POLARIMETER DEVICE PROJECT

[Joan Guarro Flo]

Hello,

You can see in these graphics the first TheGiver's results of the standard polarized star HD43384 comparing them with AFOSC (ESO) ones.

The ripples that you can notice in TheGiver graphics have appeared in this star not, on other. Neither any filter nor horizontal gathering
has been applied.

I hope that you enjoy them.

Cheers, J. Guarro.

[Joan Guarro Flo]

Hello,

We are close to obtaining good results.

J. Guarro.

[Joan Guarro Flo]

Hello,

Parallelly to TheGiver observations and their outcomes, some people are working to get good reduction software, in this way, I would show here two pictures of Polarimetric by Toni Jové, who has been working for some months in this software for spectropolarimetric observations.

Actually, at the moment the FITS reduction sequence is ISIS, Polarimetric, and also, PlotSpectra.

You can see something in these two pictures.

Cheers, J. Guarro.

[Joan Guarro Flo]

Hello,

Ferdinando Patat (ESO), recommended that a good overlap of the HWP and Wollaston prism axes is essential for the good functioning of any spectropolarimeter.

Following this advice, I added both rods to TheGiver, I'll check it next clear night...

Greetings, J. Guarro.

[Joan Guarro Flo]

Hello,

The last job was worth it. The results have improved in precision.

J. Guarro.

[Joan Guarro Flo]

Hello,

I left here a series of graphics from last night's polarimetric observations taken during a good and short sky window.

I haven't preferred to make many comments about them, and I really would appreciate it if you could give your opinion and tips about it.

Cheers, J.Guarro.

[Martin Dubs]

Hello Joan,

for some time I have not been very active in spectroscopy. So I was very surprised when I recently checked the ARAS forum and noticed your post on the polarimeter. I am impressed. In a short time you have produced an instrument with high precision. Congratulations. I know how difficult are polarization measurements. Many years ago, I did polarization laser spectroscopy of chemical reaction products (https://meteorspectroscopy.org/wp-conte ... 1986-1.pdf). At that time there where no polymer halfwave plates, so I used quartz Fresnel rhombs, which have almost no retardation errors over a very wide wavelength range, but with a small aperture. The polymer retarder are certainly more convenient.
To your measurements:
In some earlier spectra I noticed some ripple in the long wavelength part. I suppose this could be caused by the detector cover window reflections combined with poor alignment of the different polarization measurements. In the latest spectra this has disappeared, so I suppose you have that under control now. In the latest measurements of unpolarized stars I notice some polarization effects of the H-alpha line. I do not know if this is real or the effect of a wavelength calibration error. I am not sure, but you could check with more measurements between 90 and 157.5°. These should give the same results as the 0 to 67.5° measurements but with different polarizations on the detector. I do not know if these additional measurements can eliminate systematic errors, but at least the additional measurements help with the S/N ratio and show the reproducibility. I think you should give it a try.

I am looking forward to your next measurements. Keep going!

Best regards, Martin

[Joan Guarro Flo]

Hallo Martin,

It's always a great pleasure to receive news from you! Many thanks for your encouragement.

Yes, polarization measurements have their quit, you know that the matter is a measure of the % of the % of the target light.
I linked to your PDF, your job is impressive, specialized, and exhaustive, it's easy to realize that it took a lot of months of hard work.

About my measurements: First I would to say that very often I make little mistakes, but every now and then I make a huge one, similar to as you can see in my previous message, where all the supergiant star graphs are wrong due to one oversight and mistake that I made during the spectropolarimetric image reduction.

Making a public mistake on punctual times is healthy for your main overall if you recognize it. That is the reason, that I apologize for it and sent corrected all these graphs again.

About the ripples, first I'm still an apprentice, also if we see the different graphs we can notice that some ripples could be characteristics of the own star, asidesones in the red, their origin could be from the weak signal, due to the low camera detective in this region.

About the Hydrogen climbs in the unpolarized stars, they're here and I don't know how to erase them, is it another mistake of mine?

Here we're enjoying three cloudy and rainy months with a few clear nights, but on the next occasion I'm going to apply your advice and take the new observations with 8 angular positions instead of 4 ones, I think that is a good idea and I'll show them here next time.

Please, let me know your opinion about these graphs, please, criticize them.

A hug, Joan.

[Joan Guarro Flo]

Hello,

One handicap that you can stumble on is spectropolarimetry is the inexistence of one software for reducing your observations,
due to the fact that there are few people and equipment that are dedicated to this observational activity, and everyone invented,
adapted, and made their own software for it.

In our case, some people had helped us with their work, and with their essential advice, so at the moment,  Antoni Jové gathered
all of them and made the Polarimetric, which is a very good and useful bridge between ISIS and PlotSpectra.

You can see two images of it here.

Regards, J. Guarro.

[Joan Guarro Flo]

Hello,

In this post, you can see two Be stars. About HD 57682 the straight "noise" lines in Theta Angle, I believe they are due to some
residual software calculation values due to the low % polarimetry level of this star.

One can suppose that a non-polarized star doesn't have any polarization Theta Angle, and it's starting to be defined when
the polarization also starts to manifest.

By contrast the Be HD45314 with a bit more than 1% of polarization, its Theta Angle is more consistent.

But in both cases, from around the 6200 Angs. to 7500 ones,  we can notice one notable noise increment, which is the next issue to mend.

Regards, J.Guarro.