Abstract: Cyg OB2 no. 12 is a hot B-class super-supergiant in the OB association with the highest absolute magnitude known in our Galaxy. It has been very little observed photometrically. Our goal is to determine the rapid variability of the star.

Full Text of Proposal

Comments by OPC

General Comments: The proposers want to search for rapid photometric variability in the hypergiant Cyg OB2 #12.

Visibility:Target is visible in the first half of the night.

Special Comments: The timescale to be addressed is not clear (minutes, hours?). The probably most interesting timescale is hours, say one observation every hour. Since the target is rather faint in U due to interstellar extinction (the intrinsic colour of a B5 supergiant is about B-V=-0.1), and given the lesser sensitivity of the detector, it might be better to observe in V band.

Expected time consumption (including overhead): 3 to 5 exposures of about 10 min for V=11.5 spread over the first half of the night.

Proposed facility:OHP (or other suitable northern facility).