First stars of the ρ Ophiuchi dark cloud

XMM-Newton view of ρ Oph and its neighbors

¹ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90147 Palermo, Italy
e-mail: pilli@astropa.inaf.it
² SAO-Harvard Center for Astrophysics, 60 Garden St., Cambridge, 02138 MA – US, UK

Received: 10 February 2016
Accepted: 20 May 2016

Abstract

Star formation in molecular clouds can be triggered by the dynamical action of winds from massive stars. Furthermore, X-ray and UV fluxes from massive stars can influence the life time of surrounding circumstellar disks. We present the results of a 53 ks XMM-Newton observation centered on the ρ Ophiuchi A+B binary system. ρ Ophiuchi lies in the center of a ring of dust, likely formed by the action of its winds. This region is different from the dense core of the cloud (L1688 Core F) where star formation is at work. X-rays are detected from ρ Ophiuchi as well as a group of surrounding X-ray sources. We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS+All-WISE catalogs. Based on IR and X-ray properties, we can distinguish between young stellar objects (YSOs) belonging to the cloud and background objects. Among the cloud members, we detect three debris-disk objects and 22 disk-less − Class III young stars.We show that these stars have ages in 5−10 Myr, and are significantly older than the YSOs in L1688. We speculate that they are the result of an early burst of star formation in the cloud. An X-ray energy of ≥5 × 10⁴⁴ erg has been injected into the surrounding mediumover the past 5 Myr, we discuss the effects of such energy budget in relation to the cloud properties and dynamics.