2 Observations

The observations were carried out using the NRAO12 m radio telescope, at Kitt Peak, Arizona, in November 1999, Table 2 lists the observed transitions.

   

Table 2: Molecular line list.

Transition	$\nu_{\rm ul}$	$E_{\rm u}$	$A_{\rm ul}$
	(GHz)	(cm-1)	(s-1)
H2CO 21,1-11,0 (ortho)	150.498	15.7	6.468 $\times$ 10-5
H2CO 51,4-51,5 (ortho)	72.409	45.8	8.011 $\times$ 10-7
H213CO 21,2-11,1(ortho)	137.450	15.1	4.928 $\times$ 10-5
HDCO 21,1-11,0	134.285	9.3	4.587 $\times$ 10-5
HDCO 40,4-30,3a	256.585	21.5	4.736 $\times$ 10-4
HCN 1-0 (triplet)	88.632	2.96	2.426 $\times$ 10-5
H13CN 1-0(triplet)	86.340	2.88	2.224 $\times$ 10-5
HC15N 1-0	86.055	2.87	2.203 $\times$ 10-5
DCN 1-0 (triplet)	72.415	2.42	1.312 $\times$ 10-5
DCN 2-1(multiplet)b	144.828	7.25	1.259 $\times$ 10-4
c-C3HD 22,0-11,1c	137.455	6.27	5.335 $\times$ 10-5

^a Observed towards only three sources, due to high $T_{\rm SYS}$.
^b Observed by Buckle & Fuller (2001).
^c Tentative identification of lines seen in the H₂¹³CO band.

The 3 mm receivers were used to observe the HCN1-0 and DCN1-0 transitions, the H₂CO5_1,4-5_1,5 transition frequency being covered by the DCN1-0 band, the 2 mm receivers were used for the H₂CO2_1,1-1_1,0, HDCO2_1,1-1_1,0 and H₂¹³CO2_1,2-1_1,1 transitions and the 1 mm receivers were used for the HDCO4_0,4-3_0,3 line. The MAC spectrometer was in 2 IF mode with 16384 channels. The H¹³CN and HC¹⁵N transitions were observed simultaneously, with the 3 mm receiver, using 4 IF mode with an offset of 285 MHz between the pairs of filter banks, though in the end, the HC¹⁵N lines were not above the level of the noise. In all cases the spectra were observed using 24 kHz channels, giving a velocity resolution of $\sim$0.04 kms^-1, except for the DCN2-1 spectra, observations of which are described in Buckle & Fuller (2001).

The weather was clear, with typical sytem temperatures of 180-300 K for the 3 mm receiver and 200-350 K for the 2 mm receiver, while for the brief time we used the 1 mm receiver, the system temperature rose to $\sim$1000 K. Pointing was checked every two hours or so and errors found to be $\sim$5-6''.

All data were calibrated by the usual chopper wheel method and corrected for $\eta_{\rm m}^*$, the efficiency at which the source couples to the main diffraction beam, to give $T_{\rm MB}$. In all cases we have assumed a filling factor of 1, i.e. we have assumed that the source fills the main diffraction beam of the telescope. This may not be strictly true for our low-frequency transitions (the beamwidth of the 12 m telescope is 90'' at 70 GHz), however, as we are primarily interested in the ratios of our column densities, any errors introduced by this assumption should cancel out.

The spectra we obtained are shown in Figs. 1 and 2.

Figure 1: Spectra of H2CO (left), H213CO (centre) and HDCO (right) observed towards the sources in our survey. The 31,2-22,1 transition of c-C3HD has been tentatively identified in the H213CO spectra towards B5IRS1, L1448 mms, L1448 NW and L1527.

Figure 2: Spectra of HCN (left), H13CN (centre) and DCN (right) obtained towards the sources in our survey. The approximate expected position of the H2CO 51,4-51,5 transition is indicated on each DCN spectra.

