Nights on Mars Hill

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Messier 17 The Swan Nebula

M17,Swan Nebula,Omega Nebula, NGC6618,Lobster Nebula

Messier 17 The Swan Nebula

Distance: 5,000 Light Years                                Telescope: Takahashi TOA-130
Magnitude: 6.0                                                        Camera: QSI 683
Size: 11 Arc-minutes                                              Mount: AP 900
Age: Approx. 1 Million Years                              Exposures: L 12×360 Bin 1, RGB 12×180 Bin 2

Messier 17 is an emission nebula in the constellation Sagittarius. M17 is also known as the Omega, Swan, or Lobster nebula and lies in the Sagittarius arm of our galaxy. The illumination sources for the nebula are a group of stars behind the bright central gaseous region. These stars are not seen in visual images but are responsible for the unusual whitish color of this region. At first it would appear that any image of this area is over exposed but the whitish color comes from a mix of the reddish emission gas mixed with reflections of bright star light from the surrounding area. The entire nebula is an active star formation region. Surrounding the bright central region is a large emission cloud. This cloud has a very lumpy structure which indicates future star cluster development.

Above and to the right of M17 is IC 4706 and IC 4707 and these are both listed as stars with nebulosity.

This image was captured in one night from my house located in a Bortle 6 zone. I did try to capture this object two years ago with a 65mm refractor and a DSLR but was not really satisfied with the object or the results. I decided to try it again with a larger scope and CCD camera and I am happy I did. I was pleasantly surprised with the results considering the short exposure times. One thing that did surprise me was the lack of detailed information on M17. I searched several sites and most parroted each other. I then tried Google Scholar and found some more info but not as much as I expected for such a common target.

[SEDS]

 

NGC 6888 The Crescent Nebula

NGC 6888, Crescent Nebula, Caldwell 27, Sh2-105

NGC 6888 The Crescent Nebula Ha+OIII

Distance: 5,000 Light Years               Telescope: Takahashi TOA-130
Magnitude: 7.4                                       Camera: QSI 683
Size: 18×12 Arc-minutes                     Mount: AP 900
Age: 250-400K Years                             Exposures: L 15×900 Bin 1, Ha+OIII 7×900 Bin 1

NGC 6888, the Crescent Nebula, is an emission nebula in the constellation Cygnus. The illuminating source is the Wolf Rayet star WR 136. In general a Wolf Rayet star is a very large hot star that is rapidly shedding mass in the form of ultraviolet radiation. WR 136 is estimated to be 250,000 times brighter than our sun, 15 times more massive, and with a temperature of 70,000 Kelvin. With WR 136, the ejected matter is leaving at a speed of 6.1 million kilometers per hour. This high speed matter hits the ambient dust and gas and gives the Crescent nebula its shape. Part of the surrounding gas and dust is previously ejected material from WR 136 when it was a red giant about 250,000 years ago.

NGC 6888 is a windblown bubble formed by a Wolf-Rayet star that is shedding very hot material in to the surrounding inter stellar medium. It is the gas and dust in the surrounding medium that is compressed in to a thin shell giving the nebula its shape. There are actually two waves of shocked gas, one corresponding to the shocked stellar wind and the other to shocked interstellar gas. The hot interior of this bubble is where the energy is stored and subsequently used for driving the entire structure.

The top image is composed of 900 second Ha and OIII images. The entire area around the nebula is rich in OIII while the interior area is stronger in Ha. This is the first time I tried imaging the Crescent nebula in narrow band and was a bit surprised to see the large OIII ejection area outside of the arc. I did a bit of research on this and a 2014 paper [arXiv:1310.2801v2] said the following:
“The hot gas in NGC 6888 is distributed inside the optical shell delineated by OIII emission. The spatial distribution of the X-ray emission shows enhancements towards the caps and a blowout present in the NW region of NGC 6888. This blowout, not discussed in previous studies, has no Ha counterpart, but an outer skin of OIII is detected. The X-ray emitting gas is, thus, traced by Ha clumps inside the nebular shell and by the blowout. No clear evidence of limb brightening is detected.”

The image below is an LRGB combination captured from my house in an orange zone. The exposures are L 900 seconds bin 1 + RGB 450 seconds bin 2. I was pleasantly surprised that I could get 15 minutes at F7.7 without any difficult gradients.

