The Low-Mass Astrometric Binary LSR1610-0040

Abstract

Even though it was discovered more than a decade ago, LSR1610-0040 remains an enigma. This object has a peculiar spectrum that exhibits some features typically found in L subdwarfs, and others common in the spectra of more massive M dwarf stars. It is also a binary system with a known astrometric orbital solution. Given the available data, it remains a challenge to reconcile the observed properties of the combined light of LSR1610-0040AB with current theoretical models of low-mass stars and brown dwarfs. We present the results of a joint fit to both astrometric and radial velocity measurements of this unresolved, low-mass binary. We find that the photocentric orbit has a period $P=633.0\pm 1.7$ days, somewhat longer than previous results, with eccentricity of $e=0.42\pm 0.03$, and we estimate that the semi-major axis of the orbit of the primary is $a_1\approx 0.32$ AU, consistent with previous results. While a complete characterization of the system is limited by our small number of radial velocity measurements, we establish a likely primary mass range of $0.09-0.10M_{\odot }$ from photometric and color-magnitude data. For a primary mass in this range, the secondary is constrained to be $0.06-0.075M_{\odot }$, making a negligible contribution to the total I-band luminosity. This effectively rules out the possibility of the secondary being a compact object such as an old, low-mass white dwarf. Based on our analysis, we predict a likely angular separation at apoapsis comparable to the resolution limits of current high-resolution imaging systems. Measuring the angular separation of the A & B components would finally enable a full, unambiguous solution for the masses of the components of this system.

31 Pages, 13 Figures, 6 Tables, Accepted to The Astronomical Journal

References in corpus (5)

• New evolutionary sequences for extremely low mass white dwarfs: Homogeneous mass and age determinations, and asteroseismic prospects
• Efficient fitting of multiplanet Keplerian models to radial velocity and astrometry data
• The AllWISE Motion Survey and The Quest for Cold Subdwarfs
• Trigonometric parallaxes of ten ultracool subdwarfs
• Trigonometric Parallaxes for Two Late-Type Subdwarfs: LSR1425+71 (sdM8.0) and the Binary LSR1610-00 (sd?M6pec)

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