Best practice for developing ...

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Best practice for developing ...

Postby Rainer Ehlert » Sat Jan 05, 2019 5:16 pm

... spectra images

Hi,

First a Happy New 2019 and lots fof clear sky :-)

Now I am retired from my day job and I found aout that 24/7 is not enough for this Astronomy hobby. Also having installed better mounts with which I am very satisfied finally I can go troublefree for exposures times of 15 and 30 minutes for a single image. Also the pointing is much better then before.

Long time no active in Spectrographing and now a University here in Mexico approached me to make some images of Hot stars for them like HD 14947, HD 15570, HD 16691 and many others.

I have a LISA at f/5.6 on a AT 8" RC telescope. Originally the scope if f/8.0 and I am using a 0.7x reducer from Optec Inc.

Yesterday I made some test images from the HD 14947 using 120, 300 and 900 seconds exposure times, 10 and 7 images each, and now I would like to know what is the best practice for stacking these images. The imaging session was very interesting the star seemed to be nailed onto the slit :-) ( Sorry I do not remember the slit width but so far I never turned it since getting the LISA) Is it the 23micron one ?

I have MaxIM DL as well as PixInsight for processidn the images. In Maxim there are five alternatives but so far I only have seen 2 known ways in PixInsight which are Average and Median and still do not understand what Maximum and Minimum is in PixInsight.

Should I use Sum in MaxIM DL or what is best ?

Of course I made Dark and Bias frame. Is it mandatory to use a Flat image too ?

One more question. How do I know the resolution after developing the spectrum ? I normally use RSpec for the spectrum analysis. I really never did understand Vspec enough and RSpec is very intuitive and easy to work with.

I also made some images using the Neon lamp insige the LISA and now I will ahve to learn how to calibrate my LISA again using that images. The middle line of the 5 H-alpha lines is exactly at 1167 pixels where it should be as the calculation in the manual.

Thanks very much in advance for any tips and regards

Rainer

PD on the attached image you can see LISA in the back scope as well as how my equipment looks now

IMG_4078_C1.jpg


IMG_4083_C1_ICE.jpg
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IMG_4082_C1_ICE.jpg
IMG_4082_C1_ICE.jpg (201.08 KiB) Viewed 1067 times
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°

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Re: Best practice for developing ...

Postby Rainer Ehlert » Sat Jan 05, 2019 10:44 pm

Hi,

I have been playing with my spectrum images and found out, yes, flat is mandatory in order to get the correct shape of the spectrum.

Now I have to find out the correct exposure time.

regards Rainer
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°

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Re: Best practice for developing ...

Postby Olivier GARDE » Sun Jan 06, 2019 11:23 am

Hi Rainer,

You have a very nice setup.

For processing spectra, you have to use a dedicated software.

You can use ISIS who can process LISA spectra :
http://www.astrosurf.com/buil/isis-software.html

with ISIS, you have to use the calibration with .lst file (explain in the website) because the calibration lampe in the calibration module is a Neon/argon lamp (not only Neon lamp)

or other free software like Vpec, spcaudace, bass, etc...

You have to take flat, but it's easy with a LISA with the calibration module (take about 30 tungstènes to improve sur SNR in the blue part of the spectrum)

ISIS calculate the resolution after processing a spectrum.
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Re: Best practice for developing ...

Postby Rainer Ehlert » Sun Jan 06, 2019 6:00 pm

Hi Olivier,

Well yes those two mounts were a self made retirement present :D Before those two iOptron CEM 120EC2 I had two Losmandy G11 but they were not up to the task of carrying all those telescopes. Some of them were colecting dust in the corner. Now every scope has a function :mrgreen:

Thank you very much for the explanation.

I am at the moment taking a new series of flats. I have the calibration module on my LISA with NEON lamp and the FLAT maker lamp.

Later I will post what happened with my first flats I took. Perhaps the exposure time for the flat was much too long ¿?

Will try the ISIS software. At the moment I am using RSpec from Tom Field in USA.

Thank You and regards Rainer
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°

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Re: Best practice for developing ...

Postby Rainer Ehlert » Sun Jan 06, 2019 11:12 pm

Hi,

Well I am getting better results and I know why I had a strange profile after applying a flat image.

Here is an example of HD 14947 of the test which is much better then before.

Exposure time was 900s for each image and I made 7 of it and processed in MaxIM DL.

Will keep testing the developping ...