NGC 6888, Crescent Nebula, Caldwell 27, Sh2-105

NGC 6888 The Crescent Nebula LRGB

 

Messier 16 The Eagle Nebula

M16, Messier 16, Eagle Nebula, Star Queen Nebula, IC 4703

Messier 16 The Eagle Nebula

Distance: 7,000 Light Years                            Telescope: 10” RC
Magnitude: 6.4                                                    Camera: QSI 683
Size: 7 Arc-minutes                                           Mount: AP 900
Age: Approx. 2 Million Years                          Exposures: L 11×600 Bin 1, RGB 11×300 Bin 2

Messier 16 is an open cluster in the constellation Serpens. The cluster is very young at 2 million years and was formed from the surrounding gas and dust known as IC 4703. The cluster contains about 460 stars with the brightest at magnitude 8.24. The entire area is commonly known as the Eagle nebula or Star Queen nebula. M16 contains many very hot young stars and the ultraviolet radiation emitted from these stars is the illuminating source of IC 4703. These young stars are also responsible for the shaping of the elephant trunk structures seen in my image. These young stars are Type O stars which are very hot, very large, and emit large amounts of ultraviolet radiation in the form of a solar wind. It is this solar wind which sculpts the shape of the denser dust in the region. It is also the solar wind which can destroy any planet and star formation in the immediate area of newly formed stars by blasting away any remaining gas and dust. This ultraviolet radiation is also giving the entire nebula a hollowed out look as it pushes gas and dust away from the cluster. However, farther out this same solar wind provides an initiation force to stimulate star formation because it shocks and heats cooler gas and dust.

The large dust structures in my image are shaped from the ultraviolet radiation of nearby stars in the cluster. The dark dust structures are commonly known as elephant trunk structures because of their shape. One of the more famous ones is seen in this image and has been dubbed the Pillars of Creation. This area is shown in the middle of my image as a multi-pronged feature. The pillars contain Evaporating Gaseous Globules (EGG) that are smaller denser areas of gas and dust and are thought to be star formation areas. The smaller dust structures outside of these elephant trunk structures are called globules and it is thought that these are future protostars.

[SEDS, Wikipedia, NOAO.edu, Universe Today]

NGC 6946 The Fireworks Galaxy

NGC 6946, Fireworks Galaxy

NGC 6946 The Fireworks Galaxy

Distance: 10 Million Light Years                  Telescope: 10” RC
Magnitude: 8.9                                                   Camera: QSI 683
Size: 11 x 10 Arc-minutes                               Mount: AP 900
Age: Approx. 10 Billion Years                        Exposures: L 10×900 Bin 1, RGB 10×450 Bin 2

NGC 6946, the Fireworks galaxy, is a spiral galaxy in the constellation Cepheus. It is a relatively large face on spiral galaxy that lies along the galactic plane and it is this view through the galactic plane that presents the rich foreground star field. The asymmetrical shape of NGC6946 may be the result of earlier gravitational interactions with nearby galaxies. Classified as a type Sc galaxy, NGC 6946 has well defined arms containing star clusters, Ha regions, and dust lanes. There is a lot of active star formation in NGC 6946. It is not clear what is causing this as there hasn’t been any recent interaction with other nearby galaxies. One thought is the spiral galaxy has a strong nuclear bar at its core. The bar shape is formed as the orbits of nearby stars become unstable and become elliptical. More and more stars follow this pattern and the bar shape becomes more defined. The formation of this bar is thought to induce star creation in the surrounding gas by concentrating it in the core area.

NGC 6946 is also called the Fireworks galaxy. This is in part because of the high star formation rate but also because of the large quantities of supernovas. From 1917 to 2009 there have been nine supernova, by comparison our Milky Way galaxy averages one per century. There is also a large halo of gas that extends out from the galaxy disk and it is thought that this halo is the ejected neutral gas resulting from the high rates of star formation and supernova.
[SEDS, University Today]

NGC 2264 The Christmas Tree Cluster

NGC 2264, Christmas Tree Cluster

NGC 2264 The Christmas Tree Cluster

Distance: 2,400 Light Years                           Telescope: Televue NP101 + .8 Reducer
Magnitude: 3.9 Central Cluster                   Camera: QSI 683
Size: 20 Arc Minutes                                         Mount: AP900
Age: 2-4 Million Years                                      Exposure: SII 2×900, Ha 29×900, OIII 6×900

Commonly known as the Christmas Tree Cluster, NGC 2264 is actually the catalog number given to the open star cluster and Cone nebula in the constellation Monoceros. The above image also contains the Fox Fur nebula and Snow Flake cluster.

