[LVAS] December Observer's Challenge - NGC-474 Galaxy Group
roger ivester
drivester at hotmail.com
Sat Jan 2 10:56:49 PST 2010
Fred,
First read, looks great...
roger
The moon and stars to govern the night..... Psalm 136:9
From: rayworth1969 at hotmail.com
To: lvas at lvlug.org
Date: Sat, 2 Jan 2010 11:57:03 -0600
Subject: [LVAS] December Observer's Challenge - NGC-474 Galaxy Group
MONTHLY OBSERVER’S CHALLENGE
Las Vegas Astronomical Society
Compiled by:
Roger Ivester, Boiling Springs, North Carolina
&
Fred Rayworth, Las Vegas, Nevada
With special assistance from:
Rob Lambert, Las Vegas, Nevada
December 2009
NGC-474 Galaxy Cluster
Introduction
The purpose of the observer’s challenge is to encourage the pursuit of visual observing. It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, we will be happy to include them in our monthly summary. Observing is not only a pleasure, but an art. With the main focus of amateur astronomy on astrophotography, many times people tend to forget how it was in the days before cameras, clock drives, and GOTO. Astronomy depended on what was seen through the eyepiece. Not only did it satisfy an innate curiosity, but it allowed the first astronomers to discover the beauty and the wonderment of the night sky.
Before photography, all observations depended on what the astronomer saw in the eyepiece, and how they recorded their observations. This was done through notes and drawings and that is the tradition we are stressing in the observers challenge. By combining our visual observations with our drawings, and sometimes, astrophotography (from those with the equipment and talent to do so), we get a unique understanding of what it is like to look through an eyepiece, and to see what is really there. The hope is that you will read through these notes and become inspired to take more time at the eyepiece studying each object, and looking for those subtle details that you might never have noticed before. Each new discovery increases one’s appreciation of the skies above us. It is our firm belief that careful observing can improve your visual acuity to a much higher level that just might allow you to add inches to your telescope. Please consider this at your next observing session, as you can learn to make details jump out. It is also a thrill to point out details a new observer wouldn’t even know to look for in that very faint galaxy, star cluster, nebula, or planet.
NGC-474 Galaxy Cluster
The NGC-474 galaxy cluster (or group) consists of three relatively bright galaxies. They are: NGC-467 (mag. 12.9), NGC-470 (mag. 12.5), and NGC-474 (mag. 12.4). This is a fascinating little trio of galaxies, especially because the catalogued largest one, NGC-474, does not visually appear as large as nearby NGC-470. The reason is that NGC-474 has an outer halo that is extremely faint. It has been seen in 18” instruments and larger as just a faint brightening of the black background. In 1994, Roger Ivester wrote a paper concerning the apparent missing matter in NGC-474. The text of that report is quoted as follows:
The NGC 470-474 Controversy – Missing Matter Revealed by Roger Ivester
My observations on Thursday, December 1, 1994, included three spiral galaxies in Pisces, NGC-467, NGC-470, and NGC-474, each separated by only a few minutes of arc. It became apparent immediately that NGC-470 was the largest and most easily seen of the group, but when I referred to the NGC 2000.0 Catalogue, it listed NGC-474 as being over twice as large as either NGC-470 or NGC-467. At this point, I concluded that NGC-474 must have a halo that could not be seen visually, or at least not from my back yard. The next day I located a photo of this group, but it did not show a faint outer arm, nor was any halo apparent. The view appeared very similar to what I had seen through my telescope. I decided that another observation was needed, and made a note in my log to “view at next session.”
On Monday, December 16, I went to a dark site in the South Mountains about 30 minutes north of my home in Boiling Springs, North Carolina. This would prove to be the perfect site for another observation, notes and a sketch of these three galaxies. I saw NGC-474 as round, diffuse and with a brighter nucleus. NGC-470, appeared elongated, diffuse, and twice as large as NGC-474. Next, NGC-467 appeared round, faint halo, with a brighter nucleus, and situated a few minutes N of an 8th magnitude star. It was almost the same apparent size as NGC-474. All three galaxies were very easy to locate, relatively bright, and showed excellent contrast. Again I was bothered concerning the size listing of NGC-474. My sources indicated that it was the largest of these galaxies, but NGC-470 was clearly the largest in my telescope and in a photo that I had looked at earlier. Could there be an error in the 7.9” size I read from the NGC 2000 Catalogue, an error which was perpetuated by the other sources? A table of diameters (in arc minutes) from different sources is listed below.
