Thank you for replies. I am asking about the color of the nebula because I know that green color isn't usual. At
http://www.irida-observatory.org/Nam...346/NGC346.htm the nebula has a blueish color. It was used LRGBHa filters.
I have few information about the cluster and nebula.
The cluster has low metalicity. It has size of approximately 350 light years. It has an unusual number of variable stars, among these there are many slowly pulsating B stars.
About the nebula I only found information saying it is a H II region. For this information the color of nebula should be cyan. I read that Hydrogen has emission only on violet - 410nm, blue - 434 nm, cyan - 486 nm and red 656 nm
The green color can be from atmosphere action ? The target is very low on my field: maximum 40 degrees.