Object Of The Week January 28, 2024 - NGC 1931 "The Fly" and Parsamian 1

[Uwe Glahn]

NGC 1931
Typ: Open Cluster (OCL 441, Cr 68, St 9) + Emission Nebula (LBN 810, Sh 2-237)
RA: 05h 31m 26s
DEC: 34° 14' 42"
Size: 6'
Mag: 10.1 vmag

Parsamian 1
Typ: Reflection Nebula
RA: 05h 31h 04s
DEC: 34° 11' 00"
Size: 1.1'

Just 1° west of Messier 36, or just NE of the more famous IC 405/410 complex we could find a nice and bright nebula with a beautiful embedded open cluster, all named NGC 1931.

In 1793, Wilhelm Herschel first noticed the nebula and the cluster and described the object as "very bright, large, round, bright triple star in middle". The smaller reflection nebula Parsamian 1 only 4' south was first mentioned by the Armenian astronomer Elma Parsamian. Working at the Byurkan Astrophysical Observatory (BAO) she searches after cone shaped nebula and listed 23 objects.

From the astrophysical aspect, both objects belongs to the Auriga OB1 association. The view goes through the "Auriga window" trough the galactic anticenter and allows us a deep and distant look in the outer regions of our galaxy. Bhatt et al [1994BASI...22..291B] gives a distance of around 7000 ly. The SOS [10.1088/0004-6256/149/4/127] confirm this distance and give an age of 2 Myr to the young cluster. To sum up, our objects are located in the space between our local Orion Arm and the more distant Perseus Arm. It is flanked by the nearer IC 405 (1500 ly) and the more distant IC 410 (12000 ly).

But what makes NGC 1931 so interesting in the telescope. First the nebula, which is often called the "mini-Orion nebula". The relative bright centre of around 3' is already visible in smaller telescopes. Because of the combination of reflection and emission parts, the nebula is already visible without any filter. UHC filters don't bring a massive effect and let the nebula shining equally bright. The open cluster inside is dominated by a very small (10") equilateral triangle of stars of around 11mag. Larger telescopes could verify the cluster character by showing the much fainter stars of the cluster just south of the triangle. Parsamian 1 is much fainter but doable in mid size telescopes. His shape is running from E to SW, starting from an 11mag variable star.

picture Bernhard Hubl, 12", LRGB
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home (http://www.astrophoton.com/NGC1931.htm)

sketch Uwe Glahn, 27", 293x, NELM 7m0+, Seeing IV
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home (http://www.deepsky-visuell.de/Zeichnungen/NGC1931.htm)

GIVE IT A GO AND LET US KNOW

[Clear Skies]

An intriguing object, even more so because of what I know about it ever since our resident encyclopedia Scott H. recently delved deeper into the nature of the nebula NGC1931. But I will of course leave it to Scott to provide further comments on that..!

There are 6 observations in my log for NGC1931, the first one way back in 2006, the most recent one in January 2020 (https://clearskies.eu/astronomy/observing/sessions/sessions2020/20jan2020/) in northern France, using my 14" SCT @ 168x / 29', filtered and unfiltered:


17mm Nagler T4: A NE-SW elongated, small, quite bright, irregular glow. Slightly brighter to the NW of two mag. 12.5 stars aligned ENE to WSW with a mag. 14 star to their NW and another mag. 14 star slightly farther to the WSW (part of the double star HJ367). On the SSW edge of the glow is a mag. 14.5 star. Using AV it is clear that the western part of the nebula is the brightest.

The reflection nebula Parsamian 1 to the south is not visible.






17mm Nagler T4, Lumicon UHC: Using this filter the nebula is slightly larger and is clearly brightest west of the middle.






17mm Nagler T4, Lumicon OIII: Using this filter the nebula remains visible but is clearly much fainter than it is with use of the UHC filter.

As the observing notes reveal, Parsamian 1 stayed out of sight. I have yet to observe this object from a better (darker) location.

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The guide above - click here to download (https://clearskies.eu/csog/downloads/dsfootw2024#4) - on page 2 contains notes from various catalogs for both NGC1931 and Parsamian 1. Francis Pease's note (another tip off the hat to Scott for bringing these notes (https://ui.adsabs.harvard.edu/abs/1917ApJ....46...24P/abstract) to my attention) actually point directly to the nebula that was first cataloged by Elma Parsamian. If only Pease had taken the effort to provide it (and other objects) with a designation of his own, most of us would probably know him for much more than his M15 globular.

[Raul Leon]

Hi, here's my observation from 1/5/2019: Ngc 1931 open cluster with emission nebula in Auriga ; magnitude: 10.1 ; size: 4' x4' ; small but fairly bright; no filter used; I used a 4.5 Delos at 392x with my 14.5 StarStructure f/4.3
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[wvreeven]

I remember pointing my homemade 6" Newtonian telescope at NGC 1931 from my balcony in Utrecht back in the 90s and actually seeing nebulosity. My observations with my 20" telecope confirm the reflection/emission nature of the nebula. Using UHC and OIII filters actually worsens the view and my best view was without filters.