The Multiple Young Stellar Objects of HBC 515: An X-ray and Millimeter-wave Imaging Study in (Pre-main Sequence) Diversity

TL;DR

This study uses X-ray and millimeter-wave imaging to analyze a diverse multiple young stellar object system, revealing how star mass, binarity, and X-ray activity influence disk evolution and star-disk interactions.

Contribution

It provides the first detailed multi-wavelength characterization of the HBC 515 system, highlighting the diversity and evolutionary stages of its YSOs and their impact on disk lifetimes.

Findings

All five YSOs are X-ray sources, with HBC 515A being the dominant X-ray emitter.

HBC 515B is confirmed as a protostar with strong millimeter emission.

HBC 515A is a massive, X-ray luminous binary that has shed its disk early.

Abstract

We present Chandra X-ray Observatory and Submillimeter Array (SMA) imaging of HBC 515, a system consisting of multiple young stellar objects (YSOs). The five members of HBC 515 represent a remarkably diverse array of YSOs, ranging from the low-mass Class I/II protostar HBC 515B, through Class II and transition disk objects (HBC 515D and C, respectively), to the "diskless", intermediate- mass, pre-main sequence binary HBC 515A. Our Chandra/ACIS imaging establishes that all five components are X-ray sources, with HBC 515A - a subarcsecond-separation binary that is partially resolved by Chandra - being the dominant X-ray source. We detect an X-ray flare associated with HBC 515B. In the SMA imaging, HBC 515B is detected as a strong 1.3 mm continuum emission source; a second, weaker mm continuum source is coincident with the position of the transition disk object HBC 515C. These results strongly support the protostellar nature of HBC 515B, and firmly establish HBC 515A as a member of the rare class of relatively massive, X-ray luminous "weak-lined T Tauri stars" that are binaries and have shed their disks at very early stages of pre-MS evolution. The coexistence of two such disparate objects within a single, presumably coeval multiple YSO system highlights the influence of pre- MS star mass, binarity, and X-ray luminosity in regulating the lifetimes of circumstellar, planet-forming disks and the timescales of star-disk interactions.