Spectroscopy

[Merlin66 (Ken)]

Another comment. If you have an UV-IR filter it may well be worth trying on this camera. My Baader has a UV cut-off just below 400nm and an IR cut-off at 700nm. This covers most (all) the visible spectrum and "focuses" the graph in this region. Just a thought.

[Merlin66 (Ken)]

http://www.cloudynights.com/photopos...01sa-illum.jpg

Maurice Gavin prepared this graphic based on discussions re the resolution of the SA grating in a converging beam.
The resolution of any grating is measured by the number of lines illuminated by the star.
If the grating is placed say 20mm infront of the CCD in an f10 beam, the size of the star image at the grating will be 2mm.
If the grating is say 100lpm, then the out of focus star image passes through only 200 lines of the grating. If the distance is doubled to 40mm, the resolution is also doubled!!!!
You can see then why it's always better to work in a large collimated beam of light through the grating; it illuminates more lines!!!

[theodog (Jeff)]

Hi All,

My last night efforts I think may have lead to some success.
I thought I would gather data on a F star, having done an A classification.
Having found one near B Car, I am now trying to relocate it in Guide to post details. When I located it the first time Guide stated that its Class (F5) was uncertain.

The images;
Plot based on 1x40sec -drk and bias
My data -blue
Library spec x my data -green
I measure the resolution at 22.9 A/Pix
Order
F5i, F5v, K01ii, K0iv and M0v.

If I am going about this correctly I should be looking at the closest match. This I believe is the K0iv spec.

I have also included the .dat file of the F5? plot.

Feedback please.

[Terry B]

Originally Posted by theodog

Now that is supprising. I will spec some other stars to check this out. It was the ST7e.

Thanks Terry. I now have some idea how to process the spectra.

Is the 3rd image straight from your camera or have you processed the .spc info in some way?

Hi Jeff
Sorry I haven't replied but I've been away from the puter.
My graph has been corrected for the instrument response. This is done by dividing it by the catalogue spectra, smoothing out any emission or absorption lines and then dividing the original graph by the smoothed graph.
This works if the star has a reasonably smooth spectra to start ie an A F or G star.
I have saved some standard smooth graphs and use them on other stars.

[Terry B]

Originally Posted by Merlin66

Good analysis Terry!
An extraordinary outcome; 24.1 A/pixel is pretty low resolution even for a SA grating... the distance to the chip could be increased i.e. almost doubled. The severe drop off in the blue-UV is not unusual, but the deep absorption threw me- it just looked to much like a H beta point! Moral of the story? - the info's in the spectra - somewhere!
Looks like Terry's curve has at least been corrected for CCD response and fitted to the Planck curve. ( Tutorial #5)
I've got to ask... Jeff - what was the issue with your first betcar spectra?
Are you doing some pre-processing??

My resolution depends on which camera I use. With my ST9E at f8 I get ~32A/pixel as the pixels are 20um square. If I use my Audine type camera with a KAF0401E CCD at 9um pixels I get ~12.4A/pixel.
I can't easily increase the distance with the ST9 as I run out of back focus and it is a hassle to change the cameras. I use the ST9 for photometry so leave it in place usually on the scope.
It is a trade off I suppose.

[Merlin66 (Ken)]

Jeff,
Those are looking good!! I'll "play" with them later
Exactly which star did you image?
With the data you've collected you should be able construct a camera calibration......
Next step, when you get a good match, is to look for the metal absorption lines......
Gray's "Spectrum" is a great way of building a comparison specta....

[theodog (Jeff)]

Originally Posted by Merlin66

Exactly which star did you image?

I am sure now that the star I imaged was Hipparcos #44599 or TYC 9203 2759.
Guide 8 gave its Spec Type as F6II-III or F5 ?
"Spectral type is from miscellaneous sources". -Guide 8

Although my graphs don't demonstrate this. So leads to confusion.

[renormalised (Carl)]

The problem with F class giants is that they're in the Instability Strip....they tend to be Cepheids, which means their spectra may vary as they pulsate. That can throw your readings out if you don't know what you're looking at. Here's a site that might help out..... McMaster Cepheid Photometry and Radial Velocity Archive

[theodog (Jeff)]

Cheers Renormalised.
Unfortunately my cataloge states that "No variability detected (stable)".
But it's only early days and I have much to learn. I need to image more classes of stars to nail this technique.

[Terry B]

I had another go with my ST9 and took 7 images of Gam Vel. This is the brightest WR star and has great lines. The dispersion is only 32A/pixel with this setup but it still is a nice image.

[renormalised (Carl)]

Originally Posted by theodog

Cheers Renormalised.
Unfortunately my cataloge states that "No variability detected (stable)".
But it's only early days and I have much to learn. I need to image more classes of stars to nail this technique.

I'd find that a little incredulous....nearly all A, F and G class giants show some sort of variability. Unless it's in a quite period, of course. Polaris, for example, just went through one of these phases. It's a classic Cepheid, but the periodicity and the luminosity changes almost disappeared at one stage. They became so small it was almost impossible to measure them, but now it's slowly coming back to normal. Probably was going through some state in its evolution into a red supergiant, at a later stage.

