Searching for gas emission lines in Spitzer Infrared Spectrograph (IRS) spectra of young stars in Taurus

Abstract

Our knowledge of circumstellar disks has traditionally been based on studies of dust. However, gas dominates the disk mass and its study is key to understand the star and planet formation process. Spitzer can access gas emission lines in the mid-infrared, providing new diagnostics of the physical conditions in accretion disks and outflows. We have studied the spectra of 64 pre-main-sequence stars in Taurus using Spitzer/IRS observations. We have detected H2 (17.03, 28.22 $\mu$m) emission in 6 objects, [Ne II] (12.81 $\mu$m) in 18 objects, and [Fe II] (17.93, 25.99 $\mu$m) in 7 objects. [Ne II] detections are found primarily in Class II objects. The luminosity of the [Ne II] line, is in general higher for objects known to drive jets than for those without known jets, but the two groups are not statistically distinguishable. We have searched for correlations between the line luminosities and different parameters related to the star-disk system. The [Ne II] luminosity is correlated with X-ray luminosity for Class II objects. The [NeII] luminosity is correlated with disk mass and accretion rate when the sample is divided into high and low accretors. We also find correlations between [NeII] luminosity and mid-IR continuum luminosity and with luminosity of the [O I] (6300 Å) line, the latter being an outflow tracer. [Fe II] luminosity correlates with mass accretion rate. No correlations were found between H2 luminosity and several tested parameters. Our study reveals a general trend toward accretion-related phenomena as the origin of the gas emission lines. Shocks in jets and outflowing material are more likely to play a significant role than shocks in infalling material. The role of X-ray irradiation is less prominent but still present for [Ne II], in particular for Class II sources, the lack of correlation between [Fe II] and [Ne II] points toward different emitting mechanisms.

24 pages, 10 figures Accepted for publication in Astronomy and Astrophysics

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• Understanding the water emission in the mid- and far-IR from protoplanetary disks around T~Tauri stars
• On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope
• Tracing High-Energy Radiation from T Tauri Stars Using Mid-Infrared Neon Emission from Disks
• Using Multiwavelength Variability to Explore the Connection between X-ray Emission, the Far-Ultraviolet H2 Bump, and Accretion in T Tauri Stars
• A Search for Spatially Resolved Infrared Ro-Vibrational Molecular Hydrogen Emission from the Disks of Young Stars
• Observational Constraints on the Stellar Radiation Field Impinging on Transitional Disk Atmospheres
• The gas disk: Evolution and chemistry
• Revealing Ionization Conditions of Sz 102 with Spatially Resolved [Ne III] Microjets