Forum der Vereinigung der Sternfreunde

Hallo,

für einige Testaufnahmen mit dem MiniSpec musste Pleione am 15.01.17 herhalten.

Dort hat sich das Profil nun zum 07.01.17 (Daten aus BeSS) deutlich geändert. Mal so blöd gefragt, was passiert dort denn im Moment? Bildet sich da eine neue Scheibe aus?

Das fand ich ganz interessant und so habe ich gestern, am 16.01.17 weitere Daten gewonnen (leider fing die geliehene EQ5 an zu spinnen, daher weniger Integrationszeit). Dort ist innerhalb eines Tages eine weitere Veränderung zu sehen.

Ist das real oder liegt es am Spektrografen oder dem mäßigen SNR? Ich bin mir da ein wenig unsicher bei den ganzen Problemen die ich hatte.

Die Daten sind quick&dirty in BASS reduziert, welches ich nutze, bis ich mich in MIDAS oder IRAF durchgekämpft habe.

Viele Grüße und CS
Christoph

Hallo Christoph, wenn ich mich recht erinnere (ich habe mein Diplom über UV-Spektren von Be-Sternen gemacht) ist Pleione in seiner aktiven Phase ein Be-Shell Stern, also kein normaler Be-Stern. Er hat sogar Phasen ganz ohne Scheibe. Im Gegensatz zu einer stabilen Be-Sternscheibe ist die Hülle (shell) hochaktiv und wird durch Sternstrahlung regelmäßig abgeworfen. Daher die sehr variable Halpha-Linie. Es sieht so aus, als wäre da wieder eine Hülle (zentrale Emission) neben der Scheibe (Flügelemissionen).
Gruß, Thomas

Hello Christoph,

There are spectra for Pleione added to BeSS every few days. All the spectra I checked over the past 2 years show a similar shape with a central absorption and 2 emission wings. There is no central emission as your spectrum shows so I think your spectrum is unusual. I suggest you first look at your spectrum image. You should be able to see the central emission without any processing. If that confirms it is real and not an artifact I recommend reporting it on the ARAS forum. There are probably more recent spectra taken which have not yet been uploaded to BeSS that you will be able to compare with.

Cheers
Robin

Hallo Christoph:

Possibly Robin is right, your graphic Pleione can be deformed by some artifact.

I have no observations 20160115. spend the nights 14 and 16.

Cheers, Joan.

Hi Robin and Joan, I checked the spectra and believe you are right. But is the center emission in Christoph's spectra really an artifact? Seems to be too broad for that.
Cheers, Thomas

Hallo Thomas,

I'm not sure, I think Christoph would have to return to observe the star, exactly the same instrument. We could then see what happens.

It would be fantastic, that Christoph's observation a reality.

The Ernst Pollmann, many years ago that follows the evolution of the star. He knows very well. Could you give your opinion.

Greetings, Joan.

Indeed, Joan, that is the best he can do. Some years ago, Christian Buil bublished the attached pictue (figure 14.24 on page 498 in our book). 28 Tau is in pure emission. The star definitely varies a lot. In addition, eta Tau shows a wine bottle profile which is invisible in Christoph's spectrum. So, maybe we are wrong.
Cheers, Thomas

Hi all,
ok, I think it make sense to write in english. I’ll try .
Thank you for your thougts! It went very interesting.
Due to the bad weather conditions I can’t get spectra in the next time. Perhaps at Sunday there will be a chance.

If it is an other star than Pleione, I think this star can’t be brighter than 4. Mag. I’ve taken a singleshot by 1200sec integration time. Otherwise the spectra will be overexposed.

I have reduced the Data of the bright nearby star. Perhaps a comparison to the Data of Christian Buil will help. I attached some data. Feel free to use it for own investigations to solve this problem/question.

Greetings
Christoph

Hmm, 27 Tau?

There might be a chance...?!

I will going to reduce stacked data of the bright star later. Perhaps it is better for identifying.
Christoph

Ah OK. That makes sense. So is this is a slitless spectrograph? (Can you remind me of the design Christoph?)
27 Tau is the bright star in the image and shows H alpha in absorption as expected (it is not Be) and as it appears in Buil's image.
28 Tau is above it. The central emission is clear in the image but this is very surprising as Joan's spectra taken the day before and the day after do not show any central emission or any variation at all!

