Corona Borealis 'Fab Four' Variables

Variables R, S, T & U Coronae Borealis

I am monitoring variables R, S, T, and U Coronae Borealis over a multi-year period that began in the summer of 2024 when I acquired Origin. From the beginning I have used 10-second exposures and 10-minute integration times. The approximate positions of these 4 stars are shown as red dots in my drawing.

Recent Magnitudes (AAVSO)

R CrB, 5.9 V, August 13, 2025
S CrB, 8.0 V, August 13, 2025
T CrB, 9.6 V, August 13, 2025
U CrB, 7.8 V, August 9, 2025

References

"Stellar Opposites: R and T Coronae Borealis", Sky & Telescope, 72(2), August 1986, p. 161.
"S and U Coronae Borealis", Sky & Telescope, 75(6), June 1988, p. 631.

R Coronae Borealis

Discussion

On this date, the visual magnitude of this peculiar variable was approximately 6.1 according to AAVSO data. You can see that it is significantly brighter than HD 141352 (7.4) in the image. This giant can randomly drop in brightness to 15 every few years. Since that hasn't occurred since sometime before August 2023, it could happen any day this fall (2025).

Logbook

Date & Time: August 7, 2024, 9:24 pm
Location: Kempt Shore, Nova Scotia, Canada, 45°N
Conditions: Partly cloudy
Sunset: 8:35 pm
Moonset: 10:05 pm
Moon Phase: Waxing crescent (12%)
Technical: 10-sec exposures, 10-min integration, line power, no filter, no post-processing

R CrB in Simbad Database

S Coronae Borealis

Discussion

On this date, the visual magnitude of this Mira long-period variable was approximately 7.8 according to AAVSO data. This is dimmer than nearby HD 136654 at 6.88 even though it appears brighter here. Note that these two stars are different in colour, orange (+1.30) versus yellow (+0.54), respectively. S CrB has a period of 360 days and a visual magnitude range of about 7 to 13.

Logbook

Date & Time: August 11, 2024, 10:46 pm
Location: Kempt Shore, Nova Scotia, Canada, 45°N
Conditions: Clear
Sunset: 8:27 pm
Moonset: 11:38 pm
Moon Phase: First quarter (54%)
Technical: 10-sec exposures, 10-min integration, line power, no filter, no post-processing

S CrB in Simbad Database

Corona Borealis 'Fab Four' Variables

Variables R, S, T & U Coronae Borealis

R Coronae Borealis

Discussion

Logbook

S Coronae Borealis

Discussion

Logbook

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