Salas, J.; Maíz Apellániz, J.; Gamen, R. C.; Barba, R. H.; Sota, A.; Sanchez-Bermudez, J.; Alfaro, E. J.
The Astronomer's Telegram, #5571 (2013).
As part of a photometric campaign of Cyg OB2 carried out with an amateur 35 cm telescope, we discovered a brightening of Cyg OB2-4 B (RA=20:32:13.117, dec=+41:27:24.25 J2000). The star maintained approximately constant magnitudes of RJohnson= 11.23 and IJohnson = 10.47 during the 2012 summer campaign. When the campaign resumed in 4 June 2013 the star retained the previous magnitudes but in a few days it started a progressive brightening that reached RJohnson = 10.66 and IJohnson = 9.78 in late August.