Revisiting Stellar equatorial rotational velocities with Gaia DR3 line broadening -- the dependence on temperature, mass and age

TL;DR

This study leverages Gaia DR3 vbroad measurements to investigate stellar rotation as a function of temperature, mass, and age across FGK main-sequence stars, confirming the Kraft break at $T_{ m eff}\approx 6{,}500\,\mathrm{K}$. By combining vbroad with FLAME ages and radii, the authors derive the specific angular momentum $SAM = v_{\rm broad} \cdot R$ and analyze its evolution in four mass bins using a scaled age $t_{FLAME}/TAMS$, extending beyond the MS. They find that hot stars slow their rotation only after MS departure, while cool stars spin down rapidly on the MS, with SAM showing consistent trends; these patterns align with magnetic braking anchored in convective envelopes. The work provides empirical constraints on angular-momentum evolution and gyrochronology, and outlines the need for joint analyses with other surveys and improved post-MS spin-down modeling.

Abstract

We used more than $10^5$ Gaia DR3 line broadening vbroad measurements to examine stellar rotation as a function of stellar temperature, mass and age. The large sample clearly displays the Kraft break at $\sim 6{,}500$\,K, or mass of $\sim1.3\,M_{\odot}$-while vbroad are small, on the order of $10$-$20$ km/s, for stars cooler than the Kraft break, they sharply rise above the break, reaching up $\sim100$ km/s with temperature of $7{,}000$ K. To follow the stellar rotation as a function of age, we consider vbroad as a function of scaled age-stellar age divided by the relevant Terminal Age Main Sequence (MS), for four narrow mass bins. We find that stellar rotation deceleration is slow during the MS phase and fast afterwards for stars hotter than the break, whereas deceleration rate is relatively high and does not vary much for the cool stars. Our findings are consistent with the theory that stellar rotation slowing is due to magnetic breaking, emanating from magnetic fields that are anchored to the stellar convective envelopes. Therefore, deceleration is high in cool stars, but in hot stars only after they leave the MS and develop convective outer layers

Figures (3)

• Figure 1: Extinction-corrected Gaia CMD of $1{,}116{,}716$ stars sample with reliable vbroad measurements from Gaia DR3, and an Age value in FLAME. Point density is presented via point alpha value, colored by the stars' evolutionary stage ($Age/TAMS$) in 5 discrete ranges. The dashed blue curve was used to separate the MS from evolved stars. Stars below the curve are the final clean MS sample used in this work ($424{,}270$ stars).
• Figure 2: Left: Projected rotational velocity (vbroad) versus effective temperature, taken from Gaia GSPphot. Hotter stars tend to rotate more rapidly as presented here. Right: Projected rotational velocity (vbroad) versus stellar mass, taken from Gaia FLAME for $354{,}849$Gaia MS stars. Filled and open circles are data points taken from Fig 3. of kraft67.
• Figure 3: Upper: Stellar Gaia's vbroad vs. the corresponding GSP-Phot's evolutionary stage in four FLAME-mass bins. with width of $0.1\,M_\odot$. Bin centers are at $1.3\,M_\odot$, $1.4\,M_\odot$, $1.5\,M_\odot$ and $1.6\,M_\odot$. We use Gaia scaled age---defined as the stellar age in units of the stellar interpolated TAMS (see text). Our distributions are plotted as translucent black dots, signifying point density. Lower: The stellar specific angular momentum vs. its scaled age.