As Found on “The Astronomer’s Telegram”- Superoutburst of Cataclysmic Variable B8 in NGC 6791

Astronomical observations from around the globe are posted to “The Astronomer’s Telegram” ( to share information and to seek additional observations. For myself, I use it to find sources of the observed changes in our atmosphere and plausible causes for our climate change.

Below, ATel #3507, posted 7/24/2011

Subjects: Optical, Cataclysmic Variable

The Kepler Mission observed a superoutburst from the cataclysmic variable B8 in NGC 6791 in the newly released quarter 8 data. The super-outburst began on BJD 2455592 and lasted two weeks. Superhump oscillations are clearly seen at maximum and during the decline.

B8 in the old, metal-rich cluster NGC 6791 was spectroscopically confirmed as a cataclysmic variable (CV) by Kaluzny et al. (1997, ApJ, 419, 153) but its orbital period has not been determined. Ground-based observations shows B8 spends most of its time near V=21 mag with two magnitude outbursts consistent with a dwarf nova classification (Mochejska, Stanek, & Kaluzny 2003, AJ, 125, 3175).

Monitoring of B8 by Kepler using a 1-min cadence in Cycle 2 confirms the 1.5 magnitude outbursts lasting two to three days and now show a superoutburst with an amplitude of 3 magnitudes. The average superhump period is 2.097+/-0.003 hours indicating an orbital period just under the period gap and that B8 belongs to the SU UMa class of CV. In the first two days of the outburst the superhump peak-to-peak amplitude is 0.3 mag and the period is 2.109+/-0.003 hours. The superhump period decreases with time at a rate of P-dot=2e-4.

Below is an artist’s representation of a ‘cataclysmic variable’-


Below found at

NGC 6791 is an open star cluster in the Lyra constellation.[1] It was discovered by Friedrich August Theodor Winnecke in 1853. 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. This is contrary to the typical rule-of-thumb where older means more metal-poor. Compounded with the fact that it has an unusually high population of stars, NGC 6791 is among the most studied clusters in the sky.[3][4]

Observation data (J2000 epoch)
Constellation Lyra
Right ascension 19h 20m 53s[1]
Declination +37° 46.3′[1]
Distance ~13,300 ly (4078 pc)




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