[renormalised (Carl)]

Originally Posted by Terry B

I had another go with my ST9 and took 7 images of Gam Vel. This is the brightest WR star and has great lines. The dispersion is only 32A/pixel with this setup but it still is a nice image.

Very nice spec' Terry

[theodog (Jeff)]

Originally Posted by renormalised

I'd find that a little incredulous....nearly all A, F and G class giants show some sort of variability.

Apparently not this one;

"Comments from the Hipparcos Catalog:
Hipparcos #44599
Click here for SIMBAD data
RA (J2000.0): 09 05 08.83
declination -72 36 09.7
(Above is the computed position for J1991.25)
magnitude in Johnson V: 4.47
Magnitude derived from ground-based observations
Trigonometric parallax 7.18 ± 0.45 milliarcseconds
Proper motion in RA: -8.44 ± 0.48 milliarcseconds/year
Proper motion in dec: -4.72 ± 0.39 milliarcseconds/year
Mean BT magnitude: 5.217 ± 0.002
Mean VT magnitude: 4.540 ± 0.002
Johnson B-V colour: 0.607 ± 0.010
Johnson B-V source is ground-based observations
Color index (V-I) in Cousins' system: 0.67 ± 0.02
Median magnitude in Hipparcos system (Hpmag): 4.5979 ± 0.0005
Scatter on Hpmag is 0.004 magnitudes
Hpmag is based on 118 observations
Hpmag at maximum (5th percentile): 4.59
Hpmag at minimum (95th percentile): 4.61
No variability detected ("constant")
CP -72 779
Spectral type F6II-III
Spectral type is from miscellaneous sources"

From Guide 8.

[renormalised (Carl)]

I'd be wary of the Hipparcos catalogue...it named quite a few stars as NSV (Newly Suspected Variables) when in fact they weren't.

I've got a paper for you here and 2 MS Word documents on the stars they looked at. Hip44599 is listed as HR3643...it's F9II and definitely variable, but very small amplitude = 0.02mag, probably why it appears as "constant".

You'll also have plenty of other stars to look at from the lists

[theodog (Jeff)]

Originally Posted by renormalised

I'd be wary of the Hipparcos catalogue...it named quite a few stars as NSV (Newly Suspected Variables) when in fact they weren't.

You'll also have plenty of other stars to look at from the lists

Cheers Renormalised, will do so soon.

Terry,
I have managed to spec Gamvel myself and have the raw results below Resol= 13A/pix through the 4" f9.
Do these seem right to you?
If so, I'm on the right track & what do I do from here?

[renormalised (Carl)]

Here's a copy of the document that is referred to by the other paper....

[Terry B]

Originally Posted by theodog

Cheers Renormalised, will do so soon.

Terry,
I have managed to spec Gamvel myself and have the raw results below Resol= 13A/pix through the 4" f9.
Do these seem right to you?
If so, I'm on the right track & what do I do from here?

This is verygood. It is quite similar to mine. I have corrected mine for the instrument response. This star probably isn't a good one to use as the basis for working out the instrument response. Choose a A or F star taken with the same configuration as Gamvela.
Open it and calibrate it. Then open a catalogue spectra of the same class of star.
Divide your spectra by the catalogue spectra. This will give you something like the first pic. The raw image is blue and the divided in green.
Then under the radiometry tab there is a function called "compute continuum"
Hit this and another toolbar appears. Push the first button to make it select points. Then select points along the continuum missing the absorption or emission lines.
When you are happy push the 4th button and a sloder appears. Change the number to 2000 and push the x10 button. I found it needs to be about 1200 to give a nice smooth graph. The result is your instrument response graph.
Go into the edit menu and push the replace button. Replace the ref 2 withthis graph then save the profile. It will then save it for future use.
After this you need to divide your raw gamma vela spectra by the instrument response graph. It should end up looking more like mine.

[theodog (Jeff)]

Thanks Terry.
I have been working through this proceedure but have many divide by zero and unforseen error messages. I did almost get an instrument curve once.
It seems Vspec errors are a problem.

[sheeny (Al)]

Originally Posted by theodog

Thanks Terry.
I have been working through this proceedure but have many divide by zero and unforseen error messages. I did almost get an instrument curve once.
It seems Vspec errors are a problem.

I got a heap of those for a while too, Jeff. I found I got on top of them when I started cropping the spectrum before doing the division. Are you doing that?

Al.

[Heian (Mark)]

Hi Jeff,
I don't know if you saw it, but back at post #52 of this thread, I added a pdf file of some emails I got from Robin Leadbetter on how to process a spectra to get an instrument response from an image.
I've added it to this post as well.
If you follow the steps from Robin, it should work fine. I have avoided Vspec errors by doing it his way
The curves / spectra you're collecting look pretty good to me...

cheers
Mark