In general, we saw less molecular line emission towards the Orion sources, though the H¹³CN spectra towards RNO43 and HH111 are particularly noisy. HCN1-0 lines towards L1448 mms, L1448 NW and L1551IRS5 show significant self-absorption, particularly in the main component of the triplet. The additional lines seen in the H₂¹³CO band towards B5IRS1, L1448 mms, L1448 NW and L1527 have been tentatively identified as the 2_2,0-1_1,1 transition of deuterated cyclopropenylidene (c-C₃HD) at 137.455 GHz. The H₂CO5_1,4-5_1,5 transition was not seen towards any of the sources. Spectra of the DCN2-1 transition have been presented in Buckle (2001). Tables 3 and 4 present linewidths and integrated intensities from Gaussian fits to the lines,

 

 

Table 3: Linewidths and integrated intensities for the observed transitions of formaldehyde and deuterated cyclopropenylidene, 1$\sigma$ uncertainties are given in brackets, upper limits are 3$\sigma$.

Line	Source	$\Delta v$	$\int{T_{\rm MB}{\rm d}v}$
		(kms-1)	(K kms-1)
H2CO	B5IRS1	0.66 ($\pm$0.02)	0.771 ($\pm$0.077)
21,1-11,0	L1448 mms	1.96 ($\pm$0.03)	2.013 ($\pm$0.181)
	L1448 NW	1.53 ($\pm$0.02)	3.962 ($\pm$0.198)
	HH211	1.02 ($\pm$0.01)	3.152 ($\pm$0.126)
	IRAS03282	0.96 ($\pm$0.03)	0.934 ($\pm$0.100)
	L1527	1.02 ($\pm$0.04)	1.120 ($\pm$0.123)
	L1551IRS5	1.08 ($\pm$0.01)	2.722 ($\pm$0.136)
	RNO43	0.88 ($\pm$0.03)	0.873 ($\pm$0.096)
	HH111	1.33 ($\pm$0.03)	1.342 ($\pm$0.161)
H2CO	B5IRS1	--	<0.069
51,4-51,5	L1448 mms	--	<0.171
	L1448 NW	--	<0.249
	HH211	--	<0.078
	IRAS03282	--	<0.141
	L1527	--	<0.069
	L1551IRS5	--	<0.105
	RNO43	--	<0.156
	HH111	--	<0.201
H213CO	B5IRS1	--	<0.074
21,2-11,1	L1448 mms	--	<0.090
	L1448 NW	0.99 ($\pm$0.09)	0.164 ($\pm$0.061)
	HH211	0.48 ($\pm$0.06)	0.166 ($\pm$0.071)
	IRAS03282	--	0.090
	L1527	0.44 ($\pm$0.05)	0.100 ($\pm$0.027)
	L1551IRS5	0.52 ($\pm$0.07)	0.080 ($\pm$0.016)
	RNO43	--	<0.078
	HH111	0.97 ($\pm$0.13)	0.095 ($\pm$0.047)
HDCO	B5IRS1	0.67 ($\pm$0.10)	0.054 ($\pm$0.034)
21,1-11,0	L1448 mms	1.28 ($\pm$0.14)	0.126 ($\pm$0.077)
	L1448 NW	0.72 ($\pm$0.04)	0.405 ($\pm$0.069)
	HH211	0.44 ($\pm$0.03)	0.149 ($\pm$0.021)
	IRAS03282	0.52 ($\pm$0.10)	0.073 ($\pm$0.030)
	L1527	0.44 ($\pm$0.02)	0.237 ($\pm$0.026)
	L1551IRS5	0.71 ($\pm$0.04)	0.210 ($\pm$0.036)
	RNO43	--	<0.108
	HH111	0.60 ($\pm$0.08)	0.110 ($\pm$0.051)
c-C3HD	B5IRS1	0.46 ($\pm$0.06)	0.049 ($\pm$0.021)
22,0-11,1	L1448 mms	1.00 ($\pm$0.12)	0.100 ($\pm$0.040)
	L1448 NW	0.75 ($\pm$0.10)	0.106 ($\pm$0.046)
	L1527	0.35 ($\pm$0.03)	0.153 ($\pm$0.021)

   

Table 4: For HCN1-0; the average linewidth and total integrated intensity of the triplet state. For H¹³CN and DCN; linewidths and integrated intensities for the strongest component of each multiplet transition. 1$\sigma$ uncertainties are given in brackets, upper limits are 3$\sigma$.

