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2. Observations and data analysis

 

2.1. Observational procedure

The observations were performed in April 1995 with the Effelsberg 100-m radio telescope. The tex2html_wrap_inline1605 (1, 1) and (2, 2) lines (frequencies equal 23694.495 MHz and 23722.633 MHz, respectively) were observed simultaneously using a K-band maser amplifier. The system temperature in the main beam temperature scale (see below) was tex2html_wrap_inline1609. The spectrometer was a 1024 channel autocorrelator split into 2 halves of 12.5 MHz each. The velocity resolution was tex2html_wrap_inline1611.

The antenna HPBW was tex2html_wrap_inline1613tex2html_wrap1637. The observations were performed in the position-switching mode with the reference position displaced by tex2html_wrap_inline1617 to the west. The integration times were tex2html_wrap_inline1619. Initially, tex2html_wrap_inline1621 point maps with 40tex2html_wrap1639 spacing were obtained for most sources. Then, the mapping was continued with the same spacing according to the initial results and extended normally to tex2html_wrap_inline1625 of the peak antenna temperature value. Pointing was checked periodically by observations of nearby continuum sources; the pointing accuracy was tex2html_wrap_inline1627tex2html_wrap1641.

We express the results in units of main beam brightness temperature (tex2html_wrap_inline1631). The main beam efficiency of the antenna at this frequency is tex2html_wrap_inline1633. The primary calibration source was NGC 7027 for which we assumed the flux density as given by Ott et al. (1994). The elevation gain correction for point sources (Altenhoff, private communication) was applied to the data. We saw no variations of the beam width with the elevation, so this correction should be applicable to extended sources too. The correction factor was tex2html_wrap_inline1635 in the elevation range of our observations.

2.2. Source list

 

Name

tex2html_wrap_inline1643(1950) tex2html_wrap_inline1645(1950) l b tex2html_wrap_inline1651d zIRAS PSC tex2html_wrap_inline1657 Remarks
tex2html_wrap_inline1659 tex2html_wrap_inline1661 tex2html_wrap_inline1663 tex2html_wrap_inline1665) tex2html_wrap_inline1667 tex2html_wrap_inline1669 (kpc) (kpc) (pc)(tex2html_wrap_inline1671)

S 74

19 06 14.9 05 31 10 39.86 -1.23 7.0 2.1tex2html_wrap_inline1675-45 19062+0531 tex2html_wrap_inline1679
S 76 E 18 53 46.2 07 49 30 40.50 +2.54 7.0 tex2html_wrap_inline1683 93 18537+0749 tex2html_wrap_inline1685 otex2html_wrap_inline1687, W45
S 86 19 41 41.2 23 21 46 59.64 -0.18 7.7 1.9tex2html_wrap_inline1691 -6 19416+2321 tex2html_wrap_inline1695
S 87 19 44 13.5 24 28 00 60.88 -0.13 7.6 2.3tex2html_wrap_inline1699 -5 19442+2427 tex2html_wrap_inline1703 o
S 88 B 19 44 41.4 25 05 17 61.48 +0.10 7.7 tex2html_wrap_inline1707 3 19446+2505 tex2html_wrap_inline1709 o
S 90 19 47 05.2 26 43 21 63.12 +0.44 7.6 4.0tex2html_wrap_inline1713 31 19470+2643 tex2html_wrap_inline1715
S 93 19 52 56.0 27 04 54 64.14 -0.47 7.7 3.2tex2html_wrap_inline1719 -26 19529+2704 tex2html_wrap_inline1723
S 100 19 59 50.0 33 24 20 70.29 +1.60 9.5 8.0tex2html_wrap_inline1727 223 19598+3324 tex2html_wrap_inline1729 o, K3-50
S 145 22 27 12.2 63 58 21 108.19 +5.52 8.8 0.9tex2html_wrap_inline1733 87 22272+6358A tex2html_wrap_inline1735 o, L1206
S 146 22 47 30.9 59 39 03 108.20 +0.58 10.9 4.7tex2html_wrap_inline1739 48 22475+5939 tex2html_wrap_inline1741
S 161 B 23 14 01.9 61 21 22 111.89 +0.88 9.9 2.8tex2html_wrap_inline1745 43 23140+6121 tex2html_wrap_inline1747
S 199 02 57 35.6 60 17 22 138.30 +1.56 10.2 tex2html_wrap_inline1751 57 02575+6017 tex2html_wrap_inline1753 o, IC1848A
S 201 02 59 20.6 60 16 08 138.50 +1.64 10.2 2.1tex2html_wrap_inline1757 60 02593+6016 tex2html_wrap_inline1759
S 231 05 35 48.8 35 43 41 173.47 +2.55 10.8 2.3tex2html_wrap_inline1763 102 05358+3543 tex2html_wrap_inline1765 o
S 255 06 09 57.9 18 00 12 192.60 -0.05 11.0 tex2html_wrap_inline1769 -2 06099+1800 tex2html_wrap_inline1773 o, S254/S258
RNO1B 00 33 53.3 63 12 32 121.30 +0.66 9.4 0.85tex2html_wrap_inline1777 18 00338+6312 tex2html_wrap_inline1779 o, L1287
BFS 48 05 48 04.8 25 45 29 183.35 -0.58 10.6 2.1tex2html_wrap_inline1783-21 05480+2545 tex2html_wrap_inline1787

Table 1: Source list. The letter ``o" in the last column means an outflow detected as given by Wu et al. (1996) except S 76 E

tex2html_wrap_inline1789Brand & Blitz (1993); tex2html_wrap_inline1791Plume et al. (1992); tex2html_wrap_inline1793Blitz et al. (1982); tex2html_wrap_inline1795Henning et al. (1992); tex2html_wrap_inline1797Avedisova & Palous (1989); tex2html_wrap_inline1799Yang et al. (1991); tex2html_wrap_inline1801Fich & Blitz (1984); tex2html_wrap_inline1803Mattila et al. (1996); tex2html_wrap_inline1805assumed.  

