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IC4603

IC 4603 is a reflection nebula in Scorpius that is the core region of the Rho Ophiuchi Complex. IC 4603 is a good representation of a reflection nebula which is formed by dense interstellar dust clouds reflecting nearby star. For IC 4603, the bright star, SAO184376, with 7.90 magnitude is the main source of light for the blue reflection nebula. Often times reflection nebulae are predominantly blue for two reasons. First, they are blue for the same reason that the sky is blue. In interstellar dust clouds and the atmosphere on earth, blue is scattered more than red because it travels as shorter waves. Second, reflection nebulae are not as colorful as emission nebulae because the energy from the nearby stars is sufficient enough to scatter light to make the dust visible but is not quite enough to ionize the gas of the interstellar dust clouds to create an emission nebula.

At first glance, it is hard to tell if these images contain real or illusory nebulosity. Back in 1895, there was a similar debate on dim nebulosity of the star cluster NGC 2264 between Issac Roberts and E. E. Bernard. Bernard with his 6-inch f/5.2 wide field camera first took a widefield image of NGC 2264 which showed a nebulosity all around NGC 2264. However, Roberts with his 20-inch f/5 telescope enlarged Barnard's image fivefold and saw nothing but virtual pinpoints of stars. Roberts argued that the nebulosity on Bernard's image is illusory and it stemmed from the poor resolution of the Bernard's camera. It turns out that Roberts was wrong for a few reasons. Visibility depends on the surface brightness of the diffuse nebula. In both Barnard's and Roberts' images of NGC 2264, there is a large region where there are essentially no stars at all. Barnard says, "that this is real diffused nebulosity there is no reason whatever to doubt." Also, Barnard pointed out that Roberts' images did not contain very faint interstellar clouds because he had short exposure time and narrow field of view. Similarly, these images of IC 4603 are narrow field images with short exposure time of 60 seconds. Compare these images with this image by Rolf Olsen which is widefield with longer exposure time.

Looking closely at these images and comparing them with the Orion Nebula, it is possible to imagine the spatial image of IC 4603. Both IC 4603 and Orion nebula each have one or two bright stars that are at the center of the nebula, illuminating the dust clouds that have shapes of a "bowl" around the bright stars. From the Earth, when we look at the IC 4603, we are looking down the "bowl" with the stars in the center. However, when we look at the Orion nebula, we are looking at the side of the "bowl." So, even though, in IC 4603, we are not able to see distinct contrasts and shapes of interstellar clouds that are present in the Orion Nebula, we can see the irregular "edges" of the bowl that seem darker.

We took images for four nights to get these images. First night, I could not see anything in the images because I did not realize how faint the nebula was and used exposure time that was too short to catch the nebula. Next night, I used longer exposure time but the images contained fuzzy light graduating from west to east. It turns out that there was a full moon fifteen degrees away from our target object. Third night, R (Red) and V (Green) images were great but the B (Blue) images did not contain enough information in them. This is why my color image of IC 4603 is slightly greener than it should be. Fourth night, to add some texture to the nebula, we took C (Clear) images. Images below are Clear images with different contrast to emphasizes different parts of the nebula. Left shows the brighter and smaller parts of nebula right around the stars. Right shows the fainter and broader parts of nebula all around the stars.

IC4603IC4603

 

References:

Hirshefeld, Alan. "The Nebula War." Sky & Telescope Jun. 2016: 36-40. Print.

Olsen, Rolf, IC 4603 - The Turbulent Heart of the Scorpion 2016. Auckland, New Zealand. Web. 3 May 2016. <http://www.rolfolsenastrophotography.com/Astrophotography/Nebulae/i-dJL49Pc>

"Index Catalog Objects: IC4600-4649." <http://cseligman.com/text/atlas/ic46.htm>

Wikipedia, "Reflection Nebula."

Right Ascension (J2000) 16:25:24
Declination (J2000) -24:23:24
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure x number of images for each filter B, V, and R (60s x 40); C (60s x 80)
Image dimension 688x452 pixels; 15.0x8.0 arcminutes
Date/time observed

March 16, 2016, 11:44 UT

April 22, 2016, 08:42 UT

May 3, 2016, 06:14 UT

May 6, 2016, 07:30 UT

 

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