Beginning with a Lisa

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Rainer Ehlert
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Joined: Thu Sep 29, 2011 9:36 pm

Re: Beginning with a Lisa

Post by Rainer Ehlert »

Francois Teyssier wrote:Hi Rainer,
Could you show us some same samples of your spectra.
I remember you've got good (very) results
François
Hi Francois,

Thanks for the Flowers :oops:

See below some recent spectrum images I have done and where I focused on approximately the 5000A to 6000A wavelength area. I am exposing now with a QSI520i with a Kodak KAI-2020M CCD chip to a maximum of about 32.000 ADU. The chip full well depth is 45.000 electrons. I do this because of V-Spec. I have done test going up to 60.000ADU (16bit depth) but V-Spec can not (¿ still or has it been changed ? :? ) process those images correctly as the spectrum is always overexposed and in other software it is OK.
Albireo-010x-median.jpg
Jupiter-050-0035s-median.jpg
Markab-B9.5III--020-030s-median.jpg
Vega-020x-median.jpg
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Francois Teyssier
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Re: Beginning with a Lisa

Post by Francois Teyssier »

Because of the appearance of mist on my telescope, I had to re-focus.
It appears a slight difference in the appearance of the blue edge
ZETPER2.PNG
ZETPER2.PNG (16.83 KiB) Viewed 18393 times
ZETPER1.PNG
ZETPER1.PNG (18.58 KiB) Viewed 18393 times
Note the second one is almost perfect.

François Teyssier
Francois Teyssier
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Re: Beginning with a Lisa

Post by Francois Teyssier »

Hi Rainer,

There is a significant difference between Markab et Vega.
Did you take the two spectra that night, with the same settings?

The continuum trace is very fine. Can you remind us what telescope you are using?

About the focale : the major interest of Lisa is to get get faint (very faint objects). If you use a reducer, you increase the signal (about factor 2 between F/D = 10 and F/D = 6, i.e. 1 mag).

Kind regards

François
Rainer Ehlert
Posts: 135
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Re: Beginning with a Lisa

Post by Rainer Ehlert »

Hi Francois,

No, Vega is from a few weeks earlier but Jupiter, Albireo and Markab are from 2 weeks ago, same weekend, with the new focusing workflow ...

OK, about the f/10 and f/6 difference, so it is 1 : 1.6 and then f/8 to f/5 is the same :mrgreen: which is my setup.

I am using an 8" Astrotech Ritchey-Chretien
http://www.astronomytechnologies.com/pr ... 77&c=10607
with the OptecInc NextGen 0.7x reducer
http://www.optecinc.com/astronomy/catalog/17409.htm
LISA-AT8RC.jpg
LISA-AT8RC.jpg (370.5 KiB) Viewed 18392 times
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Christian Buil
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Re: Beginning with a Lisa

Post by Christian Buil »

Hi Rainer,

The LISA is optimized for telescope faster then f/5. Of course, you can use LISA with f/6, f/8, f/10, ... telescope.

But... for my setup and observatory (no very good seeing) the captured signal at f/10 (direct focus of my SCT) is lower by a factor 2 to 3 relative of a f/6.3 usage of LISA spectrograph (add of a focal reducer). For a max. signal to noise ratio, use a fast configuration :!: The difference is significant.

Now comparison with Benjamen Lhires III 150 l/mm observation of HD57682 :

Image

La résolution obtenue avec LISA est assez fortement supérieure à celle de ta configuration Benjamin. En outre, tu va moins loin que LISA dans l'UV (en concevant l'optique j'ai veillé à ce que LISA donne une image relativement correcte dans le bleu - une partie du spectre particulièrement interessente astrophysiquement parlant).

Le réglage peut y être aussi pour quelque chose ? Le fait d'obtenir un spectre étroit dans l'extrémité du spectre ne signifie pas obligatoirement que la résolution spectrale est élevée. Ca peut même être l'inverse en présence d'astigmatisme, si celui-ci est orienté suivant l'axe spectral.

Here a typical comparison between a LISA spectral profile at the focus of a f/10 and f/6.3 télescopes. From 4000 A to IR, the difference is very small from the two profile. With my setup (focal reducer model and LISA adjustment) the spectrum come to be more sharp at f/10 for wavelength down to 3950 A :

Image

Note the quality of spectral calibration (thanks to ISIS special procedure for LISA ;) ). Note also the rich spectral contain in the blue part (compare with Benjamin spectrum).

