# Dynamical masses for the Hyades binary 80 Tauri

## TL;DR

This paper demonstrates that accurate dynamical masses for binary stars in the Hyades cluster can be derived solely from astrometric data, without radial velocities, using precise proper motion measurements from Hipparcos and Gaia.

## Contribution

The study introduces a method to determine component masses of binary stars using only astrometric data, expanding mass measurement techniques beyond traditional radial velocity methods.

## Key findings

- Masses of 80 Tau components are consistent with existing mass-luminosity relations.
- Astrometric data alone can yield reliable stellar mass estimates.
- The results support current stellar evolution models.

## Abstract

The empirical mass-luminosity relation in the Hyades cluster rests on dynamical mass determinations for five binary systems, of which one is eclipsing and the other four are visual or interferometric binaries. The last one was identified and first measured more than 20 years ago. Here we present dynamical mass measurements for a new binary system in the cluster, 80 Tau, which is also a visual pair with a much longer orbital period of about 170 yr. Although we lack the radial-velocity information that has enabled the individual mass determinations in all of the previous binaries, we show that it is still possible to derive the component masses for 80 Tau using only astrometric observations. This is enabled by the accurate proper motion measurements from the Hipparcos and Gaia missions, which constrain the orbital acceleration in the plane of the sky. Separate proper motion values from Gaia for the primary and secondary provide a direct constraint on the mass ratio. Our mass measurements, M(A) = 1.63 (+0.30/-0.13) M(sun) and M(B) = 1.11 (+0.21/-0.14) M(sun), are consistent with the mass-luminosity relation defined by the five previously known systems, which in turn is in good agreement with current models of stellar evolution.