Chemical stratification in the Orion Bar: JCMT spectral legacy survey observations
(Corrigendum)

M. H. D. van der Wiel^1,2 - F. F. S. van der Tak^2,1 - V. Ossenkopf^3,2 - M. Spaans¹ - H. Roberts⁴ - G. A. Fuller⁵ - R. Plume⁶

1 - Kapteyn Astronomical Institute, PO Box 800, 9700 AV, Groningen, The Netherlands
2 - SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
3 - I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
4 - Astrophysics Research Centre, School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN, UK
5 - Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester, M13 9PL, UK
6 - Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada

A&A 498, 161-165 (2009), DOI: 10.1051/0004-6361/200811391

Abstract
The integrated line intensities in Table 1 of Van der Wiel et al. (2009, A&A 498, 161) should be modified due to an error in the adopted channel widths: values are reduced by 20% for C₂H, H₂CO and SO, reduced by a factor 5 for C¹⁸O and HCN, and increased by 40% for ¹³CO. Derived column densities for C₂H, H₂CO and SO are decreased by 20%; for C¹⁸O it is increased by 40%. Corrected abundance values of C₂H, H₂CO and SO are a factor <2 smaller than the originally published values. The values for HCN column densities and abundance are replaced by lower limits. Consequences for the discussion and conclusions are minor. In addition, the southwest arrow in Fig. 1 should be shifted to the southwest by 10 .

Key words: ISM: molecules - ISM: structure - ISM: individual: Orion Bar - stars: formation - errata, addenda

1 Numerical values in Table 1

Due to an error in the adopted spectral channel widths, the integrated line intensities obtained in the original publication (Van der Wiel et al. 2009) should be corrected by the following factors: 0.84 for C₂H, 0.83 for H₂CO, 0.85 for SO, 0.21 for C¹⁸O, 0.18 for HCN, and 1.41 for ¹³CO.

The values in the last three columns in Table 1 of Van der Wiel et al. (2009) should be updated following Table 1 of this erratum. Note that the HCN column densities are now lower limits, and the limits to the ¹³CO column density are unchanged. The reduced line strength for C¹⁸O allows for an optically thin column density estimate. The new C¹⁸O column density is 40% higher than the original, optically thick, estimate.

Table 1:   Corrected values for integrated line strength and derived column densities of observed molecular lines.

In the caption of Fig. 1, values for maximum integrated intensity for each map should be: 13.3 Kkms^-1 for C₂H, 8.7 for H₂CO, 7.7 for SO, 19.9 for C¹⁸O, 70.5 for HCN, and 276.8 for ¹³CO. The figure is reproduced in this erratum (Fig. 1) with the corrected numbers in the caption.

Figure 1: Images of molecular emission, observed with the JCMT toward the Orion Bar of the species and transitions listed in Table 1. Line intensities are integrated over 5-8 kms-1, depending on the line width. The C2H transition shown here is the 49/2-37/2 transition; the other transition shows a similar spatial distribution. Contour levels are drawn at 10, 20, ..., 90% of the maximum integrated intensity for every map: 13.3 Kkms-1 for C2H, 8.7 for H2CO, 7.7 for SO, 19.9 for C18O, 70.5 for HCN, and 276.8 for 13CO. Note that the measured maximum  values across the northeast slices (Table 1) are not the same as the highest value across the entire map. The grayscale background image shows Spitzer Space Telescope 8 m continuum emission. The filled circle in each frame indicates the beam size at the relevant frequency. Axes are annotated with right ascension and declination (J2000).

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The vertical scaling in the original Fig. 2 should change by the factors mentioned above for the respective molecules (Fig. 2 in this erratum).

	Figure 2: Profiles of molecular emission along slices perpendicular to the ionization front at position angle 225 (see arrows in Fig. 1): ( top panel) through the northeast core; ( bottom panel) through the southwest core. The zero point of the distance scale is placed at the C18O peak position: (RA = ,  = ) for the northeast slice and (RA = ,  = ) for the southwest slice.
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The derived N(H₂) in Sect. 3, last paragraph, is now 1.0  10²³ cm^-2. The resulting molecular abundances are: x(C₂H) = 2  10^-9, x(H₂CO) = 4  10^-10, x(SO) = 7  10^-10, x(HCN) > 5  10^-10.

The following parts of the discussion (Sect. 4) are affected. The C₂H abundance discrepancy decreases. Somewhat fortuitously, the discrepancy between modeled and observed H₂CO abundance almost vanishes if the ``observed'' H₂CO column density is derived based on the LTE assumption; in the likely case that H₂CO is not completely in LTE, the gas-phase model still underestimates its abundance. The SO abundance discrepancy increases to a factor 1.4  10⁴.

2 Arrow in Fig. 1

The arrow in Fig. 1 indicating the southwest slice is misplaced. It should go through the southwest peak of the C¹⁸O emission (coordinates RA = ,  = , as correctly stated in the caption of Fig. 2) instead of through the SO emission peak. The correct position of the southwest arrow is shown in Fig. 1 of this erratum.

The authors would like to thank Isidore Bedikoglou and Markus Cubick for noting the errors in our original publication.

References

All Tables

Table 1:   Corrected values for integrated line strength and derived column densities of observed molecular lines.

All Figures

	Figure 1: Images of molecular emission, observed with the JCMT toward the Orion Bar of the species and transitions listed in Table 1. Line intensities are integrated over 5-8 kms-1, depending on the line width. The C2H transition shown here is the 49/2-37/2 transition; the other transition shows a similar spatial distribution. Contour levels are drawn at 10, 20, ..., 90% of the maximum integrated intensity for every map: 13.3 Kkms-1 for C2H, 8.7 for H2CO, 7.7 for SO, 19.9 for C18O, 70.5 for HCN, and 276.8 for 13CO. Note that the measured maximum  values across the northeast slices (Table 1) are not the same as the highest value across the entire map. The grayscale background image shows Spitzer Space Telescope 8 m continuum emission. The filled circle in each frame indicates the beam size at the relevant frequency. Axes are annotated with right ascension and declination (J2000).
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In the text

	Figure 2: Profiles of molecular emission along slices perpendicular to the ionization front at position angle 225 (see arrows in Fig. 1): ( top panel) through the northeast core; ( bottom panel) through the southwest core. The zero point of the distance scale is placed at the C18O peak position: (RA = ,  = ) for the northeast slice and (RA = ,  = ) for the southwest slice.
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In the text