Cluster Roslund 4 + Nebula IC 4954/5

Object Description

Roslund 4 is a Trümpler II 3 m n open star cluster and about 6.3 million years old. Translated this means: a cluster with a medium number of member stars (m=medium), which stands out from the environment and shows a slight concentration (II) and has a rather uneven distribution of brightness among the cluster members (3="bright and faint stars in the cluster"). The "n" stands for a nebula involved in the star cluster.

Roslund 4 + IC 4954/5
Roslund 4 + IC 4954/5: Open cluster Roslund 4 with nebula IC 4954/5; 500 mm Cassegrain f=3625 mm f/7.2; SBIG STL11K; 240+50+50+50 min LRGB; Bernese Highlands; © 2015 Radek Chromik
Roslund 4 + IC 4954/5
Roslund 4 + IC 4954/5: Open cluster Roslund 4 with nebula IC 4954/5; Takahashi Mewlon 250 CR (f=2500 mm / f10), SBIG ST-8300; 11L x 1200 sec 1×1, 13R, 11G, 13B 2×2 x 600 sec; Bernese Highlands; © 2016 Bernhard Blank, Dragan Mihajlovic

IC 4954 and IC 4955 is an emission and reflection nebula about 330 arcseconds in size in which Roslund 4 is embedded. The nebula exhibits strong variations in brightness and therefore breaks up into three regions, labeled Ced 175a, Ced 175b, and Ced 175c. These go back to a work by Sven Cederblad at the Lund Observatory in Sweden (1946).

— 1998, Frank H. Leiter

Name  : Roslund 4
R.A.  : 20h 05m 00s
Dec.  : +29° 11' 59"
v Mag.: -
Diam. : 5'
No.*  : 30
Br.*  : <11.5

Further infos at CDS: Roslund 4

«Revised New General Catalogue and Index Catalogue», «Historically Corrected New General Catalogue», Dr. Wolfgang Steinicke, 2021 [277]
NameRADecTypeBmagVmagDimDreyer DescriptionIdentification
IC 4954 20 04 45.0+29 15 12RN3.00 × 3.0D neb *, iF, * 11 closeLBN 153, CED 175
IC 4955 20 04 53.0+29 11 24RN5.00 × 5.0Fine neb * 12LBN 153, CED 175

How to find Roslund 4?

Star cluster Roslund 4 is located in the constellation Vulpecula, which lies between Sagitta and Cygnus. This is favorable for observation in the months of May to October. Originating from 15 Vulpeculae, a 4.6 mag star, 50 arc minutes north-northeast is a 13 arc minute wide pair of 7th magnitude stars HD 190167 and southerly HD 190228 . Beyond the more northerly of the two stars, the connecting line 15 Vul - pair is extended by a further 50 arc minutes.

Chart Roslund 4
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

Because the Roslund Catalog star clusters were found spectroscopically, they are considered difficult for the visual observer. Despite the Trümpler classification mentioned above, this also applies to Roslund 4. However, the bright nebula IC 4954 simplifies the observation considerably.

200 mm aperture: Even in a moderate sky you can see the brightest parts of it from about 20 cm aperture and about a dozen stars can be found around this nebula. However, one can hardly speak of «detached».

Roslund 4, IC 4954, IC 4955
Roslund 4, IC 4954, IC 4955: Pencil drawing; 400 mm f/5 Newton, 9 mm eyepiece; © 14. 8. 1998 Frank H. Leiter

400 mm aperture: At 40 cm aperture, Roslund 4 remains an inconspicuous star cluster barely visible against the background; however, the number of faint (fainter 12th magnitude) stars increases significantly. For the visual observer, IC 4954 breaks up into three bright nebulae, which are clearly visible in the 9 mm eyepiece at 400 mm f/5. High magnification should be used for Ced 175c, the northernmost part, as it is small and very close to a 10th magnitude star. In the drawing, the faintest members of the open star cluster have been omitted and the brightest clouds of nebula IC 4954 are shown. No filter was used; the drawn region is about 5x7.5 arc minutes.

— 1998, Frank H. Leiter

References

149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; klima-luft.de/steinicke (2021-02-17)