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Home | History | Science | Observations | LG Members
Observations of the Local Group of Galaxies
WLM
WLM was discovered in 1909 by Max Wolf on a photographic plate taken at Heidelberg with a 6" camera. He then arranged for the galaxy to be photographed with the 24" Waltz refractor . He published his discovery in the "Astronomische nachrichten". The publication was not widley known. A rediscovery occoured in 1926 by P.J.Mellotte. He noted the galaxy while inspecting the Franklin-Adams Chart plates. Mellotte remarked:"The appearence of this nebulae and of Barnards nebulae NGC 6822 is strikingly similar on the plates"
He also made note that the nebulae had been marked earlier by Knut Lundmark. The galaxy now derives it's name from the initials of its discoverers, Wolf, Lundmark and Mellotte.
WLM had been observed many times between 1926 and 1956 to locate Cepheid variables to determin the galaxies distance. All attempts failed to reveal any pulsating variable stars. Eventualy in 1956 Humason measured the heliocentric velocity to be -78 ±20 km/s-1. This velocity showed that WLM was a member of the Local Group and a nearby galaxy. Only Cehpeid variables with periods of 10 days or less are observed in WLM. This appears due to either a lack of stars between 7-11 solar masses or the metal abundences in the galaxy prevented these mass stars from entering the Cepheid variable phase.
The absolute magnitude of the brightest red and blue supergiant stars in WLM appears to be -7.0 with an apparent magintude of 17.6. The galaxies total absolute magnitude is -14.7.
WLM is located 4.2 million light years distant. This distance puts WLM on the edge of the Local group. Its closest neighbour is IC 1613 which is 1 million light years away, making WLM one of the most isolated galaxies in the group.
Recent observations have shown an extensive halo around WLM composed of old red stars. These halo stars have a comparable age to the older stars in the Milky Way, and are much older than the stars that make up the main body of the galaxy. With it's extended halo the galaxy WLM is 8000ly across, almost twice the size previously thought.
WLM has one Globular cluster (see "Maps" below) associated with it. Calculations of it's age put it at 14.8 billion years old. The colour magnitude Diagram of the cluster shows that it is is a normal old globular. The brightest stars in the cluster are -2.5 absolute magnitude. The R.A. and DEC for the cluster are 00hr 1min 49.9sec and -15° 28' 01". It was discovered by Humason in 1956.
Andrew Murrell observing from Australia using a 20" ƒ/5
WLM lies near the border of Cetus and Aquarius and is best found by starting at R aquarius and then moving 4.5 degrees due east. The galaxy is visible in scopes 10" and larger with medium to high magnifaction. Through the 20" the galaxy appears as an 8' by 3' haze and has an even surface brightness. No nucleus is visible. The edge of the galaxy was illdefined against the sky background. In scopes of 16" and larger the observer may be able to catch a glimps of WLM's globular cluster. It appears as a 16th magnitude star almost 3' west of the centre of the galaxy and about 1' south of a 14.5 magnitude star.
Steve Dillinger observing from Colorado USA using a 20" ƒ/3.95
WLM is a big elongated galaxy about 3 times longer than it's width. No central condensation was seen. The globular cluster was not seen.
The WLM Globular Cluster
The WLM globular is marked on the following finder chart as the star marked D. I have also included the photoelectric magnitedes for the marked stars. The brightest stars may just be within range of the large scopes 20" and larger.
Maps and Photos
ESO photo showing the halo surrounding the galaxy WLM. The dimensions on this photo is 8 x 11.5. This corresponds to a real diameter of 10,000 x 6,000 light years.
Photo courtesy of ESO.
Photo courtesy of Martin Germano.
