Publications of the MPIfR
Optical & Infrared
Interferometry Group
Naoi, T., Tamura, M., Nagata, T.,
Nakajima, Y., Suto, H., Murakawa, K., Kandori, R., Sasaki, S.,
Nishiyama, S., Oasa, Y., Sugitani, K.
Near-Infrared Extinction in the Coalsack
Globule 2
The Astrophysical Journal, Volume 658, Issue 2, pp.
1114-1118 (2007)
Abstract
We have conducted J, H, and Ks imaging observations for the Coalsack
Globule 2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope
at SAAO, and determined the color excess ratio, E(J-H)/E(H-Ks). The
ratio is determined in the same photometric system as our previous
study for the rho Oph and Cha clouds without any color transformation;
this enables us to directly compare the near-infrared extinction laws
among these regions. The current ratio E(J-H)/E(H-Ks) = 1.91 +- 0.01
for the extinction range 0.5 < E(J-H) <1.8 is significantly
larger than the ratios for the rho Oph and Cha clouds (E(J-H)/E(H-Ks) =
1.60-1.69). This ratio corresponds to a large negative index alpha =
2.34 +- 0.01 when the wavelength dependence of extinction is
approximated by a power law which might indicate little growth of dust
grains, or larger abundance of dielectric non-absorbing components such
as silicates, or both in this cloud. We also confirm that the color
excess ratio for the Coalsack Globule 2 has a trend of increasing with
decreasing optical depth, which is the same trend as the rho Oph and
Cha clouds have.
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