The Cone nebula is the triangular shaped dark nebula in the left center of my image. Behind the Cone nebula is a small emission nebula that provides a contrasting back drop. This area is illuminated by the NGC 2264 open star cluster and also the bright star S Monocerotis. This cluster is blasting away at the Cone Nebula with ultraviolet radiation. There is a beautiful Hubble Space Telescope image that shows this here.

The star cluster NGC 2264 is very young at 2-4 million years. It occupies the area between the brighter star S Monocerotis and the Cone nebula. This cluster contains mainly Type O and B stars but other types of stars are present in their pre main sequence phase. Star formation is still occurring in this cluster as evidenced by a high number of pre main sequence stars that pulsate on their way to becoming main sequence stars. Present estimates of stars in the cluster number about 1,000.

In my image, the Fox Fur nebula is an emission nebula just below the bright star S Monocerotis. This nebula resembles an above view of a fox with its head looking at S Monocerotis. I want to return to this object next winter with a longer focal length telescope. The above wide field image does not bring out the detail that this fine target contains.

[Cornell University, SEDS]

Ha Version:

NGC 2264, NGC 2264 Ha, Christmas Tree Nebula Ha

NGC 2264 The Christmas Tree Cluster Ha Version

Messier 92

M92, NGC 6341

Messier 92

Distance: 26,700 Light Years                            Telescope: 10” RC F8
Magnitude: 6.4                                                       Camera: QSI 683
Size: 14 Arc Minutes                                             Mount: AP 900
Cluster Type: Globular Class IV                       Exposure: L 8×240 Bin 1, RGB 8×120 Bin2

Messier 92 is a class IV globular cluster in the constellation Hercules. M92 is estimated at 14 billion years in age and thought to be the oldest globular cluster in the galaxy. This age estimate is partially based on the low metallicity counts in the stars of M92. Low metallicity indicates that the globular cluster was formed very early from gas and dust that was not yet enriched with metals.

M92 has 24 variable stars as of July 2012. [Christine Clement’s Catalog of variable stars in M92] Of these 17 are classified as RR Lyrae type variables. The other 7 are type SXP which is short for SX Phoenicis, a type of variable star with low metallicity and very short periods. M92 also has blue straggler stars with the heaviest concentration in the center of the cluster. A blue straggler star is a young hot star that is thought to have formed from an interaction with another star. During this interaction, the stars shed material and the cores merge to form a new star.

M92 will be within 1 degree of the North celestial pole in about 14,000 years. This will be the result of the Earths 25,772 year precession cycle.

[SEDS, Wikipedia]

 

Messier 12

M12, NGC 6218

Messier 12

Distance: 16,000 Light Years                      Telescope: 10” RC F8
Magnitude: 6.7                                                 Camera: QSI 683
Size: 16 Arc Minutes                                       Mount: AP 900
Cluster Type: Globular Class IX                 Exposure: L 7×240 Bin 1, RGB 7×120 Bin2

Messier 12 is a globular cluster in the constellation Ophiuchus. Like all globular clusters, M12 is very old at 13 billion years. M12 contains about 200,000 stars but what is unusual about M12 is that it missing a lot of the low mass stars typically found in globular clusters. One explanation is the galactic orbit of M12 takes it closer to the galactic core than many other globular clusters. As M12 moves through the core area the lower mass stars are stripped away by the massive gravitational pull of the dense core area. This could explain the Class IX rating given to this cluster. The Class IX rating means that M12 has a loosely concentrated core area.

M12 is home to variable stars, blues stragglers, and red giants. What is unusual is that M12 only has 13 variable stars which is a small quantity for globular clusters. M12 is also populated with blue stragglers which are younger hotter stars that have formed as a result of interaction with other older stars. The red giants are large cool stars that are at the end of their lifespan.