The only other suggestion i have is that you are getting a double image. (I think Uwe saw this with a sample of the Star Analyser 100 grating used at high resolution) This could make the 2 emission peaks look like 3. Perhaps you could try measuring a star with a single narrow emission line to check?

Cheers
Robin

Hi Robin, I wouldn't expect it to be a double image because the other spectral features are all single. Christoph, you should check again, anyway.
Cheers, Thomas

Hi Robin,
yes the spectrograph is slitless. It is a MiniSpec from Daniel Sablowski. It is designed for f/5. In it works a 1200 lines/mm grating from Thorlabs.
As telescope there is a 100/1000 MTO with 0,5x reducer.
I attach the Data within the SimSpec-excelsheet.

My Data are from two days, the 15. and also like Joans from the 16.
I’ve take also data from other Stars (Y Cas, VV Ceph, omega Ori) at both days.

Greetings
Christoph

Hello all:

Attach a pdf 28Tau the star, where it sees the "slow" evolution of H-alpha from 20011029 to 20131112. The data are the BeSS.

I also want to say that from the year 2008 I regularly observe this star, now bring 250 of the H-alpha spectrographic observations of the Tau 28. I've never seen any changes compulsive.

Changes in the H-alpha always been soft. I speak as an observer, not a theorist.

In short, and nobody gets upset. It may well be that the graph of the H-alpha 28Tau it's true, but I do not believe it.

Friendly, Joan.

Hello Cristoph,
Ah yes, I missed the date on the first one. So we have your and Joan's spectra both taken on 16th.
http://forum.vdsastro.de/download/file.php?id=6722
http://forum.vdsastro.de/download/file.php?id=6724

If the change is real it must be very fast then. There is also perhaps some emission in the line at ~6460A in your spectrum? (But of course this could be real or an artifact too. The problem with slitless spectrographs is that each line has the shape of the star image). What was the time of your observation on 16th ? How close in time to Joan's was it ?

Cheers
Robin

Hi all,

indeed there is a lot speaking for, that the data isn’t real. Anyway I’m interested what caused the third Peak. This may prevent for such artifacts in future.
And the shape (similar to a Gaussian bell curve?!) can cause artifacts?! Is it possible to circumnavigate this Problem, for example by extracting only the brightest part of the spectra?

At the 16th I took the data from 18:50 till 19:20.

Greetings
Christoph

Me again,

Ernst Pollmann asked me to copy the following text in this thread:

Dear colleagues
our ARAS monitoring program don't show such a dramatical changes, how it is suggested by the (incorrect) spectra comparisons here in this forum.

One of our monitoring partner (Olivier Garde) sent me right now a new spectrum of yesterday.
It says, the typical profile characteristic is unchanged (as expected).

I hope that this will help, to understand, that the confusion came from the Be star eta Tau (instead of 28 Tau), taken by Christoph.


Ernst Pollmann

If this is right, can anybody explain, why the spectra is not brighter and which star caused the bright spectra nearby?
Greetings
Christoph

Hello Christoph,

Ernst's suggestion that you have measured eta Tau is not correct. There is no evidence that you have the wrong star. (Certainly not eta Tau). The two stars in your image agree with the relative positions and brightness of 27 Tau and 28 Tau. I agree that it is very unlikely that what you see in your spectrum is real. We do not have an explanation though.

Cheers
Robin

Christoph,

Here is the latest H alpha spectrum of eta Tau in BeSS. The profile shape does not match the one in your spectrum (the emission line in eta Tau is inside a clear wide absorption line. This is not the case in your spectrum.) This confirms that you did not measure eta Tau by mistake.

Cheers
Robin

OK this is ~2 hours before Joan took his "normal looking" spectrum.

What you saw was repeated on 2 days though. You must go back to the same star again and tell us what you see. This is good fun

Robin

Hi Christoph!

Great to get expert knowledge from the outside to avoid incorrect spectra comparisons in this forum. From my point of view Herr Pollmann misses the well-known wine bottle profile in eta Tau. I do not consider myself as a Be star expert but see this shape. Hence, I agree with Robin, that's not an eta Tau spectrum! And it is not the expected 28 Tau spectrum, as Joan points out.
The eta Tau BESS spectrum indicates an almost pole-on view while your spectrum is more one from intermediate latitudes. And Joan's series sometimes shows self-absorption by the disk indicating an edge-on view.

This is somewhat tricky, indeed... and detective fun. You should carefully measure it again.

