Dust and atomic hydrogen nearρ Ophiuchi
Tóm tắt
We discuss the distribution of dust and atomic hydrogen in and around a small dark cloud nearρ Ophiuchi. Although the obscuration reaches values as high as 8 magnitudes, the values ofN
H derived inside the cloud do not differ markedly from those found at nearby, less obscured points. At low values of the obscuration, dust and hydrogen isophotes show satisfactory agreement, i.e.,N
H increases withN
G. However, we find thatN
H starts decreasing for sufficiently large values ofN
G. In the entire range of optical extinctions investigated our observations are satisfied by an expression of the typeN
H=AN
G exp (-BN
G). Interpretation of this relationship suggests that an appreciable part of the hydrogen has been converted to molecular form inside the cloud. A tentative method for calculating the time elapsed since the conversion process began is proposed.
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