Variation of the extinction law in the Trifid nebula

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Table 2

Color excess ratios and resulting extinction law parameters.

	E_{H − K_s}/E_{K_s − [3.6]}	E_{K_s − [3.6]}/E_{[3.6] − [4.5]}	E_{[3.6] − [4.5]}/E_{[4.5] − [5.8]}	A_H/A_{K_s}	A_[3.6]/A_{K_s}	A_[4.5]/A_{K_s}	A_[5.8]/A_{K_s}

A_V < 15	1.446 ± 0.002	3.508 ± 0.011	1.087 ± 0.007	1.563	0.611 ± 0.002	0.500 ± 0.003	0.398 ± 0.005
A_V > 20
case A	1.446 ± 0.002	1.915 ± 0.018	1.496 ± 0.089	1.563	0.611 ± 0.002	0.408 ± 0.003	0.272 ± 0.011
case B	1.749 ± 0.003	2.317 ± 0.027	1.810 ± 0.091	1.563	0.678 ± 0.006	0.540 ± 0.003	0.463 ± 0.007

case B, β = 1.6				1.520	0.703 ± 0.005	0.573 ± 0.003	0.500 ± 0.007
case B, β = 1.8				1.601	0.656 ± 0.006	0.507 ± 0.003	0.424 ± 0.007



Román-Zúñiga et al. (2007) for Barnard 59				1.55	0.619 ± 0.029	0.512 ± 0.022	0.459 ± 0.024
Flaherty et al. (2007) for Orion				1.55	0.636 ± 0.003	0.540 ± 0.003	0.504 ± 0.003
Chapman et al. (2009) for Ophiuchus, Perseus and Serpens				1.52	0.640 ± 0.030	0.530 ± 0.030	0.460 ± 0.030

Weingartner & Draine (2001) with R_V = 3.1					0.40	0.25	0.17
Weingartner & Draine (2001) with R_V = 5.5					0.60	0.49	0.40

Notes. The two rows for A_V > 20 mag represent different cases for A_[3.6]/A_{K_s}: case A propagates the same value as for small extinction, case B takes the actual measured value. We assume the power-law index β = 1.7 (i.e. A_H/A_{K_s} = 1.563) and results for β = 1.6 and 1.8 are provided for case B. The main results from the literature for dense interstellar medium directions and from a dust model are indicated for comparison.

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