Updated High-Temperature Opacities for the Dartmouth Stellar Evolution Program and their Effect on the Jao Gap Location

TL;DR

This paper updates stellar population models with new high-temperature opacities, showing a slight shift in the predicted Jao Gap location, which may be too subtle for current observations.

Contribution

It introduces the use of OPLIB opacities in modeling the Jao Gap, refining the predicted stellar density feature compared to previous OPAL-based models.

Findings

Updated models shift the Jao Gap by ~0.05 mag

Difference between OPLIB and OPAL models is likely undetectable

Models confirm the sensitivity of the Gap to metallicity and opacity

Abstract

The Jao Gap, a 17 percent decrease in stellar density at $M_G \sim10$ identified in both Gaia DR2 and EDR3 data, presents a new method to probe the interior structure of stars near the fully convective transition mass. The Gap is believed to originate from convective kissing instability wherein asymmetric production of $^{3}$He causes the core convective zone of a star to periodically expand and contract and consequently the stars' luminosity to vary. Modeling of the Gap has revealed a sensitivity in its magnitude to a population's metallicity primarily through opacity. Thus far, models of the Jao Gap have relied on OPAL high-temperature radiative opacities. Here we present updated synthetic population models tracing the Gap location modeled with the Dartmouth stellar evolution code using the OPLIB high-temperature radiative opacities. Use of these updated opacities changes the predicted location of the Jao Gap by $\sim0.05$ mag as compared to models which use the OPAL opacities. This difference is likely too small to be detectable in empirical data.