  Recent works highlight the importance of stellar X-rays on the evolution of
the circumstellar disks of young stellar objects, especially for disk
photoevaporation. A signature of this process may be seen in the so far
tentatively observed dependence of stellar accretion rates on X-ray
luminosities. According to models of X-ray driven photoevaporation, stars with
higher X-ray luminosities should show lower accretion rates, on average, in a
sample with similar masses and ages. To this aim, we have analyzed X-ray
properties of young stars in the Orion Nebula Cluster determined with Chandra
during the COUP observation as well as accretion data obtained from the
photometric catalog of the HST Treasury Program. With these data, we have
performed a statistical analysis of the relation between X-ray activity and
accretion rates using partial linear regression analysis. The initial
anticorrelation found with a sample of 332 young stars is considerably weaker
compared to previous studies. However, excluding flaring activity or limiting
the X-ray luminosity to the soft band (0.5 - 2.0 keV) leads to a stronger
anticorrelation, which is statistically more significant. Furthermore, we have
found a weak positive correlation between the higher component of the plasma
temperature gained in the X-ray spectral fitting and the accretion rates,
indicating that the hardness of the X-ray spectra may influence the accretion
process. There is evidence for a weak anticorrelation, as predicted by
theoretical models, suggesting that X-ray photoevaporation modulates the
accretion rate through the inner disk at late stages of disk evolution, leading
to a phase of photoevaporation-starved accretion.

Solar and Stellar Astrophysics;High Energy Astrophysical Phenomena