Roslund star cluster

The Roslund star clusters are a collection of 7 clusters in a 600 square degree large area in Vulpecula, Sagitta and Cygnus. They were discovered and spectroscopically examined on photographic plates with a limiting magnitude of 12m5. Because of the low limiting magnitude these clusters should be observable with 4 to 6 inch telescopes. Two (Ro 5 and Ro 6) are even objects for binoculars.
I observed all 7 clusters and made sketches of 5.
I wrote an article about this project which can be found in the German deep sky journal Interstellarum No. 24.


Roslund 1

right ascension: 19h45m   declination: +1731'   diameter: 3.0'   # of stars: 15   Trumpler classification: 41p-
Roslunds description:
The stars form a main sequence beginning with B9 V stars of the 10th magnitude and reaching spectral type A7 at the plate limit
My observation:
5m4, 100x, relative large, about 20 stars, in S more loose and brighter stars, in NE fainter stars and more concentrated. Stands out fairly well.
Roslund 1


Roslund 2

right ascension: 19h45m   declination: +2355'   diameter: 15.0'   # of stars: 20   Trumpler classification: 42p-
Roslunds description:
The brightest star (HD 186745-6 7th magnitude) is of type B8 Ia, followed by fainter stars of OB+ and OB down to OB- at the limit of the plate.
My observation:
5m4, 74x, nearly not dividable from the surrounding star field, 3 brighter stars in an right-angled triangle, the easternmost appears yellow. Westward is a small group with about 10 stars with different magnitudes.
Roslund 2


Roslund 3

right ascension: 19h58m   declination: +2028'   diameter: 5.0'   # of stars: 20   Trumpler classification: 41p-
Roslunds description:
The brightest star (10th magnitude) is of type B7 II-III, followed by middle and late B main sequence stars.
My observation:
5m4, 100x, fainter stars, the brightest are arranged in a parable shape. The vertex is to south, at the vertex I can detect a condensation. Inside the parable are some scattered stars. Weakly concentrated
Roslund 3


Roslund 4

right ascension: 20h05m   declination: +2912'   diameter: 6.0'   # of stars: 30   Trumpler classification: 23mn

Photo by Michael Breite

Roslunds description:
A cluster of OB stars of the 11-12th magnitude. Possibly connected with the two nebulae IC 4954-55
My observation:
5m6, 100x, does not stand out at all, fainter stars distributed in small groups. The reflection nebula IC 4954/55 is involved. Southern part is very faint, elongated NNW-SSE, around 6 stars with 2 doubles. The northern part is even fainter, appears as a faint halo around two stars.
Roslund 4


Roslund 5

right ascension: 20h10m   declination: +3346'   diameter: 50.0'   # of stars: 15   Trumpler classification: 42pn
Roslunds description:
The brightest stars (8th magnitude) are of type B9 V, followed by early A main sequence stars.
My observation:
5m7, 39x, very large, many bright stars, the brightest are situated in WSW, only few faint stars, very loose, no apparent concentration towards the middle, diameter about 1,3, at least 120 stars


Roslund 6

right ascension: 20h28m   declination: +3922'   diameter: 50.0'   # of stars: 30   Trumpler classification: 43mn
Roslunds description:
The stars form a main sequence beginning with Stars of type AO V of the 8th magnitude and reaching type FO at the plate limit. A K giant of the 7th magnitude, HD 195194, may be a member of the cluster.
My observation:
5m7, 50x, loose and large cluster, bright stars. Divided in western part with the brightest stars and the eastern part with fainter stars. In the middle is space lacking stars.


Roslund 7

right ascension: 20h52m   declination: +3755'   diameter: 35.0'   # of stars: ?   Trumpler classification: 42p
Roslunds description:
A somewhat doubtful cluster. The brightest stars (9th magnitude are two stars of type B9 II-III and one K giant. A few fainter late B and early A stars of class III are present.
My observation:
5m6, 74x, in comparison to the other Roslunds not that doubtful as described by Roslund, stands out fairly well, elongated
Roslund 7

Literature