IC 4756 | |
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Observation data ( J2000 epoch) | |
Right ascension | 18h 38m 31.2s [1] |
Declination | +05° 29′ 24″ [1] |
Distance | 1.3 kly (400 pc) |
Apparent magnitude (V) | 4.6 [1] |
Physical characteristics | |
Other designations | Cr 386, Mel 210 |
Associations | |
Constellation | Serpens |
IC 4756 is a large bright open cluster in the constellation Serpens. Known as Graff's Cluster, it is bright enough to be seen with the naked eye and considered a fine cluster for binoculars or small telescopes. [2]
IC 4756 is also known as the Tweedledee Cluster (paired with NGC 6633 as Tweedledum), also as the Secret Garden Cluster. [3]
Metallicity of IC 4756 is similar to the Sun, at -0.02±0.01 dex. [4]
There are some noteworthy stars in the cluster. HD 172365 [5] is a likely post- blue straggler in the IC 4756 that contains a large excess of lithium. [6] HD 172189, also in IC 4756, is an Algol variable eclipsing binary [7] with a 5.70 day period. The primary star in the system is also a Delta Scuti variable, undergoing multiple pulsation frequencies, which, combined with the eclipses, causes the system to vary by around a tenth of a magnitude. [8]
IC 4756 | |
---|---|
![]() | |
Observation data ( J2000 epoch) | |
Right ascension | 18h 38m 31.2s [1] |
Declination | +05° 29′ 24″ [1] |
Distance | 1.3 kly (400 pc) |
Apparent magnitude (V) | 4.6 [1] |
Physical characteristics | |
Other designations | Cr 386, Mel 210 |
Associations | |
Constellation | Serpens |
IC 4756 is a large bright open cluster in the constellation Serpens. Known as Graff's Cluster, it is bright enough to be seen with the naked eye and considered a fine cluster for binoculars or small telescopes. [2]
IC 4756 is also known as the Tweedledee Cluster (paired with NGC 6633 as Tweedledum), also as the Secret Garden Cluster. [3]
Metallicity of IC 4756 is similar to the Sun, at -0.02±0.01 dex. [4]
There are some noteworthy stars in the cluster. HD 172365 [5] is a likely post- blue straggler in the IC 4756 that contains a large excess of lithium. [6] HD 172189, also in IC 4756, is an Algol variable eclipsing binary [7] with a 5.70 day period. The primary star in the system is also a Delta Scuti variable, undergoing multiple pulsation frequencies, which, combined with the eclipses, causes the system to vary by around a tenth of a magnitude. [8]