[Paper Review] On the Nearby Binary Brown Dwarf WISE J104915.57-531906.1 (Luhman 16)

Eric E. Mamajek|arXiv (Cornell University)|Mar 21, 2013

Stellar, planetary, and galactic studies5 citations

TL;DR

This paper proposes the name 'Luhman 16' for the nearby binary brown dwarf WISE J104915.57-531906.1, advocating it over the unwieldy WISE designation due to the system's importance as the closest known substellar binary. Using astrometric and photometric cross-identifications with IRAS, AKARI, and GSC, and kinematic modeling, the study confirms the system is a thin disk object with ~96% probability, ruling out membership in young stellar groups.

ABSTRACT

I report some observations and calculations related to the new nearby brown dwarf at d = 2 pc discovered by Luhman (2013, ApJ Letters, in press; arXiv:1303.2401). I report archival astrometry and photometry of the new object from IRAS (epoch 1983.5; IRAS Z10473-5303), AKARI (epoch 2007.0; AKARI J1049166-531907), and the Guide Star Catalog (epoch 1995.304; GSC2.2 S11132026703, GSC2.3 S4BM006703). A SuperCOSMOS scan of a plate taken with the ESO Schmidt Telescope (epoch 1984.169) shows the source as elongated (PA = 138 deg). Membership of the binary to any of the known nearby young groups within 100 pc appears unlikely based on the available astrometry and photometry. Based on the proper motion and parallax, a Monte Carlo simulation of thin disk/thick disk/halo stars is suggestive that the binary is, unsurprisingly, most likely a thin disk star (~96%), with a ~4% chance that it is a thick disk (and negligible chance that it is a halo star). I suggest that this important new nearby binary be called by either its provisional Washington Double Star catalog identifier ("Luhman 16"), or perhaps "Luhman-WISE 1", either of which is easier to remember than the WISE identifier.

Motivation & Objective

• To advocate for a more memorable and practical name for the nearby binary brown dwarf WISE J104915.57-531906.1, given its significance as the closest known substellar binary system.
• To confirm the system's astrometric and photometric counterparts in archival surveys (IRAS, AKARI, GSC, SuperCOSMOS) across multiple epochs.
• To assess the system's kinematic membership in nearby young stellar groups using convergent point analysis and proper motion data.
• To evaluate the likelihood of the system belonging to the thin disk, thick disk, or halo populations via Monte Carlo simulations.
• To provide precise predicted positions for the binary at various epochs to aid in pre-discovery astrometric searches.

Proposed method

• Cross-identification of WISE J104915.57-531906.1 with archival sources using predicted ICRS positions at different epochs, based on Luhman's (2013) proper motion and parallax.
• Comparison of predicted positions (1983.5 to 2014) with astrometric catalogs (IRAS, AKARI, GSC, ESO Schmidt) to verify cross-identifications.
• Use of AKARI 9 μm flux and WISE [W3] magnitude to confirm cross-identification via consistent photometry.
• Kinematic analysis via convergent point calculations using proper motions and radial velocity estimates to test membership in young moving groups.
• Monte Carlo simulation of stellar populations (thin disk, thick disk, halo) using the system's proper motion and parallax to estimate membership probabilities.
• Evaluation of positional and photometric consistency between WISE, AKARI, IRAS, and GSC sources to confirm the binary's identity across epochs.

Experimental results

Research questions

• RQ1 Can WISE J104915.57-531906.1 be reliably cross-identified with archival astrometric and photometric sources such as IRAS, AKARI, and the Guide Star Catalog?
• RQ2 Is the binary brown dwarf a member of any known nearby young stellar groups (e.g., β Pic, AB Dor, Tuc-Ha, etc.) based on kinematic analysis?
• RQ3 What is the likelihood that the system belongs to the thin disk, thick disk, or halo population, based on its kinematics?
• RQ4 Can the system's position be accurately predicted at past and future epochs to enable pre-discovery astrometric searches?
• RQ5 Is a shorter, more memorable name appropriate for this important nearby substellar binary system?

Key findings

• The binary brown dwarf WISE J104915.57-531906.1 is cross-identified with the AKARI/IRC source J1049166-531907 at epoch 2007.0, with a positional offset of only 1”, confirming the match.
• The system is also consistent with the IRAS Faint Source Catalog source IRAS Z10473-5303 at epoch 1983.5, with a 7.4” separation and compatible flux levels at 12 μm.
• The Guide Star Catalog (epoch 1995.304) contains a plausible optical counterpart, and the predicted position matches the system's motion.
• Kinematic analysis using convergent point methods shows no significant membership in any known young moving group, with predicted peculiar velocities ranging from -12.8 to 14.0 km s⁻¹.
• Monte Carlo simulations indicate a 96% probability that the system is a thin disk star, with only 4% chance of being a thick disk star and negligible halo membership.
• The paper proposes the name 'Luhman 16' (or 'Luhman-WISE 1') as a more memorable and practical alternative to the unwieldy WISE designation, with the WDS confirming the inclusion of 'LUH 16' in its catalog.