Observation of light echoes around very young stars

摘要

Aims. The goal of the paper is to present newresults on light echoes from young stellar objects. Methods. Broad band CCD images were obtained overthree months at one-to-two week intervals for the field ofNGC6726, using the large field-of-view remotely-operatedtelescope on top of Cerro Burek. Results. We detected scattered light echoes aroundtwo young, low-amplitude, irregular variable stars. Observationsrevealed not just one, but multiple light echoes from brightness pulsesof the TTauri starSCrA and theHerbigAe/Be starRCrA. Analysis ofSCrA's recurring echoes suggests that the star is located13816pc from Earth, making these the closest echoes everdetected. The environment that scatters the stellar light fromSCrA is compatible with an incomplete dust shell or aninclined torus some 10000AU in radius andcontaining 2of dust. The cause of suchconcentration at 10000AUfrom the star isunknown. Itcould be the remnant of the envelope from whichthe star formed, but the distance of the cloud is remarkably similar tothe nominal distance of the Oort cloud to the Sun, leading us to alsospeculate that the dust (orice) seen around SCrAmight have the same origin as the Solar System Oort cloud. Key words: stars: protostars - stars:variables: T Tauri, Herbig Ae/Be - stars: imaging