Online material

Appendix A: Revisiting the CH₂DOH/CH₃OD abundance ratios in Orion BN/KL

To compare our high angular resolution data with previous single-dish observations, we re-calculated the temperatures and column densities obtained by Mauersberger et al. (1988) and Jacq et al. (1993) from their 30 m data for CH₃OD and CH₂DOH, respectively. The line parameters of CH₃OD and CH₂DOH used in the calculations are listed in Table A.1, and the population diagrams are shown in Fig. A.1.

CH ₃ OD

We selected only five clean CH₃OD lines (without any apparent line-blending) around 140–156 GHz detected by Mauersberger et al. (1988) with a similar resolution of 16′′–17′′ to reduce the fitting uncertainty. The CH₃OD lines detected by Jacq et al. (1993) were excluded because no CH₃OD spectra can be used to judge the possible line-blending and data quality. Effective line strengths Sμ² of the CH₃OD lines were taken from Anderson et al. (1988), and the partition function Q = 1.41 T^1.5 was used. The rotational temperature (132.4  ±  19.6 K) and column density (4.4 ± 0.3 × 10¹⁵ cm^-2) were estimated by a least-squares fit (Fig. A.1), assuming a source size of 15′′. The revised CH₃OD temperature and column density are consistent with those of Mauersberger et al. (1988), who derived a rotational temperature of 50–150 K and a column density of 1–5 × 10¹⁵ cm^-2.

Fig. A.1 Population diagrams of CH3OD and CH2DOH using the 30 m data of Mauersberger et al. (1988) and Jacq et al. (1993), respectively. The old CH2DOH effective line strengths of Jacq et al. (1993) (upper panel) and the new ones (lower panel) were used in the calculations. The beam filling factor was taken into account by assuming a source size of 15′′. The rotational temperatures and column densities were estimated by a least-squares fit, and the results and uncertainties are given in the diagrams. For CH2DOH, the red dashed line in the upper panel indicates the fit with a fixed temperature of 100 K as adopted by Jacq et al. (1993) and the one in the lower panel the fit with a temperature of 130 K (the same as the CH3OD temperature derived here).

Open with DEXTER

CH ₂ DOH

For CH₂DOH, we judge that only the three detections reported by Jacq et al. (1993) can be reliably used in the population diagrams (see Table A.1). Both old CH₂DOH Sμ² values taken from Jacq et al. (1993) and new ones (see Table A.1) provided by Parise (priv. comm.) were used in the calculations (Fig. A.1). The CH₂DOH partition function Q = 2.25 T^1.5 and a source size of 15′′ were used here.

The new values of CH₂DOH Sμ² employed in this work are based on those tabulated in the paper by Parise et al. (2002) but a factor of three higher. This revision corrects for an inconsistency with the partition function reported by Parise et al. (2002), and some dipole moment values can be quite uncertain, which may explain the discrepancy with the values used by Jacq et al. (1993) and why they were never officially released in the JPL database. However, as shown below, both the old Sμ² values used by Jacq et al. (1993) and new ones adopted here give similar estimates of the CH₂DOH column densities in Orion BN/KL. We believe that the uncertainties of the CH₂DOH Sμ² values of our present work are not dominant in the column density calculations. Nevertheless, a new spectroscopic study of CH₂DOH with a robust fitting of the Hamiltonian would definitely give better confidence in these intensities.

Using the old Sμ², a least-squares fit to the CH₂DOH data shows a low rotational temperature (about 25  ±  10 K) with a column density of 5.0 × 10¹⁴ cm^-2, consistent with the first estimate of Jacq et al. (1993), who derived a rotational temperature of 34 K and a column density of 6 × 10¹⁴ cm^-2. However, since the rotational temperatures derived by Menten et al. (1988) and Mauersberger et al. (1988) for CH₃OH and CH₃OD are about 100 K toward Orion BN/KL, Jacq et al. (1993) also adopted a higher temperature for CH₂DOH. They obtained a CH₂DOH column density of 3.9 × 10¹⁵ cm^-2, which is 2.6 times higher than our revised value (1.6 × 10¹⁵ cm^-2, see Fig. A.1 upper panel). This is because they appear to correct the beam-filling factor twice in their N_l/g_l calculations and population diagram. Therefore, the CH₂DOH column density derived by Jacq et al. (1993) with a temperature of 100 K was overestimated by a factor of 2–3.

