second try at AG Dra

Show your spectra, your results ...

second try at AG Dra

Postby SteveCuthbert » Sat Apr 19, 2014 1:07 pm

Hi
Only managed one 600sec shot at ag Dra last night until my powered usb hub stopped working, hopefully I managed it ok!

agDra.png
agDra.png (5.44 KiB) Viewed 3701 times


regards
Steve
SteveCuthbert
 
Posts: 45
Joined: Fri Aug 09, 2013 6:25 am

Re: second try at AG Dra

Postby Francois Teyssier » Sat Apr 26, 2014 10:59 am

Dear Steve,

The lines are correct, but the continuum is still wrong (it is smoother and redder)

Not easy to say weither acquisition or treatment has to be improved
You could
1. describe your procedure
2. send us the fits of the target, reference, neon and flat

François
Francois Teyssier
 
Posts: 1280
Joined: Fri Sep 23, 2011 1:01 pm
Location: Rouen

Re: second try at AG Dra

Postby SteveCuthbert » Sat Apr 26, 2014 1:35 pm

Hi Francois
As my hub stopped working I only had chance to take 1-600 sec fit of AG Dra and a 1-120sec fit of my Argon/Neon lamp for calibration see both here :-
https://www.dropbox.com/sh/2wlm7cwjhhy6una/4VbCfEAd_3
I put both into ISIS making sure the x coordinate for the 5852 line was correct to calibrate and plot the curve and then divided by the ISIS K3III reference for the response and then smoothed out the curve using the continuum tool !
It would be good if you could have a look at the fits and maybe tell me how to correct it or if my method was wrong please?
Thanks
Steve
SteveCuthbert
 
Posts: 45
Joined: Fri Aug 09, 2013 6:25 am

Re: second try at AG Dra

Postby Robin Leadbeater » Sat Apr 26, 2014 4:22 pm

Hi Steve,

I now understand why all your continuum is always flat :)
What you have been doing is removing the continuum shape. This is not the right way to correct for instrument response. (You would have to know what the spectrum of the target is in advance which we of course never know for certain, otherwise why would we be measuring it ;) )
To calculate the instrument response you must take the spectrum of a known reference star. This should be a hot A/B star (so the continuum is clear and there are few lines) taken on the same night and at a similar altitude as the target so that the atmospheric extinction is the same. You then divide this by the library spectrum of the same star and smooth as required to produce the instrument response. You then divide your target spectrum by this instrument responsr to produce the corrected final spectrum. You can see how to produce the instrument response here in section 2 for example
http://www.astrosurf.com/buil/isis/guid ... uto_en.htm

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1343
Joined: Mon Sep 26, 2011 4:41 pm

Re: second try at AG Dra

Postby Francois Teyssier » Sat Apr 26, 2014 4:41 pm

Steve,
Robin is correct

The continuum of symbiotic stars is complex.
The mean contribution is that of the giant, wich can vary (activity, orbital phase ...), but it is modified by the hot component in the blue part of the spectrum and also by recombination processes oh HI, He I and He II.

So you have to take the spectrum of a "normale" reference star.
In ARAS information letter, I propose HD 145454 (Mag = 5.4 and E(B-V) = 0)

Your spectra can be saved by using one of the recent spectra in the data base to compute the response ; but for the next trials, take your own reference.

Good continuation and keep us informed of your progress

François
Francois Teyssier
 
Posts: 1280
Joined: Fri Sep 23, 2011 1:01 pm
Location: Rouen

Re: second try at AG Dra

Postby SteveCuthbert » Sat Apr 26, 2014 8:17 pm

Thanks Robin and Francois
I really should know this by now as I`ve been taking spectra long enough :? :? . My line of thinking stems from reading the Alpy600 manual where it describes the process of taking a solar spectrum and then dividing by a G2V reference from the ISIS database which is then smoothed out by the `continuum` feature, I just assumed this to be similar for other stars although logic would suggest that taking a spectrum of a K3III star such as AG Dra and dividing it by a library K3III spectrum the end result would be the same?? So do forgive the `beginner` type questions :) but you would suggest that regardless of which star you are taking a spectrum of you would always seek out an A or B type star of similar altitude to calculate the response later?. If I take a spectrum of a star at say 70degrees altitude and also one of an A type at about 70degrees (for the response) and then try a star at 45 degrees altitude are you suggesting looking for an A or B at 45degrees also or would the former suffice for the whole evening?
Sorry if this is all basic stuff but the many tuts I`ve seen describe different ways of taking spectra using different software and I really should stick to one way, ie the correct way! :)
thanks for your patience
Steve
SteveCuthbert
 
