Perspective acceleration and gravitational redshift. Measuring masses of individual white dwarfs using Gaia + SIM astrometry

TL;DR

This paper explores how combining Gaia and SIM astrometry can precisely measure white dwarf masses by analyzing perspective acceleration and gravitational redshift, enabling improved understanding of their mass-radius relation.

Contribution

It demonstrates the potential of long-term astrometric measurements from Gaia and SIM to accurately determine white dwarf masses through perspective acceleration and gravitational redshift analysis.

Findings

Potential to measure white dwarf masses with better than 2% accuracy.

Identification of the number of nearby white dwarfs suitable for such measurements.

Discussion of challenges posed by long-period planets on astrometric signals.

Abstract

According to current plans, the SIM/NASA mission will be launched just after the end of operations for the Gaia/ESA mission. This is a new situation which enables long term astrometric projects that could not be achieved by either mission alone. Using the well-known perspective acceleration effect on astrometric measurements, the true heliocentric radial velocity of a nearby star can be measured with great precision if the time baseline of the astrometric measurements is long enough. Since white dwarfs are compact objects, the gravitational redshift can be quite large (40-80 km/s), and is the predominant source of any shift in wavelength. The mismatch of the true radial velocity with the spectroscopic shift thus leads to a direct measure of the Mass--Radius relation for such objects. Using available catalog information about the known nearby white dwarfs, we estimate how many masses/gravitational redshift measurements can be obtained with an accuracy better than 2%. Nearby white dwarfs are relatively faint objects (10 < V < 15), which can be easily observed by both missions. We also briefly discuss how the presence of a long period planet can mask the astrometric signal of perspective acceleration.