The semi-regular variable Z Ursae Majoris is currently near its maximum brightness and a week ago we had a clear evening when I thought I could try and get an image of this star with my Celestron 102 SLT. Unfortunately, the moon was in the sky and four days from full but I thought it was worth doing. I mounted the telescope on the HEQ-5 and was able to get this set up reasonably quickly. It involves pointing the axis of the drive at the pole and then aligning on a couple of stars but this went smoothly.
The above image (taken on a Nikon D90) combines 9x30s frames (at ISO 1600) using DeepSkyStacker. I have rotated the image so that north is at the top and east is to the left. I have also binned the image x2 and cropped it so it more or less matches the field in the AAVSO chart X28625AEL. This chart is appropriate for use with a telescope rather than the larger field chart for this star produced by the BAA (and useful for when observing with binoculars). Z Uma is the bright orange star marked in the centre of the field. I have also marked two other stars which are included on the chart as photometry reference stars. These are star 84 (which has a V magnitude of 8.438) and star 99 (which has a V magnitude of 9.898). Z appears much brighter than these two stars but this is in part due to the red colour of this variable star. At this time Z had a visual magnitude of about 7.
There is a good correlation between the stars you can see in this image and those in the chart. The chart has stars plotted down to magnitude 14.5 and so the limiting magnitude of this image must be about the same. If you look closely there are a few faint nebulous patches in the image which are probably faint galaxies.
All text and images © Duncan Hale-Sutton 2023
No comments:
Post a Comment