With the new CH₂DOH Sμ², we derive a somewhat higher rotational temperature (40.6 ± 14.4 K) and a column density of 5.0 × 10¹⁴ cm^-2 similar to that derived by using the old Sμ². This suggests that the uncertainties in the CH₂DOH effective line strengths do not strongly affect the CH₂DOH column density estimate in this case.

CH ₂ DOH/CH ₃ OD abundance ratios

The overestimated CH₂DOH column density derived by Jacq et al. (1993) leads to a higher [CH₂DOH]/[CH₃OD] abundance ratio (1.1–1.5) toward IRc2. The new calculation indicates that the [CH₂DOH]/[CH₃OD] abundance ratio is 0.2–0.5 with a source size of 15′′, assuming CH₂DOH and CH₃OD have the same temperature of about 130 K. For a lower CH₂DOH temperature (i.e., about 40 K), the [CH₂DOH]/[CH₃OD] ratio is even lower (about 0.1).

In addition, the CH₃OD data of Mauersberger et al. (1988) were taken at the position close to KL-W (KL-W_M hereafter, Menten et al. 1988) instead of IRc2, which was used as the central position by Jacq et al. (1993). According to our CH₃OD image (Fig. 3), the intensity observed toward IRc2 is about twice as high as that of KL-W_M, assuming a 30 m telescope beam size of about 18′′ at 140 GHz and the same filtering. Therefore, the

CH₃OD abundance in Orion BN/KL derived by Mauersberger et al. (1988) may be underestimated by 50% at most. A similar calculation (Fig. B.5) also shows that the CH₃OH column density toward KL-W_M is about 20% lower than that toward IRc2.

In short, we conclude that the revisited [CH₂DOH]/ [CH₃OD] abundance ratio derived from the previous 30 m observations is ≲ 0.6, and the [CH₂DOH]/[CH₃OH] abundance ratio is estimated to be 0.8–2.8 × 10^-3 toward IRc2, by adopting a CH₃OH column density of 4.7 ± 0.3 × 10¹⁷ cm^-2 (Menten et al. 1988) and correcting the possible density underestimate of about 20% toward IRc2 (for a source size of 15′′).

Fig. B.1 Left: channel maps of the CH2DOH doublet (Eup/k = 48.4 K) emission at 223 616.1 MHz for a synthesized beam of . Contours run from 40 mJy beam-1 (2σ) to 160 mJy beam-1 (2.77 K) in steps of 40 mJy beam-1, and the dashed contours represent –20 mJy beam-1. The bottom-right panel shows the integrated intensity (from 5 to 11 km s-1) in contours running from 0.15 to 0.45 Jy beam-1 km s-1 in steps of 0.15 Jy beam-1 km s-1, and the dashed contours represent − 0.08 Jy beam-1 km s-1. Right: channel maps of the CH3OH 7-2 − 71 E (Eup/k = 91.0 K) emission at 101 293.4 MHz for a synthesized beam of . Contours run from 50 to 350 mJy beam-1 in steps of 50 mJy beam-1. The dashed contours represent − 30 mJy beam-1 (1σ). The bottom-right panel shows the integrated intensity of CH3OH (from 5 to 11 km s-1) in contours running from 0.3 to 1.5 Jy beam-1 km s-1 in steps of 0.3 Jy beam-1 km s-1, and the dashed contours represent –0.03 Jy beam-1 km s-1. The black square marks the center of explosion according to Zapata et al. (2009). The positions of source BN, the Hot Core (HC), IRc7, and source I are marked by triangles. The positions of deuterated methanol emission peaks (dM-1, dM-2, and dM-3) and KL-W are marked by red stars.

