Cool dwarfs in wide multiple systems. Paper 3: Two common-proper-motion, late-type stars separated by over 11 arcmin

TL;DR

This paper confirms that two late-type stars with similar proper motions are a wide binary system separated by over 11 arcminutes, making it one of the least-bound low-mass star systems known.

Contribution

It provides the first detailed astrometric and photometric analysis confirming a wide, low-mass binary system with an unprecedented physical separation.

Findings

Confirmed common proper motion over 59 years

Estimated physical separation of 0.6-0.8 parsecs

Identified as one of the least-bound low-mass systems

Abstract

LP 209-28 and LP 209-27 have similar proper motions as tabulated by several catalogues. Using seven astrometric epochs spanning 59 years, we confirm a common tangential velocity by measuring a constant angular separation of rho = 666.62+/-0.09 arcsec. Accurate SDSS and 2MASS photometry indicates that they are normal dwarfs of approximate spectral types K7 V and M3 V. However, from their apparent magnitudes, both LP 209-28 and LP 209-27 are located at 200-250 pc, from where one can deduce an astonishing projected physical separation of 0.6-0.8 pc. The system Koenigstuhl 6 AB represents another world record among the least-bound systems with low-mass star components.