Five late-summer variables
These examples are an ideal test-bed for your powers of observation
SS Cygni Z
SS Cygni is a dwarf novae that resides in the constellation of Cygnus, the Swan, not far from the nice double star 75 Cygni. When it’s quiescent (in a state of inactivity), the star is approximately mag. +12.0, but during an outburst it can brighten to about mag. +8.0. SS Cygni undergoes these outbursts every seven to eight weeks, so should be checked out whenever there’s a clear night.
◁ Chi Cygni
Located fairly close to Eta (¡) Cygni at the base of the ‘Northern Cross’ asterism in Cygnus, Chi
(r) Cygni is a splendid red giant of the Mira type. Over a period of about 400 days, Chi Cygni can get as bright as mag. +3.5, before fading down to a minimum around mag. +14. Chi Cygni is throwing off material into space, material that will eventually form a planetary nebula. Aim to observe this star once a week, if possible.
△ Algol
This is an example of an eclipsing binary system – Algol (Beta (`) Persei) is, in fact, composed of three stars: Beta Persei Aa1, Beta Persei Aa2 and the fainter Beta Persei Ab. It’s the two hot primary stars, Beta Persei Aa1 and Beta Persei Aa2, that eclipse each other and these eclipses take approximately 10 hours. Algol is usually around mag. +2.1, but every 2.9 days it drops to mag. +3.4. Try to observe it each clear night.
R Scuti Z
This yellow supergiant star is an example of a RV Tauri variable. It lies close to both Beta (`) Scuti and the splendid Wild Duck Cluster, M11. The light curve for this star is quite remarkable and shows periods of deep minima and unusual ‘stand-stills’, during which its magnitude is constant for long periods of time. It’s thought that the dynamics of the star are responsible, but there are many questions yet to be answered. Observe this star every chance you get.
△ V Bootis
Another beautiful red giant, in Boötes, the Herdsman, close to Seginus (Gamma (a) Boötes). This star ranges from around mag. +7.0 to mag. +12.0 over a period of 258 days. Studies of the light curve suggest that there’s a secondary period of about 137 days, and during the early part of the 20th century the overall light curve was somewhat different (the star could be evolving away from being a Mira-type star). Aim to observe it once a week.