Eruptive Variable Stars and Outflows in Serpens NW

TL;DR

This study investigates outflows and variability of three young stellar objects in Serpens NW, revealing outflow origins, a periodic variable star likely influenced by binary interactions, and evolving reflection nebulae.

Contribution

It provides new high-resolution imaging of outflows, analyzes the photometric evolution of OO Ser, and proposes a binary-driven model for EC 53's periodic variability.

Findings

Outflows from all three objects identified and characterized.

OO Ser's brightness decline has reversed, indicating ongoing variability.

EC 53's periodic variability likely caused by accretion instabilities in a multiple system.

Abstract

We study the outflow activity, photometric variability and morphology of three very young stellar objects in the Serpens NW star forming region: OO Serpentis, EC 37 (V370 Ser) and EC 53 (V371 Ser). High spatial resolution Keck/NIRC2 laser guide star adaptive optics images obtained in 2007 and 2009 in broad-band K and in a narrow-band filter centered on the 1-0 S(1) emission line of molecular hydrogen allow us to identify the outflows from all three objects. We also present new, seeing-limited data on the photometric evolution of the OO Ser reflection nebula and re-analyze previously published data. We find that OO Ser declined in brightness from its outburst peak in 1995 to about 2003, but that this decline has recently stopped and actually reversed itself in some areas of the reflection nebula. The morphology and proper motions of the shock fronts MHO 2218 near EC 37 suggest that they all originate in EC 37 and that this is an outflow seen nearly along its axis. We identify a molecular hydrogen jet emerging from the cometary nebula EC 53. The star illuminating EC 53 is periodically variable with a period of 543 days, and has a close-by, non-variable companion at a projected distance of 92 AU. We argue that the periodic variability is the result of accretion instabilities triggered by another very close, not directly observable, binary companion and that EC 53 can be understood in the model of a multiple system developing into a hierarchical configuration.