ar X iv : a st ro - p h / 07 03 61 6 v 1 2 3 M ar 2 00 7 Detection of [ Ne ii ] Emission from Young Circumstellar Disks
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چکیده
We report the detection of [Ne ii] emission at 12.81μm 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 12.37μm from the source RX J1852.3-3700. Detections of [Ne ii] lines are favored by low mid–infrared excess emission. Both stellar X–rays and extreme UV (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(76) 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 (∼ 10MJ) we suggest using this gas line to determine the presence or absence of gas in more evolved circumstellar disks. Subject headings: line: identification – circumstellar matter – planetary systems: protoplanetary disks – infrared: stars – stars: RX J1111.7-7620, PDS 66, HD 143006, [PZ99] J161411.0-230536, RX J1842.93532, RX J1852.3-3700
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تاریخ انتشار 2007