Astrometric determination of white dwarf radial velocities with Gaia?

TL;DR

This paper explores the potential of Gaia's precise astrometric data to determine white dwarf radial velocities directly through perspective acceleration, offering a method independent of spectral analysis.

Contribution

It assesses Gaia's capability to measure white dwarf radial velocities astrometrically by analyzing proper motion and parallax data over the mission duration.

Findings

Gaia's predicted accuracy enables potential radial velocity measurements for white dwarfs.

Astrometric method can disentangle gravitational redshift from Doppler shift.

Combining Hipparcos and Gaia data enhances measurement precision.

Abstract

Usually, the determination of radial velocities of stars relies on the shift of spectral lines by the Doppler effect. Russel & Atkinson (1931) and Oort (1932) already noted that due to the large proper motion and parallax of the white dwarf (WD) van Maanen 2, a determination of the perspective acceleration of the proper motion would provide a direct astrometric determination of the radial velocity which is independent of the gravitational redshift. If spectroscopic redshift measurements of Halpha and Hbeta NLTE cores exist, a purely astrometric determination would allow disentangling the gravitational redshift from the Doppler shift. The best instrument for measuring the tiny perspective acceleration is the Gaia satellite of the European Space Agency, aiming at absolute astrometric measurements of one billion stars down to 20th magnitude with unprecedented accuracy. At 15th magnitude, the predicted angular accuracy of Gaia is about 20 micro-arcseconds. In this article, we estimate whether it is possible to measure the radial velocity of WDs astrometrically by the exchange of proper motion into radial velocity during the 5-year mission of the satellite or by combining Hipparcos data with the position measurements at the beginning of the Gaia mission (the Hundred-Thousand-Proper-Motion project HTPM).