A new nebula (halo) around IC 2220

Posted by Michael Bakich
on Thursday, May 10, 2018

One of our readers, Josep Drudis, who also is an avid astroimager, just sent me this report of a discovery he made. Nice work, Josep!

 

This image of IC 2220 shows the features the imager describes in the text. // Josep Drudis
IC 2220 is usually known as the Toby Jug Nebula. This is, apparently, due to its resemblance to a specific kind of jug that depicts characters. Nobody knows whether “Toby” had a special face shape that inspired the astronomers who named it.

The red-orange IC 2220 is, strange as it may sound, a reflection nebula. There are few known red-orange reflection nebulae in our galaxy, and they are always related to red giant stars. In this case, the star HR 3126, a type M2II red giant, has a mass of about five solar masses and a magnitude around 6.5 (it is a variable).

Usually, reflection nebulae are blue, reflecting and dispersing the light from blue stars near them. The bi-conical nebulosity IC 2220 formed by mass ejection from HR 3126 and its mass has been calculated at 0.7 solar masses. Its spectrum shows that, following the usual feature of this type of object, the reflected light is slightly bluer than the star’s original emitted light.

But there is something peculiar in this image: Apparently, the mass ejection from HR 3126, has occurred in two or three stages. This image shows two faint bubbles. Hints of some arcs of the first one are about 7.5 arcminutes to the east and west of HR 3126 (midway towards the upper left and lower right corners). The second bubble lies 5 arcminutes to the west (towards the lower right corner) and around the main nebula. These features are not captured in normal LRGB images, the normal choice of filters for reflection nebulae. For my image, I added exposures through a Hydrogen-alpha (Ha) filter, and it is the only one where these bubbles show up.

My initial intention of using an Ha filter was to capture any faint red nebulosity in the background. But once the bubbles popped up in the initial Ha master image (a stack of six 30-minute exposures), I took 15 more 30-minute ones in order to get a deeper, less noisy, image.

It was my 10-year-old daughter, Anna, who was playing with the DDP tool in CCDStack with the Ha master image, who first noticed it. I have thus dubbed these bubbles Anna’s Nebula. I have not yet found any earlier mention of bubbles around IC 2220. I have found many excellent images of IC 2220 online, most of them even better detailed and showing the object’s structure much better than mine, but none of them (all of them taken in LRGB) shows the additional bubbles.

By combining exposures from three other imagers, the author was able to confirm his discovery. // Andrealuna Pizzetti, Tel Lekatsas, and Christian Sasse
Three astrophotographers, Andrealuna Pizzetti, Tel Lekatsas, and Christian Sasse have also taken Ha pictures of this region to try to confirm the existence of these bubbles. The integration of their nineteen 10-minute exposures (see below) taken through another 20-inch telescope, shows the same bubbles’ position and shape, confirming them.

For a larger version of my H-alpha/LRGB image and more information about how this image was taken, please go here.

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