Source NGC-470 NGC-474
NGC 2000.0 3.0 7.9
Burnham’s Celestial Handbook 1.7 x 1.1 0.4 x 0.4
T. Lorenzin’s 1000+ 3.2 8
The Observer’s Guide, Nov/Dec 1991 3.0 x 2.0 7.9 x 7.2
Deep Sky Field Guide to Uranometria 2000.0 3.0 x 1.8 10.0 x 9.2
Nearby Galaxies Catalog 3.2 11.6
D. Eicher’s Deep Sky Observing w/Small Telescopes 1.7 x 1.1 0.4 x 0.4
Astronomy Magazine, January 1993 3.0 x 2.0 7.9 x 7.2
Luginbuhl & Skiff, Observing Handbook & Catalog 3.0 x 2.0 7.9 x 7.2
I expressed my concern to Tom English, Professor of Astronomy and Physics at Gardner-Webb University, who promptly gathered all available reference material on NGC 474 from his extensive astronomy library at the University. Tom called me on Saturday afternoon, January 7, and invited me to research the data. While I was busy checking each source, Tom was checking the Sky & Telescope Cumulative index to locate past issues with information on NGC-474. Tom left the lab and returned with a March 1988 issue of Sky & Telescope with a research note on the galaxy and an accompanying photo. My quest was about to end. On page 244, there was the photo that would resolve the problem. It showed both NGC-470 and NGC-474 overexposed, with a very faint halo surrounding the latter. A quick measurement of each galaxy in the photo showed that, with the halo considered, NGC-474 is indeed about 2 ½ times the size of NGC-470, consistent with the NGC 2000 listings.
A closer look at the list of sources gives an indication that this pair has been a source of confusion to many observers. It also reveals that cataloged information tends to propagate from one publication to the next. We all use various catalogs for background information (such as size and magnitude) as we set our observing agendas, and too often we do not follow up on this information by making actual measurements ourselves. Note that five of the sources listed have the same 3.0 and 7.9 arc minute sizes for NGC-470 and NGC-474, respectively. Burnham and Eicher list identical measurements in their guides as well, but with NGC-470 attributed as the larger galaxy, just as I had noted. In their observing notes, Luginbuhl and Skiff indicate that NGC-470 appears closer to 2’ x 1’, with NGC-474 somewhat smaller. In the Nov/Dec issue of The Observer’s Guide, I saw my frustration mirrored in the statement that NGC-474 “is much smaller than its catalog size. Apparently, its outer halo is so faint that it is not visible.”
Roger Ivester 1994
Below are the actual entries from Burnham and Skiff & Luginbuhl.
Burnham’s Celestial Handbook: Robert Burnham, Jr.
NGC-470: “Pretty bright, pretty large, little elongated. Pair with NGC-474.”
NGC-474: “Pretty bright, small, round, suddenly much brighter middle.”
Observing Handbook and Catalogue Of Deep-Sky Objects: Skiff and Luginbuhl.
NGC-467: “This galaxy is moderately faint in 25cm (10”). The halo is circular about 1’ across, and brightens to a core that shows a few stellarings at 200X. A mag. 13.5 star is visible just over 2’ SW; another slightly fainter star lies closer to the W.”
NGC-470: “This galaxy appears as a round, diffuse blob in 25cm, about 1.5’ diameter. The core is brighter and occasionally shows a faint stellaring in its center. Two faint stars separated by about 40” lie 2.2’ S, and another star is visible 1.7’ N. In 30cm (12”), the smoothly textured halo is elongated in pa 150º, extending to about 2’ X 1’ and showing a moderate central concentration. A third faint star is visible 2’ S.”
NGC-474: “In 25cm this galaxy appears slightly brighter but a little smaller than NGC-470. It is diffuse and has a very small nucleus. With 30cm, it has a bright nonstellar nucleus, and a low surface brightness halo extending to 1.2’ diameter.”
