Object of the Week, March 27: Polaris - and the first degrees around

[Uwe Glahn]

Object of the Week, March 27: Polaris - and the first degrees around

Objects:
- Polaris (star)
- "Engagement Ring" (asterism)
- PGC 138464 (galaxy)
- NGC 3172 "Polarissima Borealis" (galaxy)
- NGC 188 (open cluster)
- "Polaris Flare" (galactic cirrus cloud)

Many of us starts our session with looking at Polaris - by checking the Seeing conditions, testing the collimation, adjust the finder telescope or setting the EQ-mount. But what is around?

Starting with Polaris itself, the star is in real a triple star system. The brightest component Aa is around 2vmag bright and part of the variable Cepheid family. The yellow supergiant with 5.4 solar masses is around 450 ly (Gaia) away. The brighter and further off component B with its 8.7vmag can easily resolved at 18.4" distance to Aa. The bright enough companion Ab with its 9.2vmag is only 0.17" away from Aa and so not reachable for amateur astronomy.

Looking at the finder telescope or searching eyepiece with low power or binoculars, we can find a nice asterism directly south of Polaris. The "Engagement Ring", "Polaris Ring" or simply "Diamond Ring" consists of around a dozen stars in a nearly one degree circle.

Going deeper, we can ask which is the nearest Deep Sky object around Polaris. To be more precise, Polaris is around 0.7° away from the North Celestial Pole, but let us assume Polaris as zero. With common telescopes, PGC 138464 could be the culprit. The nice spindle is around 5' north of Polaris. Infrared measuring listed the galaxy with 14mag. My own observation with 27-inch was positive. I could catch a somewhat elongated glow just with direct vision, when Polaris was out the field. I have no clue what minimum aperture is needed, but that is your turn to find out.

The more prominent neighbour galaxy is NGC 3172 which is also called "Polarissima Borealis". With its distance of around 1.5° east of Polaris it still don't need any tracking of the telescope, a funny side issue of this object. The nearly round and very diffuse galaxy looks boring at the first impression. But the direct neighbourhood with its more or less faint companion galaxies makes it more attractive. Brightest galaxy is MCG+15-01-010 only 1.6' SW. With 16bmag it needs a mid size telescope to see it. Stretched images shows a large 3.5'x3' ring around the galaxy. I could not see this ring but it could maybe a target for very large telescopes?

4° south we can find the very interesting open cluster NGC 188 Interesting and beautiful even for larger instruments. With an age at five to six billion years, the object counts to the most ancient of the known open clusters. It is worth a note that the cluster lies far above the plane of our galaxy because of the mentioned age and his drift apart. While the cluster is famous for its low surface brightness, I could catch it during very good transparency with my 8x30 binoculars. Larger instruments shows the many of the around 120 member stars of the cluster.

If all the described stuff is not fascinating enough, the region offers another very faint but spectacular object - the galactic cirrus called "Polaris Flare". Péter Csordás showed a 7° field around Polaris with its very faint nebula. Expert Mel Bartels sketched and described the nebula as faint among the huge number of observed ISM. I observed this region several times and always had less difficulties to see the nebula as for example the more famous ISM near M 81/82.

DSS red 30'x30'
Polaris_30r.jpg

sketch Engagement Ring and Polaris Flare: 4" binocular telescope, 14x, NELM 6m5+
PolarisFlare.jpg
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sketch NGC 3172: 27", 172x-419x, NELM 7m0+, Seeing III
NGC3172.jpg
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sketch NGC 188: 20x125 binocular, NELM 6m0+
NGC188.jpg
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Now it is your turn, give it a go and let us know.

[lamperti]

The Engagement Ring is often overlooked; great at low magnification; good for star parties too.
NGC-188 takes magnification well.
I need to try a couple of the others suggested.

[j.gardavsky]

Hello Uwe,

and thank you for reminding the area of skies around the Polaris!
It is really a very nice "all seasons" area of skies.

The Polaris Flare,
and in a narrower sense the nearly circular glow surrounding the Polaris is well visible through the binoculars 8x56 up to 15x85, with its condensations HSVMT 1, 9, 8, MW 1, and LBN 606. The visually observable Heitgausen (1993) condensations have required more magnification, like trough the 15x85 binoculars.

