Probing stellar accretion with mid-infrared hydrogen lines

Elisabetta Rigliaco, I. Pascucci, G. Duchene, S. Edwards, D. R. Ardila, C. Grady, I. Mendigutía, B. Montesinos, G. D. Mulders, J. R. Najita, J. Carpenter, E. Furlan, U. Gorti, R. Meijerink, M. R. Meyer

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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 Spitzer archive. We focus on the two brighter H I lines observed in the Spitzer spectra, the H I (7-6) at 12.37 μm and the H I (9-7) at 11.32 μm. We detect the H I (7-6) line in 46 objects, and the H I (9-7) in 11. We compare these lines with the other most common gas line detected in Spitzer spectra, the [Ne II] at 12.81 μm. We argue that it is unlikely that the H I emission originates from the photoevaporating upper surface layers of the disk, as has been found for the [Ne II] lines toward low-accreting stars. Using the H I (9-7)/H I (7-6) line ratios we find these gas lines are likely probing gas with hydrogen column densities of 1010-1011 cm-3. The subsample of objects surrounded by full and transitional disks show a positive correlation between the accretion luminosity and the H I line luminosity. These two results suggest that the observed mid-IR H 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 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 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 yr-1. We discuss some advantages of extending accretion indicators to longer wavelengths, and the next steps required pinning down the origin of mid-IR hydrogen lines.

Original languageEnglish (US)
Article number31
JournalAstrophysical Journal
Volume801
Issue number1
DOIs
StatePublished - Mar 1 2015

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Keywords

  • accretion, accretion disks
  • circumstellar matter
  • infrared: stars
  • line: identification
  • stars: activity

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Rigliaco, E., Pascucci, I., Duchene, G., Edwards, S., Ardila, D. R., Grady, C., Mendigutía, I., Montesinos, B., Mulders, G. D., Najita, J. R., Carpenter, J., Furlan, E., Gorti, U., Meijerink, R., & Meyer, M. R. (2015). Probing stellar accretion with mid-infrared hydrogen lines. Astrophysical Journal, 801(1), [31]. https://doi.org/10.1088/0004-637X/801/1/31