Object of the Week, January 31 2021 - NGC 1491, the "Fossil Footprint Nebula"

[Uwe Glahn]

Name: NGC 1491 = Sh 2-206 = LBN 705
RA: 04 31 16
Dec: +51 18 34
Constellation: Perseus
Size: ~ 5'x4' (central bubble), ~ 25'x25' (outer regions LBN 705)

High in the sky between the stars Capella and Mirfak we found the nebula complex of NGC 1491. Discovered by William Herschel at 1790 indicates, that this nebula was and is a target for us visual observer.

Deep photographs show a large, around 25'x25' nebula, mainly shining in red but also blue colors. Looking somewhat deeper shows an open structure around the blue (O5) 11mag star BD +50 886 which ionized with its strong stellar winds mainly the center of the nebula [1]. This process creates an interesting combination of an "elephant's trunk" like ionization front 1.1' west and a thin shock front only 0.2' west of the star.

For us observer the nebula is in fact small but bright and especially the center is shining in the [OIII] band [2]. So, a 4-inch telescope could show the nebula at all. The first structures within the ionization front is in reach of an 14-inch telescope or maybe smaller. Unfortunately I could not pick up the shock front with my 27-inch, but maybe someone else was more successful?

[1] http://articles.adsabs.harvard.edu/pdf/1976A%26A....48...63D
[2] https://www.astrobin.com/xpj9do/0/

whole field ~70'x40'
Peter Maasewerd, 5", Ha/[OIII]/R-G-B [2]
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center field ~25'x20'
Peter Maasewerd, 5", Ha/[OIII]/R-G-B [2]
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DSS blue, 10'x10'
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sketch: 27", 293x, [OIII], NELM 7m0+, Seeing IV
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home (http://www.deepsky-visuell.de/Zeichnungen/NGC1491.htm)


As always,

"Give it a go, let us know"!

[Ivan Maly]

This is a very impressive object. I have this observation from December 2012, with my old 16" from a Bortle 2-3 site.

At 45x it is a round diffuse patch, on the E side of which is a star. 225x does not change the dimensions of the nebulosity appreciably. The star is now on its E edge and the W side is brightest. The bright part extends around the star to the N but there is little nebulosity to the S. There seem to be some threshold stars involved in the brightest patch. OIII filter improves the contrast with the background dramatically but does not alter the shape or extent of the nebulosity. However, the W and NW edge now appears relatively sharp. The nebulosity concentrates toward this edge, the center of whose curvature roughly coincides with the star.

[wvreeven]

I have an observation done with my old, home made 6" Newtonian telescope from 2005 in the Netherlands:

Visible at 25x, 51x and 105x without a filter. Visibility gets a bit better using an OIII filter. At 105x about 15' wide and round.

[oliva]

Hi Uwe,

I observed the nebula from Roque de los Muchachos at 2300 asl in January 2016 with my 14 inch Dobson and saw this:

Directly next to a star, a fairly bright nebula appears at a small distance. Is already directly visible when looking for it. Best observed at 114x and OIII. Semicircular shape or more precisely with e.g. slight bars that are slightly skewed. In an extension, another faint, oval part of the nebula is visible. At the longer and lighter bar, a flag goes off towards the central star. Can be enlarged relatively high up to 168x.

4190

Oliver

[Raul Leon]

Hi here's my observation from 10/17/2009: Ngc 1491 bright nebula in Perseus ; magnitude: 11.3 ; size: 5'x4' ; fan-shaped nebulosity, brighter along the Northern edge used Lumicon OIII filter, which gave it more contrast. Two stars are superimposed in the nebulosity. I used a
10mm Radian at 158x with my 14.5 Starstructure Dob f/4.3 4191

[Clear Skies]

This nebula reveals quite some detail and provides for a pleasant observation. Of the three observations I logged the most recent one was in November 2018 from the French Ardennes. It must have made quite an impression as I rated it 8/10. In my 14" SCT:

Quite a bright, NNE-SSW elongated, clearly irregular glow with more faint nebulosity to the ENE. Using AV the brightest part, on the SW side, is subtly wider towards the SE. Using AV the brightest western part clearly shows irregular structure. ESE of the brighter part is a mag. 10.5 star.


With a UHC filter: Using this filter the nebula is much clearer, as is the irregular structure. The brighter western part has a slightly curved shape with the bulge towards the WNW. The fainter NE part of the nebula is only visible with AV and slightly fans out towards the NNE.


OIII filter: Using this filter the brighter part of the nebula remains clearly visible but the effect is not as good as that of the UHC filter.


One my website, I have added a new page for Deep Sky Forum's Objects of the Week (https://clearskies.eu/csog/downloads/dsfootw/): the objects for this year in CSOG format. When I publish CSOG 2.4, I will add observing guides for all OOTW's since 2012.

[akarsh]

Turned out I have 3 observation logs on NGC 1491 even though I don't recognize the object in my memory.

Observation 1: With John Tatarchuk's 25" telescope on Nov 27, 2011 presumably from near Pontotoc, TX. You can tell logging or sketching was not something I practiced:
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Observation 2: With my 18" on Nov 28, 2013 while battling frost in Atoka, OK (Texas Astronomical Society's observing site):
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Observation 3: With my 18" on Dec 11, 2015 from Ft. Griffin State Historic Site west of Fort Worth, TX [this site was not very dark and one could see a huge light-dome from the DFW metroplex]:
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