The Polaris Flare has a continuation into the molecular clouds of Cepheus, and on the other side of the skies into Camelopardalis,
a documentary sketch is here,

CHGC.jpg

Under my not really frequent Botle 3 skies, the central glow of the Polaris Flare is visible even with the unaided eyes.

Clear skies,
Jiri

[Steve Gottlieb]

Currently, NGC 3172 has a declination of close to +89.1° and is further from the pole than Polaris. But when discovered by John Herschel in 1831, the declination was +89.9° and it was less than 5' away. It nearly marked the celestial pole!

[Robin]

Hi everyone,

I gave some of these objects a try a few weeks ago with my 20" Dobsonian. Here are my notes and some sketches:

The engagement ring asterism
Way too large for the small field of view with 20". I observed it a few month ago, when I tested my 60 mm ED Apo visually. Unfortunately, I did not sketch it back then.


NGC 3172 and PGC 36268:

Both of these galaxies constitute a roughly equilateral triangle with a 12 mag star. PGC 3628 looks more diffuse. NGC 3172 has a non-stellar, slightly bright, center. 20", 419x.

NGC3172Robin.jpg


PGC 138464

First of all, it is really exciting that there is an observable galaxy that close to Polaris. I had not been aware of this galaxy before reading Uwe's post.
When observing with 20", the biggest challenge was keeping Polaris out of the field of view. I used a 5 mm DeLite eyepiece, yielding 461x magnification and 8' field of view. It constitutes a triangle with a few arc minutes edge lengths with two 14 mag stars. At averted vision, I could hold it intermittently and lost it several times. Faint, small, and diffuse. It was hard to find the averted vision sweet spot.
Strangely, it is listed with 11.2 bmag in the Glade 2.3 catalog according to Simbad:
http://vizier.cds.unistra.fr/viz-bin...2&recno=267292
Perhaps they included some stray light of Polaris when doing aperture photometry? Based on my visual observation and some experience with similarly faint galaxies, I would put it at roughly 16.0-16.5 bmag.

PGC138464Robin.jpg


Polaris Flare


Based on the photo taken by Péter Csordás I tried to observe several fragments of Polaris Flare. By the way, the photographer uploaded his photo on astrobin, where a helpful coordinate overlay can be seen: https://www.astrobin.com/hhctar/D/?nc=AnonymousUser

With 20" f/4, ParaCorr II, and 31 mm Nagler eyepiece (yielding 74x magnification, 6.7 mm exit pupil, and 1.1° field of view) I was unable to see the large-scale structure that Uwe saw with 4". But I was successful with two patches of this IFN:

Region around 01h35m +87°45', size: 60' x 20-30': Faint and large-area glow, roughly shaped like Lake Constance (for those who are familiar with European geography). So it was roughly shaped like the letter "Y" and I was able to see that the region of sky between the two tips of the Y was slightly fainter than the Y itself.

Region around 23h40m +86°55', size: 60' x 30': Faint and large-area glow. The edge at larger right ascension was a little easier than other parts of it.

I tried both of these regions with a BlueCCD filter, as recommended by Jiri in several threads on different forums, but in this case the BlueCCD filter did not help me. A few months ago I observed LBN 698 with the same instrument and with such a filter, and figured out that it increased contrast. I cannot really explain this difference, but it might be related to sky conditions and the type of light pollution filtered out by the filter. I observed Polaris Flare at a different location with better sky conditions North of zenith. In this case, the naked-eye limiting magnitude at zenith was better than 6.5 mag.

I also tried the following five regions, but all of those were negative observations:

03h34m +88°34', size: 20' x 65'

03h45m +87°20', size: 60' x 30'

22h00m +88°15', size: 40' x 10': Faint glow suspected, but not for sure. I'd rate it as a negative observation.

21h30m +80°55', size: 15' x 5'

15h45m +83°40', size: 60' x 60' with a dark lane in its center on the photo


To summarize, it is possible to see some fragments of IFN with 20" f/4 given sufficiently dark skies and sufficient contrast sensitivity of an observer. When trying to observe these IFN patches, I think one should not expect sharp nebulae, but one should rather start by examining the general sky brightness in the eyepiece and then move the telescope back and forth by several fields of view in different directions. After a while, some very subtle variations of sky brightness become apparent. I observed these two patches of Polaris Flare on two different nights, spending 30-45 minutes on them each time.

PolarisFlare1Robin.jpg

PolarisFlare2Robin.jpg

Clear skies

Robin