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Title:
Three Millimeter Continuum Studies of Sagittarius B2
Authors:
Kuan, Yi-Jehng; Mehringer, David M.; Snyder, Lewis E.
Publication:
Astrophysical Journal v.459, p.619 (ApJ Homepage)
Publication Date:
03/1996
Origin:
APJ
Astronomy Keywords:
ISM: DUST, EXTINCTION, GALAXY: CENTER, ISM: H II REGIONS, ISM: INDIVIDUAL NAME: SAGITTARIUS B2, RADIO CONTINUUM: ISM, STARS: FORMATION
DOI:
10.1086/176926
Bibliographic Code:
1996ApJ...459..619K

Abstract

Continuum emission at 4.9, 8.3, 78.5, 81.5, 84.9, 87.9, 106.9, and 109.9 GHz was observed in Sgr B2. Spectral indices near 3 mm are alpha = -0.31 + 0.03 and -0.2 t 0.2 for Sgr B2(N') and Sgr B2(W), respectively, and are attributed to the optically thin free-free emission. Free-free emission contributes significantly to the 3 mm continuum in Sgr B2(M), but the positive slope of the continuum spectrum (alpha = 1.0 + 0.3) indicates the presence of dust grains. Sgr B2(N) is dominated by thermal dust emission with a steep spectral index alpha = 4.6 + 0.5. The 3 mm continuum spectra yield the grain emissivity exponents fl = 1.7 + 1.3 and 3.7 + 0.7 for Sgr B2(M) and Sgr B2(N), respectively. The grain emissivity law derived for Sgr B2(N) is significantly higher than most for other molecular clouds. Thus Sgr B2(N) appears to be a very unusual dust core. The most likely explanation is that the region contains ice-coated core-mantle grains. The existence of ice-coated core-mantle grains implies the mean dust temperature in the Sgr B2(N) dust core is less than 150 K. The short lifetime of the core-mantle phase and the high value of n _{2 }indicate that Sgr B2(N) is quite young and in a very early stage of star formation.

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