Same type of comparison for a B9IV (HD27295), used for extract instrumental response :

Image

And here a comparison of HD27295 spectrum taken with LISA F/10 spectrum and a professionnal instrument (NOAO data base) of the same star - the shorten displayed wavelength is 3850 A :

Image

(the continuum is rectified - not the very high consistency ot result :) )

You download comparison files here :

http://astrosurf.com/buil/forum/lisa_lhires.png
http://astrosurf.com/buil/forum/lisa_compa.png
http://astrosurf.com/buil/forum/lisa_compa2.png
http://astrosurf.com/buil/forum/lisa_compa4.png

Christian B
Benjamin Mauclaire
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Re: Beginning with a Lisa

Post by Benjamin Mauclaire »

Hello Christian,

It's clear that LISA's resolution is better than LHIRES 150 g/mm.
What was your slit size?
How long were your exposures and how many?

It looks like resolution at f/d 10 input is rather the same.
It would be rather usefull how f/d ration impact with the same deep sky object.

Focal reducer does absorbe a fraction of light. Internal LISA tripplet does it too.
With that facts, what is the expected total magnitude gain with LISA?

How could I be able to switch between the two setup (LHIRES3 2400 and LISA) without any modification of the main telescope focus?
Actually, I'm able to switch between LHIRES3 and CCD for photometry without any focus change, just need a little touch on electric focuser for fine results. All instrumentation are pluged on the electric focuser at f/d 10 cassegrain focus.

Benji
Spcaudace spectroscopy software: saving you hundred hours of frustration.
Christian Buil
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Re: Beginning with a Lisa

Post by Christian Buil »

For the HD57682 spectrum with LISA at f/6.3, the exposure time is 9 x 60 sec (compare with your 5 x 600 sec exposure with Lhires III 150 l/mm...). For the f/10 image, the exposure time is 17 x 180 s (a very windy night - half of the time the star is out
of the slit).

The slit width is 35 microns.

My answer for exposure time and LISA efficiency is here:

http://astrosurf.com/buil/isis/etclisa/etclisa.html

Christian B
Rainer Ehlert
Posts: 135
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Re: Beginning with a Lisa

Post by Rainer Ehlert »

Hi Christian,

Thanks for that interesting comparison.

Maybe I will do some comparisons end of the year during Christmas Holidays and see what comes out with my AstroTech 8" at f/8 and F/5.

From what I read about the slit size perhaps I change to 35µ slit.
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Francois Teyssier
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Re: Beginning with a Lisa

Post by Francois Teyssier »

Hi Rainer,

The choice of the slot depends on the brightness of your target, all else being equal (transparency of the sky, homing ...). Tries to use the slot 23 mcm up, it gives you a much better resolution.
I pass to the slot 35 mcm from 11-12 mag.
The choice also depends on the distribution of energy: certian mag 12 star are easier targets than 10 mag.
Good luck and tell us your current tests.

Kind regards

François Teyssier

PS: have you tried you back into ISIS?


Le choix de la fente dépend de la luminoisté de ta cible, toutes choses égales par ailleurs (transparence du ciel, autoguidage ...). Essaye d'utiliser la fente 23 mcm au maximum, elle te donne une bien meilleure résolution.
Je passe à la fente 35 mcm à partir de mag 11-12.
Le choix dépend aussi de la répartition de l'énergie : certiane étoiles de mag 12 sont plus faciles que des cibles à mag 10.
Bonne continuation et tiens nous au courant de tes essais.

PS : as tu essayé de te replonger dans ISIS ?
Olivier Thizy
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Re: Beginning with a Lisa

Post by Olivier Thizy »

Rainer,

The input collimator is F/5. If you use a faster scope, you will loose light inside the spectrograph as light will go outside the collimator diameter.

But you can always use a slower scope such as F/6.3 or even F/10 scope. The disadvantage of doing so is that you will loose more light at the slit entrance. The exact loss would depend on your telescope diameter and your actual seeing. But it would certainly be smaller than using a faster than F/5 scope.

Cordialement,
Olivier Thizy
Vous ne verrez plus des étoiles comme avant !
http://www.shelyak.com/en/
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