Year: 2015
Type: article
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 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 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.
Source: The Astrophysical Journal
Authors: 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
Institutions: University of Arizona, ETH Zurich, Centre National de la Recherche Scientifique, Institut de Planétologie et d'Astrophysique de Grenoble, Université Grenoble Alpes, University of California, Berkeley, Smith College, California Institute of Technology, The Aerospace Corporation, Goddard Space Flight Center, Eureka Scientific, University of Leeds, Centro de Astrobiología, Infrared Processing and Analysis Center, Ames Research Center, Search for Extraterrestrial Intelligence, Leiden University, Leiden Observatory
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: G2312550209, G5625111430
OpenAlex ID: W1967774865