Would somebody please explain me why I have that steep fall off in the Blue side or UV area ? Is this due to the fact of the protectyion window of the camera ? I have no filter at all except the window which covers the CCD chamber.

Rainer

HD14947_900s_7img_median_flat15.0s.jpg
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Re: Best practice for developing ...

Postby Rainer Ehlert » Sun Jan 06, 2019 11:46 pm

Hi Olivier,

Just downloaded ISIS.

How do I change the software to English language ?

Thank You and regards Rainer
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°

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Re: Best practice for developing ...

Postby Robin Leadbeater » Mon Jan 07, 2019 5:17 pm

Rainer Ehlert wrote:Hi Olivier,

How do I change the software to English language ?



"Configuration", "Langue", "Anglais"

Then close and re-open the program

ISIS is definitely better than RSpec if you want to produce research quality spectra. It does all the processing from the raw images, including producing the master offsets, darks and flats, making the geometric corrections and subtracting the sky background before binning the spectrum and calibrating it using the calibration lamp. there is a special tutorial for the LISA here
http://www.astrosurf.com/buil/isis/guid ... uto_en.htm

Robin
Last edited by Robin Leadbeater on Mon Jan 07, 2019 5:29 pm, edited 1 time in total.
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Re: Best practice for developing ...

Postby Robin Leadbeater » Mon Jan 07, 2019 5:27 pm

Hi Rainer,

Rainer Ehlert wrote:Hi,

Would somebody please explain me why I have that steep fall off in the Blue side or UV area ?


Is this the spectrum after applying the instrument response? If so I suspect you have not accurately fitted the instrument response at the blue end. This can be difficult because the signal is low in this area because of the camera and grating sensitivity and the low output from the flat lamp. See this recent thread for example.
viewtopic.php?f=8&t=2201
(Google translates from French quite well)

Cheers
Robin
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Re: Best practice for developing ...

Postby Rainer Ehlert » Mon Jan 07, 2019 5:44 pm

Robin Leadbeater wrote:Hi Rainer,

Rainer Ehlert wrote:Hi,

Would somebody please explain me why I have that steep fall off in the Blue side or UV area ?


Is this the spectrum after applying the instrument response? If so I suspect you have not accurately fitted the instrument response at the blue end. This can be difficult because the signal is low in this area because of the camera and grating sensitivity and the low output from the flat lamp. See this recent thread for example.
viewtopic.php?f=8&t=2201
(Google translates from French quite well)

Cheers
Robin


Hi Robin,

Happy New Year 2019.

Thanks for the answer in regard to the blue part of the spectrum. I read the topic in question but still do not know what to do. There is no conclusion so far I understoos or perhaps I am just dense.

Can I use daylight for making FLATS ? or must it be exactly those 4700 K color temperature ?

regards Rainer
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Re: Best practice for developing ...

Postby James Foster » Mon Jan 07, 2019 6:30 pm

Hi Rainer,

I made the leap to ISIS about 2 years ago and my spectral data is much more accurate and reproducible(with others data) after learning the essentials; I haven't mastered much beyond the basic calibration and instrument response calcs. I also use MaxDL(V5) like yourself and you will need to rename your bias, dark, &
object .fits files to easily process under Isis. Isis has a utility for this, but I found this program more useful for file re-naming:
https://www.bulkrenameutility.co.uk/Main_Intro.php

I use the following directory structures/files names for Is processing (example of one I did 1-year ago for LISA):
Image

The main directory, ___CCDHome01Jan18(-9)CDK17-LISA-23micronSLIT, is where all the object(s), Neon-Ar calibration, & Tungsten flats are located.
The sub-directory, calib is where the bias (o-files), darks, & cosme files are located from previously taken data; see:
Image

I also copy the flats, taken after each object's spectrum the same night, from the main directory into this sub-directory to process under the IS Masters tab as shown here:
Image

The sub-directory, ALL Processed Spectra_BeSS Check, is the place I put each fully processed object spectra that is ready for BeSS submission.

All of these calibration steps are discussed in detail in Christian Buil's excellent guide to Isis which he authored:
http://www.astrosurf.com/buil/isis/guide_lisa/tuto_en.htm

Btw, here is my usual instrument set-up for taking LISA spectra in my light-polluted city of Los Angeles:
Image

Please don't be afraid to ask questions. Many folks here are most helpful in having others master Isis spectral processing.

James
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