NGC 474 -- Jan 5th APOD

[akarsh]

Jan 5th's Astronomy Picture of the Day shows shells around the galaxy NGC 474. Comparing the DSS to antennae galaxies, it looks like it will be more difficult to see these shells than to see the tidal tails of the Antenna galaxies (but DSS is not calibrated, so we can't be sure). I couldn't see the tidal tails of Antenna galaxies with a 25" under my usual observing conditions.

What does it take (i.e. what aperture, what kind of skies) to see these shells around NGC 474?

-- Akarsh

[Uwe Glahn]

I think it is more a question of transparency. I tried the shells with my 16" and 27". Both times with negative results, transparency was good with 16" and very good with 27". With 27" NGC 470 shows spiral structure but again, no sign of the shells.

[akarsh]

Thanks for the report Uwe! Seems like I must defer trying this till I have access to large aperture and west Texas.

Regards
Akarsh

[Dragan]

Here's the link for anyone who may be interested that hasn't seen it....

http://apod.nasa.gov/apod/ap140105.html

[Marko]

That is a highly complex pattern of stars and an amazing picture too. I should think the two fairly 'bright' segments offer the best promise in larger scope. What I am most 'shocked' about is this being a line of 3 I never visited this group. I won't see this intriguing pattern but I do hope to visit this group next new moon. Thanks for the info!

[akarsh]

Mark, what do you mean by a line of 3 in this context? Didn't get you.

Nice to meet you here too!

Regards
Akarsh

[akarsh]

It looks like the shells should be visible in Jimi's 48". I wonder if he has seen it.

[Ciel Extreme]

What I find striking is how symmetrical and “hard-edged” these shells seem to be. The brightening at the outer edges of the shells seem to imply lines of millions (billions?) of stars lined up and orbiting the central region of the galaxy. What else could account for the uniform brightness at the edges which extend for thousands and thousands of light years?

[akarsh]

Hi DSF

A bunch of us (Steve Gottlieb, Alan Agrawal, Bob Douglas, and me) observed this weekend with Jimi Lowrey's 48" 'Barbarella'. We observed this object on Saturday night.

The good news is that the 48" did show the shells. All of us saw them.

I found the object rather difficult. A dark patch in the direction of NGC 470 from the core, that is seen in the POSS I image, was felt on multiple occasions with averted vision. Two "inner" shell popped in and out with averted vision. I was able to clearly discern the outermost ripple seen in POSS I in the region directly away from NGC 470, by moving the core of NGC 474 out of the field-of-view, thereby isolating a curved bright region in a dark background.

I'm waiting to hear from Steve Gottlieb, for I'm sure his logs and report will be way more illuminating than my post.

Clear Skies!

Regards
Akarsh

[akarsh]

474_dss_ann.jpg

Here is an annotated image. Fragment '4' was the one that I was able to isolate and observe. '2' is the dark patch that I was talking about in the previous post, that Jimi pointed out to me. Region '1' and '3' were also felt with averted vision. There were instants of time when the entire ripple structure came alive.

Regards
Akarsh

[Steve Gottlieb]

Here are my completed notes on NGC 474. The first arc fragment mentioned in my notes is Akarsh's #4, the second arc is #3, and the third is probably #1. Actually, since we didn't describe to each other (in other words, influence) what segments we were were noticing, I'm pleased they match pretty closely! The distances mentioned were based on my eyepiece diagram. I've also added my notes on NGC 470.

NGC 474: The outer halo of NGC 474 was examined closely at 375x for evidence of the outer, concentric shells and circular streams that are visible on deep images. Immediately there was a strong sense of arcs from two more different shells. The easiest arc to confirm was the outermost on the eastern side, which curves south from a mag 13.3 star situated 3.3' NE of center. The arc passes through a mag 16.3 star and extends 30°-40°. A second outer arc on the northeast side is half the distance (~1.6') to the center. This arc has a stronger curvature and measures 50°-60°. Only a single outer arc (slightly more difficult to confirm) was noted on the southwest side, 2'-2.5' from center. My rough sketch shows it also curving ~50°-60°. Additional inner arcs or ripples were strongly sensed in the main halo of the galaxy, but too subtle and fleeting to pinpoint locations. The center is sharply concentrated with a very prominent 1' core, which is itself sharply concentrated to a small, blazing nucleus.

NGC 470: very bright, elongated 3:2 ~NNW-SSE, ~1.8'x1.2', the bright core contains an intense circular nucleus. Two spiral arms are visible with the brighter and better defined arm on the southwest side of the core. It extends ~40" SW-NE and is fairly narrow and straight. A second matching arm to the northeast of the core also extends SW-NE, but has a lower contrast. Neither arm clearly connects to the nucleus, so they appear more as bright arcs.

[akarsh]

Hi Steve

Thanks for sharing your observations -- this gives me more confidence in my own, because we agree on the segment coming out of the star! It's nice to see your very detailed logs. Thanks.

Regards
Akarsh