exotic

July / August

narrowband image by Lionel Mulato, mouseover: OIII

WR134

A largely unknown Wolf-Rayet shell around WR 134 in Cygnus

20 10 14.19   +36 10 35.1  (WR 134)

This Wolf-Rayet bubble is not listed in any catalog, despite it is well visible on the DSS. When I observed this shell for the first time during spring of 2009, I knew of only a single prior observation by Matthias Kronberger. My interest in this shell was stimulated by a narrow band image by JP Metsävainio. The WR shell is visible in the right part of this mosaic as a distinctly blue OIII crescent, using the Hubble palette version.

The shell is roughly half ways between the Tulip Nebula, Sharpless 101, and the Crescent Nebula, NGC 6888, which is, by the way, another WR shell. With my 22" Dob, the WR shell is not or only hardly visible without filter and reacts extremely well to the OIII filter. With filter it appears as a crescent of roughly 15', opened towards east. Its appearance and brightness is similar to that of another WR shell Sharpless 308 in Canis Major, which is, however, considerably larger.

This shell is not difficult at all and is also faintly visible with my 8" Dob and OIII filter from my suburban backyard.

The association of the shell with WR 134 is not certain, despite that WR 134 (the middle star in the distinct row of three stars) is in the center of the bubble. Instead WR 135, another mag 8 WR star about 15' east of WR 134 was suspected to be the true origin of the shell. This would agree as well with the further OIII emission on the image linked above.

Another fantastic images of this shell was taken by Don Goldman.

DWB 111

A HII propeller in Cygnus

20 16 00.00   +43 40 12.0

The region around Gamma Cygni is littered with faint extended nebulosity (though Gamma Cygni itself is not associated with it at all and instead a foreground object!). While there are parts closer to the line of sight of Gamma Cygni, that are relatively bright and not difficult at all to observe (such as the Butterfly Nebula, IC 1318), the more distant regions are usually considerably fainter. 

The Propeller Nebula DWB 111 is a more condensed area roughly 4 degrees NNW of Gamma Cygni, that is well accessible for visual observation. Using a wide field low power eyepiece equipped with H beta filter, you can sweep the area of the propeller, using the distinct superimposed  pattern of field stars for orientation.

The southern wing of the propeller can, by the way, be traced even further south than indicated by the image to the left.

Sharpless 106

An unusual bipolar nebula in Cygnus

20 27 27.10   +37 22 39.0

Sharpless 106 appears on images as a wonderful bipolar nebula about 3 degrees SW of Gamma Cygni. Even on the DSS, the nebula appears quite bright and should therefore be an easy object at the eyepiece.

That's the theory. In practice this object has challenged me during many observing sessions, using all available filters. But I failed in detecting even the apparently bright southern lobe of it.

Entering at some point Friedl Lamprecht, who advised use no filter at all. Et voila, there it was, though still not an easy object. Using 350x with my 22" Dob, the southern lobe was visible using indirect vision as a very faint extended object. It disappeared as as soon as I switched from unfiltered to UHC using my filter slide.

Even though Sharpless 106 looks like a regular bipolar PN, it isn't. It is not a pure emission nebula, but obviously involves a major amount of light scattered by dust particles, such that chances for successful observation are best unfiltered.

The unusual bipolar shape of the nebula is the consequence of a buried young OB star, which is surrounded by a thin disk of matter, confining the light of the star along the axis of the disk. The molecular cloud into which the star is embedded is an active star forming region with a number of YSOs.

Paper by Klaus Hodapp about Sharpless 106

The lower left image is a near-IR image:  Oasa,Y., et al. (2006) Astronomical Journal ,131,1608

A newer image taken by the HST is here.

NGC 6946 and NGC 6939

A nice pair in Cepheus

20 34 52.7   +60 09 14.0   (NGC 6946)

20 31 30.0   +60 39 42.0   (NGC 6939)

The open cluster NGC 6939 and the Fireworks-Galaxy NGC 6946 are only 40' apart of each other in the SW corner of the "house" of Cepheus. In my 15x70mm binoculars, both objects are in the same field and form a nice contrast, in particular if one is aware of the widely differing distances of both: The cluster is at a distance of a mere 5000 Lys in our galactic neighborhood, while the galaxy is about 2000 times farther away at about 10 million Lys.

Despite its distance, the galaxy NGC 6946 is visible already with an aperture of 70mm in my binoculars as a small diffuse patch of light. In larger instruments, the spiral arms of this face-on Scd galaxy become more and more apparent. With my 22" Dob, I can see at first sight the elongated central part of the galaxy with its bright core. Towards SE, in the direction of two foreground stars, this central part is sharply lined out by a dark lane of the spiral arms.

