F14.10 deg GLAT Gaia Galactic latitude at epoch 2015.0 (b) 51- 56 F6.3 mag <Gmag> Gaia G-band mean magnitude (photgmean_mag) 58- 68 E11.5 e-/s e_<FG> Error on G-band mean flux (photgmeanfluxerror) 70- 80 E11.5 e-/s <FG> Gaia G-band mean flux (photgmean_flux) 82- 87 F6.3 mag Jmag 2MASS J magnitude (j_m) 89- 93 F5.3 mag e_Jmag ? Error on Jmag (j_msigcom) 95-100 F6.3 mag Hmag ? 2MASS H magnitude (h_m) 102-106 F5.3 mag e_Hmag ? Error on Hmag (h_msigcom) 108-114 F7.3 mag Ksmag ? 2MASS Ks magnitude (ks_m) 116-120 F5.3 mag e_Ksmag ? Error on Ksmag (ks_msigcom) 122-124 A3 --- Qual 2MASS quality flags (ph_qual)
Byte-by-byte Description of file: oritgas.dat
Bytes Format Units Label Explanations
1- 5 I5 --- HIP ?=- HIP number (hip) 7- 25 I19 --- Source Gaia Source ID (source_id) 27- 40 F14.10 deg RAdeg Gaia right ascension (ICRS) at epoch 2015.0 (ra) 42- 55 F14.10 deg DEdeg Gaia declination (ICRS) at epoch 2015.0 (dec) 57- 70 F14.10 deg GLON Gaia Galactic longitude at epoch 2015.0 (l) 72- 85 F14.10 deg GLAT Gaia Galactic latitude at epoch 2015.0 (b) 87- 92 F6.3 mag <Gmag> Gaia G-band mean magnitude (photgmean_mag) 94-104 E11.5 e-/s <FG> Gaia G-band mean flux (photgmean_flux) 106-116 E11.5 e-/s e_<FG> Error on G-band mean flux (photgmeanfluxerror) 118-126 F9.3 mas/yr pmRA Gaia proper motion in right ascension direction (pmra) 128-136 F9.3 mas/yr pmDE Gaia proper motion in declination direction (pmdec) 138-143 F6.2 mas Plx Gaia Absolute barycentric stellar parallax (parallax) 145-150 F6.3 mas/yr e_pmRA Standard error of pmRA (pmra_error) 152-157 F6.3 mas/yr e_pmDE Standard error of pmDE (pmdec_error) 159-162 F4.2 mas e_Plx Standard error of Plx (parallax_error)
Acknowledgements: Eleonora Zari, zariem(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 18-Dec-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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