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¹²CO observations of the molecular cloud encompassing Sharpless 222 (LK Hα101) Christie, Richard Allan


The 4.57 meter millimetre wave telescope at the University of British Columbia has been used to partially map a region around Lk Hα101 one half degree in diameter centered on α(1950) = 04H26M34s.0 (right ascension), Ϭ (1950) = 35°13'00" (declination) in the J=1—0 transition of ¹²C¹⁶O. Our ¹²CO results show a wide region of ¹²CO emission, but the exact boundaries are as yet undetermined. The north and west boundaries have been determined. We suspect the emission extends as far as a visual extinction of 1 magnitude which covers a region almost one degree across and several degrees long. The average radiation temperature, T*A , is 10 K. Within our survey field we found a large fragmented area with five hot spots (20 K). Since ¹³CO observations were not made ¹³CO data was generated from the ¹²CO observations. Both the ¹²CO and ¹³CO temperature contours have five hot spots within a single envelope of colder CO emission located southeast of Lk Hα101. Three CO clouds (#1, #2, and #3) are resolved at Lk Hα101 (7.2,-10.8), Lk Hα(101 (0.0,-10.8), and LkHα101 (7.2,-5.4). Their masses were calculated from the generated 13CO column densities and are 49M, 41M, and 25M respectively. Two other clouds (#4 and #5) on the limit of resolution are located at Lk Hα101 (3.6,-5.4) and Lk Hα101 (0.0,-1.8) and have masses of 11M0 and 25M0. Each of these fragments is embedded in the same 13 K ¹²CO contour centered on Lk Hα101 (3.6,-7.2). The mass is calculated from the fabricated ¹³CO data and should not be relied upon very strongly. It is in error by at most a factor of two. Peak HI emission contours (Dewdney and Roger 1981) are anticorrelated to our peak CO contours. The HI lies to the northwest. This indicates that the peak CO and HI features are located in different regions. The peak HI column densities derived from both the fabricated ¹²CO data and HI observations agree. They are ~1.3 x 10²¹ atoms cm⁻². From star counts we made of the region we see that the stronger CO emission correlates with regions of stronger visual extinction. The peak HI occurs where the extinction is low. The exciting star has presumably been able to dissociate H2 into HI to the northwest where the visual extinction is lower. Dewdney and Roger (1981) have modelled this asymmetry reasonably well by assuming there is a steep discontinuity of density near Lk Hα101 to the east. The positions of infrared stars from the Steward Observatory Near Infrared Photographic Sky Survey provide meager evidence for the 'Blister' model (Israel 1977, Gilmore 1978) and suggest that star formation was initiated on the edge of the cloud and proceeded inwards. Our CO hot spots could well be the next generation of infrared stars. Confirmation will require a more complete map with better resolution of the region around Lk Hα101 (3.6,-7.2).

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