An algorithm to calculate the relative orbit, ephemeris, and individual masses of unresolved astrometric binaries. Example of application on the newest Gaia DR3 binaries: the ESMORGA catalog

Abstract: The recent Gaia Data Release 3 has unveiled a catalog of over eight hundred thousand binary systems, providing orbital solutions for half of them. Since most of them are unresolved astrometric binaries, several astrophysical parameters that can be only derived from their relative orbits together with spectroscopic data, such as the individual stellar masses, remain unknown. Indeed, only the mass of the primary, $\texttt{m1}$, and a wide interval, $\texttt{[m2_lower, m2_upper]}$, for the secondary companion of main-sequence astrometric binaries have been derived to date (Gaia Collaboration et al., 2023). In order to obtain the correct values for each component, we propose an analytic algorithm to estimate the two most probable relative orbits and magnitude differences of a certain main-sequence or subgiant astrometric binary using all available Gaia data. Subsequently, both possible solutions are constrained to the one that is consistent with $\texttt{m1, m2_lower}$ and $\texttt{m2_upper}$. Moreover, we deduce not only the correct values of the individual masses for each binary but also the size of the telescope necessary to resolve their components. The workflow of our algorithm as well as the ESMORGA (Ephemeris, Stellar Masses, and relative ORbits from GAia) catalog with more than one hundred thousand individual masses, spectral types, and effective temperatures derivated from its application are also presented.