Reply To: M45 by daylight.

Forums General Discussion M45 by daylight. Reply To: M45 by daylight.

Dr Paul Leyland

I have now done a little more analysis of the images taken on 2024-02-16 and believe that I have identified three stars in M45.

The first step was to co-add all the images which did not show any stars and use the result as a flat field. Not having taken any true flats with the i’ filter this was the best I could do. It actually worked extremely well when applied to the images which did contain stars.

It was quite impossible to put a WCS on the images so I examined each for distinctive objects which may be found by comparing with the DSS2 survey. I knew the image scale (0.6 arcsec/pix) and approximate camera angle (-177 degrees) so when a double star was found on image number 47, I could tell that the centroids were calculated as 9.5arcsec apart and at a PA of 225 degrees, the primary being markedly brighter than the secondary. Wandering around the Pleiades I came across HD23964A and HD23964C in SIMBAD and cross-referenced with the Washington Double Star catalog where their separation is given as 10.4arcsec in PA 235 degrees with magnitudes of I=6.74 for component A and (R=9.71, J=8.93) for component C. Very satisfactory!

From that the approximate error in the RA and Dec positioning of the mount could be calculated; it came to about 1 minute in RA and -0.3 degrees in declination.

Another bright star, slightly brighter than HD23964, was found in image number 40. Sure enough 26 Tau, at magnitude V=6.46 and J=5.68, was found well within an arcminute of the predicted position. I am reasonably confident of this identification.

Given how easy it is to pick up 9th magnitude objects in the near infra-red with an exposure where the sky almost but not quite saturates the CCD, I think I’ll try to find some more Messier objects in daylight. Call me crazy if you wish.

The attached images show these two objects.