Line	Source	$\Delta v$	$\int{T_{\rm MB}{\rm d}v}$
		(kms-1)	(K kms-1)
HCN	B5IRS1	0.43 ($\pm$0.01)	0.542 ($\pm$0.705)
1-0	L1448 mms	1.48 ($\pm$0.03)	1.747 ($\pm$0.140)
	L1448 NW	1.40 ($\pm$0.01)	4.576 ($\pm$0.275)
	HH211	1.01 ($\pm$0.01)	2.127 ($\pm$0.149)
	IRAS03282	0.69 ($\pm$0.02)	0.688 ($\pm$0.083)
	L1527	0.48 ($\pm$0.02)	0.391 ($\pm$0.070)
	L1551IRS5	0.74 ($\pm$0.01)	0.877 ($\pm$0.096)
	RNO43	0.99 ($\pm$0.05)	0.584 ($\pm$0.123)
	HH111	0.89 ($\pm$0.05)	0.949 ($\pm$0.247)
H13CN	B5IRS1a	--	--
1-0	L1448 mms	1.11 ($\pm$0.07)	0.299 ($\pm$0.057)
	L1448 NW	1.27 ($\pm$0.08)	0.460 ($\pm$0.069)
	HH211	0.83 ($\pm$0.10)	0.206 ($\pm$0.037)
	IRAS03282	0.91 ($\pm$0.07)	0.129 ($\pm$0.036)
	L1527	0.41 ($\pm$0.06)	0.092 ($\pm$0.022)
	L1551IRS5	0.62 ($\pm$0.07)	0.114 ($\pm$0.024)
	RNO43	--	<0.135
	HH111	--	<0.117
DCN	B5IRS1	0.49 ($\pm$0.04)	0.200 ($\pm$0.030)
1-0	L1448 mms	1.27 ($\pm$0.06)	0.681 ($\pm$0.075)
	L1448 NW	1.01 ($\pm$0.05)	0.843 ($\pm$0.084)
	HH211	0.92 ($\pm$0.07)	0.397 ($\pm$0.052)
	IRAS03282	0.71 ($\pm$0.04)	0.267 ($\pm$0.032)
	L1527	0.39 ($\pm$0.03)	0.180 ($\pm$0.023)
	L1551IRS5	0.73 ($\pm$0.05)	0.285 ($\pm$0.037)
	RNO43	--	<0.144
	HH111	--	<0.141
DCN	B5IRS1	0.57 ($\pm$0.05)	0.131 ($\pm$0.042)
2-1	L1448 mms	1.07 ($\pm$0.09)	0.476 ($\pm$0.071)
	L1448 NW	1.03 ($\pm$0.09)	0.515 ($\pm$0.041)
	HH211	0.81 ($\pm$0.06)	0.224 ($\pm$0.029)
	IRAS03282	0.64 ($\pm$0.05)	0.180 ($\pm$0.034)
	L1527	--	<0.111
	L1551IRS5	0.85 ($\pm$0.07)	0.233 ($\pm$0.037)
	RNO43	0.81 ($\pm$0.08)	0.121 ($\pm$0.034)
	HH111	--	<0.153

^a Source not observed at this frequency.

or 3$\sigma$ upper limits on the non-detections. For the HCN1-0 triplet transition, which is likely to have significant optical depth, we made use of the "HFS'' method of the data reduction software package "CLASS'', which attempts to fit the three lines in an LTE approximation, and returns an estimate for the average linewidth and for the optical depth of the main component. For the other multiplet transitions we measured the integrated intensity of the strongest component of the multiplet, then corrected the column densities for the expected statistical weight of the strongest line at LTE; 0.556 for H¹³CN and DCN1-0, and 0.446 for DCN2-1. Uncertainties in $\int{T_{\rm MB}{\rm d}v}$ were estimated from the noise in the spectra. For the HCN1-0, DCN1-0 and H₂CO2_1,1-1_1,0 transitions the lines were strong compared to the noise and the uncertainties in $\int{T_{\rm MB}{\rm d}v}$ are better than 15%. For the HDCO2_1,1-1_1,0, H₂¹³CO2_1,2-1_1,1, H¹³CN1-0 and DCN2-1 transitions the uncertainties are mostly between 15 and 30%, though a few scans have uncertainties of >40%.