AAVSO: American Association of Variable Star Observers

A Photometric Study of the Eclipsing Binary LO Ursae Majoris

Volume 49 number 2 (2021)

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Edward J. Michaels
Waffelow Creek Observatory, 10780 FM 1878, Nacogdoches, TX 75961; astroed@ejmj.net


Multicolor photometric observations of the eclipsing binary LO UMa are presented. Photometric models were determined simultaneously from four sets of light curves using the Wilson-Devinney program. The results indicate LO UMa is a semidetached Algol type binary with a mass ratio of q = 0.62 and primary and secondary star spectral types of F9 and K8, respectively. Based on available times of minimum light, the O – C curves revealed a sinusoidal oscillation with a period of about 16.4 years and an amplitude of 0.0238 day. Two possible causes of the period variation were considered, changes in the quadrupole moment of the secondary star caused by magnetic activity (Applegate mechanism) and the light-time effect of a third body orbiting the binary. It was found that the most plausible explanation for the period oscillation is an unseen body, with a mass of no less than 1.55 M⦿, orbiting the binary. A main sequence star of this mass would be the dominant light source in the system. However, spectra and observed color do not support a star of this mass, nor did the photometric solution find any indication of third light. A massive non-radiating third body suggests a possible neutron star candidate.