Cool dwarfs in wide multiple systems: Paper I: Two mid-M dwarfs in a loosely-bound common-proper-motion pair

TL;DR

This paper introduces Koenigstuhl 4 AB, a wide binary system of two mid-M dwarfs with a very large separation, highlighting its significance as one of the least bound late-type binary systems known.

Contribution

First detailed study of Koenigstuhl 4 AB, revealing its wide separation and association with an X-ray source, expanding knowledge of cool dwarf binary systems.

Findings

Koenigstuhl 4 AB is a wide binary with a 5700 AU separation.

The primary star is associated with a ROSAT X-ray source.

The system is among the least bound binary systems with late-type components.

Abstract

This is the first of a series of works devoted to investigate cool dwarfs in wide multiple systems. Here, I present Koenigstuhl 4 A and B, two bright, intermediate M dwarfs with a common high proper-motion and separated by 299 arcsec. At the most probable distance of the system, 19 pc, the projected physical separation is 5700 AU, which makes Koenigstuhl 4 AB to be one of the least bound binary systems with late-type components found to date. I also associate the primary with a ROSAT X-ray source for the first time.