An Orphan No Longer? Detection of the Southern Orphan Stream and a Candidate Progenitor

TL;DR

This paper reports the detection of the southern arm of the Orphan Stream extending to a declination of -38°, and identifies a candidate progenitor remnant, enhancing understanding of the stream's structure and origin.

Contribution

First detection of the southern, possibly trailing arm of the Orphan Stream, extending its known length and identifying a potential progenitor remnant using the Dark Energy Camera survey.

Findings

Stream detected to declination -38°

Identified a possible progenitor remnant with 137 ± 25 stars

Observed an 'S' shape indicating transition from leading to trailing arms

Abstract

Using a shallow, two-color survey carried out with the Dark Energy Camera, we detect the southern, possibly trailing arm of the Orphan Stream. The stream is reliably detected to a declination of $-38^\circ$, bringing the total known length of the Orphan stream to $108^\circ$. We find a slight offset or "S" shape in the stream at $\delta \simeq -14^\circ$ that would be consistent with the transition from leading to trailing arms. This coincides with a moderate concentration of $137 \pm 25$ stars (to $g = 21.6$) that we consider a possible remnant of the Orphan progenitor. The position of this feature is in agreement with previous predictions.