Table 4
Measured upper limits to the H2 emission line ratios and theoretical line ratios expected for H2 at LTE, and H2 excited by UV, X-ray, and shocks (Mouri 1994; Tiné et al. 1997; Nomura et al. 2007).
|
|
|
|
|
||
| Observed | ||
| HD 97048 | <0.20 | <0.22 |
| HD 100546 | <0.55 | <0.39 |
| LTE | ||
| T = 500 K | 0.44 | 1.8 × 10-5 |
| T = 1000 K | 0.27 | 0.005 |
| T = 2000 K | 0.21 | 0.085 |
| T = 3000 K | 0.18 | 0.21 |
| UV pure radiative fluorescencea | ||
| nT = 102 − 104 cm-3 | ||
| χ = 1−104 | 0.38–1.18 | 0.52–0.58 |
| UV thermal + fluorescenceb | ||
| nT = 105 − 106 cm-3 | ||
| χ = 102 − 104 | 0.27–0.34 | 0.0062–0.025 |
| X-ray | ||
| Lepp & McCray (1983)c | 0.23 | 0.010 |
| Draine & Woods (1990)d | 0.21–0.20 | 0.097–0.075 |
| Tiné et al. (1997)e | ||
| T = 500 K, nH = 105 − 107 cm-3 | 0.28–0.49 | 0.01–0.35 |
| T = 1000 K, nH = 105 − 107 cm-3 | 0.28–0.29 | 0.001–0.006 |
| T = 2000 K, nH = 105 − 107 cm-3 | 0.21–0.22 | 0.013–0.082 |
| Shockf | 0.23 | 0.084 |
| Nomura CTTS disk modelsg | ||
| X-ray irradiation | 0.23 | 0.06 |
| UV irradiation | 0.25 | 0.02 |
| X-ray+UV irradiation | 0.24 | 0.03 |
Notes.
Models of pure radiative UV fluorescent H2 emission spectra produced in low-density (n ≲ 104 cm-3) cold isothermal photodissociation regions from Black & van Dishoeck (1987).
Models of H2 infrared emission spectra in dense (n ≳ 104 cm-3) static photodissociation regions exposed to UV radiation that both heats and excites the H2 gas from Sternberg & Dalgarno (1989).
Parameters: nT = the total density of hydrogen atoms and molecules; χ = UV-flux scaling relative to the interstellar radiation field;
X-ray heating models of Lepp & McCray (1983) assume an X-ray luminosity in the 1–10 keV band of 1035 erg s-1. Here are given the line ratios of their model b.
X-ray excitation models of Draine & Woods (1990) provide the expected H2 line emissivity efficiencies assuming a rate of absorption of X-ray energy γ = 2 × 10-19 erg s-1, nH = 105 cm-3, and monochromatic X-rays of 100 eV. In the case of the H2 1-0 S(1) line, they obtain efficiencies of 9.1 × 10-3,7.9 × 10-3, and 4.8 × 10-3 for an X-ray energy absorbed per H nucleus of 1, 10, and 62.3 eV respectively. In HD 97048 and HD 100546, we measured H2 1-0 S(1) luminosities of 1.9 × 1029 and 3.4 × 1028 erg s-1 respectively. Using the Draine & Woods (1990) H2 1-0 S(1) line efficiencies, these H2 1-0 S(1) luminosities would imply a LX from 1030 to 1031 erg s-1, somewhat brighter than the LX ∼ 1029.5 measured in Herbig Ae stars (Telleschi et al. 2007).
Tiné et al. (1997) models do not prescribe a specific X-ray input luminosity. They assume electrons of 30 eV and use as input parameters the ionization rate ζ (10-8 to 10-17 s-1), nH(10 − 107 cm-3), and T = 500,1000,2000 K (see Tables 8 and 9 of Tiné et al. 1997). These models include, in addition to the effects of X-rays, the effects of collision processes of H2, with H2, H, and He on the resulting H2 emission spectrum.
Nomura et al. (2007) CTTS models assume a LX ∼ 1030 erg s-1 and LFUV ∼ 1031 erg s-1. Here are given the line ratios of the models with maximum grain radii amax = 10 μm.
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