The X-Ray Environment During the Epoch of Terrestrial Planet Formation: Chandra Observations of h Persei

TL;DR

This study uses Chandra X-ray observations of the h Persei cluster to analyze stellar X-ray activity, its evolution with stellar age and mass, and implications for terrestrial planet formation environments.

Contribution

It provides new X-ray data for a 13-14 Myr-old cluster, linking stellar activity to spectral type and age, and assesses X-ray impact on forming terrestrial planets.

Findings

X-ray luminosity peaks at ~10^30.3 erg/s for cluster stars.

Stars > 1.5 Msun fall out of X-ray saturation by 10-15 Myr.

No correlation between X-ray activity and IR excess from warm dust.

Abstract

We describe Chandra/ACIS-I observations of the massive ~ 13--14 Myr-old cluster, h Persei, part of the famous Double Cluster (h and chi Persei) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V < 23. Roughly 142 have optical magnitudes and colors consistent with cluster membership. The observed distribution of Lx peaks at Lx ~ 10^30.3 ergs/s and likely traces the bright edge of a far larger population of ~ 0.4--2 Msun X-ray active stars. From a short list of X-ray active stars with IRAC 8 micron excess from warm, terrestrial-zone dust, we derive a maximum X-ray flux incident on forming terrestrial planets. Although there is no correlation between X-ray activity and IRAC excess, the fractional X-ray luminosity correlates with optical colors and spectral type. By comparing the distribution of Lx/L* vs. spectral type and V-I in h Per with results for other 1--100 Myr-old clusters, we show that stars slightly more massive than the Sun (> 1.5 Msun) fall out of X-ray saturation by ~ 10--15 Myr. Changes in stellar structure for > 1.5 Msun stars likely play an important role in this decline of X-ray emission.