2013 Annual Science Report
NASA Goddard Space Flight Center Reporting | SEP 2012 – AUG 2013
Long-Term Variation of High Energy Activity of Young Stars in Mass Accretion Outburst and Quiescence
High-energy photons in the young stellar environment are known to stimulate chemical reactions of molecules and producing prebiotic materials that might later be incorporated in-to comets, and through them into young planets. Observational tests are sorely needed to assess the significance of such processing for Astrobiology, and to guide development of theoretical models for chemical evolution in protoplanetary environments.
In this reporting period, we studied long-term X-ray variations of the protostar V1647 Ori that currently experiences strong mass accretion, and of many young stellar objects in the active star-forming region surrounding V1647 Ori. We also studied the relation of temporal variations in the intensities of their X-ray and optical/near-infrared (IR) emissions.
We triggered a reserved Target-of-Opportunity (ToO) observation of the erupting protostar V1647 Ori with the XMM-Newton observatory in 2013 March 9, to monitor its recent X-ray activity. The last X-ray observations of this star before the ToO observation, performed with the XMM-Newton and Swift X-ray observatories in 2010, suggested a drop in the X-ray flux by an order of magnitude. The new observation in 2013, again, showed a similarly low X-ray flux level, suggesting that the flux decrease observed in 2010 and 2013 was not caused by a short-term variation, such as rotational modulation, but was an intrinsic decay of the X-ray activity. The optical and near-IR fluxes stayed high until 2013 at the outburst peak level, and therefore the mass accretion outburst would have persisted until now. This means that a part of the mechanism that induces the X-ray activity, possibly related to the stellar magnetic field, ceased to work after ~2010. In response to this ToO observation, we triggered coordinated optical/near-IR observations of V1647 Ori using the Japanese observatory network. The optical/near-infrared fluxes did not vary significantly around the X-ray observation, while the Br gamma line (which is a good tracer of mass accretion) might have varied significantly.
In the CCD field of view of the 11 monitoring observations of V1647 Ori, the Chandra X-ray observatory detected 52 X-ray emitting young stellar objects associated with the active star-forming region Lynds 1630. The X-ray fluxes from these young stellar objects varied by orders of magnitude on yearly timescales.