Object of the Week July 13, 2014 - Sharpless 157 in Cassiopeia/Cepheus

[reiner]

Sh2-157
Cassiopeia/Cepheus

RA 23 16 04.08
Dec +60 02 06.0

Emission Nebula

Sharpless 157 is only a small star hop away from the much better known objects M52 (an open cluster) or the Bubble Nebula, NGC 7635. Its Sharpless designation is for many observers synonym with dimness and being at the edge of visibility, if at all. Sharpless 157 is none of it. If you have an OIII filter. Sh 157 was my "first contact" with the Sharpless catalog. It got started by a pioneering image by Richard Crisp in 2004, which was at that time one of the first narrowband composites.

http://www.narrowbandimaging.com/sh2_157_fsq_st10_s2hao3_page.htm

Sh-157 is excited by the Wolf-Rayet star WR 157, though it appears to be not a classical wind-blown WR bubble. With OIII filter, the main filament forms a large and visually obvious milky streak that is surrounded by other fainter filaments, which are fun to explore.

http://www.reinervogel.net/exotic/images/Sharpless 157.jpg
DSS Image of Sh-157

The brightest OIII part of the nebula is the extension that trails from the central part for about one degree towards north. In the low power eyepiece equipped with OIII filter, this long feature is immediately visible upon field sweeping (as it is very large) as a long milky bar that usually requires moving your telescope to scan its entire length. Distinct markers are the fan shaped open cluster Markarian 50 to the west and NGC 7538, a very bright and distinct small nebula about one degree north of it.

Just east of this main part is another, smaller nebulous patch (OIII). West of the main filament is another shorter and fainter filament (OIII). South of it are another two large, but diffuse areas (best with H-beta), with a small bright knot in between. This knot (sometimes referred to as Sh2-157a) shines in HII and is a distinct object without filter or with H beta filter.

http://www.reinervogel.net/Sharpless/images/Sh157_inv.jpg


“Give it a go and let us know!
Good luck and Great viewing!"

[Steve Gottlieb]

Thanks for choosing to highlight this excellent HII region. I know I haven't given it the attention it really deserves, but here are some of my notes --

18" (8/23/03): this is a beautiful object with a 31mm Nagler and OIII filter, reminiscent of one of the sections of the Veil as viewed in a small scope. The main N-S shallow arc, convex to the east, spanned a large percentage of the field. At the south end, the strip widens and is less distinct although it contains the bright knot LBN 537 = Sh 2-157a, surrounding a mag 11 star (easy without filter). A much fainter western section (roughly 20' W) also extends N-S, passing through a scattered group of stars. At the south end it appears to merge with the eastern branch.

17.5" (10/17/98): surprisingly easy, huge HII region at 100x with OIII or UHC filter. Appears as a faint, curving graceful arc, very elongated N-S and bowed out on the following side. Extends north and south of open cluster Markarian 50 which is off the west side. Appears up to 35'x8' in size with the brightest section (near Mrk 50) showing subtle structure. The bright knot Sh 2-157a = LBN 537 is situated beyond the southern end of this arc. The illuminating star is HD 219460 = WR 157, the brightest member of Mrk 50, and this object is listed as a probable Wolf-Rayet shell in ApJ, 252, 1982.

Sh 2-157a = LBN 537 was picked up at 100x as a faint, ill-defined glow surrounding a mag 11 star with a couple of fainter stars possibly involved in the nebulosity. Good view at 105x (19mm) using an H-Beta filter which dims the illuminating star. The nebulosity appears circular, fairly crisp-edged, ~2' diameter. At 220x without a filter, the diameter increases to nearly 3', although the edge blends into the general haze of the huge HII region Sh 2-157. The central star has a mag 13.5 companion close NW.

Using 220x, Mrk 50 resolved into about 10 stars within a small semi-circle. The brightest star has a very faint and close companion close following. There is a very small distinctive group of four stars within the semi-circle consisting of two mag 12.5 stars with mag 14-14.5 companions about 10"-15" south.

17.5" (11/30/91): at 100x and OIII filter; moderately bright, very large, elongated ~2:1 N-S, ~25'x10'. The brightest region is widest and shows subtle structure and brightness variations. Appears slightly fainter as extends in a lane to the NNE with a smaller extension to the south. A compact open cluster, Mrk 50, is nestled along the west edge of the center of the arc.

[Uwe Glahn]

Hi Reiner,

surprisingly I found a sketch of the Sharpless 157 Complex in my collection. Unfortunately only with 8". The possible details in bigger telescopes are of course much more. But as you said it is a wonderful starting Sharpless, also for small aperture.

8", 31x, NELM 6m5+
http://www.deepsky-visuell.de/Zeichnungen/Sh2-157.jpg

[Ivan Maly]

It looks like the "Omega" alien in the latest Tom Cruise film. Seriously, it's an impressive sketch, even if in a slightly spooky way.

[Howard B]

Like Uwe, I was surprised to find an observation of Sh 2-157 in my notes. This is from 2008 using my 28" scope:

"A relatively big and faint arc of nebulosity that shows up best with the OIII filter and is not seen without the filter. It looks a lot like the bigger arc of the Veil Nebula (as seen) through a small scope, although here there's a little open cluster, MRK 50, sitting inside the arc, just off the nebulosity. It's mainly seen as an arc of 6 stars which curve mostly opposite the nebula. There are a couple other stars nearby that might be part of the open cluster. Best at 105x, OIII filter. 21.05 SQM."

[hajuem]

Hi Reiner

Here is my current observation of this Ojektes with OII un Hß!
I had never observed this object !! Beautiful object!
1322
16"//40-100x mit OIII und Hß

Lg von Hajü
www.astromerk.de

[Steve Gottlieb]

I just ran across an interesting (unknown) historical discovery by William Herschel -- namely Sh 2-157a = LBN 537, the brightest knot in the Sh 2-157 complex! The knot is labeled in Reiner's wide-field image and very prominent in the colorized DSS image.

On November 3, 1787 (his 773rd sweep), Herschel logged "some crowded stars with vF suspected nebulosity." Because the nebulosity was only "suspected" and he didn't go back later to confirm, it was never assigned an H- designation and it didn't receive a NGC designation. But exactly at his position is Sh 2-157a.

Here are three of my observations --

18" (8/23/03): easily visible at 113x as a fairly faint, circular, 3' glow surrounding a mag 11 star. At 257x the central star has a very close mag 13.5-14 companion and several faint stars are superimposed on the glow. The nebula is a little easier to view with an H-Beta filter as it cuts the glow from the central star, though the nebulosity seems a bit smaller.

17.5" (10/17/98): picked up at 100x as a faint, ill-defined glow surrounding a mag 11 star with a couple of fainter stars possibly involved in the nebulosity. Good view at 105x (19mm) using an H-Beta filter which dims the illuminating star. The nebulosity appears circular, fairly crisp-edged, ~2' diameter. At 220x without a filter, the diameter increases to nearly 3', although the edge blends into the general haze of the huge HII region Sh 2-157. The central star has a mag 13.5 companion close NW.

17.5" (11/30/91): faint, fairly small, round, 1.5' diameter. Surrounds a mag 10 star. Unusual object as responds best to H-Beta filter with a weaker response to UHC filter and almost disappears using an OIII filter.