The radiative-convective gap: fact or fiction?

TL;DR

This study investigates the B"ohm-Vitense gap in open clusters using Gaia data and finds no clear evidence of a physical discontinuity, suggesting observed gaps may result from statistical effects and mass-color relation variations.

Contribution

The paper provides a comprehensive analysis of the B"ohm-Vitense gap using Gaia data and simulations, challenging previous interpretations of it as a physical stellar feature.

Findings

No clear gap observed in combined CMDs of clusters.

Simulated gaps can arise from random sampling and mass-color relations.

Observed gaps may be due to statistical effects, not physical discontinuities.

Abstract

Gaia characterizes the stellar populations of nearby open clusters with unprecedented precision. We investigate the B\"ohm-Vitense gap, which has been found as a prominent feature in the stellar sequence of open clusters. Using PARSEC isochrone fitting, we derive astrophysical parameters for more than 1100 stars in Praesepe, identify more than 1100 bona fide single stars in the alpha Persei (Melotte 20) open cluster, and confirm their approximate match in terms of age (approx. 710 Myr and 45 Myr) and metallicity ([M/H] approx. +0.15 dex and +0.13 dex) to the Hyades and Pleiades, respectively. By merging data of the cluster pairs, we improve number statistics. We do not find a clear gap in the combined observational G_abs vs. BP-RP color-magnitude diagram (CMD) in the stellar mass range corresponding to the location of the B\"ohm-Vitense gap. We reproduce gaps in simulated Hyades-type CMDs randomly drawn from an initial mass function. There is no strong evidence for a discontinuity originating in the transition from radiative to convective energy transport in the stellar photosphere. We conclude that the observed gaps in the stellar sequences of open clusters could be explained by small number statistics and the uneven mass-color relation at the transition from spectral type A to F.