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Astron. Astrophys. 324, 203-210 (1997)

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2. Selection criteria

The molecular cores chosen for this project have been selected from an extensive search for ammonia emission towards 26 high visual extinction regions in the TMC identified from the Palomar Observatory Sky Survey (POSS) maps and from Myers et al. (1979 ). The observed positions are located within [FORMULA] [FORMULA] [FORMULA] [FORMULA] [FORMULA] [FORMULA] [FORMULA] and +16 [FORMULA] [FORMULA] [FORMULA] [FORMULA] +30 [FORMULA]: 9 regions in the long filament which includes TMC-2 (Kutner's Cloud), 7 regions in the parallel filament to the north, containing B217 (see Fig. 1 of Walmsley et al. 1980 ), and 10 isolated optically obscured regions where no extended clouds were seen on the POSS plates. For the survey, the Haystack (USA) 37-m and the Green Bank (USA) NRAO 43-m antennas have been used with FWHP (full width half power) beam sizes of 84 [FORMULA] and beam efficiencies of about 0.25 during several runs in 1983.

Table 1 summarizes the regions where NH3 line emission was searched for. For the non-detections the r.m.s. [FORMULA] value is reported. Ammonia emission has been detected towards 9 sources. Out of these 9, 5 can be classified as dense molecular cores: L1521D, L1521F, L1524, L1535 and L1507A. L1521D, L1521F and L1524 have been already studied through H13 CO [FORMULA] and C18 O observations by Mizuno et al. (1994) and Onishi et al. (1996). Since L1535 has already been investigated by Ungerechts et al. (1982 ), through ammonia observations, we have focused our attention on the other four cores, which have been mapped in NH3, using the 100-m MPIfR radio-telescope at Effelsberg (Germany).


Table 1. Regions investigated through NH3 observations

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998