[LVAS] January 2010 Observer's Challenge - Christmas Tree Cluster and Cone Nebula

Sun Jan 31 17:18:57 PST 2010

MONTHLY OBSERVER’S CHALLENGE
Las Vegas Astronomical Society
Compiled by:
Roger Ivester, Boiling Springs, North Carolina
&
Fred Rayworth, Las Vegas, Nevada
With special assistance from:
Rob Lambert, Las Vegas, Nevada
January 2010
NGC-2264 The Christmas Tree Cluster/Cone Nebula
Introduction
The purpose of the observer’s challenge is to encourage the pursuit of visual observing.  It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, we will be happy to include them in our monthly summary.  Observing is not only a pleasure, but an art.  With the main focus of amateur astronomy on astrophotography, many times people tend to forget how it was in the days before cameras, clock drives, and GOTO.  Astronomy depended on what was seen through the eyepiece.  Not only did it satisfy an innate curiosity, but it allowed the first astronomers to discover the beauty and the wonderment of the night sky.
Before photography, all observations depended on what the astronomer saw in the eyepiece, and how they recorded their observations.  This was done through notes and drawings and that is the tradition we are stressing in the observers challenge.  By combining our visual observations with our drawings, and sometimes, astrophotography (from those with the equipment and talent to do so), we get a unique understanding of what it is like to look through an eyepiece, and to see what is really there.  The hope is that you will read through these notes and become inspired to take more time at the eyepiece studying each object, and looking for those subtle details that you might never have noticed before.  Each new discovery increases one’s appreciation of the skies above us.  It is our firm belief that careful observing can improve your visual acuity to a much higher level that just might allow you to add inches to your telescope.  Please consider this at your next observing session, as you can learn to make details jump out.  It is also a thrill to point out details a new observer wouldn’t even know to look for in that very faint galaxy, star cluster, nebula, or planet.
NGC-2264 Christmas Tree Cluster and Cone Nebula
            The Christmas Tree Cluster is an easy object for any telescope.  Shaped like a V and named the Christmas Tree Cluster by one L.S. Copeland, it is a loose scattering of between 20 and 60 stars, depending on the scope size, your observing skills, and maybe a little imagination.  Easily seen in even a 60mm refractor, it can look like the namesake Christmas Tree, or just a loose uneven clump of stars.  The tricky part is seeing the nebulosity.  As shown in long-exposure photographs, the area is a hotbed of nebulosity, with several significantly large patches in and around the area of the cluster.  One such is the Fox Fir Nebula, which is also known as Sharpless 273, and is the nebulosity usually seen visually in 10” and larger telescopes.  However, the most interesting nebulosity comes at the other side of the cluster.  Known as the Cone Nebula, it is a dark V-shaped region lit up by a faint background glow.  It is an extreme challenge to see visually through anything but the largest backyard telescopes, yet it is relatively easy to photograph.
Burnham’s Celestial Handbook: Robert Burnham, Jr.
“A very large and scattered cluster of about 20 bright stars and over a hundred fainter members.  The group forms a pattern resembling an arrowhead, about 26’ in length, pointing nearly due south.  The “tree” is thus seen upside down in the sky, but is re-inverted to the usual orientation in the astronomical telescope.  The cluster is surrounded by a vast but faint nebulosity.”  He also notes later on that the nebulosity is not seen in small telescopes.
Observing Handbook and Catalogue Of Deep-Sky Objects:  Skiff and Luginbuhl.
“This cluster is led by 15 Monocerotis, mag 4.6, and has some irregularly shaped nebulosity associated with it.  6cm (2.4-inch) shows a long, thin triangular group of stars pointing SSE.  About 30 stars are visible in a 25’ area, including nine stars in the immediate vicinity of 15 Mon.  With 15cm (6-inch), about 35 stars are countable, and some faint nebulosity can be seen.  25cm (10-inch) shows many bright stars strewn uninterestingly in a 60’ X 40’ area.  In 30cm (12-inch), the cluster is hardly distinguishable, but a little nebulosity is discernable around 15 Mon.”
