The Brightening of Re50N: Accretion Event or Dust Clearing?

TL;DR

The paper investigates a significant brightening event of the reflection nebula Re50N near a protostar, exploring whether it results from an accretion eruption or dust clearing, with implications for understanding protostellar activity.

Contribution

It presents observational evidence and analysis suggesting dust clearing due to outflow activity as the cause of the nebula's brightening, challenging the FUor eruption hypothesis.

Findings

Re50N brightened significantly between 2006 and 2014.

Spectral features indicate heavy veiling inconsistent with typical FUors.

Outflow cavity emergence likely caused the illumination change.

Abstract

The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is associated with a pair of reflection nebulae, Re50 and Re50N, which appeared sometime between 1955 and 1979. We have found that a dramatic brightening of Re50N has taken place sometime between 2006 and 2014. This could result if the embedded source is undergoing a FUor eruption. However, the near-infrared spectrum shows a featureless very red continuum, in contrast to the strong CO bandhead absorption displayed by FUors. Such heavy veiling, and the high luminosity of the protostar, is indicative of strong accretion but seemingly not in the manner of typical FUors. We favor the alternative explanation that the major brightening of Re50N and the simultaneous fading of Re50 is caused by curtains of obscuring material that cast patterns of illumination and shadows across the surface of the molecular cloud. This is likely occurring as an outflow cavity surrounding the embedded protostar breaks through to the surface of the molecular cloud. Several Herbig-Haro objects are found in the region.