Forum der Vereinigung der Sternfreunde

Hallo,

Nachdem ich mich nun im Sommerurlaub mit dem Kalibrieren von Spektren hauptsächlich beschäftigt habe, hatte ich die Gelegenheit die letzten 5 Tage bei klaren Nachthimmel einige Objekte aufzunehmen, unter anderem einige Wolf Rayet Sterne.

Nachfolgend WR 110 ein Stern Spektral type WN6

Aufgenommen mit einem Astro Tech 8" Ritchey Chretién auf f/5 reduziert mit dem Spektrographen LISA.

Rot ist meine Spektrum und Blau ein Profi referenz profil von Prof. Dr. Wolf-Rainer Hamann der Universität in Potsdam. Dr. Hamann hat Tom und mir freundlicherweise die gesamte Sammlung der WN spektren die in seinem Besitz sind zur Verfügung gestellt.

http://www.astroforo.net/astro/rspec/wo ... ann-RE.jpg

Für die aufmerksamen Betrachter ist da eine Stufe bei 4800 Ängstrom im blauen Referenzprofil, aber das ist keine Besonderheit des Sternes sondern kommt zustande da das gesamte Referenzprofil von 3 separaten dateien kommt und die Intensitäten da halt einen Sprung verursachen.

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Grüsse Rainer www.rsfotografia.com

Hi Rainer!

I switch to English because this subject could be of general use, not only for German speakers.

Wolf-Rainer gave a presentation about his WR observations and calculations during our last section conference . He is theoretician and in big need of consecutive and catalogue measurements of WR stars. In preparation of our meeting and his talk he told me that he would like to work together with amateurs, especially not only on the Cygnus WR stars but also on fainter stars at about 12th magnitude. In his talk he spoke about the instrumentals necessities, especially the necessary resolving power. At http://www.stsci.de/Drebach-VdS.pdf are the respective viewgraphs (unfortunately in German). After a general overview about the physics, their stellar winds and mass-loss rate he compares model spectra with the observations. We can see it between page 3, subpage no. 10 and page 5, subpage no. 14a. The model spectra are in red and the observations are in blue.

For example. A model spectrum of Deneb can be perfectly matched with R=40.000 (subpage no. 11). R=5000 are still fine (subpage no. 11a) but R=1000 (subpage no. 11b) is not. The absorption lines are too narrow for R=1000. This is different for emission lines as in zeta Puppis and WR stars. Here R=1000 is fine!

That means: If amateurs with low-res instrumentation need to go for broad emission line if they want to perform a campaign with reasonable output. If I would have a running instrument and enough time, I would go for such as campaign. In addition, the contact to Wolf-Rainer helps a lot to do so because it would be guided by a professional with excellent expertise on these objects. I recommend to think about a strategy, make an informal web site (e.g., http://www.stsci.de/wr140/index_e.htm ) , announce it and go with a bunch of people.

Cheers, Thomas

Hi Rainer, Have you tried normalising your spectrum to 1, say using the pseudo continuum at 5600-5700 for example? It looks like most of the lines should then match the reference intensity quite well except for the HeII line at 4700A. Is the difference in this line real or is it a zero point error or linearity problem? (I struggled for some time when I was measuring WR140 to get the zero point right. Because the "continuum" is so low, perfect dark and background subtraction is important. It is also important that the software treats negative values generated after background subtraction correctly, though I think Rspec now does this since I pointed out the problem to Tom

Cheers
Robin

Sorry, I now see from the step you mentioned at 4800A that the reference spectrum between ~4450 and 4800A is plotted relative to a different continuum level compared with the rest of the spectrum. If you have the reference fits/dat file, it should be easy enough to correct this region in the reference spectrum and then you could make a direct comparison.

Cheers
Robin

Hi Thomas,

Thank you for your comments. I already contacted Prof. Hamann. I guess I will get some answer in the near future.

I found the list of stars which are missing here in this forum and by pure coincidence I have a spectrum of WR127. This is quite a faint fuzzy with mag. 10.2. The best SNR I got on the brightest emission line was 27 and that was with 10 median stacked images of 300s. I can easily go higher with the exposure time as my mount works quite well.

Next time when I am in the observatory I will do some trial with 600 second exposure time images maybe up to 1800 second to see if it improves.

Below you can see that Light pollution already makes itself visible at 300 second exposure images. This is WR 110 at mag 9.8

http://www.astroforo.net/astro/rspec/wo ... median.jpg

I will work on this in the next opportunities. The ony problem is that I do visit my observatory every 2-3 weeks and so I also depend of good weather consitions.

I regard to your writing about an informal website, like the link you posted, I think that for the moment I am by far to unexperienced and do not know how to start this, but anybody who might be interested in taking it over, I will gladly give my spectra for being used for that project. Anyhow, I will take a closer look to that site and see how it is build up.

I have spectra of WR 110,111,113,123,127 and 134

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Grüsse Rainer www.rsfotografia.com

Hi Robin,

Thanks for the comments. What I ahve is a file with wavelengths and intensity. Maybe I try to get the difference at the step and just add this difference to the whole wavelength list starting at the step point ?

It is not easy to create that lists as the whole bandwidth is by adding 3 different lists and the lists contain 1st 2nd and 3rd order spectra values, some do others do not.

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Grüsse Rainer www.rsfotografia.com

Hi Rainer!

Five minutes exposure time is very short, indeed. I know, it should be fast for low resolution but in this case a longer exposure time is not a problem. For line effects, it does not matter if you go for 5 or 50 minutes. It would be different if you want to see fast varying line effects. But that is only possible with high resolving power starting with 5000. So, expose longer (S/N about 100) and make an accurate background reduction, as Robin said.

Yes, I understand that you are (still) unexperienced. However, by becoming more experienced you could also start establishing a small campaign together with Wolf-Rainer. What I want to say: You can wait untill you are experienced but then you could not inform and encourage others NOW to join you. In our section we need more observation campaigns so that colleagues get some success experience. So, better to do it now!

For a website I can help because the draft is present. I only do not want to fill the physical background because I am too busy with other stuff. Instead of the WR140 website I showed you, we can implement other targets also in the section website at the link "Targets" (see http://spektroskopie.fg-vds.de/index_e.htm -> Targets). I only need the respective content, as I said.

Thomas

Hi Rainer,
It is a bit difficult to know how best to combine the reference spectra without knowing exactly how they are normalised but just subtracting the difference at the step is not likely to be right.

I suggest dividing the higher part of the spectrum around 4800A (That part between the step up and the step down) by the ratio of the two spectra at the step. This will make the step go away and should scale the 4800A line region correctly relative to the rest of the spectrum. You can then normalise both spectra to 1 in the region I suggested and compare them directly.

Robin

Hi Thomas,

Thanks for your comments.

The exposure times of 300s are certainly very short, but I wanted to get a taste of what is possible at the moment.

I still have to implement at that scope a spectrograph rotator as I noticed that when I wanted to image WR 128 I had a nearby star also in the slit and so the spectrum would have not been correct

Now as the end of the year approaches my skies will become better and better as the observatory is in central Mexico what we call a semi desert area and at night I can get humidity levels of maybe 10% to 20% and only at early morning hours it starts to climb to maybe 60% to 90% or even sometimes 100% when the dew conditions are given, of course all that depends if I have clear skies at night or not

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Grüsse Rainer www.rsfotografia.com

Yes! Just go ahead and try everything. You are right, of course. Anyway, very good work...especially in that short time since you started spectroscopy.

Cherio

Hi Robin,

Thanks for the Tip.

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Grüsse Rainer www.rsfotografia.com