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Probing Stellar Accretion with Mid-infrared Hydrogen Lines

Rigliaco, Elisabetta and Pascucci, I. and Duchene, G. and Edwards, S. and Ardila, D. R. and Grady, C. and Mendigutía, I. and Montesinos, B. and Mulders, G. D. and Najita, J. R. and Carpenter, J. and Furlan, E. and Gorti, U. and Meijerink, R. and Meyer, M. R. (2015) Probing Stellar Accretion with Mid-infrared Hydrogen Lines. Astrophysical Journal, 801 (1). Art. No. 31. ISSN 0004-637X.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Pascucci, I.0000-0001-7962-1683
Furlan, E.0000-0001-9800-6248
Meyer, M. R.0000-0003-1227-3084
Additional Information:© 2015 American Astronomical Society. Received 2014 September 15; accepted 2014 December 23; published 2015 February 27. The authors thank Catherine Espaillat and Lynne Hillenbrand for providing the optical spectra and physical parameters of a few objects, and John Kwan for providing the mid-IR hydrogen line ratios. E.R. is supported by the NASA’s Astrophysics Data Analysis Program research grant to I.P. (ID: NNX11AG60G).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:accretion, accretion disks; circumstellar matter; infrared: stars; line: identification; stars: activity
Issue or Number:1
Record Number:CaltechAUTHORS:20150403-141146223
Persistent URL:
Official Citation:Probing Stellar Accretion with Mid-infrared Hydrogen Lines Elisabetta Rigliaco et al. 2015 ApJ 801 31
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56352
Deposited By: Ruth Sustaita
Deposited On:04 Apr 2015 01:43
Last Modified:09 Mar 2020 13:19

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