Gaia and massive stars in 2025

TL;DR

Gaia provides a near-complete, multi-parameter survey of massive stars, with DR3 delivering astrometry, photometry, spectroscopy, and derived parameters, and DR4 expected to expand data coverage and the massive-star census. The paper highlights both the strengths and caveats of Gaia data for hot OB stars, including parameter inference biases, limited RVS data, and the role of Gaia+2MASS filtering in extending the OB population. It reviews major results in parameter determination, binaries, photometric variability, stellar groups, and the spatial distribution of OB stars, and discusses how DR4 will enable discovery of more binaries with dark companions. Taken together, Gaia DR4 is poised to dramatically increase the known Galactic massive-star sample and uncover numerous NS/BH companions, advancing our understanding of massive-star populations and Galactic structure.

Abstract

I present some of the highlights of the Gaia mission on massive stars and discuss what the fourth data release (DR4) will bring in late 2026. In the first part of the contribution I describe the different types of Gaia products available now and for DR4 and their caveats. In the second part I present the most significant results on massive stars regarding parameter determination, binaries, photometric variability, stellar groups, and the sample and spatial distribution.

Figures (4)

• Figure 1: Values for $T_{\rm eff}$ determined by Apsis for 947 O stars with accurate GOSSS spectral classifications Maizetal11 using GSP-Phot (left) and ESP-HS (right).
• Figure 2: (left) CMD and (right) mean $G$-band photometric dispersion in mmag for the LMC Gaia DR3 sample of Maizetal23. The most prominent variability regions correspond (in increasing $G_{\rm BP}-G_{\rm RP}$) to Be stars, cepheids, and long-period variables, respectively.
• Figure 3: (left) CAMD for Galactic stars with good-quality Gaia DR3 + 2MASS data located above the 20kK ZAMS extinction track with $\hbox{$R_{5495}$}=3.1$. The arrow marks the extinction direction for $\hbox{$E(4405-5495)$} = 1.0$ mag and the labels indicate the location of the RC, RGB, and AGB stars, as smeared by extinction, (right) Same CAMD after applying Gaia + 2MASS filters to eliminate non-OB stars.
• Figure 4: Spatial distribution of the sample in the right panel of Fig. \ref{['method']} colour-coded by $G_{\rm BP}-G_{\rm RP}$ as a proxy for extinction.