Ann wrote:
Today's APOD shows us interesting detail in the most famous part of IC 1396, the Elephant's Trunk. In the picture at left (in Ann's original post), however, we can see the whole nebula in RGB. The Elephant's Trunk is not so prominent here. It can be seen at three o'clock, close to the central blue star.
That blue star, HD 206267, is responsible for lighting up the nebula and sculpting the Elephant's Trunk. The whole nebula, IC 1396, is interestingly similar to an older version of the
Trifid Nebula. The young central star of the Trifid, HD 164492, has not had time to blow away all that much of the gas and dust in its vicinity. But HD 206267 has blown away all the dust lanes right next to it, and it has blown away so much of the nearby hydrogen that the red emission nebula surrounding it glows quite dimly. The Elephant's Trunk is a feeble reminder of IC 1396's former bright and dusty glory.
Aha! Thank you Ann! You have once again expanded both my understanding and appreciation of the cosmos. When I first looked at the picture of IC 1396, I thought it was the Trifid nebula.
Ann wrote:
Matt BenDaniel's picture also shows a remarkable star in the Milky Way, Herschel's Garnet Star. It is a monstrously large star which has nothing whatsoever to do with IC 1396, due to the fact that the star is extremely extended and cool and therefore completely unable to ionize an emission nebula. The Garnet star, also known as Mu Cephei, is the orange star seen at eleven o'clock in the image.
We can be sure that Mu Cephei is older than HD 206267, the blue star ionizing the nebula. HD 206267 is young enough that it has a nebula around it in the first place, but Mu Cephei is old enough that it has run through all sorts of fusion processes in its interior. It is easy to think of Mu Cephei as the product of an earlier epoch of star formation which triggered the formation of IC 1396 and the Elephant Trunk. However, that appears not to be the case. According to Hipparcos, Mu Cephei is more distant than IC 1396. If Hipparcos is right, then Mu Cephei is a background object and completely unrelated to IC 1396.
In any case, Mu Cephei is an utterly gigantic star and more deeply orange in color than most "red giants". If you have a good pair of binoculars, why not go outside and look at it yourself?
Ann
Indeed. In addition to being really red, Mu Cephei is also variable. Repeated observations through binoculars will reveal an interesting correlation between its brightness and apparent color.
May all beings be happy, peaceful, and free.
