2 Observations

The $~{\rm ^{12}CO}$ (1-0) observations were mostly made in a single observing run in December 1988 and January 1989 using the SEST 15 m located on La Silla (Chile). Smaller data sets obtained in April 1988 and in October 1989 were also used. The $~{\rm ^{12}CO}$ (2-1) measurements were made during four runs in 1989, 1992, 1993 and 1994. Although some $~{\rm ^{13}CO}$ J = 1-0 observations had already been made in 1988, most were obtained during the 1993 and 1994 runs; the relatively few $~{\rm ^{13}CO}$ J = 2-1 observation were all made in the 1992 run. All J = 1-0 observations were made with a Schottky receiver, yielding typical overall system temperatures $T_{\rm sys}$ = 600-750 K. The J = 2-1 observations were made with an SIS mixer, yielding typical overall system temperatures $T_{\rm sys}$ = 450-750 K depending on weather conditions. On average, we obtained 1$\sigma$noise figures in a 1 km s^-1 band of 0.04, 0.10, 0.08 and 0.12 K at 110, 115, 220 and 230 GHz respectively.

In both frequency ranges, we used the high resolution acousto-optical spectrometers with a channel separation of 43 kHz. The J = 1-0 observations were made in frequency-switching mode, initially (1988) with a throw of 25 MHz, but subsequently with a throw of 15 MHz. The J = 2-1 measurements were made in double beam-switching mode, with a throw of 12' to positions verified from the J = 1-0 $~{\rm ^{12}CO}$ map to be free of emission. Antenna pointing was checked frequently on the SiO maser star R Dor, about 20$^{\circ }$ from the LMC; rms pointing was about 3''-4''. The N 11 area was first roughly sampled in the J = 1-0 $~{\rm ^{12}CO}$ transition on a grid of 80'' (double-beam) spacings, using IRAS infrared maps (Schwering & Israel 1990) as a guide. Where emission was detected, we refined the grids to a half-beam sampling of 20''. Some of the clouds thus mapped in J = 1-0 $~{\rm ^{12}CO}$ were observed in J = 1-0 $~{\rm ^{13}CO}$ on the same grid, and with 10'' grid-spacing in the J = 2-1 transitions.

   

Table 1: Catalogue of CO clouds in N 11.

