SIMBAD references

X-ray emission is characteristic of young stellar objects (YSOs) and is known to be highly variable. We investigate, via an infrared and multi-epoch X-ray study of the L1630 dark cloud, whether and how X-ray variability in YSOs is related to protostellar evolutionary state. We have analyzed 11 Chandra X-Ray Observatory observations, obtained over the course of four years and totaling ∼240 ks exposure time, targeting the eruptive Class I YSO V1647 Ori in L1630. We used Two Micron All Sky Survey and Spitzer data to identify and classify IR counterparts to L1630 X-ray sources and identified a total of 52 X-ray-emitting YSOs with IR counterparts, including four Class I sources and one Class 0/I source. We have detected cool (<3 MK) plasma, possibly indicative of accretion shocks, in three classical T Tauri stars. A subsample of 27 X-ray-emitting YSOs were covered by 9 of the 11 Chandra observations targeting V1647 Ori and the vicinity. For these 27 YSOs, we have constructed X-ray light curves spanning approximately four years. These light curves highlight the variable nature of pre-main-sequence X-ray-emitting young stars; many of the L1630 YSOs vary by orders of magnitude in count rate between observations. We discuss possible scenarios to explain apparent trends between various X-ray spectral properties, X-ray variance, and YSO classification.