Forum der Vereinigung der Sternfreunde

Hello all:

I have encountered some questions that I am not very clear about them. Hope to get your great advice & explanation.
<my ISIS is version 5.1.2>

1). Predefined mode. it has 1200L [6 lines], if this mode can ONLY be used to calibrate Ha zone?

2). For WR134, what should I fill in the "scaling profile spectral region " in the "Settings" Tab? I know that its fuction is to normalize the continuum by selecting a region where there is no spectra, no emission or absorption lines. Could you please explain deeply about it?
In addition, in "Profile" Tab there is a button "Normalize", too. what is the difference between them? How to use them correctly?

3). I know that I must redo new Instrument Response for Lhires3 after I change grating, slit,etc.. mechanical parts of it. I have read through the tutorial, but all exampls and contents are for Ha. And all data in the database and libraries in ISIS seem to be used for Ha. Then when we take spectra from other spectral ranges, i.e. 540nm, how to make the instrument response? What are the correct procedures?

Cheers,
Dong

Hello,

at time , I do not use ISIS to reduce spectra created with lhires. I prefer to do this a midas Script, but this runs only with LINUX platform.......

VSPEC couldt be another possibility, running with windows and is a freedownload. For the basic functions VSPEC is intuitiv usable, but VSPEC crashes sometimes down without clear reason.

Since my eShel is in Teneriffe I use my lhires . As soon I have clear skies
I will try to reduce my spectra with ISIS too.

If you will test VSPEC please tell me and ask me, if you will use the midas script please ask me, but then you should a little know how to use Linux .

Cheers
Berthold

Hello dear Berthold,

Thank you for your information.
Vspec can not be used with Chinese-version Windows system, some of the basic functions can never be run. So pitiable thing. And I do not use Linux.

Anyway thank you again.

Dong

Hallo Dong,
you can use Ubuntu, a free linux version on the same computer as Windows. When you start your PC you are asked each time whether you want to run Windows or Ubuntu. I have no problems with it on my Lenovo notebook.
Cheers
Christian

Hello Dong Li,

for a region different from H-alpha you have to make your own dispersion equation with the Profile - Dispersion window. For that you have to enter the wavelength and pixel position of at least two (better a few more) known calibration lines (Ne Ar etc), which you have to identify first.
For details look here:
http://www.astrosurf.com/buil/isis/tuto ... ion_us.htm
For scaling you choose a region of the continuum where there are no absorption or emission lines. By normalizing the spectrum is multiplied by a factor so that the average in the normalizing region is equal to one. The difference in the scaling in the settings and the normalize button is that the value in the settings is used when a spectrum is reduced from a CCD image, the normalize button can be applied to any spectrum for rescaling later on.
For the response function you can use the spectra from the MILES database in ISIS, which are of lower resolution but should work or you can download spectra from the UVES database
http://www.eso.org/sci/observing/tools/ ... tonow.html
This however is quite difficult because the data cannot be read directly with ISIS, so I would stay with the MILES database for a start.
Load a file from the database and save it as e.g. HDxxxxref.fit for further use.

Hope this helps and clear skies,

Martin

Hello Dear Dong,

Ok, I could not know this with Chinese windows......

I 'll study ISIS and lhires too, I 'll tell you if I can use ISIS and lhires....

Cheers
Berthold

Hi Christian, Martin & Berthold,

I am not familiar with Ubuntu and have never used it before. It sounds like a professional system? I am not sure about this, as I am not good at computer & maths.

Martin, you are so kind~ every time your explanation is like an "instrunction manual" which is so clear and simple that make me find the right way in the fog.

Great thanks to all

Cheers, Dong

Hi Dong,
Ubuntu is a professional software. The version which I mentioned is a so called emulator. That is a software which runs under a different operation system (here Windows) and generates for e. g. Linux programs an environment which enables them to run as they would do under their normal operating system. In other words, the Linux programs don't notice that they run on a Windows machine.
Cheers,
Christian

Hello Dong Li,

I will try to answer some of the questions you asked on the Teide WR campaign thread here, in order to keep the different problems sorted out a little bit. After all, the hardware problems at Teide and echelle spectra have little to do with the problems with a LHIRES at your location.
If you have a big problem, it is best to make smaller problems out of it.
Basically, taking spectra can be divided into different phases.
1. Record good spectra
2. Wavelength calibration
3. Correction of instrument response
4. Interpretation of spectra
In order to get good results, the first stage is the most important, the rest can be figured out later. Of course it helps to reduce the spectra correctly to see what you can improve in the first stage.

Record good spectra
As already pointed out by Bernard you have to move the spectrum of the star to a region where you have better intensity of the Ne calibration lines.
You do that by moving the star along the slit in the guide cam. Once you have found a good position by trial and error, remember that position and record all spectra at the same slit position. This way you can eliminate irregularities in the flat.
In addition to the star spectra and Neon calibration you also need a spectrum of a reference star. I recommend zet Aql for several reasons:
It is fairly bright so requires little time to record, but not too bright which may cause other problems.
It is close to the WR stars, so you have a good chance that the atmosphere in that area has similar transmittance as for your targert star.
It is also used for the reduction of spectra at Teide. Since these reference spectra are not always perfect it is advisable to use the same reference, so that errors in the reference spectra cancel out. This is important if you want to compare your spectra with those taken at Teide.
If you are sure that the straylight you see in the bottom part of the image is not coming from outside, which you can check by covering the telescope aperture and see if it is still there, then it is probably coming from an internal stray reflection in the spectrograph. I am not familiar with the LHIRES, but others may have encountered this problem before. It is good scientific practice to get rid of it, since if it is not present on the darks you can remove it only with the background correction, but the less you have to correct the better you can avoid errors there.

Calibration
I do not know how VSPEC does it, I recommend as Bernard, that you use ISIS, with the method of making our own calibration manually under Profile - Dipersion. For that you need a processed uncalibrated spectrum of your reference and you have to identify the lines first. Your problem is probably that one of the lines is not correctly assigned now. Bernard probably can help you there since he is looking at the same region with his LHIRES. Once you have computed a good calibration polynom you can use that for further processing of your spectra.
For WR135 and WR137 where you are interested in the C III lines around 5700 A you have the possibility to check the calibration with the Na D and H2O lines, but this is not the case for the He II line around 5400 A, so you have to do that calibration carefully.


Instrument response
Once you have a spectrum of zet Aql or another reference star we can discuss that in detail, Important is to record the WR star and the reference star without changing anything on the spectrograph settings or the telescope focusing. If you can record the reference star at the same altitude as the target star (before or afterwards) that is even better but not critical for a short wavelength region you observe.

I think this is enough for today.

For a general discussion about problem solving I recommend Robert Pirsigs book: Zen and the Art of Motorcyle Maintenance .
It is very good reading and I learnt a lot from it. A LHIRES is not so different after all from a motorcycle, it is complicated and you have to understand it and it has to be treated carefully, otherwise you get into trouble.

Regards, Martin