Open with DEXTER

Fig. B.2 CH2DOH spectra toward dM-1, dM-2, and dM-3 for a synthesized beam of . The dashed lines indicate a VLSR of 8 km s-1. The unidentified molecular lines are denoted with their frequencies. a) For dM-1, the CH2DOH 111,10 − 110,11 e1 line is blended with a broad H13CCCN J = 12–11 line (ΔV ≈ 10 km s-1) at 105 799.1 MHz. The rms noise (1σ) is 0.02 K. b–d) The dotted line indicates the CH2DOH 53,3 − 43,2e0 line at 223 691.5 MHz, which is blended with the (CH3)2CO 177,11 − 166,10 EA/AE lines at 223 692.1 MHz. The rms noise (1σ) is 0.35 K. e) The strong line to the left is the HDO 31,2 − 22,1 line at 225 896.7 MHz. Two velocity components at 7.8 and 9.0 km s-1 are seen toward dM-3. The rms noise (1σ) is 0.12 K.

Open with DEXTER

Fig. B.3 CH2DOH population diagrams of dM-1 and dM-2. a, b) Population diagrams of the high angular resolution data. The rotational temperatures are assumed to be 130 K and 85 K for dM-1 and dM-2, respectively. c, d) Population diagrams for the data smoothed to a resolution of . Low rotational temperatures and higher ones are assumed to be 60 K and 130 K for dM-1 and 66 K and 85 K for dM-2, respectively. The fits of low temperatures are plotted in black lines and higher temperatures in blue dashed lines. The CH2DOH column densities are estimated by a least-squares fit, where the uncertainties include the statistical error, the rms noise, and calibration uncertainties (10%).

Open with DEXTER

Fig. B.4 CH3OH spectra (  ×  ) toward the four positions identified in Fig. 1 in the Orion BN/KL region. The methanol rotational temperatures and column densities are estimated by a least-squares fit, where the uncertainties include the statistical error, the rms noise, and calibration uncertainties (10%). Blue dashed lines indicate the fits with fixed temperatures. Black dashed lines indicate a VLSR of 8 km s-1.

Open with DEXTER

Fig. B.5 Similar plot as Fig. B.4. CH3OH spectra were smoothed to the 30 m beam size of 25′′ to compare with the previous 30 m observations by Menten et al. (1988). Upper panels show the CH3OH spectra and population diagram taken at the same position (, , J2000) used by Menten et al. (1988) and Mauersberger et al. (1988), which is located about 5′′ to the north of KL-W (denoted as KL-WM). Lower panels show the CH3OH spectra and population diagram taken at IRc2 (, , J2000) used by Jacq et al. (1993). Blue dashed lines indicate the fits with a fixed temperature of 130 K. Black dashed lines indicate a VLSR of 8 km s-1. Note that the CH3OH column density derived toward KL-WM is about 20% lower than that of IRc2.

Open with DEXTER

Fig. B.6 a) Variation of derived CH3OH column densities with respect to different rotational temperatures toward dM-1. The corresponding [CH2DOH]/[CH3OH] abundance (derived in population diagrams) ratios are shown in red. The best-fit result corresponds to a CH3OH column density of 2.1 × 1018 cm-2 and a temperature of about 60 K. For temperatures lower than 200 K, the differences in the derived column densities are clearly smaller than a factor of about 3. The [CH2DOH]/[CH3OH] abundance ratios derived from different temperatures are lower than 1.1 × 10-3. b) Variation of the relative abundance (based on the ratio of two transitions of CH2DOH and CH3OD as seen in Fig. 3e of the two isotopologs toward dM-1 as a function of the adopted temperatures. Note that this ratio does not depend much on the temperature.

Open with DEXTER

© ESO, 2012