4 Attachment(s)
Object of the Week March 10, 2024 – Tiny and Super-Thin in Coma Berenices
NGC 4147, PGC 38669
Constellation: Coma Berenices
Type: Globular Cluster
RA: 12h 10m 06s
Dec: +18° 32’ 33”
Mag: 10.31
Size: 4.4'
UGC 7170, PGC 38748, MCG 3-31-55
Constellation: Coma Berenices
Type: Spiral Galaxy
RA: 12h 10m 37s
Dec: +18° 49’ 42”
Mag: 14.73
Size: 3.0’ x 0.2’
Two contrasting objects this week share the space in a 30” field of view in the constellation Coma Berenices. On the tiny side we visit a globular cluster, NGC 4147. On the super-thin side we visit the galaxy UGC 7170. You’ll find both somewhat challenging targets in all but the largest scopes.
Attachment 5376
©J.Shuder
NGC 4147 is the New General Catalogue identifier for a globular cluster of stars in the northern constellation of Coma Berenices. It was discovered by English astronomer William Herschel on March 14, 1784, who described it as "very bright, pretty large, gradually brighter in the middle". With an apparent visual magnitude of 10.7, it is located around 60,000 light years away from the Sun at a relatively high galactic latitude of 77.2°. This is a relatively small globular cluster, ranking 112th in luminosity among the Milky Way globular cluster population. It is considered an Oosterhoff type I cluster (OoI), despite having a relatively low metallicity. Indeed, it has the lowest metallicity of any OoI cluster known. There are 19 RR Lyrae variable star candidates and as many as 23 blue stragglers. A high proportion of the latter are concentrated near the dense core of the cluster, which is consistent with the idea that blue stragglers form through stellar mergers. The cluster lies some 70.4 ± 7.5 kly (21.6 ± 2.3 kpc) from the Galactic Center, and is relatively isolated from other globular clusters in the galaxy. The position of this cluster makes it a candidate for association with the Sagittarius tidal stream, and thus it may have been captured by the Milky Way after separation from the Sagittarius Dwarf Spheroidal Galaxy. A contour map of the cluster appears to show S-shaped tidal arms stretching to the north and south for several tidal radii. Such features are predicted for globular clusters that follow elliptical orbits and are near their apogalacticon (the point at which we are farthest from the center of the galaxy).
You will find that NGC 4147 should be visible in scopes 8” and larger; while 16” or more of aperture is necessary to begin resolving stars in this globular cluster. Kepple and Sanner in The Night Sky Observer’s Guide Volume 2 Spring & Summer share these observations of this object.
- 8”/10” scopes @ 100x: is a moderately faint, diffuse, unresolved glow containing a stellar nucleus
- 12”/14” scopes @125x: fairly bright, unresolved2.5 diameter sphere with a bright but tiny core; a few field stars stand out around an irregular periphery that seems slightly elongated NE-SW
Attachment 5377
With our edge-on view, UGC 7170 is a super-thin spiral galaxy type of Scd. UGC 7170 is classified as a member of the NGC 4155 group of galaxies, which includes NGC 4155, UGC 7170, and UGC 7133. What is really cool about this galaxy (and some other super-thin galaxies such as the “integral-sign galaxy" UGC 3697) is that it has an asymmetric warp that bends more strongly on its southern side than on it northern side. This warp is evident at both optical and 21 cm wavelengths. The similarities of the stellar and gaseous warps are consistent with a gravitational origin for the warp. The relatively small size of the halo core makes it possible to explain the warp as a gravitational bending mode of the galactic disk, if the dark halo is assumed to be slightly flattened.
My first observation of UGC 7170 (also my first super-thin galaxy) occurred on 23 March 2012. My notes from this observing run were sometimes cryptic or vague, either from extreme tiredness or raging excitement. In this particular case I had not recorded the eyepiece(s) that were used.
- Barbarella, (Jimi Lowrey’s) 48” f/4 scope: very super thin galaxy, well defined edges, clearly seen
Alvin Huey shares his observation of UGC 7170.
- 22” f/4 scope @ 185x, 255x, 306x and 383x: Considerably faint, thin, slightly brighter elongated center and very diffuse tips. Defined edges. PA = 15 and 1.8’ long. A 15.4 mag star lies 0.7’ SSE from the center.
Attachment 5379
Attachment 5378
Now it is your turn.
As always,
Give it a go and let us know!
Postscript: The Uppsala General Catalogue of Galaxies (UGC) is an essentially complete catalog of galaxies to a limiting diameter of 1.0 arcminute and/or to a limiting apparent magnitude of 14.5 on the blue prints of the Palomar Observatory Sky Survey (POSS). Coverage is limited to the sky north of declination -02.5 degrees. Galaxies smaller than 1.0 arcminute in diameter but brighter than 14.5 mag may be included from the Catalogue of Galaxies and of Clusters of Galaxies (CGCG, Zwicky et al. 1961-1968); all such galaxies in the CGCG are included in the UGC. The galaxies are numbered in order of their 1950.0 right ascension values. The catalog contains descriptions of the galaxies and their surrounding areas, plus conventional system classifications and position angles for flattened galaxies. Galaxy diameters on both the blue and red POSS prints are included and the classifications and descriptions are given in such a way as to provide as accurate an account as possible of the appearance of the galaxies on the prints.
