An HST Imaging Survey of Low-Mass Stars in the Chamaeleon I Star Forming region

TL;DR

This study uses HST imaging to analyze 20 fields in the Chamaeleon I star forming region, revealing details about T Tauri stars, their circumstellar disks, and accretion processes, and providing insights into disk evolution and star formation timescales.

Contribution

First comprehensive HST imaging survey of low-mass stars in Chamaeleon I, combining multi-wavelength data to model stellar and disk parameters and study disk evolution.

Findings

Edge-on disks cause underestimation of luminosity.

Mass accretion rates decrease with stellar age.

Some disks dissipate faster than typical timescales.

Abstract

We present new HST/WFPC2 observations of 20 fields centered around T Tauri stars in the Chamaeleon I star forming region. Images have been obtained in the F631N ([OI]6300A), F656N (Ha) and F673N ([SII]6716A+6731A) narrow-band filters, plus the Johnson V-band equivalent F547M filter. We detect 31 T Tauri stars falling within our fields. We discuss the optical morphology of 10 sources showing evidence of either binarity, circumstellar material, or mass loss. We supplement our photometry with a compilation of optical, infrared and sub-millimeter data from the literature, together with new sub-mm data for three objects, to build the Spectral Energy Distributions (SED) of 19 single sources. Using an SED model fitting tool, we self-consistently estimate a number of stellar and disk parameters, while mass accretion rates are directly derived from our Ha photometry. We find that bolometric luminosities derived from dereddened optical data tend to be underestimated in systems with high alpha(2-24} IR spectral index, suggesting that disks seen nearly edge-on may occasionally be interpreted as low luminosity (and therefore more evolved) sources. On the other hand, the same alpha(2-24) spectral index, a tracer of the amount of dust in the warmer layers of the circumstellar disks, and the mass accretion rate appear to decay with the isocronal stellar age, suggesting that the observed age spread (~0.5-5 Myr) within the cluster is real. Our sample contains a few outliers that may have dissipated their circumstellar disks on shorter time-scale.