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

**Authors:** Emily M. Boudreaux, Brian C. Chaboyer  
**arXiv:** [2301.10798](https://arxiv.org/abs/2301.10798)  
**Date:** 2023-01-25  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2301.10798v1/

## Key points

- Jao Gap phenomenon: 17% decrease in stellar density observed at $M_G \sim10$ in Gaia DR2 and EDR3 data
- Unique opportunity to probe interior structure of stars near fully convective transition mass
- Convective kissing instability caused by asymmetric production of $^{3}$He in core convective zone believed to be the origin of the Gap
- Previous models used OPAL high-temperature radiative opacities
- Study presents updated synthetic population models using OPLIB opacities with Dartmouth stellar evolution code
- Updated opacities shift predicted location of Jao Gap by approximately $\sim0.05$ mag compared to models using OPAL opacities
- Difference may be too small to detect empirically, but highlights sensitivity of Gap's magnitude to metallicity primarily through opacity effects
- Multiple groups have released high-temperature opacity tables, including OPAL and OPLIB
- OPLIB more up-to-date due to its use of plasma modeling
- Study emphasizes considering uncertainties in opacity tables when studying phenomena like the Jao Gap

## Summary

A recent study investigated the Jao Gap phenomenon, a 17 percent decrease in stellar density observed at $M_G \sim10$ in both Gaia DR2 and EDR3 data. This presents a unique opportunity to probe the interior structure of stars near the fully convective transition mass. The Gap is believed to originate from a convective kissing instability caused by asymmetric production of $^{3}$He in the core convective zone, resulting in luminosity variations. Previous models relied on OPAL high-temperature radiative opacities; however, this study presents updated synthetic population models using OPLIB opacities with the Dartmouth stellar evolution code. These updated opacities have been found to shift the predicted location of the Jao Gap by approximately $\sim0.05$ mag compared to models using OPAL opacities. While this difference may be too small to detect empirically, it highlights the sensitivity of the Gap's magnitude to metallicity primarily through opacity effects. The researchers also discuss that multiple groups have released high-temperature opacity tables, including OPAL and OPLIB, with OPLIB being more up-to-date due to its use of plasma modeling. Overall, this study provides valuable insights into how different opacity tables can affect our understanding of stellar evolution and emphasizes considering these uncertainties when studying phenomena such as the Jao Gap.