Observations/Drawings/Photos
Roger Ivester (see Rogers Pictures 003.jpg):  Observer from North Carolina
This cluster was observed on two different nights during January, using the 10-inch, with both seeing and transparency being rated as excellent.  Open cluster NGC-2264 appeared mostly sparse and coarse with a triangular shape and a dimension of approximately 1/2°.
The associated faint and mostly irregularly shaped nebulosity was fairly easy to see at low magnification.  A variety of eyepieces, and magnifications, including a nebula filter were used in an attempt to see the classic cone shape, but to no avail.
It is his opinion that the Cone Nebula is best suited for a very large scope under dark skies.  However, the image as presented in photographs, is not likely to be seen visually in most backyard scopes.
The sketch of NGC-2264 and faint nebulosity was made using a 10-inch f/4.5 reflector at 57X, using a white charcoal pencil on black drawing paper.  The field of view of the cluster and nebulosity is 70 arc minutes, or 1.14°.  All observations were made from a moderately light polluted backyard located in Boiling Springs, North Carolina (see Rogers NGC-2264.jpg).
Fred Rayworth (see Freds Astro Day 04.jpg):  Observer from Nevada
He wasn’t able to observe the object this month, but keeps a log of all his observations and had plenty of samples to choose from.  His descriptions go back to when he was still using his 16” f/6.4 Dobsonian and a 32mm Erfle eyepiece for 82X.  On 16 October, 1993, he saw a loose group surrounded by a slight haze.  On 20 March, 2004, he saw a bright star surrounded by a halo along with a scattering of stars with no definable shape. On 09 February, 2008, he saw an uneven bright clump.
He has never noted the Christmas Tree shape, and that may be because his scope was too large and showed more background stars, making the namesake shape blend into the mass of other stars. The cluster looks more like an uneven clump to him and he has noted 20 to 40 stars, depending on the night.
Never has he seen the cone shape, though he has noted the Fox Fir nebula (Sharpless 273).  The next time he has a chance, he is going to try his O-III and H-Beta filters, plus a variety of magnifications to see if he can bring out the cone.  He has one drawing that is representative of what he usually saw (see Freds NGC-2264.jpg).
Rob Lambert:  Observer from Nevada
His opportunity to observe NGC-2264 and the Cone Nebula came while at the semi-annual LVAS star party in Death Valley on 15 and 16 January.  Initially, the weather didn’t look very promising for either night of observing.  Friday night was a total washout with high thin clouds across the entire sky and patchy thick clouds that completely blocked out at least 75% of the sky.  It wasn’t even worth setting up the scopes.  Saturday night was much better as a 13-hour window of clear skies opened up Saturday just after noon and held until about 1:30 Sunday morning.
NGC-2264 had just passed the meridian by the time the park visitors departed, and he was able to observe, so it was presented well in the sky.  At first, he located the cluster with his Orion ST120.  On the color CRT monitor, the Mallincam displayed a beautiful image of the Christmas Tree, and the Cone Nebula was just visible as little dark notch pointing toward the star at the top of the tree.  He was able to see nebulosity in two areas, both primarily around the brighter stars of the cluster, 15 Monocerotis and TYC750-1719-1.  The nebulosity appeared to stretch the entire length of the cluster, but was less bright in the middle.
Fearful that he would lose the ability to observe the Cone Nebula with the approaching clouds, he centered the tip of the Cone on the CRT and moved the Mallincam down to the 10-inch LX200 to try for a closer detailed view.  He was thrilled to see the Cone, with a bubble at the top containing three stars, centered on the screen.  His alignment of the two scopes with each other had been nearly dead-on.  In the image above (see Robs Cone Nebula – LX200 – 30sec.jpg), the bubble is centered south (below and right) of TYC750-1719-1.  The Cone widens as it stretches out toward the south.  On the CRT, the Cone had tinges of red along its length and was dark and void of any light or color in its interior, except for what he thought were a few dim foreground stars.  The bubble at the top of the Cone was pink and translucent.  Three stars seemed to be trapped in whatever material shaped the bubble.  The captured image doesn’t provide anywhere near the detail or clarity that he saw on the CRT, but the Cone can be seen as a darker wedge extending down and right from TYC750-1719-1.  There is an almost straight chain of four stars that extends northeast (down and left) away from the tree-topper stars in the close-up of the Cone Nebula.
