Dr. Marcos Huerta
University of Florida

University of Florida Astronomy Colloquium - Jan. 10th, 2007

A Search for Low Mass Companions and a New Determination of Effective Temperatures for T-Tauri Stars

I present an analysis of over 300 spectra of the photospheres of young stars in order to address three outstanding questions of current interest - (1) whether or not the youngest stars are accompanied by massive substellar companions, (2), quantifying the degree to which starspots influence radial velocity measurements in young stars, and (3) establishing a scale to convert spectral observations to effective temperatures. The first question is essential for understanding the star formation process, the second question sets fundamental limits on ability of radial velocity surveys to detect planets, and the third is a key for getting accurate mass and age estimates. Results from a new radial velocity survey of T Tauri stars focus on three specific stars - DN Tau, LkCa19, and BP Tau - with the largest number of observations. All the objects show far greater radial velocity changes than radial velocity standards. For DN Tau and LkCa19, the radial velocities appear to be the result of star spots, while BP Tau's signal remains a mystery. I have written a new computer model which simulates the effect of star spots on radial velocities and can reproduce radial velocity variations of the same magnitude seen in the stellar observations. Finally, I present the results of a new method of the determination of effective temperature for weak line T Tauri stars, from the direct fitting of TiO to NextGen synthetic spectra. The new temperatures are consistently warmer (by as much as 400K) than previous determinations based on spectral type.