PROBING STELLAR ACCRETION WITH MID-INFRARED HYDROGEN LINES
- Department of Planetary Science, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85719 (United States)
- Astronomy Department, University of California, Berkeley, Hearst Field Annex B-20, Berkeley, CA 94720-3411 (United States)
- Five College Astronomy Department, Smith College, Northampton, MA 01063 (United States)
- NASA Herschel Science Center, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States)
- Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 94602-3017 (United States)
- School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom)
- Departamento de Astrofísica, Centro de Astrobiología, ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain)
- National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
- Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States)
- Infrared Processing and Analysis Center, California Institute of Technology, 770 S. Wilson Ave., Pasadena, CA 91125 (United States)
- NASA Ames Research Center, Moffett Field, CA 94035 (United States)
- Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)
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{sup 10}-10{sup 11} cm{sup –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{sup –10} M {sub ☉} yr{sup –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.
- OSTI ID:
- 22522055
- Journal Information:
- Astrophysical Journal, Vol. 801, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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