He went back to the ST120 to capture an image of the Christmas Tree Cluster.  By this time, some high haze had moved in, lessening the detail that he had seen earlier, but the cluster and its nebulosities were still clearly visible.  A faint nebulosity covers the entire cluster, but a much brighter patch of nebulosity is associated with 15 Monocerotis and the stars on the southwest side.  It surrounds the bright star and extends southwest, up into the right side of the tree.  Seeing the nebulosity associated with this cluster reminds him of coming from the outside cold into his dark family room that was being lit by only the lights of the Christmas tree.  When first seeing his tree in this light, there seems to be a haze around each of the lights, and so it is with the stars in the Christmas Tree Cluster.  This haze lessens significantly toward the center of the tree and then begins to brighten again as one approaches the star at the top.  The star topping the Christmas Tree seems to actually be two stars, TYC750-1719-1 and USNO-J064-1098+092751, which point to the bubble at the top of the Cone Nebula.  Within the cluster, he counted at least 20 brighter stars and there has to be at least 3 or 4 times that many dimmer stars in the cluster.  The Cone Nebula is centered in the wide-field image of NGC 2264, pointing down into the cluster.  One can just see the stars that reside in Cone’s bubble.  The dark void of the Cone widens and becomes an obvious dark hole surrounded by some brighter stars southeast of the top of the tree.
Although he doesn’t believe his images do justice to what he saw on the monitor (he needs to work on improving the capture process), this was an exciting challenge.  He was able to see the Cone Nebula, an object that he would never be able to see at the eyepiece with his less than perfect eyes.  He hopes to revisit this challenge on his next outing.
Note:  Rather than try to flip the images so that they matched in orientation, he decided to leave them as he saw them on the monitor.  The image of the Christmas Tree Cluster was captured with the ST120 with the Mallincam at full gain and 15-sec integration (see Robs NGC-2264 – ST120 – 15sec.jpg).  The image of the Cone Nebula was captured with the 10-inch LX200GPS with the Mallincam at full gain and 30-sec integration (once again, see Robs Cone Nebula – LX200 – 30sec.jpg).  Both images were stacked from 2 single frames and 1 dark frame to remove hot pixels only.  No other post processing was done.  The stacking software will not process a single light frame and a single dark frame; it must have at least two light frames to process.
Dave Blanchette:  Observer from Nevada
This was the first time he’s ever looked at the two objects in NGC 2264.  Therefore, he had some trouble figuring out where to shoot the image.  So the image (see Daves NGC-2264.jpg) is a combination of two 10 minute images, converted to grayscale for clarity.  It was late and there were clouds rolling in, so these were the last images he shot for the night.
Dr. James Dire:  (see Jim Dire.jpg) Observer from North Carolina
NGC-2264 is usually the designation given for a star cluster in the constellation Monoceros (mono – one, ceros – horn; The Unicorn) which is embedded in a large nebula.  The nebula spans approximately 1 degree of declination and a half degree right ascension.  If north is up, the nebula is in the shape of an inverted cone or Christmas tree.  Thus NGC-2264 is sometimes called the Cone Nebula or Christmas Tree Nebula.  Near the south end of the nebula, or the apex of the cone, lies a dark nebula, also cone shaped, with the apex on the north end.  This dark nebula is called the Dark Cone Nebula.
The actual star cluster is approximately 39 arc minutes in diameter.  His image of the Cone Nebula is centered on the star cluster, and only captures about half of the bright nebula.  This image was taken with a 190mm f5.3 Orion Maksutov-Newtonian Astrograph using an SBIG ST-2000XCM CCD camera.  It is a composite of  six 10-minute frames taken on February 23, 2009.  He has captured roughly the bottom half (north side) of the Christmas Tree (remember it is upside down) (see Jims NGC-2264.jpg).
References
(Submitted by Fred Rayworth)
Burnham’s Celestial Handbook:  Robert Burnham, Jr.
Observing Handbook and Catalogue Of Deep-Sky Objects:  Skiff and Luginbuhl 		 	   		  
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