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

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4. Results

Ammonia maps have been obtained of the four dense cores L1521D, L1521F, L1524 and L1507A in the ([FORMULA]) = (1,1) line (Figs. 1 to 4). In order to obtain the observed source size, we have determined the half maximum contours of the ammonia main beam brightness temperature ([FORMULA] ; K) and have calculated the apparent geometric mean diameter (FWHP) D = [FORMULA], where a and b are the major and minor-axis, respectively. The ammonia core sizes are 0.09 pc (L1521D), 0.07 pc (L1521F), 0.08 pc (L1524) and 0.06 pc (L1507A). Deconvolution by the 0.027 pc beam does not significantly alter these values. For those spectra where the main and satellite hyperfine components have been observed with a sufficient signal-to-noise ratio ([FORMULA] 3) we have obtained the total optical depth ([FORMULA]) and the intrinsic linewidth (FWHM) of the hyperfine components ([FORMULA] ; km s-1) using a program which fits these parameters to the observed spectra, assuming gaussian profiles in an individual component and relative opacities being consistent with the Local Thermodynamic Equilibrium (LTE) approximation. For the positions where the satellite components have intensities below the noise level, but the main component of the NH3 (1,1) line has been detected, we have fitted a single gaussian profile. Moreover, we have observed the NH3 (2,2) transition towards the peak positions of the four molecular cores.

[FIGURE] Fig. 1. Contour NH3 (1,1) [FORMULA] map of L1521D. The (0,0) position corresponds to: [FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +26 [FORMULA] 55 [FORMULA] 23 [FORMULA]. The contour levels are from 1.4 K to 2.4 K by steps of 0.2 K ([FORMULA] 1 r.m.s. noise). The empty circle shows the Effelsberg beam (HPBW), the small crosses mark measured positions.
[FIGURE] Fig. 2. Contour NH3 (1,1) [FORMULA] map of L1521F. The (0,0) position corresponds to: [FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +26 [FORMULA] 45 [FORMULA] 00 [FORMULA]. The contour levels are from 2.6 K to 6.4 K by steps of 0.4 K ([FORMULA] 2 r.m.s. noise). The empty circle shows the Effelsberg beam (HPBW).
[FIGURE] Fig. 3. Contour NH3 (1,1) [FORMULA] map of L1524. The (0,0) position corresponds to: [FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +24 [FORMULA] 28 [FORMULA] 06 [FORMULA]. The contour levels are from 2.1 K to 4.5 K by steps of 0.4 K ([FORMULA] 2 r.m.s. noise). The empty circle shows the Effelsberg beam (HPBW).
[FIGURE] Fig. 4. Contour NH3 (1,1) [FORMULA] map of L1507A. The (0,0) position corresponds to: [FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +29 [FORMULA] 38 [FORMULA] 07 [FORMULA]. The contour levels are from 2.0 K to 3.4 K by steps of 0.2 K ([FORMULA] 1 r.m.s. noise). The empty circle shows the Effelsberg beam (HPBW).

Table 2 displays the observed NH3 (1,1) line parameters regarding the peak positions: the source name, the right ascension and declination offset ([FORMULA]) of the peak position with respect to the coordinates given in Table 1, the main beam brightness temperature, the LSR velocity ([FORMULA] ; km s-1), the apparent line width (FWHM; km s-1) of the main component, the total optical depth and the intrinsic linewidth of the hyperfine components including instrumental broadening. The errors (r.m.s.) of the derived parameters are given in parentheses. Fig. 5 shows the NH3 (1,1) and (2,2) spectra of the peak position of each mapped source. Table 3 lists the observed NH3 (2,2) gaussian line parameters towards the NH3 (1,1) peak positions: the main beam brightness temperature, the LSR velocity and the FWHM line width including instrumental broadening. For L1521D, we report the observed parameters towards the (+40, +20) peak position, since the integrated ammonia emission associated with this position is slightly larger that that of the (+80, +40) peak position.

[FIGURE] Fig. 5a. Ammonia (1,1) and (2,2) spectra of the peak position of each mapped core. Source name and angular offset map position (in arcseconds) are indicated.

[FIGURE] Fig. 5b. (continued)

[TABLE]

Table 2. Observed NH3 (1,1) line parameters. The (1950) coordinates of the peak positions of the four cores are: ([FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +26 [FORMULA] 55 [FORMULA] 43 [FORMULA]) and ([FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +26 [FORMULA] 56 [FORMULA] 03 [FORMULA]) for L1521D, ([FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +26 [FORMULA] 45 [FORMULA] 00 [FORMULA]) for L1521F, ([FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +24 [FORMULA] 28 [FORMULA] 26 [FORMULA]) for L1524 and ([FORMULA] = [FORMULA] [FORMULA] [FORMULA] ; [FORMULA] = +29 [FORMULA] 38 [FORMULA] 17 [FORMULA]) for L1507A



[TABLE]

Table 3. Observed NH3 (2,2) line parameters


Table 4 gives the HC5 N (J=9-8) line parameters towards the ammonia peak positions, obtained from gaussian fits: the parameters are main beam brightness temperature, LSR velocity and FWHM line width including instrumental broadening. Fig. 6 shows the HC5 N (J=9-8) spectra.


[TABLE]

Table 4. Observed and derived HC5 N (J=9-8) line parameters


[FIGURE] Fig. 6. Cyanodiacetylene (J=9-8) spectra at the ammonia peak position of each molecular core. Source name and angular offset (in arcseconds) relative to the (0,0) positions in the ammonia maps (see Figs. 1-4) are indicated.

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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