No.	N11a	LI-LMCb	LMC-Bc	Cloud Centerd		Peak J = 1-0 CO Parameters				Peak J = 2-1 CO Parameters
				$\Delta\alpha$	$\Delta\delta$	$T_{\rm mb}$	$\Delta V$	$V_{\rm LSR}$	$I_{\rm CO}$	$T_{\rm mb}$	$\Delta V$	$V_{\rm LSR}$	$I_{\rm CO}$
				(')	(')	(K)	( $~{\rm {km~s^{-1}}}$)		( $~{\rm {K~km~s^{-1}}}$)	(K)	( $~{\rm {km~s^{-1}}}$)		( $~{\rm {K~km~s^{-1}}}$)
1		190		-10.0	-5.0	1.25	2.7	280.8	3.6 $\pm$ 0.5
2	H	190		-9.5	-3.7	1.57	2.7	276.3	4.5 $\pm$ 0.6
3		192		-9.5	-8.2	1.39	2.9	284.4	4.2 $\pm$ 0.4
4	I	192		-9.4	-10.0	2.56	5.7	279.0	15.6 $\pm$ 2.0
5	(G)	195		-8.5	-0.5	2.21	4.0	272.9	9.4 $\pm$ 0.9
6		205		-6.3	-13.5	2.61	2.5	277.7	6.8 $\pm$ 1.0
7		205		-5.0	-12.5	2.04	1.9	280.8	4.2 $\pm$ 0.6	3.27	5.0	278.4	17.5 $\pm$ 0.5
8	F	214	0456-6636	-4.4	-7.4	2.42	2.6	276.6	6.6 $\pm$ 0.8	2.68	3.0	276.4	8.4 $\pm$ 0.4
9	F	214	0456-6636	-3.0	-8.0	1.46	2.6	268.6	4.0 $\pm$ 0.6
10	B	217	0456-6629	-2.5	0	2.47	6.1	285.6	16.0 $\pm$ 1.7	5.53	5.8	285.4	34.1 $\pm$ 0.4
11	A	226		0.3	1.0	1.33	4.5	277.1	6.4 $\pm$ 0.7	3.13	4.7	276.8	15.9 $\pm$ 0.5
12	J	229		0.3	6.0	1.56	4.4	279.6	7.2 $\pm$ 1.0
13		226		1.0	2.2	1.39	3.1	283.1	4.6 $\pm$ 0.6	1.53	2.7	278.8	4.1 $\pm$ 0.5
14	C	243	0457-6632	2.9	-2.3	0.96	4.0	280.2	4.4 $\pm$ 0.9	3.32	4.0	279.6	14.3 $\pm$ 0.4
15	D	248	0457-6632	3.7	-4.3	3.00	3.8	280.7	12.0 $\pm$ 2.0	3.82	4.0	280.8	16.3 $\pm$ 0.5
16	E	251	0458-6626	4.6	3.8	1.50	5.8	268.1	9.3 $\pm$ 1.3
17	E	251	0458-6626	4.2	4.2	1.46	1.7	275.2	2.6 $\pm$ 0.4
18	E		0458-6626	5.3	5.5	2.53	3.9	271.2	10.9 $\pm$ 1.0	2.91	4.6	271.0	14.3 $\pm$ 0.4
19				6.4	6.8	1.54	3.7	271.3	6.0 $\pm$ 0.9
20				7.4	8.3	0.57	8.3	275.4	6.0 $\pm$ 0.9
21				8.7	9.2	1.14	4.8	277.0	5.8 $\pm$ 0.7
22				8.7	9.7	1.32	2.0	284.1	2.8 $\pm$ 0.9
23		268		9.0	7.5	0.58	8.0	274.7	4.9 $\pm$ 0.6
24		268		11.0	7.7	1.47	3.1	278.8	3.3 $\pm$ 1.0
25			0458-6616	10.2	12.2	0.89	3.0	273.1	2.8 $\pm$ 0.6
26			0458-6616	10.8	11.1	1.85	2.0	281.0	3.9 $\pm$ 0.6
27		266		9.8	14.7	2.01	3.9	278.4	8.5 $\pm$ 0.0
28		271		9.4	16.4	2.87	3.9	276.8	11.3 $\pm$ 0.4	1.59	4.1	277.1	6.9 $\pm$ 0.4
29		271		10.0	17.4	2.49	3.2	275.4	8.5 $\pm$ 0.4	2.78	4.6	274.7	13.6 $\pm$ 0.5

Notes: ^a Henize (1956) designation. ^b IRAS source: Schwering & Israel (1990). ^c Radio continuum source: Filipovic et al. (1996).
^d Offsets refer to central mapping position (epoch 1950.0) $\alpha_{\rm o} = 04^{\rm h}57^{\rm m}07\hbox{$.\!\!^{\rm s}$ }3$, $\delta_{\rm o} = -66^{\rm o}29'00''$.

Figure 2: Detailed map of the integrated J = 1-0 $~{\rm ^{12}CO}$ emission in the southwestern part of the N11 complex, showing the "ring'' of CO clouds associated with OB associations LH 9, LH 10 and LH 13. Positions sampled are indicated by dots. In this figure, and in the following, grey scales indicated at the right of the panel are integrated antenna temperatures. The contours, however, are chosen such that both the first contour and the contour interval correspond to 3 $~{\rm {K~km~s^{-1}}}$ in main-beam brightness temperature.

Unfortunately, frequency-switched spectra suffer from significant baseline curvature. For N11 we corrected baselines by fitting polynomials to the baselines, excluding the range of velocities covered by emission and the ranges influenced by negative reference features. The emission velocity range was determined by summing all observations. Inspection by eye suggested that this method worked well. It has the advantage that, in principle, it does not select against weak extended emission, as long as this covers the same velocity range as the brighter clouds.

The FWHM beams of the SEST are 45'' and 23'' respectively at frequencies of 115 GHz and 230 GHz. Nominal main-beam efficiencies $\eta_{\rm mb}$ at these frequencies were 0.72 and 0.57 respectively. For a somewhat more detailed discussion of the various efficiencies involved, we refer to Johansson et al. (1998; Paper VII).