Plettstone August 22-24, 2003

by Albert Highe


Friday

Temperatures hovered around the mid- to low- 60's during the night. Dew threatened, but never formed. The RH topped out at 90%, and began to drop after 2AM. No wind. Seeing and transparency were good to very good. Seeing softened a bit during the night.

Saturday

Temperatures hovered around the mid- 60's during the night. Dew was never an issue. The RH topped out at 78%. No wind. Seeing was very good and transparency was extraordinary!

Sunday

Temperatures hovered around 70F during the night. It was very dry. The RH never reached 50%. No wind. Yet, seeing and transparency were only average. However, I'm not complaining about a pleasant, average, dark night.

Scope17.5" f/4.5 ultralight
Eyepiecesmostly 7mm and 9mm Nagler T6.

Brief Summary and Selected Highlights

My primary focus was to observe galaxies in Abell 2197. In addition, I wanted to add to my list of observations in Abell 2199. A2197 and A2199 form a "Double Cluster" approximately 4-1/2 NW of M13 in Hercules. Member galaxies aren't as concentrated or as organized as in denser clusters such as A426 or A1656. One can think of this pair as the galactic analogue to the familiar "Double (star) Cluster" in Perseus.

Uranometria indicates member galaxies lie within partially overlapping circles with diameters approximately 1.5 and lying 1.5 apart. My target lists, generated by searching the NASA/IPAC Extragalactic Database (NED), include selected galaxies within 1 of each cluster center.
http://pw2.netcom.com/~ahighe/A2197.htm
http://pw2.netcom.com/~ahighe/a2199temp.htm
In addition to the apparent spatial overlap of the clusters, radial velocities of galaxies in the two clusters also overlap. Consequently, it is difficult to unambiguously assign membership to galaxies in the overlap region.

I was able to spend a total of 4-1/2 hours on A2197 and 1-1/2 hours on A2199 during the three nights. The excellent skies allowed me to observe 91 galaxies on the A2197 target list. 75 observations were new. In addition, I added 25 observations to the A2199 list, bringing the total to 78. Five objects appear on both lists.

Each target list contains 135-150 objects with photographic magnitudes as faint as 17.5. Based on the results so far, I hope to be able to observe at least 100 galaxies in each cluster.

Some Observing Details

"The Sky" planetarium databases mis-plot some galaxies in all the galaxy clusters I've studied, with the exception of Abell 1656. "The Sky" mis-plots approximately 10 galaxies in A2197 with deviations up to 2'. In A2199, over 30 galaxies are mis-plotted! In rich galaxy fields, such large deviations would cause one to incorrectly identify galaxies or miss them entirely. This is particularly true in A2199 where many of the errors occur where the concentration of galaxies is the highest. In contrast, the most recent version of Uranometria 2000 has fewer errors, but doesn't plot galaxies faint enough.

For example, "The Sky" indicates that MCG+7-34-51 and MCG+7-34-52 are a close pair of galaxies whose orientation relative to each other runs approximately north-south. In fact, the pair is located 2' north of the plotted location and their orientation is rotated 45. It is not possible to identify them correctly using "The Sky". Uranometria plots them correctly.

There is considerable confusing about the location of galaxy NGC 6141. "The Sky" apparently has at least two database entries for this object. One is 3.5' away from the correct location. The other is 22.5' away! Uranometria gives the correct location of NGC 6141. But there appears to be a misprint or second identification for it as well. In Chart A3, galaxy NGC 6147 is labeled as "6147,41". I assume this indicates that either the galaxy shares both ID's or there is a second galaxy so close to NGC 6147 that it doesn't show up as a separate symbol. Either interpretation is incorrect. There is, in fact, a faint galaxy less than 1' WSW of NGC 6147. It is MCG+7-34-22. I could hold it with averted vision 30% of the time.

Uranometria does have one clear misidentification in A2197. What it labels as MCG+7-34-92 is really CGCG224-56. MCG+7-34-92 actually is 4.25' SSW from the indicated location "The Sky" also plots MCG+7-34-92 incorrectly - showing a location approximately halfway between CGCG224-56 and its true location.

NGC 6138 is mis-plotted in "The Sky" by 2'. NGC 6138 appears to be plotted and labeled correctly in Uranometria. It wasn't too difficult to see. At 286X, I could hold it with averted vision 80% of the time. Other observations, as well as correct coordinates and other data, are listed in the tables provided on the above-mentioned web pages.

Just so you know, my data source is the NED, or in some cases, recent publications. I further confirm that all coordinates from the NED correspond to objects on Digitized Survey Images.

Conditions on Saturday were the best I've seen in at least a year. It's been a long time since I've experienced such outstanding transparency. Seeing was also very good, which permitted wonderful high power views of faint structure. For example, spiral structure was evident in M74, often regarded as one of the more challenging Messier targets for small scopes. Likewise, low surface brightness M33 showed obvious spiral arms filled with details - dust lanes, knots of stars, and puffs of nebulosity. I don't often use nebula filters on galaxies. However, a UHC filter helped to differentiate regions of nebulosity from knots of galactic star clouds. In particular, NGC 588, NGC 595, and NGC 604 (the brightest) are a few of the bright nebula visible in M33.

It was also an opportunity to check out some new equipment. Michelle had just completed her 15" f/5 and had it out for "first light". It is a beautiful scope with equally beautiful performance. At one point we were observing Stefan's Quintet in Pegasus with her 5mm Nagler T6 (380X). The Quintet was incredible - it just leapt out of the eyepiece. I can't remember ever seeing it so large, bright, and distinct. I could hold even the faintest component with averted vision 80% of the time. The galaxies in the close central pair (NGC 7318A &B) were like a pair of bright headlights. They were well separated, showing bright central cores within their fainter haloes.

It was also "first light" for some new modifications on Guillermo's 18" Obsession. He had just recently installed the Rx Design GOTO system. It performed surprisingly well, especially considering that this was essentially the first time Guillermo turned it on - a testimony to the product and Guillermo's careful installation.

This was an absolutely wonderful weekend. Thanks to all of you who shared conversation and views. My special thanks to Michelle for her continued generosity - Plettstone is a treasure.