Palomar 13, dim globular cluster in Pegasus:
Was looking to revisit NGC 7479 for more details when I spotted Pal 13 on the chart to the northeast. I’m pretty sure I’d seen Pal 2 a couple years ago, but I think my sketch shows that I was getting some haze from increasing humidity, so not a clean observation. Hard to know where the GC was in all that. So time for another go at one of these dim objects.
Palomar 13 follows a highly eccentric orbit with a period of 1-2 billion years. Its last close approach to the galactic center was around 70 million years ago. It’s a very dispersed and loosely bound cluster, and this may be its last rodeo as the next interaction with the Milky Way’s tidal forces close in may finally pull it apart into a stellar stream. It’s a case study in globular cluster evolution. Pal 5 shows similar disruption but is not as far along that path as 13. Right now, Palomar 13 is around 84,000 ly from the sun and heading further out. It’s one of the smallest and dimmest of the Palomars.
Observing: The distinct close double star at the north-northeastern edge of the FOV was a nice marker for this very faint object. Near the center of the field was a faint but steady star on the northern threshold of the cluster’s glow. Increasing magnification enlarged the hazy smudge and sharpened the contrast, but no stars in the cluster were resolved, even at 762x. The globular could be made out at all magnifications – mostly AV at 145x – but the view was direct at 381x and best at 762x. Looking at photos of how sparsely this cluster is populated, it’s a wonder it can be seen at all.
Sketching: white pastel pencils and white pastel powder on Strathmore 184 lb. black multimedia paper. A 1/8” round brush created Pal 13’s glow.
Burbage’s Chain / VV 518 – interacting galaxies in Cetus:
This group of 4 or 5 galaxies, depending on the source you’re using, was discovered by Geoffry and Margaret Burbage in 1963. 3 of the group have estimated distances from 287 mly to 291 mly. The other one or two do not have distance numbers that I could find, and given their v mags of over 17.0 it’s more than likely sure that they’re much further out and uninvolved with the closer ones. At some point it was determined that those three are interacting and were added to the Vorontsov-Velyaminov catalogue as #518 in 1977. The 4th galaxy from the southern end of the chain is NGC 247B, although at 287 mly distant it has nothing to do with NGC 247, which is only 11 mly away.
I did see 247 – finally – but it was barely noticeable as a ghostly, elongated core. No halo or detail could be made out. Really wanted to see the “Eye of the Needle” but it was not to be. The galaxy has a surface brightness of 23.0 so that may account for the difficulty. It has an overall magnitude of 9.7, but it’s quite spread out. I’m guessing that seeing the smaller galaxies in the Chain despite that are due to them being more like point sources. They were seen best at 762x not only for their small size but just as much due to the darker and more contrasty view at that magnification.
Observing: The southernmost galaxy in the Chain – PGC 2796 – makes one point of a flattened triangle with two bright stars situated near the north end of NGC 247. From there the other 3 galaxies extend to the north and are of equal distance from one another in a nearly straight line – a dotted line, I guess.
The galaxies at each end, PGC 2796 at the south and NGC 247B at the north are faint but still much brighter than the two others between them. The PGC galaxy is the largest of the group and appeared as a slightly ovalled smudge with no detail at first. Over time it brightened toward the center. It was held in direct vision only twice and that momentarily. Two tiny threshold stars winked faintly at the southern and eastern rims of the halo. NGC 247B was located by way of its threshold star, which was a very tight double. The 2:1 oval stretched away to the south-southwest from the double. The center of the galaxy showed brightening but only in averted vision. It was glimpsed directly maybe 3 times.
The two galaxies in the middle – from south to north PGCs 2794 and 2798 – were both strictly averted vision objects at v mags 15.8 and 17.5 respectively and showing no detail or central brightening. I would say PGC 2974 was seen about 50% of the time and 2798 perhaps 30%. 2798 also had a near-threshold star at its southwest tip that helped to locate it and hold it when seeing would steady enough for the star to wink into view. That was my second v mag 17.5 for the night.
Happy to have seen these after several frustrations with big neighbor NGC 247. I was hoping for a composite view, but I’ll gladly take Burbage’s Chain and call it a win.
Sketching: white pastel pencils and white pastel powder on Strathmore 184 lb. black multimedia paper. All drawing was done with a 10/0 mini Filbert brush. Image was brightened so the middle two galaxies could be seen.
Thanks for looking! The last two will be brighter! I promise!
Happy Thanksgiving everyone!
-b
Edited by bphaneuf, 27 November 2024 - 12:12 AM.
