WD 0837+199 - White Dwarf in Messier 44
WD 0837+199" is one of the few white dwarfs in Messier 44. The apparent brightness of the star is given as 17.5mag. With the known distance of
around 610 light-years, the absolute magnitude can be determined as M= +11.2mag, which corresponds to only 1/400th of the luminosity of the Sun.
The star has an effective surface temperature of 17,200 Kelvin, which corresponds to a cooling time of 180 million years. The diameter is 15,800
kilometers - making WD 0837+199 only slightly larger than the Earth, despite still having a mass of 74% of that of the sun. It is assumed that the
progenitor star had a mass of 3.1 times that of the sun.
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Even in my 20" f/3 Dobsonian, WD 0837+199 is an extremely difficult object that not only requires a dark sky, but also very good seeing.
On the day of the observation, the air was so calm that the stars appeared absolutely point-like even at a magnification of 380x. After seeing nothing
for quite a while under my black cloth, at some point I was completely dark-adapted, so that the white dwarf flashed out of the darkness every now
and then for a brief moment, only to disappear again the next moment. A few times I even managed to hold the extremely faint star for a period of
1-2 seconds.
All in all, a great, but really difficult observation, for which I would set 20" as the minimum aperture for a successful sighting.
