V832 cas

[Rainer Ehlert]

Hi,

Reading this forum I found the message about the FS Cma stars and thought I make a trial on V832 Cas as it is in a good position Was a bit difficult to find it but after a test imge and seeing the strange spectrum I knew I had nailed it

Here are my results beginning with the spectrum image. 12 subexposures of 300s exposure time each = Total 60 minutes. Taken with LISA 23µ slit on an AstroTech 8" Ritchey-Cretien telescope and a QSI520i CCD camera. Median combined and Dark frame applied.

Below the worked out spectrum

and here the *.dat file http://astroforo.net/astro/rspec/v832ca ... median.dat

Thanks for reading, looking and your comments

[Christian Buil]

Here, my version of V832 Cas spectrum http://astrosurf.com/aras/surveys/fscma/
(you can download the spectrum file).

Your configuration efficiency :

12 -------- x -------- 300 seconds ----- x ----------- 8 ------- x ----- 8 -------- x ----------- (1) --------- = -------- 230 000

| ---------------------------- | ----------------------------------- | ----------------------------- |
Number -------------------- Elementary ------------------ Mirror surface ----------- Slit relative coefficient
of frames ------------------ exposure time ---------------------------------------------------- (24 microns)


My configuration efficiency :

17 x 180 seconds x 11 x 11 x (2) = 740 000

| | | |
Number Elementary Mirror surface Slit relative coefficient
of frames exposure time (35 microns)

I collect 3X more photons, OK, but... see attached comparison - your spectrum is more noisy, more than the
flux ratio.

Many hot spots are present and the continuum signal is very faint in your data (dominated by noise).

First : the median stacking is not a very good idea for spectroscopy (because the variable level between elementary exposure induced by seeing and guiding errors)
Second : could you display a one shot raw image (300 sec exposure). for a first look, the telescope focus seem correct.
Third : could you precise the processing sofware used

Christian B

[Rainer Ehlert]

Hi Christian,

Thank you very much for that big amount of time you took in order to do a comparison of your and my spectrum. Very interesting.

I invested yesterday some more time for optimizing my hardware and it looks like I am getting better results now.

I did read it a few times in order to understand it but there are still some black holes for me Comparing your C11 to my AT 8" then you have already there a big advantage. Your mirror has 2 times the surface as mine. Is that the number you used (1) and (2) ? C11 = ~616cm² and AT8" = ~314cm²

Here are 2 single images of 300s of the series of 12 I took

If median is not a good stacking method for spectra ¿ Which one is it ? I stack my images with MaxImDL.

I use R-Spec for developing my spectra.

Question: ¿ If for getting more signal of faint objects like the one we are talking about I need to change to the 35µ slit, what happens if I use that slit for bright objects like Vega ?

More questions maybe later, still have to digest this one

Yesterday I made a new series on V832 Cas with the same setup but instead of 300s I used 600s exposure. That is at the moment the only solution I have for getting a higher SNR. Look at the comparison below

I will later do a comparison of the spectra of 300s and 600s so I can see the difference. In both cases I have 3600s of exposure time.

[Christian Buil]

Use of a 35 microns slit for target like V832 Cas. Check the difference by observing. Forget the 23 microns slit.

With 23 microns or 35 microns slit observation of Vega for calibrate is note the best choice. Observe A or B faintest star (V=2 to 5) for a good calibration (spectral and instrumental response). Because atmospheric and short exposure time on Vega, the calibration quality is poor on this star.

LISA is optimized for observation of faint stars (V=8, 9, 10, ... 15, 16), not for V=0 star !

Try to test ISIS for process V832 Cas observations for comparison purpose.
The very new version 3.4.0 add a special function for you.... : http://astrosurf.com/buil/isis/quicklook/quicklook.htm
(the interface can be configured in english and the procedure is easy - copy screen shot).

Christian B

[Rainer Ehlert]

Hi Christian,

Again thanks a lot for your comments. Slowly I think I will get to better results

Will also take a look at your recomendation of ISIS and see if now I can understand the program

I will do some tests changing the slit and see what changes especially the focus or the orientation of the slit in the guider camera ¿?

Understood that the LISA is for faint objects but from time to time one wants to make some normal stars as practice ...