What's Behind the Elephant's Trunk? Identifying Young Stellar Objects on the Outskirts of IC1396

TL;DR

This study investigates the disk lifetimes of young stellar objects in the IC 1396 region by using X-ray and Gaia data, finding consistent disk fractions across different fields despite external radiation influences.

Contribution

It provides new measurements of disk fractions in the outskirts of IC 1396 using X-ray and Gaia data, challenging previous assumptions about external radiation effects on disk dispersal.

Findings

Disk fraction in the observed field is approximately 17%, similar to the 29% in the adjacent field.

Incorporating Gaia parallaxes refines YSO identification and distance estimates.

Disk lifetimes appear unaffected by proximity to the massive star in the cluster core.

Abstract

Empirically, the estimated lifetime of a typical protoplanetary disk is $<5-10$ Myr. However, the disk lifetimes required to produce a variety of observed exoplanetary systems may exceed this timescale. Some hypothesize that this inconsistency is due to estimating disk fractions at the cores of clusters, where radiation fields external to a star-disk system can photoevaporate the disk. To test this, we have observed a field on the western outskirts of the IC 1396 star-forming region with \textit{XMM-Newton} to identify new Class III YSO cluster members. Our X-ray sample is complete for YSOs down to $1.8\,M_{\odot}$. We use a subset of these X-ray sources that have near- and mid-infrared counterparts to determine the disk fraction for this field. We find that the fraction of X-ray-detected cluster members that host disks in the field we observe is $17_{-7}^{+10}\%$ (1$\sigma$), comparable with the $29_{-3}^{+4}\%$ found in an adjacent field centered on the cometary globule IC 1396A. We re-evaluate YSO identifications in the IC 1396A field using \textit{Gaia} parallaxes compared to previous color-cut-only identifications, finding that incorporating independent distance measurements provides key additional constraints. Given the existence of at least one massive star producing an external radiation field in the cluster core, the lack of statistically significant difference in disk fraction in each observed field suggests that disk lifetimes remain consistent as a function of distance from the cluster core.