Is T Tauri North a 'Classical' T Tauri star?

TL;DR

This study uses high-resolution IR spectroscopy and spectral modeling to analyze T Tau North, revealing it is a very young, early-stage star with surface temperature differences likely caused by spots, suggesting it is a protostar ejected from its binary system.

Contribution

First detailed IR spectroscopic analysis of T Tau North, revealing its young age and surface temperature variations, indicating an earlier evolutionary stage than typical classical T Tauri stars.

Findings

T Tau N has a $K$-band temperature of 3976 K, cooler than optical measurements.

T Tau N's gravity is lower than most classical T Tauri stars.

Estimated age of T Tau N is less than 1 million years.

Abstract

We present high-resolution $H$- and $K$-band spectroscopic observations of the archetypal T Tauri star T Tau North. Synthetic spectral modeling is used to derive the $K$-band temperature, surface gravity, magnetic field strength, and rotational velocity for this star. The $K$-band spectroscopic temperature measured is $\rm T_{K\text{-band}} = 3976 \pm 90 K$, which is $\sim 1000 \, \rm K$ cooler than the temperature measured from optical observations. Our $K$-band temperature measurement for T Tau N is confirmed using equivalent width line ratio vs. temperature relations in the $H$-band, from which a $\rm T_{H\text{-band}} = 4085 \pm 155 K$ is derived. This optical vs. IR temperature difference is interpreted as cool or hot spots, or both, covering a significant part of the surface of T Tau N. The gravity derived for T Tau N $\log{g}=3.45 \pm 0.14$ is lower than the gravity of nearly every other star in a sample of 24 classical T Tauri stars in Taurus. Combining these temperature and gravity results with magnetic stellar evolutionary models, we find the age of T Tau N to be less than 1 Myr old. These results suggest that T Tau N is in an earlier evolutionary stage than most classical T Tauri stars in Taurus, arguing that it is a protostar ejected from the embedded southern binary system shortly after its formation.