Object Of The Week October 20, 2024 - Arp 15

NGC 7393, Arp 15, MCG-01-58-002, VV 68, LEDA 69874

SB(rs)c pec galaxy

Aquarius

RA: 22 51 38.1
DEC: ?05 33 26

Mag: 13.4 (B)

Diam: 1.9' x 0.9' (V)


My apologies for this very short article.

NGC 7393 is a barred spiral galaxy with a ring structure. It was discovered by William Herschel on October 5, 1785. Halton Arp cataloged it as number 15, remarking "Feature appears to be a ruptured or obscured ring. Member of group." I haven't been able to find out what group Arp was referring to. If anyone knows then please let us know here.

As for the ruptured or obscured ring, that is obvious from the DSS image and even more from this HST image.

Attachment 5560
Arp 15 (NGC 7393) with Hubble Instrument: ACS Filter: F606W proposal id: 15446 proposal PI: Julianne Dalcanton proposal link: https://archive.stsci.edu/proposal_s...n=hst&id=15446. Source: Wikipedia.

There are several galaxies in the immediate field around NGC 7393, all of which seem to be background objects. I, therefore, don't think that the ruptured ring is a gravitational effect.

I have observed this galaxy once with my 20" from a not great location and failed to see traces of the ring so I'll need to visit it again. I am curious to know what the minimum aperture is to see said ring.


As always,

"Give it a go and let us know!
Good luck and great viewing!"

30 years ago with a 18" at 97 & 332x:"Could just be seen at 97x. It was a faint even glow, slightly elongated galaxy. Diffuse."

Hi All,

I observed this galaxy a year ago on la Palma, herewith my observation note and sketch:

16" Sumerian Alkaid; Pentax XW 7mm at 259x
Immediately seen as quite large, bright and oval shaped. Somewhat brighter towards the core. A part of the elliptical ring is suspected on the N side, but the detached segment is definitely not seen.

Attachment 5561

The structure appeared more complex to me than a ring through Lowrey's 48-inch at 488x on 11/5/21:

Overall, bright, fairly large with a highly irregular appearance. The outer halo extended nearly 3:1 E-W, ~1.8'x0.6'. The brightest region is a prominent oval N-S situated just west of the geometric center. The core was seen as a small, slightly brighter patch attached on its east side. An elongated low surface brightness and diffuse halo extended ~0.5' to the west.

Two parallel arms or "tails", roughly 0.5' in length, extended due east from the brightest region. The tails bent towards each other on the east end, but didn't connect. The southern arm appeared longer due to a dim extension to the east and the northern arm was patchy. The arms were clearly separated by a darker void.

I got an old observation and sketch with my 16-inch under very good skies in the High Alps back in 2005. I definitely had to revisit it with larger aperture.

sketch: 16", 360x, NELM 7m0+
Attachment 5568
home

With Jimi Lowrey's 48" in 2016 October:

Beautiful object. A bright core lies inside an elongated ring. The hole (gap between core and ring) on the eastern side is larger and more prominent than the hole on the western side. The finger-like outward projection on the eastern side is hard to see. The region to the west of the galaxy feels brighter, in particular showing some condensation at a particular point (also seen on the DSS image). The details seemed more tractable at 488x than at 610x, although that could have been due to the seeing.

Through my 18-inch in 2020 at 345×:

"Occasionally got hints of a stellar core, the "hole", and prong-like shape flanking the hole. Needs better seeing."

I can contribute another 16" drawing (220x-294x) from 2015, Hungary. As I can see all of our 16" drawings are very similar.
Attachment 5573Attachment 5574