Forum der Vereinigung der Sternfreunde

Dear all,

due to the bad weather on Mt. Graham, I had some time to start programming a C++ code simulate échelle raw data. The idea is to use these data to test reduction pipelines, estimate expected efficiencies, spectrograph parameters and SNR values.

The output is a .txt file which includes the pixel matrix with the calculated intensity values and the very left column correspond to the wavelengths for each order to allow single order plotting and, therefore, wavelength and overlapp determination.

Attached are two of these files for an échelle spectrograph with 31.6 l/mm grating and 300 l/mm cross-disperser for two different camera focal lengths and a plot through the order n = 140. The noise is generated by random gaussian numbers due to readout and photon noise. The inclination of the orders due to the linear diserpsion of the grating cross-disperser is also taken into account. CPU time was about 166 s for a 1500 x 1000 CCD.

Next step will be the implementation of prism cross-dispersion.

cheers,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hi Daniel, obviously you work on a more solid alternative to the Excel program simechelle. That sounds great. Is this a general program task for grating AND prism cross-dispersers? I mean, in first approximation, the orders are not curved/inclined when using a grating cross-disperser.

Good luck in Arizona, Thomas

Hi Thomas,

the grating has a linear dispersion which means that the angle of diffraction increases linear with wavelength. That is why orders are inclined. A prism (glass) shows non-linear behavoir of the index of refraction and, therefore, of the angle of refraction. That is why orders are curved.

A picture of an echelle with 79 l/mm and now with F2 prism is shown. The sligth curvature is visible.

Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

OK, we talked about different things. I meant the curvature due to non-linear dispersion of a grating (only in first approximation) and prism instead of the inclination.

Cheers

Hi,

here are some 3D plots. The calculation for prism works also now.

The next step is to take care about stellar flux, CCD efficiency and all other efficiencies including atmosphere.

adios,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Daniel,
Will you make this program available to others?
Ken

_________________
" Astronomical Spectroscopy for Amateurs" - Springer

Ken,

it will not be available in the very near future. Just for some friends to check for bugs.

Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hello Daniel,

you write: The noise is generated by random gaussian numbers due to readout and photon noise.

Really the photon noise is proportional the squareroot(flux). Is that incorporated to your program code?

_________________
Herzliche Grüße / best regards

Lothar

https://lotharschanne.wordpress.com/

Hi Lothar,

yes the photon noise is sqrt(signal).

I have implemented also the stellar Planck radiation and an approximated CCD QE for commercial non-coated and front-illuminated CCD. The peak wavelength and the peak value can be set to the values of the individual CCD.

Some plots of different parameters vs. wavelength are attached.

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Some more diagrams.

The stellar flux is calculated via visual magnitude and stellar temperature.

cheers,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

And here ist a 3d landscape with grating cross-disperser. CCD QE, transmission earth atmosphere, stellar flux and efficiency of both gratings is taken into account.

ciao,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hi Daniel,

was du so alles machst wenn das Wetter schlecht ist.
Toll.

_________________
Herzliche Grüße / best regards

Lothar

https://lotharschanne.wordpress.com/

Hallo,

was Neues aus der Simulationsfront.

Habe mittlerweile die Option zur Berechnung von Emissions- und Absorptionsspektren eingebaut. Im Anhang ein Planckspektrum mit Wasserstoffabsorptionen exemplarisch gerechnet für einen 79 l/mm Échelle mit Prisma-CD. Für den selben Spektrographen auch ein Neonspektrum.

Gruß,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hallo,

hier Plots durch die beiden blauseitigen Ordnungen mit H-Epsilon und H-Delta.

Gruß,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hi all,

I made some progress with this simulation. It has now a GUI and is capable of calculating échelle, 3D and classical spectrographs. It has also some tools for fibre optics and volume phase holographic gratings.

I will post here some preliminary results of a fully Th/Ar CCD image (2500 lines, line list from UVES). This took around 2 h for calculation with a CCD of 1500 x 1024 pixels.

If one is interested in the échellogram only, this is computed in some seconds (also attached). This program will be know from now on as "SILENT - Spectrograph sImuLation & EmulatioN Tool"

The program will be available at some time for free. At this time it is in the pre-alpha phase. I would be glad if someone is willing to test the program during pre-alpha and alpha state.

best regards,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hallo Daniel,
ich bin ja immer wieder verblüfft, was du so alles machst und wie tief du dich in die Optik eingearbeitet hast.
Wir sind ja wegen des Programmpakets in Kontakt. Bin gespannt auf das testen.

_________________
Herzliche Grüße / best regards

Lothar

https://lotharschanne.wordpress.com/

Hi Lothar,

ja es macht einfach Spaß und die Nächte in Arizona sind sehr lang

Ich hoffe, dass nach der Alpha-Phase das Tool hier im Forum ankommt, aufgenommen und kommentiert/diskutiert wird.

Schöne Grüße,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/