Near-IR Fluorescent Molecular Hydrogen Emission from NGC 2023

Michael G. Burton, J.E. Howe, T.R. Geballe, P.W.J.L. Brand, PASA, 15 (2), 194
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Next Section: RESULTS
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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, tex2html_wrap_inline749 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 (1.25tex2html_wrap_inline439m), H (1.65tex2html_wrap_inline439m) and K (2.2tex2html_wrap_inline439m) band spectra were obtained at the positions of two bright Htex2html_wrap_inline441 emission filaments in the north (+33'', +105'') and south (-11'', -78'') of the source. Offsets are from HD 37903 at tex2html_wrap_inline765 (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 0.0041tex2html_wrap_inline439m, 0.0039tex2html_wrap_inline439m and 0.0098tex2html_wrap_inline439m for J, H and K bands, respectively.

Between 1.38-1.43tex2html_wrap_inline439m and 1.80-1.94tex2html_wrap_inline439m 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 1.5tex2html_wrap_inline439m and a few bright Htex2html_wrap_inline441 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 Htex2html_wrap_inline441 lines are completely unresolved at our resolution, their FWHM being < 16km tex2html_wrap_inline453 (Burton et al. 1990a). Rest wavelengths for the Htex2html_wrap_inline441 lines were computed from the tex2html_wrap_inline791 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 tex2html_wrap_inline793ergtex2html_wrap_inline563tex2html_wrap_inline565tex2html_wrap_inline439mtex2html_wrap_inline569 at 1.25tex2html_wrap_inline439m, 1.65tex2html_wrap_inline439m and 2.2tex2html_wrap_inline439m, 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.

   

Line

tex2html_wrap_inline549 Etex2html_wrap_inline813 Line Intensitytex2html_wrap_inline423 Column Density
(tex2html_wrap_inline439m) (K) (-11'', -78'')tex2html_wrap_inline425 (+33'', +105'') (-11'', -78'') (+33'', +105'')
tex2html_wrap_inline829 erg tex2html_wrap_inline563tex2html_wrap_inline565 srtex2html_wrap_inline569 tex2html_wrap_inline837tex2html_wrap_inline565

1-0 Q(1)

2.406594 6149 31.3 (2.2)tex2html_wrap_inline427 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)

Table: Htex2html_wrap_inline441 Line Intensities and Column Densities from Uncontaminated Data

tex2html_wrap_inline423Intensities have been corrected for atmospheric transmission (see text), but not for extinction.
tex2html_wrap_inline425Positions are R.A. and Declination offsets from HD 37903, in arcseconds.
tex2html_wrap_inline427Values in parentheses are the 1-tex2html_wrap_inline743 uncertainties. Upper limits are 3-tex2html_wrap_inline743.


Next Section: RESULTS
Title/Abstract Page: Near-IR Fluorescent Molecular Hydrogen
Previous Section: INTRODUCTION
Contents Page: Volume 15, Number 2

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