VISION – Vienna survey in Orion

III. Young stellar objects in Orion A^⋆

¹ Universität Wien, Institut für Astrophysik, Türkenschanzstrasse 17, 1180 Wien, Austria
e-mail: josefa.elisabeth.grossschedl@univie.ac.at
² University of Vienna, Faculty of Earth Sciences, Geography and Astronomy, Data Science at Uni Vienna, Austria
³ Radcliffe Institute for Advanced Study, Harvard University, 10 Garden Street, Cambridge, MA 02138, USA
⁴ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
⁵ Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, UK
⁶ Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, Allée Geoffroy Saint-Hilaire, CS 50023 33615 Pessac Cedex, France
⁷ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB Hertfordshire, UK
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
⁹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁰ Universidade do Porto, Dep. de Engenharia Física da Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
¹¹ Universität Wien, Fakultät für Informatik, Währinger Straße 29/S6, 1090 Wien, Austria
¹² University of Milan, Department of Physics, Via Celoria 16, 20133 Milan, Italy
¹³ University of Vienna, Faculty of Computer Science, Data Science at Uni Vienna, Austria

Received: 3 January 2018
Accepted: 27 September 2018

Abstract

We have extended and refined the existing young stellar object (YSO) catalogs for the Orion A molecular cloud, the closest massive star-forming region to Earth. This updated catalog is driven by the large spatial coverage (18.3 deg², ∼950 pc²), seeing limited resolution (∼0.7″), and sensitivity (K_s < 19 mag) of the ESO-VISTA near-infrared survey of the Orion A cloud (VISION). Combined with archival mid- to far-infrared data, the VISTA data allow for a refined and more robust source selection. We estimate that among previously known protostars and pre-main-sequence stars with disks, source contamination levels (false positives) are at least ∼6.4% and ∼2.3%, respectively, mostly due to background galaxies and nebulosities. We identify 274 new YSO candidates using VISTA/Spitzer based selections within previously analyzed regions, and VISTA/WISE based selections to add sources in the surroundings, beyond previously analyzed regions. The WISE selection method recovers about 59% of the known YSOs in Orion A’s low-mass star-forming part L1641, which shows what can be achieved by the all-sky WISE survey in combination with deep near-infrared data in regions without the influence of massive stars. The new catalog contains 2980 YSOs, which were classified based on the de-reddened mid-infrared spectral index into 188 protostars, 185 flat-spectrum sources, and 2607 pre-main-sequence stars with circumstellar disks. We find a statistically significant difference in the spatial distribution of the three evolutionary classes with respect to regions of high dust column-density, confirming that flat-spectrum sources are at a younger evolutionary phase compared to Class IIs, and are not a sub-sample seen at particular viewing angles.