Nothing to hide: An X-ray survey for young stellar objects in the Pipe Nebula

TL;DR

This study uses X-ray observations to search for evolved, diskless young stars in the Pipe Nebula, confirming its very low star formation efficiency and finding no significant population of such stars.

Contribution

It introduces an X-ray survey approach to identify diskless pre-main sequence stars in the Pipe Nebula, complementing previous infrared studies.

Findings

No significant population of evolved pre-main sequence stars detected

Supports previous low star formation efficiency estimate

Analyzed X-ray properties of YSOs in Barnard 59

Abstract

We have previously analyzed sensitive mid-infrared observations to establish that the Pipe Nebula has a very low star-formation efficiency. That study focused on YSOs with excess infrared emission (i.e, protostars and pre-main sequence stars with disks), however, and could have missed a population of more evolved pre-main sequence stars or Class III objects (i.e., young stars with dissipated disks that no longer show excess infrared emission). Evolved pre-main sequence stars are X-ray bright, so we have used ROSAT All-Sky Survey data to search for diskless pre-main sequence stars throughout the Pipe Nebula. We have also analyzed archival XMM-Newton observations of three prominent areas within the Pipe: Barnard 59, containing a known cluster of young stellar objects; Barnard 68, a dense core that has yet to form stars; and the Pipe molecular ring, a high-extinction region in the bowl of the Pipe. We additionally characterize the X-ray properties of YSOs in Barnard 59. The ROSAT and XMM-Newton data provide no indication of a significant population of more evolved pre-main sequence stars within the Pipe, reinforcing our previous measurement of the Pipe's very low star formation efficiency.