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Alternative Title

Testing the physical association of an extremely-wide substellar companion to a nearby M-dwarf binary

Publication Date

2020

First Advisor

Kimberly Ward-Duong

Second Advisor

Suzan Edwards

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Astronomy

Keywords

Astronomy, Low-mass stars, Brown dwarfs, Binary, Wide binaries, Triple systems, Spectroscopy, Astrometry, Common proper motion, Spectral energy distribution, Star formation, Binary formation

Abstract

Low-mass M-dwarfs comprise over 70% of nearby stars, and how often they are found in multiple systems provides important diagnostics of the star formation process. Yet, the frequency of their brown dwarf companions — objects too low in mass to burn hydrogen like stars, yet too massive to be planets — remains uncertain. In addition to low-mass binary frequencies placing constraints on star formation models, brown dwarfs associated with stars of known age present unique opportunities for studying these mysterious objects. Because they cool and dim throughout their lifetimes, it is difficult to ascertain fundamental parameters such as mass and age for isolated brown dwarfs. Thus, a wide brown dwarf orbiting an M-dwarf system presents an invaluable laboratory to explore their formation and evolution processes. In this thesis, I investigate one such potential system, HIP 3937. HIP 3937 consists of a closely-separated (15 AU) M-dwarf binary pair with a candidate substellar companion at a remarkable separation of 7800 AU. I use a combination of near-infrared spectra from the ARIES instrument on the MMT Observatory and broadband photometric analysis to determine spectral types of the wide companion candidate and each star in the binary pair, and use these to estimate spectroscopic distances to both objects. I measure astrometry using Gaia DR2, archival widefield photographic plates, and literature kinematic information from previous surveys to determine whether the companion is physically bound to the binary. If confirmed, this system would be one of the widest known brown dwarf companions to an M-dwarf system and an important benchmark for the study of low-mass multiple star formation. However, I find that common proper motion analysis alone is insufficient to confirm the physical association of this system, because the derived distances to each of the three components suggest that the candidate companion lies ∼ 30 pc away from the primary binary, making it highly unlikely to be bound despite its co- moving nature. This system presents a rare and interesting case study on the scarcity of wide companions to low-mass stars, and raises questions about com- mon proper motion analysis as a means for confirming wide binaries, statistics of high proper motion systems, and young stellar associations.

Rights

©2020 Michaela Susan Guzzetti. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

Comments

v, 111 pages : illustrations (chiefly color) Includes bibliographical references (pages 103-111)

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