The Multiplicity of T Tauri Stars in the Star Forming Regions Taurus-Auriga and Ophiucus-Scorpius: A 2.2 µm Speckle Imaging Survey

Citation

Ghez, Andrea Mia (1993) The Multiplicity of T Tauri Stars in the Star Forming Regions Taurus-Auriga and Ophiucus-Scorpius: A 2.2 µm Speckle Imaging Survey. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/AD5X-DA38. https://resolver.caltech.edu/CaltechETD:etd-10072004-143305

Abstract

We present the results of a magnitude limited (K ≤ 8.5 mag) multiplicity survey of T Tauri stars (TTS) in two nearby star forming regions (SFR), Taurus-Auriga and Ophiuchus-Scorpius. Each of the 69 stars in the sample was observed at K(2.2 µm) with an infrared array camera on the Hale 5-m Telescope at Palomar Observatory and imaged using two-dimensional speckle interferometric techniques.

Thirty three companion stars were found, of which 15 were new detections. A subset of 64 observations was sensitive to all companion stars in the projected linear range 14 to 225 AU and the magnitude difference range 0.0 to 2.0 mag. We used this subset and region to study the multiplicity of TTS; the frequency of companion stars within this region is 34 ± 9%, independent of SFR. We discovered a distinction between the classical TTS (CTTS) and the weak-lined TTS (WTTS) based on the binary star frequency as a function of separation; the WITS dominate the binary star distribution at the closer separations and the CTTS populate the wider separations. The cross over occurred near 100 AU, the size typically quoted for a circumstellar disk. We suggest that all TTS begin as CTTS and become WTTS when accretion has ceased, and that the nearby companion stars act to shorten the accretion timescale in multiple star systems.

Integrated over all magnitude differences the binary star frequency in the projected linear separation range 14 to 225 AU for TTS (59 ± 16%) is a factor of 3.5 greater than that of the solar-type main sequence stars (17 ± 3%). Given the limited angular separation range that we are sensitive to, i.e., both the spectroscopic and wide binaries are missed, the rate at which binaries are detected suggests that most, if not all, TTS stars have companions. We propose that the observed overabundance of companions to TTS with respect to their older counterparts on the main sequence is an evolutionary effect; in this scheme triple and higher order TTS, which are observed at higher frequencies than for the solar-type main sequence stars, are disrupted by close encounters with another star or system of stars.

Thesis Files