Open Cluster Roslund 3

Object Description

Roslund 3
Roslund 3: 30' x 30' Section of the ESO Digitized Sky Survey [195]

The Roslund catalog is a small, little-known collection of just 7 items. The objects recorded in it were not discovered after visual observation but were found during spectroscopic measurements. Therefore, they are considered to be hardly observed and are usually difficult to spot in the swarm of stars due to their location near the Milky Way. Roslund 3 is an Open Cluster with Trümpler classification IV 1 p. Translated, this means: a cluster with few members (p=poor), which hardly stands out from the surroundings (IV) and has a fairly even distribution of brightness among the cluster members.

Name  : Roslund 3
R.A.  : 19h 58m 42s
Dec.  : +20° 28' 57"
Mag.  : 10m
Diam. : 5'
No.*  : only a few
Br.*  : ca. 10m

How to find Roslund 3?

Open star cluster Roslund 3 lies about 1 degree north of γ Sagittae, the second star from the arrow's tip of constellation Sagitta. Together with this and the 5m1 star η Sagittae, the small cluster forms a north-pointing right triangle. The constellation can best be observed in the months of May to October.

Chart Roslund 3
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]
Roslund 3
Roslund 3: Übersichtskarte der Einzelsterne von D. G. Turner [138]

Visual Observation

200 mm aperture: At medium magnification one first sees a chain of stars around the tenth magnitude coming from the north, which bends to the east and then spirals in. At the northern beginning of this chain there is a small line of stars in a north-easterly direction. This can be seen as the snail's tentacles, the north-south chain as the body, and the spirals as the snail's shell - hence the name: Snail-Cluster, a north-creeping snail. The actual cluster members are only in the snail shell. The two chains mentioned happen to be there and don't belong to Roslund 3.

The description «poor» by Trümpler matches very good and even with a larger aperture not many stars follow. The dominant pentagon remains with a few fainter stars.

Frank H. Leiter

References

138WEBDA, Sternwarte Genf; obswww.unige.ch/webda
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
195ESO Online Digitized Sky Survey; archive.eso.org/dss/dss (2020-12-27)