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The filter transmissions have been measured at multiple locations accross the filter. The erosion operation is characterized by our choice of the neighborhood of every pixel which has a certain shape and size rectangle, circle, line, etc. The most extreme values are 7. This demonstrate that MegaPrime is a prime grey time instrument. Note the extremely expanded scale for the u-band. In a forthcoming paper, the table will be completed by the shell equatorial coordinates, surface brightness estimates, and the shell azimuthal widths.

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MegaCam Raw Data Description

Here is a complete listing of the differences between the headers of an “amplifier” extension before splicing and a “ccd” extension after splicing ; a “” marks the separation before and after the splicing.

Here we present images of the individual features we found in our MegaCam image and in the archival HST image Sikkema et al. Noise bands The MegaCam controller introduces very low level structures during the readout.

FITS extension Many keywords need to be updated as stated in the block added in the primary header; that same block of information is also added to each extension besides the update and addition of keywords.

Jungwiert 1 and L. Note that the new metacam filter has a red cutoff and a redder blue cutoff, which explains the lower zero point compared to the old z filter. The unit au means arbitrary unit. This transformation also depends on metalicity and therefore on galactic latitude. To suppress the effects of noise, we smoothed the original image by the median filter before applying the erosion filter.


MegaPipe takes as input detrended MegaCam images and does a careful astrometric and photometric calibration megavam them. All the shells we detected are shown in Figs.

In addition, the SNLS code courtesy Marc Betoule to produce superflat photometric grid solutions has been adapted to the new focal plane layout with 40 CCDs, and was used to produce photometric grid corrections on all new wideband filters, as well as the narrow band filters as soon as data become available.

Again, one should be sceptical of the u-band transformation. Dashed lines are for the old S filter set, while solid lines are for the new filter set. They provide a stable and controlled light source allowing the measurement and follow-up of the camera characteristics over time.

The two amplifier readouts from a single CCD are spliced together into a single file, with the central rows of the CCDs stiched back together while the overscan region on the X axis for the first amplifier are pulled to the first rows. Each CCD has a x pixels imaging area split into two x imaging areas as both chip’s amplifiers are used.

Technical considerations to prepare MegaCam observations

Even though a few candidates are highly doubtful, the number is surprisingly higher than previously reported. A few dozens across the whole mosaic. Stacking Frame physical object. The observer in direction A sees the shell as a jegacam structure. The predicted shell was not detected, but the new image revealed that the prediction was based on incorrect assumptions and poor data. This page follows the structure of the various sections found in the “General Summary” table and provides further details related to the impact they may have on an observing strategy.


The side of the square is the same as the radius of the circle.

The accreted galaxy loses orbital energy by dynamical friction. Distribution of optimally dithered exposures. Here the similarity with minimum masking ends. This will be interesting for comparison with simulations.

The angular resolution of this image was 0. Discussion and conclusions Acknowledgments References Appendix A: In a forthcoming paper, we will emgacam a quantitative photometric analysis.

If the shell is to be observed as a sharp-edged feature, the line of sight must be tangential to the shell surface Fig. The filter curves also include 1. Our erosion filter is circular and the median filter is square.

O ct 2 00 7 MegaPipe : the MegaCam image stacking pipeline at the Canadian Astronomical Data Centre

There are several reasons for this. According to the HyperLeda 2 database Makarov et al. Central Air Data Computer Photometry.