2 Attachment(s)
Object of the Week March 3rd 2024 - Palomar 4
Palomar 4
Gcl 17
Globular Cluster
UMa
R.A. 11h29m16.0s
Dec. +28°58'24" (2000)
Magnitude: 14.20
Size: 1.3'
Concentration class XII
Palomar 4 was one of the 15 globular clusters that Abell listed in his 1955 paper
https://ui.adsabs.harvard.edu/abs/19....258A/abstract . Pal 4 had actually been
first found by Edwin Hubble in 1949 and then rediscovered by A.G. Wilson in 1955 which
is the observation that led to its inclusion in the Abell paper. It is one of the furthest known
globular clusters at a distance of perhaps 351000 light years and also one of the largest with a diameter
of 150 light years. However, despite its size the cluster has quite a low density of stars. This means it is
a large halo cluster only weakly bound to the Milky Way (note here of course with the LMC at 18000 lyrs
it is almost twice as far away as that). It is thought to be the second most distant of all the Milky Way’s
globular cluster collection.
Attachment 5367
It is suspected to be part of the High Energy group of globular clusters, which are globular clusters with
no common origin. The suggestion is that they arrived by themselves or as part of a merger
with a very small dwarf galaxy. On its first discovery it was thought to be a dwarf galaxy and
was given the name the Ursa Major Dwarf. The mass of Pal 4 is suspected to be about 57000
solar masses and its initial formation parameters are suggested to be different from most other
globular clusters. Its age is suggested to be about 11.2 billion years. Its metallicity is low but
not as low as many other clusters, which suggests it may be younger than some. Interestingly
Pal 4 contains no RR Lyr variables.
Attachment 5368
My only attempts at observing Pal 4 have been with my former 20” (50cm) and current 22” (55cm)
telescopes. On both attempts I found a faint patch which showed some signs of granulation. Other
attempts with the same equipment have not shown it at all which gives an idea of the clarity, or lack
of it of skies in the UK. In most cases my observing sites are at altitudes of less than 100m (300ft).
I know that it will have been seen with much smaller instruments by observers in the US and there
are suggestions that it should be visible in a 12” (30cm), I note that the late Barbara Wilson found
this from TSP and thought it was faint in a 20” F4.
