Stellar Rotation in the Gaia Era: Revised Open Clusters’ Sequences

Abstract

The period versus mass diagrams (i.e., rotational sequences) of open clusters provide crucial constraints for angular momentum evolution studies. However, their memberships are often heavily contaminated by field stars, which could potentially bias the interpretations. In this paper, we use data from Gaia DR2 to reassess the memberships of seven open clusters with ground- and space-based rotational data, and present an updated view of stellar rotation as a function of mass and age. We use the Gaia astrometry to identify the cluster members in phase space, and the photometry to derive revised ages and place the stars on a consistent mass scale. Applying our membership analysis to the rotational sequences reveals that: (1) the contamination in clusters observed from the ground can reach up to ∼35%; (2) the overall fraction of rotational outliers decreases substantially when the field contaminants are removed, but some outliers persist; (3) there is a sharp upper edge in the rotation periods at young ages; (4) at young ages, stars in the 1.0–0.6M ⊙ range inhabit a global maximum of rotation periods, potentially providing an optimal window for habitable planets. Additionally, we see clear evidence for a strongly mass-dependent spin-down process. In the regime where rapid rotators are leaving the saturated domain, the rotational distributions broaden (in contradiction with popular models), which we interpret as evidence that the torque must be lower for rapid rotators than for intermediate ones. The cleaned rotational sequences from ground-based observations can be as constraining as those obtained from space.

Rotation Distributions around the Kraft Break with TESS and Kepler: The Influences of Age, Metallicity, and Binarity

“…We additionally find that RUWE (wide) binaries have the same distribution in rotation as single stars at a ≈99% significance, as supported by a Kolmogorov-Smirnov test (see also Mamajek & Hillenbrand 2008;Fleming et al 2019;Godoy-Rivera et al 2021). By showing that single stars and the components of wide binaries have the same rotational distribution, Figure 13 validates the use of wide separation binaries as empirical constraints for the rotational evolution of single stars (e.g., Mamajek & Hillenbrand 2008;Janes 2017;Godoy-Rivera & Chanamé 2018;Fleming et al 2019;Otani et al 2021).…”

“…Most braking laws predict angular momentum loss that goes as dJ/dt ∝ ω 3 , where the angular momentum loss strongly depends on the rotational velocity of the star (Kawaler 1988). This has the effect of producing tight rotational sequences in intermediate-age open clusters, despite the fact that stars begin their lives with a wide range of rotation periods (e.g., Meibom et al 2011Meibom et al , 2015Barnes et al 2016;Douglas et al 2017;Rebull et al 2017;Curtis et al 2020;Fritzewski et al 2020;Godoy-Rivera et al 2021).…”

Rotation Distributions around the Kraft Break with TESS and Kepler: The Influences of Age, Metallicity, and Binarity

“…We additionally find that RUWE (wide) binaries have the same distribution in rotation as single stars at a ≈ 99% significance, as supported by a Kolmogorov-Smirnov test (see also Mamajek & Hillenbrand 2008;Fleming et al 2019;Godoy-Rivera et al 2021). By showing that single stars and the components of wide binaries have the same rotational distribution, Figure 13 validates the use of wide separation binaries as empirical constraints for the rotational evolution of single stars (e.g.…”

“…This has the effect of producing tight rotational sequences in intermediate-age open clusters, despite the fact that stars begin their lives with a wide range of rotation periods (e.g. Meibom et al 2011Meibom et al , 2015Barnes et al 2016;Douglas et al 2017;Rebull et al 2017;Curtis et al 2020;Fritzewski et al 2020;Godoy-Rivera et al 2021).…”

Asteroseismology of evolved stars to constrain the internal transport of angular momentum. V. Efficiency of the transport on the red giant branch and in the red clump

“…In addition, we note that the surface rotation periods observed for MS stars with spectral type F-G are in the range P ∼ 5-25 days (e.g. McQuillan et al 2014;Santos et al 2021;Godoy-Rivera et al 2021). Although the above cited works rely on the modulation of light-curves due to magnetic spots, that could lead to an underestimation in the number of slow rotators, it has been shown by Masuda et al (2021) that the photometric samples do not lack slow rotators.…”