Probing stellar accretion with mid-infrared hydrogen lines

Abstract

In this paper we investigate the origin of the mid-infrared (IR) hydrogen recombination lines for a sample of 114 disks in different evolutionary stages (full, transitional and debris disks) collected from the {\it Spitzer} archive. We focus on the two brighter {H~{\sc i}} lines observed in the {\it Spitzer} spectra, the {H~{\sc i}}(7-6) at 12.37$\mu$m and the {H~{\sc i}}(9-7) at 11.32$\mu$m. We detect the {H~{\sc i}}(7-6) line in 46 objects, and the {H~{\sc i}}(9-7) in 11. We compare these lines with the other most common gas line detected in {\it Spitzer} spectra, the {[Ne~{\sc iii}]} at 12.81$\mu$m. We argue that it is unlikely that the {H~{\sc i}} emission originates from the photoevaporating upper surface layers of the disk, as has been found for the {[Ne~{\sc iii}]} lines toward low-accreting stars. Using the {H~{\sc i}}(9-7)/{H~{\sc i}}(7-6) line ratios we find these gas lines are likely probing gas with hydrogen column densities of 10${}^{10}$-10${}^{11}$~cm${}^{-3}$. The subsample of objects surrounded by full and transitional disks show a positive correlation between the accretion luminosity and the {H~{\sc i}} line luminosity. These two results suggest that the observed mid-IR {H~{\sc i}} lines trace gas accreting onto the star in the same way as other hydrogen recombination lines at shorter wavelengths. A pure chromospheric origin of these lines can be excluded for the vast majority of full and transitional disks.We report for the first time the detection of the {H~{\sc i}}(7-6) line in eight young (< 20~Myr) debris disks. A pure chromospheric origin cannot be ruled out in these objects. If the {H~{\sc i}}(7-6) line traces accretion in these older systems, as in the case of full and transitional disks, the strength of the emission implies accretion rates lower than 10${}^{-10}$M${}_{\odot }$/yr. We discuss some advantages of extending accretion indicators to longer wavelengths.

References in corpus (20)

• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Southern Sample
• The Magnetic Fields of Classical T Tauri Stars
• Accretion in the Rho-Oph pre-main sequence stars
• H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
• The Complete Census of 70-um-Bright Debris Disks within the FEPS (Formation and Evolution of Planetary Systems) Spitzer Legacy Survey of Sun-like Stars
• The Palomar/Keck Adaptive Optics Survey of Young Solar Analogs: Evidence for a Universal Companion Mass Function
• LkH$\alpha$ 330: Evidence for dust clearing through resolved submillimeter imaging
• X-ray irradiated protoplanetary disk atmospheres I: Predicted emission line spectrum and photoevaporation
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• High-Dispersion Optical Spectra of Nearby Stars Younger Than The Sun
• Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks Around Sun-like Stars
• c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H_2 gas-phase lines
• High spatial resolution mid-infrared observations of the low-mass young star TW Hya
• A Multiplicity Census of Young Stars in Chamaeleon I
• High-resolution Spectroscopy of [Ne II] Emission from TW Hya
• An outflow origin of the [NeII] emission in the T Tau triplet
• Physical Conditions of Accreting Gas in T Tauri Star Systems
• Herschel evidence for disk flattening or gas depletion in transitional disks
• Facing the wind of the pre-FUor V1331 Cyg

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• GIARPS High-resolution Observations of T Tauri stars (GHOsT). III. A pilot study of stellar and accretion properties
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