Possible progression of mass flow processes around young intermediate-mass stars based on high-resolution near-infrared spectroscopy. I. Taurus

TL;DR

This study uses high-resolution near-infrared spectroscopy to explore the evolution of mass flow processes around young intermediate-mass stars in Taurus, revealing a progression from stellar wind and accretion to inactivity as stars mature.

Contribution

It provides new insights into the progression of mass flow processes in intermediate-mass stars through detailed spectral analysis across different evolutionary phases.

Findings

Profiles indicate a transition from wind and accretion activities to inactivity.

Opacity in disks influences mass flow processes.

He I features suggest chromospheric activity in young stars.

Abstract

We used the WINERED spectrograph to perform near-infrared high-resolution spectroscopy (resolving power $R = 28$,000) of 13 young intermediate-mass stars in the Taurus star-forming region. Based on the presence of near- and mid-infrared continuum emission, young intermediate-mass stars can be classified into three different evolutionary stages: Phases I, II, and III in the order of evolution. Our obtained spectra ($\lambda = 0.91$--1.35\,$\mu$m) depict \HeI $\lambda$10830 and P$\beta$ lines that are sensitive to magnetospheric accretion and winds. We also investigate five sources each for P$\beta$ and \ion{He}{1} lines that were obtained from previous studies along with our targets. We observe that the P$\beta$ profile morphologies in Phases I and II corresponded to an extensive variety of emission features; however, these features are not detected in Phase III. We also observe that the He I profile morphologies are mostly broad subcontinuum absorption lines in Phase I, narrow subcontinuum absorption lines in Phase II, and centered subcontinuum absorption features in Phase III. Our results indicate that the profile morphologies exhibit a progression of the dominant mass flow processes: stellar wind and probably magnetospheric accretion in the very early stage, magnetospheric accretion and disk wind in the subsequent stage, and no activities in the final stage. These interpretations further suggest that opacity in protoplanetary disks plays an important role in mass flow processes. Results also indicate that \ion{He}{1} absorption features in Phase III sources, associated with chromospheric activities even in such young phases, are characteristics of intermediate-mass stars.