Free Access
Volume 531, July 2011
Article Number A157
Number of page(s) 38
Section Interstellar and circumstellar matter
Published online 06 July 2011

Online material

Appendix A: Photometry

A.1. VMC

The mixture of stellar and extended sources in our sample required different approaches to obtain their magnitudes. As a first step we created a stacked image per waveband (0.339″/pixel) for each object by averaging individual paw-print observations (Irwin et al. 2004). As described above, the depth in these images is uniform across all tiles with some small variation. The catalogue photometry hosted by the VISTA Science Archive (VSA) is adopted when the mergedClass flag indicates a stellar or probably stellar object. In these instances we adopt the catalogued magnitudes calculated with a small aperture of diameter 2.0″ (AperMag3) which is corrected for flux outside the aperture assuming a stellar profile. This is appropriate for compact, unresolved PNe and of course for stars. For some extended objects we can make use of uncorrected magnitudes (NoAperCorr) calculated using apertures of diameter 2.0″ (AperMag3), 2.8″ (AperMag4) or 5.7″ (AperMag6), where the aperture is visually selected to enclose the most object flux. The VSA magnitudes are based on the previously mentioned level of TKN completeness.

When catalogue magnitudes were not available for fainter extended sources we have performed our own aperture photometry on our stacked image cutouts. A specially developed plugin for ds9 (Joye & Mandel 2003) served as a wrapper for the ds9 funtools program funcnts4 which calculates the total number of counts within a given ds9 region (e.g. a circle). A circular aperture of maximal radius is chosen for each object along with multiple nearby sky apertures of the same radius. The magnitudes were then calculated using: (A.1)where S is the average of the total sky counts in all sky apertures, O is the total counts in the object aperture, T is the normalised exposure time (5 s for Ks, 10 s for J and 20 s for Y) and NZP is the nightly photometric zeropoint. We assigned a 1σ error of

0.20 mag based on the comparison between our measurements and the catalogued photometry. As no errors were given by the VSA for NoAperCorr magnitudes we also assigned them these errors. Some fields were too crowded for aperture photometry and we have remarked in Table 2 where this occurred. In one case an elliptical aperture seemed most suitable (RP789). No aperture corrections were applied to our aperture photometry.


To perform the aperture photometry we developed a similar ds9 plugin as for the VMC aperture photometry that would allow for the efficient calculation of all magnitudes per object once the IRAC and MIPS images were loaded alongside the VMC colour-composite image for guidance. The total number of sky subtracted counts per object were converted to Jy following the instrument handbooks and converted to magnitudes using the zeropoints given in the accompanying SAGE data release documentation, i.e. 280.9, 179.7, 115.0, 64.13 and 7.14 Jy for the 3.6, 4.5, 5.8, 8.0 and 24.0 μm bands, respectively. Table A.3 contains the measured magnitudes for which we have assigned 1σ errors of 0.25, 0.25, 0.30, 0.35 and 0.40 mag, respectively, based on a comparison with Hora et al. (2008) and catalogue magnitudes. These errors are larger than the 0.1–0.2 mag estimated by Hora et al. (2008) and more realistically reflect the inherent difficulty in selecting optimal object and sky apertures under sometimes very challenging circumstances. This is particularly true at 8.0 μm where diffuse PAH emission in the field creates a highly variable background. An excellent example is Mo38 which has negligible background at shorter wavelengths. If our sky aperture is placed in a background minimum SE of the PN we reproduce [8.0] = 12.9 mag of Hora et al. (2008). However, a placement immediately West of the PN on a similar background level as the PN results in [8.0] = 13.7 mag – a difference of 0.8 mag! In the case of a few bright objects we used the catalogued magnitudes and their errors. Very extended HII regions were not measured.

Table A.1

Optical magnitudes from Zaritsky et al. (2004).

Table A.2

VMC magnitudes.

Table A.3

SAGE MIR magnitudes.

Appendix B: Images

We present colour-composite images for our sample in two sets of figures. Figure B.1 contains the VMC images made from stacked Ks (red), J (green) and Y (blue) images, WFI images made from either Hα (red), [O III] (green) and B (blue) images or for objects in Table 4 Hα (red), MB 485/31 or MB 604/21 (green) and [O III] (blue), and Spitzer SAGE images made from [5.8] (red), [4.5] (green) and [3.6] (blue) images. Figure B.2 contains VMC and SAGE images for objects lacking ESO WFI coverage.

In each set of figures the objects are ordered following Table 2. VMC images include circles with the RP2006b measured Hα radius. Depending on the ratio of Hα to [O III] emission, PNe may appear red as in RP265 (no [O III]), yellow as in MG60 (Hα/[O III]  ~  1) or green as in SMP78 ([O III]  >  Hα). Exceptions include MG76, where [O III] was replaced by V due to missing coverage, and objects in Table 4, in which case PNe may appear red (Hα only) or pink ([O III] and Hα).

thumbnail Fig. B.1

(Left column) VMC Ks (red), J (green) and Y (blue) colour-composite; (middle column) Spitzer SAGE [5.8] (red), [4.5] (green) and [3.6] (blue); (right column) Optical Hα (red), [O III] (green) and B (blue) excluding MG76 and objects in Table 4 which are Hα (red), continuum (green) and [O III] (blue). Each image is 30 × 30 arcsec2 with north up and east to left.

Open with DEXTER

thumbnail Fig. B.2

Similar to Fig. B.1 but for objects without WFI coverage in two sets of two columns: (left columns) VMC colour-composite; (right columns) SAGE colour-composite. SMP 4 and SMP 6 have no SAGE coverage.

Open with DEXTER

© ESO, 2011

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