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Carbon Star U Lyrae

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About this observation
Observer
Mike Foylan
Time of observation
17/03/2016 - 11:10
Object
U-Lyrae (GSC 3134:1708)
Observing location
Cherryvalley Observatory (I83) Ireland
Equipment
0.2-m SCT
SBIG STL 1301E CCD
Photometric Filters BVR
Exposure
R-Filter: 20s x5, G-Filter: 39s x5, B-Filter: 86s x5. All images flat fielded, aligned and median combined
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In the center of this image is Carbon Star U-Lyrae, it is a Mira type variable. In order to capture accurate colour representation of Carbon Stars Cherryvalley Observatory was required to calibrate or match the colour separation photometric filters to CCD as best as possible. This was achieved by using a simple process of using a white (G2V type Star which was well placed and at a high elevation) selected from the Hipparcos catalogue (in this case HIP 43882) using the same exposure time for each filter (but not saturating the star) and taking approximately ten images for each filter and median combine them. Then the flux was measured for each channel and using the highest value number (in this case the R channel) which was then set to 1, the G and B channels were found by dividing into R which gave the result of G-channel = 1.9 and B-channel = 4.1. These values can vary slightly depending on elevation of target object.

We can also see the faint open star cluster of NGC 6791 (upper left) at a distance of ~14,000 light years, also in the Lyra constellation. At roughly 8 billion years old, and with an Iron to Hydrogen abundance ratio that is more than twice that of the Sun, it is one of the oldest and most metal-rich clusters in the Milky Way. It is also one of the largest open clusters known within our Galaxy.

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