The Membership and Age of the Planet-hosting Young Star IRAS 04125+2902

TL;DR

This paper refines the age and membership of the young star IRAS 04125+2902, establishing it as approximately 3 million years old and clarifying its association with a specific Taurus group, using comparative analysis with known stellar populations.

Contribution

It provides a detailed analysis of IRAS 04125+2902's age and membership, correcting previous assumptions and demonstrating the limitations of model isochrones for young low-mass stars.

Findings

IRAS 04125+2902 is approximately 3 million years old.

The star belongs to a small group behind the Taurus clouds.

Model isochrones are unreliable for young low-mass stars.

Abstract

A transiting planet was recently discovered around a star in the Taurus star-forming region, IRAS 04125+2902, making it one of the youngest known planets. The discovery paper cited two age estimates for IRAS 04125+2902, one based on a comparison to two sets of model isochrones in the Hertzsprung-Russell (H-R) diagram and a second age reported by an earlier study for a putative population in Taurus that includes IRAS 04125+2902 (D4-North). However, the model isochrones in question differ significantly for most temperatures and luminosities of young low-mass stars, and do not reproduce the observed sequences for the TW Hya and 32 Ori associations (10 and 21 Myr). Meanwhile, as found in my previous work, D4-North is a collection of field stars and fragments of several distinct Taurus groups and older associations, so its quoted age is not meaningful. The true parent population for IRAS 04125+2902 is a small group that is ~35 pc behind the L1495 and B209 clouds (B209N). I have analyzed the age of B209N through a comparison to TW Hya and 32 Ori. The M star sequences in the latter two associations have the same shapes, but the sequence for B209N is flatter, indicating that >M4 stars at ages of <10 Myr fade more quickly than stars at earlier types and older ages. For the one member of B209N that is earlier than M4 (IRAS 04125+2902), I estimate an age of 3.0+/-0.4 Myr based on its offsets from TW Hya and 32 Ori, which by happenstance is similar to the value derived through the comparison to model isochrones.