Abstract
We report the detection of [Ne II] emission at 12.81 μ in four out of the six optically thick dust disks observed as part of the FEPS Spitzer Legacy program. In addition, we detect a H I (7-6) emission line at 12.37 μm from the source RX J 1852.3-3700. Detections of [Ne II] lines are favored by low mid-infrared excess emission. Both stellar X-rays and extreme ultraviolet (EUV) photons can sufficiently ionize the disk surface to reproduce the observed line fluxes, suggesting that emission from Ne+ originates in the hot disk atmosphere. On the other hand, the H I (7-6) line is not associated with the gas in the disk surface, and magnetospheric accretion flows can account for at most ∼30% of the observed flux. We conclude that accretion shock regions and/or the stellar corona could contribute to most of the H I (7-6) emission. Finally, we discuss the observations necessary to identify whether stellar X-rays or EUV photons are the dominant ionization mechanism for Ne atoms. Because the observed [Ne II] emission probes very small amounts of gas in the disk surface ∼ 10-6 MJ ) we suggest using this gas line to determine the presence or absence of gas in more evolved circumstellar disks.
Original language | English (US) |
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Pages (from-to) | 383-393 |
Number of pages | 11 |
Journal | Astrophysical Journal |
Volume | 663 |
Issue number | 1 I |
DOIs | |
State | Published - Jul 1 2007 |
Keywords
- 3532, RX J1852.3
- 3700)
- 7620, RX J1842.9
- Circumstellar matter
- Infrared: stars
- Line: identification
- Planetary systems: protoplanetary disks
- Stars: individual (HD 143006, PDS 66, [PZ99] J161411.0-230536, RX j1111.7
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science