OB Stars and Cepheids From the Gaia TGAS Catalogue: Test of their Distances and Proper Motions

TL;DR

This study uses Gaia TGAS data for young distant stars to test and calibrate their distance scales and proper motions, finding small adjustments needed for Cepheids and OB stars to improve Galactic rotation models.

Contribution

It introduces a method to calibrate stellar distance scales using Gaia TGAS parallaxes and proper motions, specifically applied to Cepheids and OB stars for Galactic rotation analysis.

Findings

Cepheid distances should be reduced by 3%

OB star distances should be increased by 9%

Improved Galactic rotation parameters derived from these adjustments

Abstract

We consider young distant stars from the Gaia TGAS catalog. These are 250 classical Cepheids and 244 OB stars located at distances up to 4 kpc from the Sun. These stars are used to determine the Galactic rotation parameters using both trigonometric parallaxes and proper motions of the TGAS stars. In this case the considered stars have relative parallax errors less than 200%. Following the well-known statistical approach, we assume that the kinematic parameters found from the line-of-sight velocities $V_r$ are less dependent on errors of distances than the found from the velocity components $V_l$. From values of the first derivative of the Galactic rotation angular velocity $\Omega{'}_0$, found from the analysis of velocities $V_r$ and $V_l$ separately, the scale factor of distances is determined. We found that from the sample of Cepheids the scale of distances of the TGAS should be reduced by 3%, and from the sample of OB stars, on the contrary, the scale should be increased by 9%.