Molecular hydrogen emission from protoplanetary disks. II. Effects of X-ray irradiation and dust evolution

被引:135
|
作者
Nomura, H. [1 ]
Aikawa, Y.
Tsujimoto, M.
Nakagawa, Y.
Millar, T. J.
机构
[1] Kobe Univ, Dept Earth & Planetary Sci, Kobe, Hyogo 6578501, Japan
[2] Queens Univ Belfast, Sch Math & Phys, Astrophys Res Ctr, Belfast BT7 1NN, Antrim, North Ireland
[3] Rikkyo Univ, Dept Phys, Tokyo 1718501, Japan
来源
ASTROPHYSICAL JOURNAL | 2007年 / 661卷 / 01期
关键词
line : formation; molecular processes; planetary systems : protoplanetary disks; radiative transfer;
D O I
10.1086/513419
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Detailed models for the density and temperature profiles of gas and dust in protoplanetary disks are constructed by taking into account X-ray and UV irradiation from a central T Tauri star, as well as dust size growth and settling toward the disk midplane. The spatial and size distributions of dust grains are numerically computed by solving the coagulation equation for settling dust particles, with the result that the mass and total surface area of dust grains per unit volume of the gas in the disks are very small, except at the midplane. The H-2 level populations and line emission are calculated using the derived physical structure of the disks. X-ray irradiation is the dominant heating source of the gas in the inner disk and in the surface layer, while the UV heating dominates otherwise. If the central star has strong X-ray and weak UV radiation, the H-2 level populations are controlled by X-ray pumping, and the X-ray-induced transition lines could be observable. If the UV irradiation is strong, the level populations are controlled by thermal collisions or UV pumping, depending on the dust properties. As the dust particles evolve in the disks, the gas temperature at the disk surface drops because the grain photoelectric heating becomes less efficient. This makes the level populations change from LTE to non-LTE distributions, which results in changes to the line ratios. Our results suggest that dust evolution in protoplanetary disks could be observable through the H2 line ratios. The emission lines are strong from disks irradiated by strong UV and X-rays and possessing small dust grains; such disks will be good targets in which to observe H-2 emission.
引用
收藏
页码:334 / 353
页数:20
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