The spiral arms are quite obvious with this galaxy, winding counter-clockwise around the core. In particular the arm starting at the W of the core appears well defined due to a number of bright star forming regions with their massive young bluish stars. These star forming regions are the reason that over the last 100 years, 19 (!) supernovae had been detected in this galaxy, as many as in no other galaxy. This western spiral arm can be followed, winding quite a bit away from the core, becoming less conspicuous and ending in an again brighter patch after about half a turn. This brighter part is situated in an elongated triangle of foreground stars.

On the eastern side, a broader and less well defined structure emanates from the core. After careful observation, this can be split into two spiral arms, that can, however, not be traced as far as their western counterpart.

The open cluster NGC 6939 is only 40' northwest of the galaxy. It is conspicuous already in my binoculars as a diffuse glow, which is bordered at its northern side by three brighter stars of 10th magnitude. At 12x, a nice blinking effect can be observed: With direct vision, in particular the three stars at the edge of the cluster are obvious, while averted vision brings the cluster out. At this magnification, it still appears diffuse. In my only slightly larger 80mm refractor at 45x, its brightest members are resolved. In particular at the SW side of the cluster, a mag 11 star pops out. With my 22" Dob, the cluster is finally fully resolved and the estimated 100 members show a quite uniform brightness, typical for an old and evolved cluster. The stars appear to form V-shaped rows that remind a bit to the similarly shaped rows of stars in the cluster M11 in Scutum, lending it its nickname, Wild Duck Cluster.

The changes of Gyulbudaghian's Nebula on the red POSS Platten during more than four decades

Boyd, 2012SASS...31...65B

PV Cephei and Gyulbudaghian's Nebula

An FU Ori Stern and a variable nebula

20 45 53.94   +67 57 38.7

PV Cephei is a pre-main sequence star about 90' west of NGC 7023 and only 15' west of a mag 7 star.

 PV Cephei is a so-called Young Stellar Object, which is a star in the transition from a proto star to a main sequence star with stable hydrogen fusion. During this stage of star development, the star is still surrounded by a partly dense envelope formed by the remainders of the molecular cloud in which the star was formed. Only at the poles of the star are clear areas in the envelope. These are funnel-shaped and allow light to leave almost unhindered, shining on the inner surface of these openings. Depending on the perspective of the observer, this results in characteristic fan-shaped or bipolar reflection nebula.

In the case of PV Cephei, a slanted view from above onto one of these funnels is offered to us, resulting in a fan-shaped reflection nebula, bearing the exotic name Gyulbudaghian's Nebula or GM 1-29. Its northern part has a roughly triangular shape, while the juxtaposed southern part is considerably attenuated by absorption of the molecular cloud.

What can one expect at the eyepiece of this surely very interesting object? To be honest: At present almost nothing! During several observations with 22" aperture between 2008 and 2010, I suspected twice an extremely faint little glow at the right position. During a single observation in October 2011, an extremely faint mostly stellar object was visible as a very difficult object. This was likely a bright knot within the nebula, as suggested by  the series of images below.

Nevertheless, this object is of interest for visual observers for the following reason: PV Cephei is a highly variable star of the so-called FU-Orionis type. This is a particular sub-stage during the stage of a T-Tauri star (which our sun went through as well), during which outburst of up to 6 magnitudes are not rare. For this reason, Gyulbudaghian's Nebula used to be accessible even to smaller telescopes every once in a while. Similar variable nebula around pre-main sequence stars are Hubble's Variable Nebula, NGC 2261, around R Monocerotis in Monoceros and Hind's Variable Nebula, NGC 1555, around T Tauri, which are, however much less variable than Gyulbudaghian's Nebula.

The last outburst was around 2005, when this nebula was visible even with a 10" telescope, as evident from this drawing by Martin Schönball. Since then, however, Gyulbudaghian's Nebula was a border line object even for very large Dobs. But the recent years have showed that this may change rapidly. Therefore, give it a try and you might experience one of these surprising outbursts.

updates

08/2013: The nebula has considerably brightened and is now visible as a relatively bright fan-shaped glow, even with direct vision. PV Cep, the star, could not be discerned.