Observations/Drawings/Photos
Roger Ivester (see Rogers Pictures 003.jpg): Observer from North Carolina
The NGC-474 compact galaxy cluster located in the constellation of Pisces is a most interesting group consisting of galaxies NGC-467, NGC-470 and NGC-474. All three galaxies will fit easily within a 1/2° field of view. They are positioned mostly E to SW.
The descriptions and sketch were all made using a 10-inch reflector with 114X with a 0.58° field of view (see Rogers NGC-470 Galaxy Cluster.jpg).
The most western galaxy is NGC-467 which appears round with greater overall concentration as compared to the other galaxies. It is situated about 4 minutes west of an 8th mag. star. The outer halo is very faint and round with a brighter middle.
NGC-470 is located between NGC-467 and NGC-474. The texture is very even and smooth with a very subtle brightening in the central region. It appears elongated with a N-S orientation. This galaxy clearly appears as the largest of the group.
NGC-474 is visually the smallest member of the cluster. The halo is very faint and diffuse with a very bright, almost stellar nucleus. The galaxy appears mostly round.
Fred Rayworth (see Fred At Sawmill.jpg): Observer from Nevada
He had the opportunity to check this galaxy trio out for the second time on 21 November, 2009. Sky conditions were not ideal, but improved as the night wore on. With a quarter moon in the sky, he was surprised at how much it lit up the sky on what he thought was a clear night. However, as the moon sank into the Las Vegas skyglow, the sky became darker and darker and he had no trouble finding this fine group.
Using his Meade 16” f/4.5 LightBridge along with a 26mm Orion Q-70 (70X) and a Hyperion 17mm (108X), he made the following observations:
NGC-474: Supposed to be the largest of the trio of NGC-467 and NGC-470, however it didn't look that way. NGC-474 was the second brightest but looked smaller than NGC-470. May have been a halo beyond the core, but couldn't tell for sure.
NGC-470: Nice almost round glow, with the hint of an oval shape. Brightest of the trio with NGC-467 and NGC-474. At 108X, it was still a soft almost round glow. No details.
NGC-467: Soft round glow with almost a stellar core. Easy to see, but no detail, even at 108X (see Freds NGC-474 Group.jpg).
Rob Lambert: Observer from Nevada
This month's objects were even a greater challenge detail-wise for him than was last month’s NGC-891, even with the Mallincam. All three of the galaxies were small and dim compared to some of the objects he’s recently observed. They are part of the ARP-227 galaxy group.
Start with a general overview of all three galaxies as seen in the image below (see Robs Pisces Trio.jpg). North is toward the bottom center of the image with west being to the right. Magnification is approximately 32X. At first look, all three galaxies aren't much more than fuzzy stars, with NGC-470 appearing to be the largest of the three. A closer look at the cores of the three galaxies leads one to believe something different than what is initially seen, especially for NGC-474. NGC-474 has a much brighter, larger, and more easily defined core, hinting that it is much larger than either of the other two. Regarding their shape, the halos of NGC-467 (see Robs NGC-467.jpg) and NGC-474 appear to be round while NGC-470 is elongated from northwest to southeast. If one looks closely at NGC-474; however, what appears to be faint, disconnected spiral arms on the NE and SW sides of the galaxy are seen. These disjointed limbs are what identify NGC-474 a shell galaxy (see Robs NGC-474-470.jpg).
Dr. James Dire (see James Dire.jpg) Observer from North Carolina
Attached is a picture of the galaxy group containing NGC-467, NGC-470 and NGC-474 (see Jims NGC-470-474 Legend.jpg). The picture is a combination of 22 ten-minute exposures with his 190mm (7.5”) Mak-Newt at f/5.3 using his SBIG ST-2000XCM CCD camera. In addition to these three galaxies, he has labeled the brightest star in the field of view and 5 nearby, faint 16-17th magnitude galaxies.
The aperture was too small and the sky at his location too bright to do NG- 467, NGC-470 and NGC-474 any justice. Plus, the seeing would need to be sub-arcsecond to pick up the detail needed in these galaxies. NGC-467 and NGC-470 do not have much spiral structure but both have extensive halos, which he did not pick up.
References
(Submitted by Fred Rayworth)
Burnham’s Celestial Handbook: Robert Burnham, Jr.
Observing Handbook and Catalogue Of Deep-Sky Objects: Skiff and Luginbuhl
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