Object DUO 2: A New Binary Lens Candidate

TL;DR

This paper reports the discovery and analysis of an unusual variable star, DUO 2, with a potential binary lens system involving a small-mass companion, supported by light curve data and centroid shift measurements.

Contribution

It introduces a new binary lens candidate with detailed modeling and confirms the binary nature through imaging and centroid shift analysis.

Findings

Detected a star brightening by over two magnitudes in 6 days.

Identified a binary lens system with a separation of about 1 arcsecond.

Provided evidence of blending and centroid shift supporting the binary lens interpretation.

Abstract

We present the light curve of an unusual variable object, DUO 2, detected during the search for microlensing events by the DUO project. The star remained stable for more than 150 days before it brightened by more than two magnitudes in 6 days in the B and R bands. The light curves are achromatic during the variability. We consider possible explanations of the photometric behavior, with particular emphasis on the binary lens interpretation of the event. The masses of the lenses are quite small, with the companion possibly in the range of a brown dwarf or even a few times of Jupiter. We report evidence of blending of the source by a companion through the first detection of shift in the light centroid among all the microlensing experiments. This shift sets a lower limit of $0.3^{\prime\prime}$ on the separation between the stars. The best lens model obtained requires moderate blending, which was what motivated us to check the centroid shift that was subsequently found. The best lens model predicts a separation of $1^{\prime\prime}$ between the two blended stars. This prediction was recently tested using two CCD images taken under good seeing conditions. Both images show two components. Their separation and position angle are in good agreement with our model.