09/2013 bright, fan shaped, direct vision

10/2014 much fainter, only a structureless glow with averted vision

11/2015 nebula is immediately visible, but fainter than in 2013, it appears with indirect vision fan shaped with an angle of approximately 60°, PV Cep is visible indirectly  as a very faint stellar point

Boyd, 2012SASS...31...65B, click on image for larger scale

More about Young Stellar Objects and finder chart of  PV Cephei is here. More about PV Cephei itself is here on the web page by Greg Crinklaw.

The OIII image above is a close-up of the southern bubble (click to enlarge), image by Sara Wager

The southern part of the Veil complex

Simeis 3-210 in Cygnus

20 53 07  +29 38 57

The Veil Nebula is composed of a vast number of filaments, of which many have distinct proper names (in German, we call them Welle, Hexenbesen or Knochenhand) and which cannot complain of being overlooked by visual observers. A very nice finder chart of these different filaments has been compiled here by Steve Gottlieb.

In the very south of the complex, however, is a filament that is rarely visited and that bears the catalog designation Simeis 3-210. It is best accessed starting from the eastern bright filament via a small but distinct knot (H in Steve's chart) leading to the distinct mag 6.3 star HD198976, or from the Wave via the Witch's Broom and a few filaments perpendicular to it.

This part of the Veil is considerably fainter than the well known bright filaments and also fainter than Pickering's Wisp. Using a medium-sized to large Dob equipped with OIII filter, it is nevertheless well visible.

The two brightest and best defined filaments are directly (2) at HD 198976 or a bit offset (1). The following filament 3 is broader, more diffuse and quite fainter. It trails far towards SW and it takes some time to become distinct in front of the Milky Way background. East of it are two bright stars, which help you find your way. At another brighter star south of it starts filament 4, which is again a bit fainter and reveals a bifurcation. The southernmost area 5 is extremely  faint and very difficult as it blends into the Milky Way background. From here, the bubble turns again north and filament 6 is again a bit easier, but still pretty faint, while filament 7 again blends almost completely into the starry background.

Sharpless 157

Sharpless for beginners in Cassiopeia/Cepheus

23 16 04.08  +60 02 06.0

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.

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 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. West of the main filament is another shorter and fainter filament. South of it are another two large, but diffuse areas, 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.

More about the observation of Sh2-157 and other Sharpless nebula can be found here.

Very detailed narrow band images of this area have been taken by Richard Crisp and Dean Salman. Richard Crisp's image of 2004 has actually stimulated my interest in observing this object and all the other Sharpless objects that followed over time.

Sharpless 129

Sharpless for experts in Cepheus

21 10 00.00   +59 42 00.0

Very different from Sharpless 157, this HII region is marked in most star charts as a ring- or crescent-shaped nebula around a central pair of stars. Its appearance even in the Cambridge Star Atlas does, however, not say much about its visibility.

Sharpless 129 is a typical H beta object with only negligible OIII emission. The most distinct parts of the nebula is surprisingly the northern part of the arc, extending from the distinct condensation in the image towards NW. At the eyepiece of a 16" Dob, it could be traced over at least one degree. The southern part, that appears more distinct on the DSS image, could be observed as well, though it was less well defined.

Surprisingly, Nicolas Outters discovered on OIII images a huge squid shaped object, Outters 4, superimposed on Sharpless 129, which was presumed to be a planetary nebula or the outflow of a massive young star. More about this here (scroll down).

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click for finder chart

Pease 1

A planetary nebula in the globular M15 in Pegasus

21 29 58.33   +12 10 01.2  (M15)

Pease 1 is the by far easiest PN within a globular cluster. "Easy" being relative, of course.

I have observed Pease 1 several times with telescopes ranging from 14 to 22", all operated on equatorial platforms, which helps a lot when trying to find your star hop through a globular cluster. Pease 1 can be identified by blinking with an OIII or UHC filter, making it stand out from all the other stars in M15. Blinking can be achieved by  holding the filter between your eye and the eyepiece and by comparing the view with and without filter. A filter slide does not help, as it requires re-focusing after each change. A high-power eyepiece in the range between 3 and 5mm with large eye relief is here the best choice for the usual f/4 to f/6 Dobs.

