OBSERVATIONS

The spectra presented here were obtained on UT 1989 November 28-December 1 and 1991 January 19 on the UK Infrared Telescope (UKIRT) on Mauna Kea, Hawaii, using the facility 7-element grating spectrometer of that time, CGS2. The sky was viewed through a roughly circular field, in RA and declination. Observations were obtained by sky-chopping at a few tenths of a Hertz on reference positions 120'' from the source.

J (1.25m), H (1.65m) and K (2.2m) band spectra were obtained at the positions of two bright H emission filaments in the north (+33'', +105'') and south (-11'', -78'') of the source. Offsets are from HD 37903 at (B1950). The J-band data for (+33'', +105'') were obtained during the 1991 observations and the other data during the 1989 run. J and H band measurements employed a 633 lines/mm grating used in first order for J and second order for H, and a 300 lines/mm grating used in second order for K. The spectral resolutions were 0.0041m, 0.0039m and 0.0098m for J, H and K bands, respectively.

Between 1.38-1.43m and 1.80-1.94m there is severe atmospheric absorption of the radiation. To check consistency of the measurements either side of these wavebands the J and H band spectra were overlapped near 1.5m and a few bright H lines in the H and K bands were simultaneously measured with the 633 lines/mm grating. These flux checks indicated that flux calibrations between bands were consistent with one another to within 20% and that none of the J, H or K band spectra needed rescaling.

Absolute wavelength calibration and spectral resolution were determined from spectra of an Argon lamp. The H lines are completely unresolved at our resolution, their FWHM being < 16km (Burton et al. 1990a). Rest wavelengths for the H lines were computed from the energy level determinations of Dabrowski (1984). We estimate the error in absolute wavelength calibration to be less than one third of a resolution element.

Absolute fluxes were determined by comparison with observations of the star BS 1543 (spectral type F6V, apparent magnitudes J=2.35, H=2.15 and K=2.07), obtained adjacent in time to the NGC 2023 observations. We adopted a blackbody temperature of 6,100K and zero-magnitude flux densities of ergm at 1.25m, 1.65m and 2.2m, respectively, to determine the flux density of the calibrator at the wavelength of each line (Oke & Schild, 1970; Kurucz, Peytremann & Avrett, 1974). Brackett and Paschen series absorption lines in its spectrum were artificially removed prior to division by it.

Table: H Line Intensities and Column Densities from Uncontaminated Data

Line		E	Line Intensity		Column Density
	(m)	(K)	(-11'', -78'')	(+33'', +105'')	(-11'', -78'')	(+33'', +105'')
			erg sr
1-0 Q(1)	2.406594	6149	31.3 (2.2)	8.0 (1.0)	111.0 (7.8)	28.5 (3.6)
1-0 Q(3)	2.423731	6951	12.5 (1.1)	4.2 (0.8)	68.9 (6.1)	23.1 (4.4)
1-0 Q(4)	2.437491	7584	4.8 (1.0)	2.4 (0.6)	28.1 (6.0)	13.8 (3.7)
1-0 S(0)	2.223299	6471	8.2 (0.7)	3.5 (0.4)	45.7 (3.8)	19.5 (2.1)
1-0 S(1)	2.121831	6951	18.1 (1.5)	6.6 (0.7)	70.0 (5.8)	25.6 (2.6)
1-0 S(2)	2.033756	7584	7.1 (0.8)	3.5 (0.4)	22.6 (2.6)	11.3 (1.4)
1-0 S(8)	1.714660	14220	0.9 (0.3)	<0.9	4.2 (1.2)	< 4.2
2-0 O(3)	1.335422	11789	3.1 (0.6)	1.4 (0.3)	16.2 (3.0)	7.4 (1.6)
2-0 Q(1)	1.238343	11789	2.7 (0.7)	1.9 (0.5)	11.0 (2.9)	7.5 (1.9)
2-0 Q(3)	1.247324	12550	2.2 (0.6)	0.9 (0.3)	13.3 (3.5)	5.6 (1.8)
2-0 S(1)	1.162223	12550	2.8 (0.7)	1.7 (0.5)	10.7 (2.7)	6.6 (1.9)
2-0 S(2)	1.138238	13150	2.7 (0.7)	1.6 (0.5)	8.0 (2.2)	4.8 (1.4)
2-0 S(4)	1.099817	14764	2.2 (0.7)	<1.0	4.9 (1.7)	< 2.2
2-1 S(1)	2.247721	12550	6.4 (0.6)	4.4 (0.5)	18.1 (1.7)	12.5 (1.3)
2-1 S(2)	2.154225	13150	3.0 (0.5)	1.6 (0.4)	7.3 (1.1)	3.8 (0.9)
3-1 S(1)	1.232986	17818	3.5 (0.8)	1.8 (0.4)	5.7 (1.3)	2.9 (0.7)
3-1 S(4)	1.167158	19911	1.9 (0.5)	1.2 (0.4)	2.0 (0.5)	1.2 (0.4)
3-1 S(7)	1.130405	23069	2.0 (0.6)	1.6 (0.6)	1.9 (0.6)	1.5 (0.6)
3-2 S(1)	2.386447	17818	2.7 (0.7)	1.6 (0.5)	8.1 (2.1)	4.6 (1.4)
3-2 S(2)	2.287026	18386	1.0 (0.4)	0.9 (0.3)	2.6 (1.0)	2.4 (0.8)
4-2 O(3)	1.509865	22079	2.5 (0.4)	2.2 (0.5)	3.1 (0.5)	2.8 (0.6)
4-2 S(2)	1.284625	23295	2.4 (0.6)	1.1 (0.3)	2.1 (0.5)	1.0 (0.3)
4-2 S(5)	1.226300	25623	2.5 (0.6)	1.0 (0.3)	1.7 (0.4)	0.7 (0.2)
4-3 S(3)	2.344479	23955	0.9 (0.6)	0.6 (0.4)	3.0 (1.8)	1.8 (1.3)
5-3 Q(1)	1.492938	26735	2.0 (0.4)	1.1 (0.3)	1.6 (0.3)	0.9 (0.2)
5-3 Q(4)	1.515792	27878	1.0 (0.4)	0.3 (0.2)	1.3 (0.5)	0.4 (0.3)
5-3 Q(5)	1.528641	28498	1.3 (0.2)	1.0 (0.4)	1.8 (0.3)	1.3 (0.5)
5-3 Q(6)	1.544261	29228	<1.0	0.7 (0.3)	<1.3	0.9 (0.4)
6-4 Q(1)	1.601535	31063	1.6 (0.3)	1.3 (0.4)	1.1 (0.2)	0.9 (0.3)
6-4 Q(2)	1.607386	31303	1.6 (0.4)	1.2 (0.3)	1.6 (0.4)	1.2 (0.3)
6-4 Q(4)	1.628084	32132	<0.8	1.7 (0.4)	< 1.0	2.0 (0.5)
6-4 S(0)	1.536884	31303	1.0 (0.3)	1.0 (0.3)	1.1 (0.4)	1.1 (0.4)
7-5 S(4)	1.539990	37220	<0.6	1.0 (0.4)	< 0.4	0.7 (0.3)
8-6 S(3)	1.701797	40115	1.0 (0.3)	1.0 (0.3)	4.5 (1.2)	4.5 (1.5)
10-7 O(3)	1.548851	44902	<0.7	0.7 (0.3)	<0.6	0.7 (0.3)

© Copyright Astronomical Society of Australia 1997