S. T. Harrold | Searcharxiv

arXiv2014

Puoko-nui: a flexible high-speed photometric system

We describe a portable CCD-based instrumentation system designed to efficiently undertake high time precision fast photometry. The key components of the system are (1) an externally triggered commercial frame-transfer CCD, (2) a custom GPS-derived time source, and (3) flexible software for both instrument control and online analysis/display. Two working instruments that implement this design are described. The New Zealand based instrument employs a Princeton Instruments (PI) 1k x 1k CCD and has been used with the 1 m telescope at Mt John University Observatory, while the other uses a newer 1k x 1k electron-multiplying CCD supplied by PI and is based at the University of Texas at Austin. We include some recent observations that illustrate the capabilities of the instruments.

astro-ph.IM↗

arXiv2008

A sub-AU outwardly truncated accretion disk around a classical T Tauri star

We present the Spitzer Infrared Spectrograph (IRS) spectrum of SR20, a 5--10 AU binary T Tauri system in the $ρ$ Ophiuchi star forming region. The spectrum has features consistent with the presence of a disk; however, the continuum slope is steeper than the $λ^{-4/3}$ slope of an infinite geometrically thin, optically thick disk, indicating that the disk is outwardly truncated. Comparison with photometry from the literature shows a large increase in the mid-infrared flux from 1993 to 1996. We model the spectral energy distribution and IRS spectrum with a wall + optically thick irradiated disk, yielding an outer radius of 0.39$_{+0.03}^{-0.01}$ AU, much smaller than predicted by models of binary orbits. Using a two temperature $χ^2$ minimization model to fit the dust composition of the IRS spectrum, we find the disk has experienced significant grain growth: its spectrum is well-fit using opacities of grains larger than 1 $μ$m. We conclude that the system experienced a significant gravitational perturbation in the 1990s.

astro-ph↗