[Science Blogs, ESO/ESA, SEDS]

Messier 5

M5, NGC 5904

Messier 5

Distance: 24,500 Light Years                          Telescope: 10” RC F8
Magnitude: 5.6                                                     Camera: QSI 683
Size: 23 Arc Minutes                                           Mount: AP 900
Cluster Type: Globular Class V                       Exposure: L 10×240 Bin 1, RGB 10×120 Bin2

Messier 5 is a large globular cluster in the constellation Serpens. At 13 billion years old it is one of the older globular clusters. It is also fairly large at 23 arc minutes but the majority of the cluster extends out about 17 arc minutes. Like most globular clusters, the stars in M5 were formed at about the same time. The largest short lived stars went supernova early in the clusters life cycle and blew out the remaining gas and dust in the region effectively removing the material for future star formation. The remaining stars fell along the main sequence and were smaller and cooler. This cluster also has many RR Lyrae variable stars and a large amount of Blue Stragglers. The RR Lyrae variable star is a star that fluctuates in brightness over a regular period. To date, 97 RR Lyrae variables have been cataloged. The blue stragglers are stars that are bluer and hotter than the surrounding stars in the cluster. This should not happen in a globular cluster as all stars are formed at about the same time. One theory is two stars had an interaction where they lost outer layers and merged in to one newer hotter star. Another theory is that the two stars had an interaction where one’s outer layers were stripped donating this material to the other star.

Globular clusters are rated according to the distribution of their stars. This rating system was formed by Harlow Shapley and Helen Sawyer Hogg and is known as the Shapley-Sawyer Concentration Class. The ratings use Roman Numerals starting at I and ending at XII. Roman numeral I is used for globular clusters with most of their mass at the core with little surrounding stars away from the core. Roman numeral XII is used for globular clusters with a very loose core with minimal structure. M5 is classified as a Class V globular cluster which describes the cluster as having intermediate concentrations of stars.

[SEDS, Wikipedia]

Messier 53

Messier 53, M53, NGC 5024

Messier 53

Distance: 58,000 Light Years                                        Telescope: 10” RC F8

Magnitude: 7.6                                                                     Camera: QSI 683

Size: 13 Arc Minutes                                                         Mount: AP 900

Cluster Type: Globular Class V                                   Exposure: L 10×240 Bin 1, RGB 10×120 Bin2

Messier 53 is a class V globular cluster in the constellation Coma Berenices. At a distance of 58,000 light years its 13 arc minute diameter translates to about 220 light years in diameter. It is one of the furthest globular clusters from the galactic center at 60,000 light years. Like most globular clusters this cluster is populated with many older stars, RR Lyrae variables, and blue stragglers. All stars in globular clusters form at about the same time so they should be about the same age. The discovery of younger blue stars threw a wrench in to the conventional thinking. Why where there younger hotter stars in the cluster? One theory about blue stragglers is that they are stars that have been stripped of their outer layers through interaction with other stars leaving a hotter core. Another theory is that two stars have merged in to one giving the appearance of a younger hotter star. The RR Lyrae type variable stars are also a common feature in globular clusters and these variables typically have a short period. Named after the first discovered variable star of this type, RR Lyrae, these variable stars are about half the mass of our sun, older than our sun, and also hotter than our sun. The variation in brightness is due to the increase and decrease in size of the star as its outer layers pulsate. The variable star will be brightest at its smallest size and dimmest at its largest size. These periods can be timed with great accuracy.

[SEDS, Universe Today, Wikipedia]

Messier 13

Messier 13, M13

Messier 13

Distance: 25,100 Light Years                                        Telescope: 10” RC F8

Magnitude: 5.8                                                                     Camera: QSI 683

Size: 20 Arc Minutes                                                         Mount: AP 900

Cluster Type: Globular Class V                                   Exposure: L 14×300 Bin 1, RGB 14×150 Bin2

Messier 13 is a large Class V (medium star density) globular cluster in the constellation Hercules. This cluster contains over a million stars* and shows well in short exposure images. M13 is very old at 14 billion years but contains some blue straggler stars which indicate much younger stars. One theory about blue straggler stars formation says they are older stars that have merged together from gravitational interaction and as a result are hotter that the surrounding stars. Another possibility is the stripping of outer layers from the star from interaction with other stars.

*Kevin Tran UC Davis July 29, 2009 reports over a million stars

Like all globular clusters, the stars of M13 formed about the same time and are about the same age. We know this because many of the earliest stars of globular clusters were very large and had a very short lifespan. During their demise they went supernova and blew any remaining gas and dust out of the area thereby depriving the area of any materials for star formation. What is left after these first few million years is the smaller stars that fall in to the main sequence and these are what we see today. The star density in the core area is very dense. There are several hundred thousand stars within a 6 parsec area around the core. In contrast, the nearest star to our sun is 1.3 parsec away. Could you imagine what the day and night sky would look like from a star near the core of M13? It would be awesome!

[Michael Warren McCutcheon, Department of Physics, McGill University, Montreal, April 11, 2011]

[SEDS, Wikipedia]

 

 

 

 

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