Cherio, Thomas

PS: Olivier Garde is a forum member. Maybe he can give more solid information.

Hello all,

Ernst Pollmann Include this text in this conference.


"The here discussed triple peak emission (in the slit less spectra) results from mistakes in guiding in declination.
Intermittent correction in that axis did lead to a displacement of the emission components in dispersion direction. Nobody can expect that the real profile of the eta Tau spectra will be recognizable, when such massive mistakes occur. As Christoph itself wrote at the beginning: the mounting EQ 5 did not work very well.

Ernst Pollmann"


I think that is a good point of view, so if Christoph wants to repeat the observation must also keep false, the equatorial mount.

Beware, the spectrograph of Christoph has no slit !! It's has too many things on the counter. I do not give more laps.

Friendly, Joan.

Hi all,
yes it is somekind of detective fun!
So we can say, that the star is right. I will go for taking data from 28 Tau and also eta Tau as soon as the weather allowed it. For this test I will take both, the EQ-5 and the GPD2.

But if this problem is caused by the mount, why is only the Ha line at only one spectrum affected?

To place the star on the chip and get the focus I’ve taken some pictures of 20sec. They showed also the triple line. This 20sec pictures where taken without autoguiding with the Lacerta MGen. For the longtime pictures I used the autoguider.

I see that a slit can solve many problems. Robin, if my memory serves me right, you pointed it in another thread out, that in future I want to go for a system with slit ...
Greetings
Christoph

Joan!
It might be that Christoph did not guide perfectly well. It is up to him to test his procedure again. But he certainly does not make „massive mistakes“ (this is really not my wording). He is still learning and on his way to become a good observer. And it might be that we all do not know what we are talking about. But we, including Christoph, want to learn from each other and surely make „mistakes“ by doing so. However, all these mistakes help us to learn more and go through this difficult subject.
Cheers, Thomas

Hello Joan,

Yes I agree. Guiding errors could certainly cause the problem in this slitless spectrum. Your spectrum taken within 2 hours of Christoph's is enough proof for me that Christoph's spectrum is not correct. It is curious how well the incorrect spectrum shape was repeated on two nights though. I am not convinced that we have got to the real cause of the problem but perhaps we never will.

Cheers
Robin

Hallo Thomas:

We are all exposed to errors and false interpertacions. No one can be left out myself Right arrow day I sent false alarms about the WR140. We are all the same height, close to ambiguous situations.

Christopher was very brave and we have appreciated his effort. I hope to continue doing spectroscopy and send their results.

It is not my intention to lecture anyone. I'm not in this situation. The written word is sometimes too hard, too serious. Also help the change of language.

Very sincerely, Joan.

Thanks a lot, Joan, well said!

Very true. I think the quality of Christoph's spectra are very impressive, particularly for a slitless spectrograph. All the spectra except for this star seem to match what is expected.

Cheers
Robin

Hi,
thank you all! There is absolut no problem for me with these mistakes and setbacks .

As a astronomer at the ESO-Camp to one of our spectroscopy groupmember in the club said: Astronomy can really be fun, but about 90 percent contains of search for problems and solve them!

The next days I will look up for the settings of the Autoguider. Till now I used it only .

Unfortunatly this evening the weather isn’t that good the weather forecast tell.
If there are news, I will report.
Christoph

For Pleione (28 tau) I agree with Robin and Juan. I took a spectrum on January 19th and it is similar to the other spectra already in BESS database.



For the 2nd spectrum, it may be Atlas, Taygeta or Celeno ?



Cheers

Olivier GARDE

Hi all,
last Weekend I was able to took some new spectra. Over the week I was very busy. But now I will report.
First the profile was as expected. Then I begun to play with the parameters of the MGen and was able to reproduce the error by choosing a high tolerance for triggering a guide-impulse. I used only the EQ5 for the Test.

So we can really say, that the error was caused by the bad tracking.

Thanks for your help! Also Ernst Pollmann. One step forward ! I never thought, that spectroscopy is so vulnerable for any influences .

One night later unfortunatly the screw of the Dovetail Clamp broke and the whole Setup dropped to the ground. For luck, nothing was really damaged. But I have to readjust the Setup.

Greetings
Christoph

Very well, Christoph! As you said, one step forward.
Spectroscopy is not more vulnerable than imaging. For both cases, you need to guide well for longer exposure times.
Cheers, Thomas