Chandra Observations of Six Peter Pan Disks: Diversity of X-ray-driven Internal Photoevaporation Rates Doesn't Explain Their Rare Longevity

TL;DR

This study uses Chandra X-ray observations of six Peter Pan disks, revealing their X-ray properties are typical for their age and type, and suggesting their long disk lifetimes are due to low FUV flux rather than internal photoevaporation.

Contribution

It provides the first X-ray characterization of Peter Pan disks, challenging the idea that internal photoevaporation explains their longevity and highlighting the role of low FUV flux.

Findings

Peter Pan disks have X-ray luminosities similar to weak-lined T-Tauri stars.

X-ray photoevaporation rates suggest these disks have already passed rapid gas dispersal.

Low FUV flux likely contributes to the prolonged disk lifetimes.

Abstract

We present Chandra X-ray observations of 6 previously-identified Peter Pan objects, rare 40 Myr systems with evidence of primordial disk retention. We observe X-ray luminosities (0.8-3.0 keV) ranging from log Lx 27.7-29.1. We find that our Peter Pan sample exhibits X-ray properties similar to that of weak-lined T-Tauri stars and do not exhibit evidence of stellar accretion induced X-ray suppression. Our observed Peter Pan X-ray luminosities are consistent with that measured for field dM stars of similar spectral type and age, implying their long primordial disk lifetimes are likely not a consequence of unusually faint X-ray host stars. Our derived X-ray photoevaporative mass loss rates predict our systems have passed the point of rapid gas dispersal and call into question the impact of this internal mechanism for primordial disk dispersal around dM stars. Our qualitative assessment of the surrounding Peter Pan environments also does not predict unusually low levels of external photoevaporation relative to other respective moving group members. Overall, our results suggest Peter Pan disks may be a consequence of the low FUV flux incident on the disk in low-mass DM stars given their relatively lower levels of accretion over the course of their pre-main-sequence evolution.