Pease 1 is at the northern edge of M15. You will need precise finder charts to locate it, which you can find here on the web page by Douglas Snyder or, alternatively, by clicking on the image on the left side. Even though some images of M15 suggest the PN to be deep in the core of M15, its position is actually at the edge of the core region. This is also evident from this recent HST image. The star hop described by Doug Snyder is relatively easy and the position of Pease 1 is relatively exposed at a distinct "edge" of M15's core region. This edge separates a star-rich area towards west from a star-poor region east of it. Pease 1 is close to the outer end of this distinct edge. With a big Dob and good seeing, this PN is relatively easy to see and to confirm with blinking. This is, of course, very different under less than optimal seeing

More information about Pease 1 is here :

http://messier.seds.org/more/m015_h2.html

http://www.blackskies.org/peasefc.htm

NGC 7129 and 7142

A nice pair: an open cluster and a reflection nebula in Cepheus

21 42 55.92   +66 06 10.8  (NGC 7129)

The reflection nebula NGC 7129 and the open cluster NGC 7142 are close to the center of the "house" formed by the constellation of Cepheus. With my 8" Dob, the reflection nebula NGC 7129 is the more distinct of the two objects. Even under sub-par observing conditions in my back yard, the RN is visible as an obvious glow around two mag 10 stars using my low power eyepiece. As the light of the nebula is reflected and scattered star light, nebula filters are not particularly helpful here.

Using my 22" Dob, the nebula becomes a very detailed object. Using 200x, another non-stellar condensation is visible about 1' N of the central pair of stars and just W of a faint star (right arrow during mouse-over on lower image). Somewhat more distant are more condensations that are somewhat larger but more diffuse: One is 5' towards N around a mag 12 star, which is erroneously assigned to NGC 7133 on some charts (left arrow). About the same distance towards NW is the second around a star of similar brightness, bearing the designation IC 5132/5133.

The open cluster NGC 7142 is located about 25' SE of NGC 7129. Using my 8-Inch Dob at 50x, it appears as a diffuse patch of about 8' diameter, flanked by a conspicuous chain of three mag 10 field stars towards NE. At 100x, the open cluster is already partially resolved with about 10 stars standing in front of a diffuse background. Using my big Dob, the cluster appears as a completely resolved loose cluster of about 50 stars. With big telescopes, this cluster appears much less interesting than with smaller instruments. NGC 7142 appears to be an old open cluster with a star population of homogeneous brightness, correlating with the reported age of the cluster of about 4.5 billion years.

IC 5146

Dirk Bausch

Cocoon Nebula IC 5146

A transforming reflection/emission nebula at the end of the dark cloud B168

21 53 24   +47 16 01

The Cocoon Nebula IC 5146 is situated in the constellation Cygnus at the end of a distinct elongated dark cloud, Barnard 168. This cloud is visible already in the finder or at low magnification as a very elongated starless region in the otherwise dense milky way field. This is not an incidental superposition. On the contrary, the Cocoon Nebula is part of this dark molecular cloud, which is excited by young star of a star cluster in formation, Collinder 470 (or at least a member of it). The Cocoon Nebula has therefore just transformed from a dark molecular cloud to an emission nebula.

At the eyepiece, both stages can be discerned visually. Without filter, the most conspicuous part of the complex is the loose small group of stars of the young star cluster Cr 470 at the end of the dark cloud. After more careful inspection, a feeble glow becomes apparent that fills this end of the starless area of the dark cloud. Switching to an H-beta filter, the emission parts of the nebula become prominent and the size of the nebula shrinks noticeably. The part of the nebula visible without filter consists therefore at least in its outer parts mostly of starlight reflected by dust of the complex. Both parts, the emission nebula visible with H-beta filter and the reflection nebula visible in particular without filter, are of about the same brightness, but vary noticeably in form, structure and size.

Cassiopeia A

The youngest supernova remnant in Cassiopeia

23 23 24.00  +58 48 54.0

Cassiopeia A  (wiki article) is a very young supernova remnant (SNR), the light of which arriving presumably around 1680. Due to the strong galactic absorption, it was probably not noticed except for Flamsteed. Presumably, this is the youngest SNR of your galaxy. The image to the right is a DSS image of it.

This SNR is again one of these objects, that I had tried before without success and that proved to be not that difficult another time under actually not too different conditions. Alerted by positive reports on the AmAstro Yahoo-group, I decided to give it another try in December 2009.

Without filter at 200 and 350x, I suspected a slightly elongated glow at the correct location, which involves, however, also several faint stars. Three stars, forming and equilateral triangle, could be just held with the crescent-shaped SNR glow going right through that triangle. Using the UHC filter, the SNR was well and steadily visible as a small crescent and best at 200x. This crescent-shaped glow was now clearly not due to stars. Using my Lumicon OIII filter, it was still well visible, though not as distinct as with UHC filter. After inspection of the images, this is the central part of the northern arc of the SNR. On the DSS image, the triangle is marked. The crescent-shaped glow extended somewhat beyond this triangle.

