Simultaneous Far-infrared and X-ray Monitoring of Young Stellar Objects in the Coronet Cluster

Abstract

Context: Multi-wavelength time domain analysis of Young Stellar Objects (YSOs) is a relatively new method within star formation research which may lead to better constraints on fundamental star formation processes. Such young objects are known to be strong X-ray emitters whereas in the far-infrared we are mainly probing the protoplanetary disk of these YSOs. Protostars are known to be variable in the X-ray, likely due to magnetic coronal activity. Far-infrared variability is still little understood and has only been detected once, but the possibility of finding variability in both wavelengths will allow us to compare processes that may be happening in the corona (X-ray) and the disk (far-infrared).

Aims: Here we present the first simultaneous XMM-Newton and Herschel short-timescale variability analysis of the YSOs in the Coronet Cluster. Located in the Corona Australis Molecular Cloud complex, this is a young (<2 Myr), nearby (149.4 ± 0.4 pc) star-forming region populated with several Class 0 and I protostars as well as a number of T Tauri stars. We analyze the X-ray and far-infrared variability separately so we can then look for first signs of potential correlated variability in this unique experiment.

Methods: We use archival images taken by the Herschel Space Observatory at 100 µm and 160 µm and the XMM-Newton Space Telescope in March 2012 over five epochs with 1, 2, 4, and 8 days between epochs, allowing us to probe for variability on many intermediate timescales.

Results: In the far-infrared, eleven objects are detected in the 100 µm band and eight in the 160 µm band, and seven of these are detected simultaneously in the X-ray band. All seven protostars display some level of X-ray variability and three exhibit far-infrared variability. The most variable far-infrared source is the T Tauri star S CrA and the most variable X-ray source is the Class 0 protostar IRS 7e, which had a are in the final epoch of up to 36 times the flux of previous epochs. The Class I protostar IRS 1 seemed to exhibit correlated variability with a far-infrared peak in the first epoch and an X-ray peak in the second epoch.

Conclusions: We find a first case of possibly correlated and time-delayed variability, where the far-infrared peak follows the X-ray peak. This suggests that magnetic coronal activity could indeed be affecting the protoplanetary disk on timescales of days. A future detailed comparison with models will lead to unique empirical constraints, taking into account both this apparently correlated case and the remaining variability.