WIYN Open Cluster Study LXII: Comparison of Isochrone Systems using Deep Multi-Band Photometry of M35

TL;DR

This study compares various stellar isochrone models using deep multi-band photometry of M35, revealing their strengths and discrepancies in fitting observed stellar data across different mass ranges.

Contribution

It provides a detailed comparison of multiple isochrone systems and atmosphere models against new deep photometry, highlighting areas for improvement in stellar modeling.

Findings

Padova and PARSEC produce higher temperatures for low-mass stars.

Dartmouth and Y2 with BT-Settl fit optical data well but are too blue in IR.

Discrepancies suggest incomplete molecular spectral modeling in IR.

Abstract

Current generation stellar isochrone models exhibit non-negligible discrepancies due to variations in the input physics. The success of each model is determined by how well it fits the observations, and this paper aims to disentangle contributions from the various physical inputs. New deep, wide-field optical and near-infrared photometry ($UBVRIJHK_S$) of the cluster M35 is presented, against which several isochrone systems are compared: Padova, PARSEC, Dartmouth and Y$^2$. Two different atmosphere models are applied to each isochrone: ATLAS9 and BT-Settl. For any isochrone set and atmosphere model, observed data are accurately reproduced for all stars more massive then $0.7$ M$_\odot$. For stars less massive than 0.7 M$_\odot$, Padova and PARSEC isochrones consistently produce higher temperatures than observed. Dartmouth and Y$^2$ isochrones with BT-Settl atmospheres reproduce optical data accurately, however they appear too blue in IR colors. It is speculated that molecular contributions to stellar spectra in the near-infrared may not be fully explored, and that future study may reconcile these differences.