A SEARCH FOR NH IN THE LARGE MAGELLANIC CLOUD

Observations and Data Reduction

The observations were taken during the period 1994 February 12-21 using the Parkes telescope. The feed at the frequency of the observed (J,K) = (1,1) transition (23.694495 GHz) only illuminates the inner 44 m of the telescope, resulting in a FWHP beamwidth of 1'.4 (20 pc at the LMC distance of 50 kpc). The efficiency of the Parkes telescope at this frequency is . The receiver was a single-channel maser. Owing to relatively high humidity at the time of the observations, typical system temperatures were 130 to 160 K.

=1mm

Table 1: Observed Positions in the 30 Dor Region and around N159

no.	Position		rms	Source Type	Associated Objects	Reference
	(J2000)	(J2000)	mK
1	05 36 03.75	-69 30 24.02	11.9	HI condensation		(4)
2	05 37 23.98	-69 33 22.63	17.6	HI condensation		(4)
3	05 37 47.6	-69 10 21.0	23.8	HI condensation		(4)
4	05 39 17.0	-69 03 20.0	19.0	HI condensation		(4)
5	05 39 34.57	-69 45 33.6	9.21	CO condensation	LI-LMC 1501	(3)
6	05 39 52.1	-69 45 10	21.8	Continuum Source		(1)
7	05 39 58.8	-70 10 57.6	24.6	CO condensation	Molecular Cloud Complex 35	(2)
8	05 40 03.9	-69 37 50.37	8.33	HI condensation		(4)
9	05 40 06.5	-69 44 44	11.8	IRAS Point Source	LI-LMC 1518	(1)
10	05 40 09.0	-69 44 34.0	15.9	CO condensation		(1)
11	05 40 37.05	-70 10 40.37	10.5	CO condensation	LI-LMC 1541	(3)
12	05 42 58.9	-69 45 12.5	12.5	CO condensation	LI-LMC 1609	(3)

(1) Hunt & Whiteoak (1994); (2) Cohen et al. (1988); (3) Israel et al. (1993); (4) This paper

The AT autocorrelator was configured to process two bands, each with 2048 channels. The first band was at the (J,K) = (1,1) transition, and the second band was used to observe the (2,2) transition at 23.722633 GHz, which is not discussed any further. The channel spacing was 7.8 kHz (0.1 kms) with a total bandwidth of 16 MHz (202.4 kms). At the start or end of every observing day, strong Galactic sources were observed for calibration purposes. These sources were near the outflow region associated with the Herbig Ae star RCrA (Anglada et al 1989) and the HII region OMC-2 in Orion (Batchelor et al. 1977). The data for each position were averaged with a weight proportional to the inverse square of the system temperature for each integration. Baselines were fitted and subtracted and a Gaussian smooth was applied resulting in a velocity resolution of 0.4 kms. The first two positions (Nos. 3 & 10 in Table 1) were observed in beam-switching mode, using a 1 Hz synchronous waveguide switch to alternate between two beams separated by 4'.5 on the sky. However, the remaining positions were observed in position-switching mode where each object was observed in a sequence consisting of 5 min on source and 5 min on a nearby `blank-sky' region. The total integration times were typically 3 hours for each pointing.

HI

We briefly describe the 21 cm HI data used to help choose our target pointings. The data consists of five sets of 12-hr observations obtained in 1993 January, March, May and July with the Australia Telescope Compact Array. The uv-plane was well sampled to distances of 7 k (1.5 km), resulting in a synthesised FWHP beamwidth of 45'' (11 pc). We used a correlator configuration with a bandwidth of 4 MHz, divided in 1024 channels, resulting in a channel spacing of 0.8 kms. The center frequency was 1419 MHz, corresponding to a center heliocentric velocity of 297 kms. Three adjacent fields, listed in Table 2 were observed. Each field has an extent limited by the primary antenna beamwidth of 34' (490 pc) FWHP, resulting in a combined field of approximately ( pc) centred approximately 12' (170 pc) SSW of 30 Dor. The HI spectra used in this paper were extracted from the resulting data cube.

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Table 2: Phase centres of fields, observed in HI with the Compact Array

Field-No.	Position		centred on
	(J2000)	(J2000)
1	05 35 27.9	-69 16 31.6	SN1987A
2	05 38 47.0	-69 05 50.1	30 Doradus
3	05 38 47.0	-69 27 49.8	Giant Molecular Cloud

© Copyright Astronomical Society of Australia 1997