Posts: 45
Joined: Fri Aug 09, 2013 6:25 am

Re: second try at AG Dra

Postby Francois Teyssier » Sun Apr 27, 2014 6:32 am

No problem, Steve, this is the objective (or one of them) of the forum to help new observers (and to improve the results)

A (or B) type stars are used as reference to compute the response (atmospheric+instrumental) for two reasons :
- the continuum of the objects we observe are not kwown, complex or variables
- A/late B stars show only a few number of lines (at least, less than hotter or coller stars)

The reference star must be, approximatively at the same altitude than the target (say the difference must be under 5° ; it depends of the altitude)
You have to take a reference for each target ( exception : the altitude is high, the exposure time is low, all the targets are in the same zone)
You have to take reference star each night because atmospheric conditions may change

I always take the same reference for one target.
During collective survey, we use the same refernce star

To choose a refrence star, here's a spreadsheet
http://www.astronomie-amateur.fr/Documents%20Spectro/ReferenceStarFinder.xlsm
Try to choose a reference whose interstellar extinction is low

Also, here's an abacus showing the acceptable difference of altitude between target and reference
http://www.astronomie-amateur.fr/Documents%20Spectro/Ref_013.pdf
Example :
Your acquire a spectrum of the target at a mean altitude of 50°(vertical scale)
You accpet on error of 3% (choose the curve), you get : the difference between target and refrence must be under 3 ° (under mean atmospheric conditions)

The see than under an altitude of 30°, the goal is challenging !

All the best,

François
Francois Teyssier
 
Posts: 1280
Joined: Fri Sep 23, 2011 1:01 pm
Location: Rouen

Re: second try at AG Dra

Postby SteveCuthbert » Sun Apr 27, 2014 6:57 am

Excellent reply Francios, many thanks for the advice.
Regards
Steve :D
SteveCuthbert
 
Posts: 45
Joined: Fri Aug 09, 2013 6:25 am

Re: second try at AG Dra

Postby SteveCuthbert » Sun Apr 27, 2014 1:48 pm

Hi Francois
I took an image last night of AG Dra again and used for response calculation a nearby B type star HD 145454 and get a reasonable response curve for the Alpy600 thus -
responsecurve.png

which I use to correct the HD145454 profile thus -
HD145454smoothed.png


I then process AG Dra using a 600sec exposure plus a 600sec dark plus a cosmetic and also using the above response curve and get this profile
Beforesmoothed.png

This is then smoothed out to give this final curve -
AG Dra.png
AG Dra.png (5.51 KiB) Viewed 3634 times


which strangely enough looks a lot like my original and does not have the shape I`ve seen of other profiles of AG Dra?? More practice maybe ?
Regards
Steve
SteveCuthbert
 
Posts: 45
Joined: Fri Aug 09, 2013 6:25 am

Re: second try at AG Dra

Postby Robin Leadbeater » Sun Apr 27, 2014 3:26 pm

Hi Steve,

No need to do the final step. The result after dividing by the instrument response is the one you want. Your IR looks reasonable, except perhaps it is over smoothed at the extreme blue end and therefore does not quite fit the continuum and is probably causing the flick up in your ref star spectrum compared with the true library version. I am not familiar with AG Dra though so I cannot say if this is correct. Over to you Francois :)

Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1343
Joined: Mon Sep 26, 2011 4:41 pm

Next

Return to Spectra, results, information on activity ...

Who is online

Users browsing this forum: No registered users and 2 guests

x