The ρ Ophiuchi region revisited with Gaia EDR3

Two young populations, new members, and old impostors^⋆,⋆⋆

¹ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Wien, Austria
e-mail: natalie.grasser@univie.ac.at
² Data Science at University of Vienna, Währinger Straße 29, 1090 Vienna, Austria
³ Radcliffe Institute for Advanced Study, Harvard University, 10 Garden Street, Cambridge, MA 02138, USA
⁴ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
⁵ University of Milano, Via Celoria, 16, 20133 Milano, Italy
⁶ Flatiron Institute, Simons Foundation, 162 Fifth Avenue, New York, NY 10010, USA

Received: 28 January 2021
Accepted: 6 June 2021

Abstract

Context. Young and embedded stellar populations are important probes of the star formation process. Their properties and the environments they create have the potential to affect the formation of new planets. Paradoxically, we have a better census of nearby embedded young populations than of the slightly more evolved optically visible young populations. The high accuracy measurements and all-sky coverage of Gaia data are about to change this situation.

Aims. This work aims to construct the most complete sample to date of young stellar objects (YSOs) in the ρ Oph region.

Methods. We compile a catalog of 1114 Ophiuchus YSOs from the literature and cross-match it with the Gaia EDR3, Gaia-ESO, and APOGEE-2 surveys. We apply a multivariate classification algorithm to this catalog to identify new, co-moving population candidates.

Results. We find 191 new high-fidelity YSO candidates in the Gaia EDR3 catalog belonging to the ρ Oph region. The new sources appear to be mainly Class III M stars and substellar objects and are less extincted than the known members, while we find that 28 of the previously unknown sources are YSOs with circumstellar disks (Class I or Class II). The analysis of the proper motion distribution of the entire sample reveals a well-defined bimodality, implying two distinct populations sharing a similar 3D volume. The first population comprises young stars’ clusters around the ρ Ophiuchi star and the main Ophiuchus clouds (L1688, L1689, L1709). In contrast, the second population is slightly older (∼10 Myr), more dispersed, has a distinct proper motion, and is possibly from the Upper Sco group. The two populations are moving away from each other at about 4.1 km s⁻¹ and will no longer overlap in about 4 Myr. Finally, we flag 17 sources in the literature sample as likely impostors, which are sources that exhibit large deviations from the average properties of the ρ Oph population. Our results show the importance of accurate 3D space and motion information for improved stellar population analysis.