Making the most of some clear weather Cherryvalley Observatory imaged some Carbon Stars which are very interesting in their own right. This amateur astronomer was sparked into doing so due to the wonderful and interesting observation write-ups by Aubrey. I therefore dedicate this work to Aubrey.
While there is still a lot more processing work to do across a number of Carbon Stars I would like to present in this instance; U Camelopardalis:
flic.kr/p/EPnR3n
U Camelopardalis or U Cam is a dying, carbon-rich star which was once a very long time ago similar to our Sun. It is located in the constellation of Camelopardalis (The Giraffe) and is approximately 1500 light-years distant from Earth.
U Cam demonstrates a snap-shot in time which allows us to look billions of years into the future where our Sun will be at a similar Red Giant phase.
U Cam has virtually depleted its hydrogen supply with only a thin Hydrogen shell outside the core still fusing due to the extremely intense heat, the vast majority of the hydrogen was fused into Helium long ago and then virtually all the Helium fused into Carbon thus the core of the star is essentially an extremely intense ball of burning Carbon.
The star is tethering on the edge, a fight between gravity and nuclear processes which has caused the star’s outer layers to swell greatly in size in order to keep it’s so called hydrostatic equilibrium. The energies involved in this process at the core of the star gave enough momentum to cause the outermost layers to expand energetically and ultimately to be blown off into the surrounding space in a rather beautiful symmetrical shell which scientists believe took place some 700 years ago and was initiated by a chain of procedures that only took about 50 years to complete. U Cam is one of a few rare stars scientists have detected at this point in its stellar progress.
The Hubble Space Telescope has taken this wonderful image of U Camelopardalis, in the image you can clearly see the thin shell, while the shell looks impressive it is in actuality very tenuous.
www.nasa.gov/multimedia/imagegallery/image_feature_2302.html
Star Details…
Distance: ~1,500 light years
Magnitude Range: +7.7 to +9.5
Colour Index B-V: 4.1
Period: 412 Days
R.A. & DEC: 03 41 48.174 +62 38 54.39
Semi-regular pulsating Star – Red Giant
Spectral Type: C3,9-C6,4e(N5)
Variability Type: SRB; Semiregular late-type (M, C, S or Me, Ce, Se) giants with poorly defined periodicity (mean cycles in the range of 20 to 2300 days) or with alternating intervals of periodic and slow irregular changes, and even with light constancy intervals (RR CrB, AF Cyg). Every star of this type may usually be assigned a certain mean period (cycle), which is the value given in the Catalogue. In a number of cases, the simultaneous presence of two or more periods of light variation is observed.
Image details: The how - I found this to be a good method!
In order to capture an accurate colour representation of U Camelopardalis 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 G2V Star 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 = 1.88 and B-channel = 4.06, hence the different exposure times as described below. BVR Image of a G2V Star which shows in stark contrast that to a Carbon Star!:
flic.kr/p/DZVczd
R-Bessell Photometric Filter: 15 seconds x4 exposures, flat fielded, aligned and median combined
G-Bessell Photometric Filter: 29 seconds x4 exposures, flat fielded, aligned and median combined
B-Bessell Photometric Filter: 63 seconds x4 exposures, flat fielded, aligned and median combined
B-V-R folder images were then aligned and stacked to give Master B, V and R images; these were then colour combined in CCDSoft v5
CCD Operating Temperature: -40 Degrees Centigrade
Field of View: 46 x 37 arcmins
Pixel Array: 1280 x 1024
Pixel Size: 16um x 16 um
Plate Scale: 2.17 arcsec/pixel
0.2-m SCT+SBIG STL 1301E CCD
f/ratio: 7.6
