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| - Gravitationally bound cores in a molecular cirrus cloud
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| - Using MAMBO at the IRAM 30 m telescope we have observed a dense core in the cirrus cloud MCLD 123.5+24.9 in the dust continuum emission at 250 GHz. The core is detected as an elongated filament with an extent of $4.\!'2\times 0.\!'7$, corresponding to 0.18 pc $\times$0.03 pc at an adopted distance of 150 pc. We find a close correlation between the continuum emission and previously observed C 18O (1 $\to$0) line emission. Using standard dust models we derive hydrogen column densities of up to 10 22 cm -2. The total mass for the filament is about 0.66 $M_{odot}$. We also present observations of the HC 3N (3 $\to$2), (4 $\to$3), and (10 $\to$9) emission lines obtained with the MPIfR 100 m and the IRAM 30 m telescopes. The distribution is very different from the dust continuum and the C 18O (1 $\to$0) line emission. HC 3N is concentrated in two distinct clumps located at the ends of the filament seen in the other tracers. Based on a LVG analysis of the HC 3N transitions we derive column densities of $N({\rm HC_3N})/\Delta v\approx10^{13}$cm -2/kms -1 and volume densities of $n({\rm H}_2)\approx10^5$ cm -3. We find that the HC 3N clumps have masses of 0.13 and 0.19 $M_{odot}$. Our data demonstrate that the cirrus cloud cores are gravitationally bound, and that they show chemical structure indicating different evolutionary stages within the cloud.
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