Here is a narrow band image by Richard Crisp and here is a detailed finder chart. 

More about Cas A is here.

Jones 1

A ghostly PN in Pegasus

23 35 53 +30 28 06

Jones 1 is one of the few of those big planetary nebula that emits almost purely OIII light. This is a nice treat for us visual folks.

The PN is relatively easy to find next to a group of stars in the middle of the northern edge of the Pegasus square. Without OIII filter, it is hardly visible even in a big telescope. With filter, however, it appears all of a sudden as a large and ghostly PN. At first sight, the two brightest parts N and S of the (not visible) central star. After a while, the western part can be discerned as well, yielding a C-shaped glow open towards E, according to the image on the left side.

Adam Block/Mount Lemmon SkyCenter/University of Arizona

R Aquarii

White Dwarf eats Red Giant

23 43 49.46   -15 17 04.1

R Aquarii is a symbiotic double star consisting of a Mira-type Giant and a White Dwarf (more about this here). Every once in a while, the system spews out matter, which forms spiraling filaments that are known as Cederblad 211.

My observing report of December 2009: I had observed R Aqr already a few weeks before with a 16" Dob by less than optimal seeing. This time, the seeing was good. Using my 22" Dob at 500x without filter, I saw first only the red star, no nebula. Inserting the OIII filter, the brightness of the object was only slightly reduced and the nebula was now visible as a slightly elongated patch around the now very much attenuated star. Switching back to the filterless view, this nebula was now visible as well (how comes it went unnoticed the first time?). On one side, the NE side, a faint extension trailed towards N with a brighter knot at its end. On the other side, the nebula extended as a rather broad feature. Using my Astronomic UHC filter (with a red pass band), the red Mira-type star was less attenuated, with my Lumicon H beta filter, mainly the red star was visible.

At some moments, I suspected even more nebulosity further towards S, as indicated in the rough sketch.  

Due to the variability of the Mira star (presently between 6th and 11th magnitude with a period of 387 days), it is interesting to compare observations made during different phases. The observing report above dates from a time close to a maximum. Subsequent observations close to a minimum revealed the northern extension well without filter, as the main star was no longer disturbing. Pre-requirements for such a low-declination object are, of course, good seeing and culmination.

More about this object is here.

The image had been taken by Adam Block and shows well the outer filaments (more details here). The part that I observed corresponds to the inner part, that appears whitish in the image.

Sh2-174 in OIII and HII

Stephane Zoll

Sharpless 174

A large PN with run-away central star in Cepheus ?

23 46 49   +80 56 20

23 46 49   +80 56 20

Sharpless 174 has a size of about 10'x15' and belongs hence to the very large planetary nebula. Its central star has a relatively large proper motion. During its movement through the interstellar matter, the PN looses part of its shell which is left behind as a trail visible in HII light. The central star is therefore no longer in the center of the HII-emitting part of the PN. Due to the apparent lack of a central star. Sh2-174 was classified after its discovery as an HII region. The part of the nebula, that shines in OIII light is, however, concentric around the hot central star. The parts of the PN that are visible in HII and OIII light appear therefore slightly displaced (see animation to the left).

This displacement is visible at the eyepiece. The PN is quite faint, but still bright enough to allow for a detection of the slight displacement when switching from H beta to OIII filter. The disk of the PN appears diffuse without clear edges. OIII emission is displaced to the NW, while H beta and hence HII emission is more extended and displaced towards SE, in agreement with the narrow band images. Using an UHC filter, both components appear simultaneously, yielding a round appearance of the PN.

RW Tweedy, R Napiwotzki, The planetary nebula abandoned by its central star

Meanwhile, the nature of Sharpless 174 as a PN is being questioned again. David Frew notes that the White Dwarf is too old for being the central star of a PN. Furthermore, spectroscopic studies do not confirm co-movement of the emission nebula with the moving White Dwarf. Finally, the "PN" shows neither limb brightening, which would be expected if the emitting gas where a PN shell and not a filled sphere, nor a bow shock, as it would be expected for such an old and diluted PN due to interaction with the interstellar medium.

Sharpless 174 is therefore likely not a PN (i.e. a shell of material ejected from the central star at the end of its AGB phase), but rather a interstellar medium ionized by the moving White Dwarf. The shift of the emission zones and the lag of the HII zone behind the OIII zone reflects the longer recombination time of HII as compared with OIII.

David Frew, thesis