The objects for the observations (Table 1 (click here)) were selected primarily from the list of dense molecular clouds associated with Sharpless HII regions studied earlier in the J=1-0 HCN, tex2html_wrap_inline1809, tex2html_wrap_inline1811 and tex2html_wrap_inline1813 lines by Burov et al. (1988), Zinchenko et al. (1990) and Pirogov et al. (1995). The selection was made according to the criteria similar to those used in Paper I, i.e. the flux in the IRAS Point Source Catalogue at tex2html_wrap_inline1815 tex2html_wrap_inline1817 should be larger than 500 Jy. However, the right ascension of tex2html_wrap_inline1819 instead of tex2html_wrap_inline1821 as in Paper I was considered. In addition, several clouds from Papers I and II were included for detailed mapping in the ammonia lines. Most of these objects are associated with tex2html_wrap_inline1823 masers.

Almost all of the selected targets represent sites of high mass star formation except S 145 (L 1206) and RNO 1B (L 1287) where mostly intermediate mass stars are born.

The source coordinates are presented in Table 1 (click here) together with the estimates of the galacto-centric distance of the source (tex2html_wrap_inline1825), its distance from the earth (d) and its height above the galactic plane (z). We adopted IRAS positions as central coordinates of the sources. For some clouds very different distance estimates have been published. For the sake of the homogeneity of the results we adopted, where available, the spectrophotometric distances given by Brand & Blitz (1993). Some other references to the distance estimates are given in Table 1 (click here). The galacto-centric distances were calculated using the standard IAU value for tex2html_wrap_inline1831 of 8.5 kpc.

In Col. (10) we present the IRAS luminosities of our sources calculated as in Henning et al. (1990).

2.3. Data reduction and analysis

 

We have reduced the data and produced maps using the GAG (Groupe d'Astrophysique de Grenoble) software package. The measured spectra were fitted by the function tex2html_wrap_inline1833 (tex2html_wrap_inline1835 is the optical depth in the j-th component) describing one or more ammonia hfs patterns assuming gaussian velocity distributions and equal widths of the hfs components in each pattern. The derived parameters were the line intensities, LSR velocities and FWHM for the opacity distribution. For the spectra of sufficiently good quality it was possible to derive the optical depth as a sum of the peak opacities of the main group of hyperfine components from this fit.

The next steps in the data analysis were the derivation of the rotation temperature tex2html_wrap_inline1839, kinetic temperature tex2html_wrap_inline1841 and total ammonia column density tex2html_wrap_inline1843). These estimates have been made according to the procedure described by Harju et al. (1993).

From the ammonia column densities we derived hydrogen column densities and masses of the cores assuming the tex2html_wrap_inline1845 relative abundance of tex2html_wrap_inline1847 (see the discussion by Harju et al.).

We estimated the source areas (A) by integrating the column densities over the maps presented in Sect. 3 (click here) and dividing these values by the peak column densities. The angular sizes were found then from tex2html_wrap_inline1851. It is worth mentioning that for a gaussian brightness distribution this estimate gives the size at the tex2html_wrap_inline1853 level which is by a factor of tex2html_wrap_inline1855 larger than the size at the half-power level. Then the linear dimensions (L) were determined using the distances from Table 1 (click here). Some sources are elongated so that these sizes represent geometric mean values between their axes. We attempted to take into account the beam size in an approximate way (as in Zinchenko 1995). We use ``deconvolved'' sizes defined as tex2html_wrap_inline1859 where tex2html_wrap_inline1861 is the antenna beam width at the corresponding level. Of course, this procedure accounts for the beam size only approximately because many cores are elongated or have a rather complex brightness distribution. The density estimates have been corrected accordingly. Actually, these corrections do not exceed a few percent.

The mean densities were obtained as the peak column densities divided by these sizes. The masses were estimated from the integrals of the column densities. A factor of 1.36 (the ratio of total gas mass to hydrogen mass, e.g. Hildebrand 1983) was applied to derive the total mass of the cloud. The average line widths are the widths of the average source spectra and include therefore velocity gradients in the source. The virial masses have been calculated as in Paper II.

  figure305
Figure 1: The integrated tex2html_wrap_inline1863 (1, 1) line intensity maps (grey-scale). The levels start from 15% of the peak intensities in steps of 7.5%. The velocity ranges are indicated in Table 2 (click here). Solid and dashed contours correspond to the blue- and red-shifted velocity intervals, respectively (see text). The levels for these contours are the following: from tex2html_wrap_inline1865 with tex2html_wrap_inline1867 increment a), from tex2html_wrap_inline1869 with tex2html_wrap_inline1871 increment b), from tex2html_wrap_inline1873 with tex2html_wrap_inline1875 increment c, g, h, j), from tex2html_wrap_inline1877 with tex2html_wrap_inline1879 increment f), from tex2html_wrap_inline1881 with tex2html_wrap_inline1883 increment i) The crosses show the positions of the strong IRAS point sources listed in Table 1 (click here). The triangles indicate the positions of the tex2html_wrap_inline1885 masers. The asterisks mark the positions of near-IR sources from the CIO catalogue. The dotted contours correspond to the CS J=2-1 maps from Paper II

 figure331
Figure 1: continued

 figure340
Figure 1: continued


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