Optical Spectroscopic Monitoring Observations of a T Tauri Star V409 Tau

TL;DR

This study presents optical spectroscopic monitoring of the T Tauri star V409 Tau, revealing light obscuration by a distorted circumstellar disk and variable accretion activity through spectral line analysis.

Contribution

First detailed spectroscopic monitoring of V409 Tau linking spectral features to photometric variability and accretion processes.

Findings

Light variation caused by disk obscuration.

Stable absorption line equivalent widths despite brightness changes.

Variable inverse P Cygni profile indicating unsteady accretion.

Abstract

We report the results of optical spectroscopic monitoring observations of a T Tauri star, V409 Tau. A previous photometric study indicated that this star experienced dimming events due to the obscuration of light from the central star with a distorted circumstellar disk. We conducted medium-resolution (R ~10,000) spectroscopic observations with 2-m Nayuta telescope at Nishi-Harima Astronomical Observatory. Spectra were obtained in 18 nights between November 2015 and March 2016. Several absorption lines such as Ca I and Li, and the H alpha emission line were confirmed in the spectra. The Ic-band magnitudes of V409 Tau changed by approximately 1 magnitude during the observation epoch. The equivalent widths of the five absorption lines are roughly constant despite changes in the Ic-band magnitudes. We conclude that the light variation of the star is caused by the obscuration of light from the central star with a distorted circumstellar disk, based on the relationship between the equivalent widths of the absorption lines and the Ic-band magnitudes. The blue component of the H alpha emission line was dominant during the observation epoch, and an inverse P Cygni profile was observed in eight of the spectra. The time-variable inverse P Cygni profile of the H alpha emission line indicates unsteady mass accretion from the circumstellar disk to the central star.