Resolved Spectroscopy of M Dwarf/L Dwarf Binaries. III. The "Wide" L3.5/L4 Dwarf Binary 2MASS J15500845+1455180AB

TL;DR

This paper reports the discovery and detailed characterization of the widest known L dwarf-L dwarf binary, providing valuable data for understanding low-mass stellar systems and their evolution.

Contribution

It presents the identification and detailed analysis of a wide L dwarf binary, including spectral types, physical separation, and implications for low-mass binary formation.

Findings

Confirmed physical association through proper motion and spectrophotometric distances.

Measured a projected separation of approximately 30 AU, the widest among known L dwarf pairs.

Identified the system as an excellent candidate for age and atmospheric studies.

Abstract

We report the identification of 2MASS J15500845+1455180 as a 0"9 L dwarf visual binary. This source is resolved in Sloan Digital Sky Survey (SDSS) images and in near-infrared imaging with the IRTF SpeX imager/spectrometer. The two components, oriented along a north-south axis, have similar brightnesses in the near-infrared (Delta{K} ~ 0.2 mag), although the fainter northern component is redder in J-K color. Resolved near-infrared spectroscopy indicates spectral types of L3.5 and L4, consistent with its L3 combined-light optical classification based on SDSS data. Physical association is confirmed through common proper motion, common spectrophotometric distances and low probability of chance alignment. The projected physical separation of 2MASS J1550+1455AB, 30+/-3 AU at an estimated distance of 33+/-3 pc, makes it the widest L dwarf-L dwarf pair identified to date, although such a separation is not unusual among very low-mass field binaries. The angular separation and spectral composition of this system makes it an excellent target for obtaining a precise lithium depletion age, and a potential age standard for low-temperature atmosphere studies.