Spectrum of 3C273

[robjn]

I have had this quasar on my list since seeing Robin's observation on his website a couple of years ago when I first bought my Staranalyser but only now have I had a go myself.

The image was stacked with bias, dark & flat calibration but the original processing was very noisy even though I could see the Ha line clearly. I re-processed with a sum stack and more careful processing in VSpec including calibration for instrument response which gave a less noisy result. I used the Balmer lines of a field star for wavelength calibration.

The first processing gave Ha 7582A and Hb+OIII 5635A(see http://www.astrosurf.com/~buil/us/spe6/quasar.htm) giving z=0.155, 0.155
The reprocessed result gave Ha 7593 and Hb+OIII 5631A giving z=0.157, 0.154. I'm very pleased with the results which compare well with the published value of z=0.158.
Even though 3C273 is very distant it felt close to home when I read this today 
http://www.eso.org/public/outreach/press-rel/pr-2009/pr-17-09.html

Thanks,
Rob.

[alexthegreek]

Nice work Rob !
And you got really close to the  z values !

[robin_astro]

That is an excellent result. I like the way  H alpha and beta show clearly in the image (Is that H gamma and perhaps even delta I can see in the graph too?)

With a result like that you should try for APM 08279 +5255 (z = 3.87)
http://www.threehillsobservatory.co.uk/astro/spectra_22.htm
It was marginal for me but I think I picked up the drop at the edge of the Lyman forest.  I keep meaning to have another go at it.

Cheers
Robin

[robjn]

Thanks very much Alex & Robin.

I hadn't thought of looking for any more Balmer lines but I'll check when I get home and see if any match up.

I have been used to nice bright objects so far - stars, WR Stars etc. where the signal is really good so I was initially a bit dissapointed at the background noise on this one!
I remember looking at your APM 08279 +5255 result Robin, another great result. I agree the setup I have should make this possible, my biggest problem is light pollution giving high backgrounds. I have used a Lumicon deep-sky filter to good effect in normal imaging but it would block the critical lines for this object  so long exposures instead I guess. I'll give it a go - I love a challenge!

Thanks,
Rob.

[Roger Banks]

This is very interesting and inspiring work Rob (/Robin)
Is the Staranalyser or an equivalent available in 2" mounted or 50mm round unmounted format?
Rog

[robin_astro]

Is the Staranalyser or an equivalent available in 2" mounted or 50mm round unmounted format?
Rog

Hi Rog,

The Star Analyser is only supplied in a 1.25 inch filter cell, though if you can find a way to mount it you do not have to worry about vignetting as long as you  place the zero order star image in the unvignetted part of the field. (The spectrum diverges after the grating and so is not affected by vignetting.)
Baader used to make some larger gratings (They are not stocking them currently) but they were much more expensive as the cost of gratings is pretty much proportional to the area.

Robin

[Roger Banks]

Thanks for that Robin - would be nice to pop one into the CFW - what sort of physical depth is the glass on it's own?

[robin_astro]

Thanks for that Robin - would be nice to pop one into the CFW - what sort of physical depth is the glass on it's own?

It is a a sandwich of the grating on one glass and a cover glass protecting the grating surface. The thickness of the complete sandwich is about 1.5mm. Originally the assembly could be removed from the cell but I believe now it is bonded in place to preserve the orientation and to give double protection against moisture ingress. You could contact Bob Hawksley at the manufacturers www.patonhawksley.co.uk and he might be able to provide you with one off the production line before it is put in the filter cell. 

I am surprised nobody makes a 1.25 to 2 inch filter convertor. I remember looking round for one a while back without success.

Robin

[Roger Banks]

Thanks Robin - the Astrodon filters are about 3-4mm thick so this will not be a problem. I could always turn an adaptor up in the lathe but there is not enough gap in the CFW for the whole mounted unit as is - I'll drop him a line I think - have some K!

[robjn]

...Is that H gamma and perhaps even delta I can see in the graph too?

You were absolutely right Robin, H-gamma (4340) is the next main peak to the left measuring around 5020-25 (z=0.157-0.158).
H-delta (4102) is less clear but assuming a single peak measures 4765-70 (z=0.162-0.163).
Thanks for pointing them out 
Rob.

[robin_astro]

have some K!

What camera do you use and the distance from the filter to the CCD in your setup? (The dispersion depends on the distance and you need enough to give you a reasonable length of spectrum but not too much that it does not fit in the frame)

Robin