# The mass, luminosity and mass-loss rate of the donor of the V1487 Aql/GRS 1915+105 binary system

## TL;DR

This study models the donor star in the GRS 1915+105 binary system, constraining its mass, luminosity, and mass-loss rate using observational data and evolutionary models, revealing a low-mass giant with specific characteristics.

## Contribution

The paper provides the first detailed modeling of the donor star in GRS 1915+105, constraining its mass and properties independently of distance, and estimates its mass transfer rate and duty cycle.

## Key findings

- Donor star mass is at least 0.28 solar masses.
- The donor is a K5 III giant.
- Mass transfer rate is well below the critical rate.

## Abstract

The donor in the microquasar GRS 1915+105 is a low-mass giant. Such a star consists of a degenerate helium core and a hydrogen-rich envelope. Both components are separated by a hydrogen burning shell. The structure of such an object is relatively simple and easy to model. Making use of the observational constraints on the luminosity and the radius of the donor, we constrain the mass of this star with evolutionary models. We find a very good agreement between the constraints from those models and from the observed rotational broadening and the NIR magnitude. Combining the constraints, we find solutions with stripped giants of the mass of $\geq\!0.28{\rm M}_{\odot}$ and of the spectral class K5 III, independent of the distance to the system, and a distance-dependent upper limit, $\lesssim\!1{\rm M}_{\odot}$. We also calculate the average mass transfer rate and the duty cycle of the system as a function of the donor mass. This rate is much below the critical rate (at which the system would become persistent), and the duty cycle is less than 20 per cent.