M33详细

HII regions in the Triangle galaxy, M33

http://www.astrosurf.com/patricio/DS/DS-M33-regHII.htm

The Triangle galaxy (M33, NGC 598) is one of the galaxies where it is easier to see internal structures. It is a relatively close galaxy that is located about three million light years away, it is flat and it is easy to appreciate its spiral structure even with small aperture telescopes. In addition, it is possible to observe many HII regions and star clouds.

The Triangle Galaxy, M33, NGC 598.Image: Digital Sky Survey

An H II region is a bright gas cloud, essentially hydrogen, in which massive blue stars (type OB) form. These stars are very hot and emit ultraviolet light with great intensity, which ionizes the gases of the nebula around them. The H II regions are so named because of the large amount of ionized hydrogen they contain. HI and HII are antiquated names that are still used in astronomy to refer respectively to neutral (ie atomic) hydrogen and ionized hydrogen. In an HII region most of the hydrogen is not ionized, not even in the excited state, but excited hydrogen is common there and when it loses that excitation an electron falls into a lower orbit and releases energy in the form of light. Of all the possible light emissions from these atoms we are interested in those that occur in the visible regions of the spectrum and that correspond to the Balmer series H alpha (emission in red light) and H beta (emission blue-green). Other emissions are produced in infrared, violet and ultraviolet, but from the point of view of visual observation they are not interesting. Using narrow band filters we isolate these emissions and block others singularly those produced in continuous spectrum. The contrast thus increases. but from the point of view of visual observation they are not interesting. Using narrow band filters we isolate these emissions and block others singularly those produced in continuous spectrum. The contrast thus increases. but from the point of view of visual observation they are not interesting. Using narrow band filters we isolate these emissions and block others singularly those produced in continuous spectrum. The contrast thus increases.

The most prominent of the M33 HII regions is so large and bright that it has been included in the New General Catalog as NGC 604. This HII region is located at the NE end of M33, specifically at the distal end of one of the arms. Visually it is very close to a star of magnitude 9.35 in the Milky Way. This region is about 1500 light years in diameter and at that size dwarfs the HII regions of our own galaxy. Suffice it to say that the Orion Nebula (M42) has a diameter of just 14 light years and is 1,500 light years from Earth. Additionally, NGC 604 contains some 200 giant blue stars that make it glow while the Orion Nebula has just four.

Region H II NGC 604.**Image: http://hubblesite.org

We recently made the observation in Las Majadas under undesirable meteorological conditions, with a lot of humidity and clouds. We used a 16 ”Newton mount telescope Dobson equipped with a filter wheel that allowed us to alternate the view of the galaxy without a filter and with an NPB narrow band filter and thus compare both images with great ease. By inserting the NPB filter the peripheral regions of the galaxy and the star clouds disappeared but the HII regions and even the core of M33 remained bright. For observation, we used an 8mm Ethos eyepiece that offered us magnifications of x228, a 1.7mm exit pupil and a sufficient field to simultaneously see the core of M33 and NGC 604. By inserting the NPB filter the core continued to shine but NGC 604 markedly enhanced it. Other HII regions were also visible but with the clouds threatening rain our observation we did not dedicate more time to them than to verify their presence.

M33 and NGC 604.Image modified from one provided by NASA