What is in 30 Dor?

[Terry B]

Dear All
I took a spectra of the centre of 30 Dor a couple of nights ago with my LISA spectrograph.
The first image is from the guider showing where the slit of the spectrograph is positioned.
http://www.iceinspace.com.au/forum/attachment.php?attachmentid=123919&stc=1&d=1349489329

The light that hits the black line(the slit) in the image passes through the slit and then goes on to make the spectrum.

http://www.iceinspace.com.au/forum/attachment.php?attachmentid=123920&stc=1&d=1349489484

You can clearly see the spectra of the stars in the middle of the image plus the lines of the emission cloud surrounding them.
The graph is below
http://www.iceinspace.com.au/forum/attachment.php?attachmentid=123921&stc=1&d=1349489484
I have labelled the emission lines. The absorption lines in the IR region are all from atmospheric water and are not part of the stars spectra.
Cheers

Terry

[DavidTrap]

Looks like your getting some interesting data Terry.

Have you seen this - saw the link on CloudyNights

http://www.stsci.de/wr134/index.htm (Link)

From what I can deduce, the dec of these stars are around +36. Is that visible from your observatory? Or could you spare a couple of weeks to go to Teneriffe?

DT

[Terry B]

+36 is a bit hard for me I'm afraid. :D

I've had a question about how this all works so here is my simple answer.

The spectrograph essentially has a little glass mirror in it with a narrow gap in the mirror. This is the "slit". It is 23um wide. The telescope focuses an image onto the mirror and a small, narrow band of light passes throught the gap in the mirror. The image that I posted is an image from a guide camera. it looks at the front of the mirror so you see the star field with a "gap" in it. The quality of the image is pretty crappy because to achieve the focussed image of the mirror, the guide camera has to look through a small doublet lens. This is not high quality as it is only intended to assist in centering the target on the slit and guiding.
The light that passes through the slit is then focussed by a lens onto a dispertion grating which then splits it into the spectrum. This is then refocussed onto the imaging camera to produce the image of the spectra.
I then select a small vertical region of this and to create the graph of the spectra. Just after taking the images I then illuminate the slit with a neon light. This then produces a spectra of the neon that can be used to calibrate the spectra of the target.
The spectra are always displayed with the blue end to the left and the red to the right.
All as clear as mud.

:P

Terry

[Merlin66]

terry,
good results, good description of a reflective slit spectroscope!
Well done.

[Rob_K]

Good stuff Terry, talk about a great answer to a question I've been too afraid to ask! :D An easy-to-follow description of exactly how a slit works. :thumbsup:

Cheers -