LMC & Tarantula Nebula

Rob_K · #1 19-10-2009, 01:19 PM

After drawing a blank last night with a particular target near the LMC (too dim), I backed off to 55mm to take a 'happy snap' of the area. The LMC 'spectrum' is a nice hazy rainbow, but the Tarantula Nebula, effectively a point source at this scale, appears to show a very dim spectrum illuminated by two very bright spots in the blue & red.

Did a quick-&-dirty Google but didn't find anything. Has anybody done anything on this object, or got any information? Thanks.

http://i727.photobucket.com/albums/w...8Oct09crop.jpg

Star Analyser, Canon 400D, 55mm, 2 x 90 sec @ ISO 1600, F/4.5.

Cheers -

Heian (Mark) · #2 19-10-2009, 01:58 PM

Rob,
just my guess, but you've probably got H alpha (red) + OIII (blue)...

In any case, you've managed to catch many a spectra on that shot

cheers....
Mark

theodog (Jeff) · #3 19-10-2009, 07:38 PM

My guess would be Ha & Hb?

Merlin66 (Ken) · #4 20-10-2009, 10:35 AM

As the Tarantula is basically Hydrogen.. my first guess would be the Hb and Ha. There's also another emission (mid frame) fainter but with similar Hb and Ha.
If I can find my Atlas I'll check out the position.
Update:
According to Urano Vol2, map A24
The faint Hb and Ha near centre appears to be coming from S dorado, a Var involved in NGC 1910 - can someone else check this out??

Rob_K · #5 22-10-2009, 10:06 PM

Thanks for your input guys! I've done a quick calibration on it and I think the blue is the OIII line at 500.7nm rather than the H-beta at 486.1, assuming that the red line is H-alpha at 656.3nm.
I didn't notice the other faint one, thanks Merlin!

It appears to me to come from NGC 1910, another bright nebulous area in the LMC, but I'd would welcome a correction on that.

Interesting really, presumably if you zoomed in on the Tarantula Neb, the spectrum would show as two Tarantula images (three if the H-beta 'line' showed), equivalent of two or three narrowband images for the price of one! Might try it if I get time.

Cheers -

Rob

Merlin66 (Ken) · #6 22-10-2009, 10:21 PM

NGC1910 is a cluster, so it should not be giving emission spectra.
It might be the variable s Dorado which is involved.

Rob_K · #7 22-10-2009, 10:46 PM

Sorry Merlin, I should have said that it's the emission nebula around NGC 1910. The cluster itself was not bright enough to register on my shot, but the nebula has.

Edit: Now I'm not so sure! The nebula has very faintly given a blue patch, but the H-alpha 'blob' isn't there. Went back to the full-size image and can't really find anything. Maybe I'm not looking in the right spot...

Cheers -

Rob_K · #8 23-10-2009, 01:16 AM

I imaged the Tarantula Neb at 200mm (11 x 90 sec) and it gave a clearer picture. It seems to show a little at around the Hb area, although a slit would be needed to confirm this. Two attached pics show the Tarantula Nebula with spectrum (note the blue 'ghost nebula'!), and a composite showing the various features along with an unfiltered DSLR shot taken the other night (scale may vary).

Link below is to the full frame from tonight (reduced size) - very colourful, LOL! It shows lots of similar spectra to Tarantula, from little nebulae here and there.

http://i727.photobucket.com/albums/w...DSSredsize.jpg

Didn't get up into the area Merlin was referring to - hope somebody else did...

Cheers -

Merlin66 (Ken) · #9 23-10-2009, 06:25 PM

The shape of the emission features shows clearly the regions of Hydrogen and Oxygen- as you said a cheap method of narrowband imaging!
Imagine saying " I have Hb OIII and Ha images taken with effective 20A bandwidth filters" -cool!!