Symbiotic Stars in the APOGEE Survey: The Case of LIN 358 and SMC N73 (LIN 445a)

TL;DR

This study characterizes two symbiotic binary systems in the Small Magellanic Cloud using multi-wavelength data, spectral analysis, and orbit fitting, revealing their mass transfer mechanisms and orbital parameters for the first time.

Contribution

It provides the first orbital parameters and global SED fitting for LIN 358 and SMC N73, advancing understanding of their accretion processes and variability.

Findings

LIN 358 likely undergoes wind Roche lobe overflow.

Orbital periods are >270 and >980 days for SMC N73 and LIN 358.

Spectral variability suggests possible eccentric orbit effects.

Abstract

LIN 358 and SMC N73 are two symbiotic binaries in the halo of the Small Magellanic Cloud, each composed of a hot white dwarf accreting from a cool giant companion. In this work, we characterize these systems using a combination of SED-fitting to the extant photometric data spanning a broad wavelength range (X-ray/ultraviolet to near-infrared), detailed analysis of the APOGEE spectra for the giant stars, and orbit fitting to high quality radial velocities from the APOGEE database. Using the calculated Roche lobe radius for the giant component and the mass ratio for each system, it is found that LIN 358 is likely undergoing mass transfer via wind Roche lobe overflow while the accretion mechanism for SMC N73 remains uncertain. This work presents the first orbital characterization for both of these systems (yielding periods of >270 and >980 days, respectively, for SMC N73 and LIN 358) and the first global SED fitting for SMC N73. In addition, variability was identified in APOGEE spectra of LIN 358 spanning 17 epochs over two years that may point to a time variable accretion rate as the product of an eccentric orbit.