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# Evolving morphology of resolved stellar Einstein rings

Slava G. Turyshev and Viktor T. Toth

Submitted on 20 September 2022

## Abstract

We consider strong gravitational lensing by nearby stars. Using our wave-optical treatment of lensing by a compact mass, we study Einstein rings that may form around such stellar lenses. These large and bright rings are resolvable by existing instruments. Such lensing events take place in hours or days, with peak light amplification lasting several minutes. Many such events may be predicted using the Gaia astrometric catalogue. Serendipitous discoveries are also possible. Fortuitous alignments can be used to confirm or discover and study exoplanets. For lenses that have dense stellar regions in their background, these events may occur annually or more often, warranting their continuous or recurrent monitoring. Resolved imaging and spectroscopy of the evolving morphology of an Einstein ring offers knowledge about both the lens and the source. The angular size of the Einstein ring amounts to a direct measurement of the lens mass. The changing orientation of the major and minor images of the source offers astrometric information. The event duration helps determine the source's size. The sky position of planetary lensing events constrains the planet's orbit. Spectroscopy of the ring allows for direct investigations of the source. The frequency and predictability of these events and the wealth of information that can be obtained by imaging motivate observational campaigns using existing facilities or new instruments dedicated to the search and study of Einstein rings that form around nearby stars. As a specific example, we consider a predicted 2028 lensing of a red giant by $\alpha$ Centauri A.

## Preprint

Comment: 26 pages, 10 figures, 2 table

Subjects: Astrophysics - Instrumentation and Methods for Astrophysics; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics; General Relativity and Quantum Cosmology