AStroart 7 photometry & Astrometry question

[AdrianoV]

Ok verificato, nella cartella di download c'erano 900 file, forse in fase di copiatura nella cartella locale ne sono passati solo 300.
Tutto ok.
Grazie.

[iandh2010]

OK, so I got my AA7 as an upgrade to AA5 as a download.

There does not appear to be any Star Catalogues included with my download.

So where do I find the GSC to use with Astrometry and Photometry?

[iandh2010]

Thanks Fabio,
I have now installed the GSC catalogue and I have managed to follow along with the Tutorial #3.9 and got both the Astrometry and Photometry working for M57.

However when I load in M27.fit and reposition the Star Atlas on M27 I cannot see any obvious correlation between the stars. So then I tried automatic mode and I got a message in the top left corner of the Atlas window saying "No Match".

I have downloaded the UCAC4 Star Atlas using FileZilla in binary mode, and I see that there are 5 sub-folders, including u4i and u4b.
There are also some files including ucac4fix.html this says that I nee to run a fix on some of the UCAC4 data set by running modif3.py on my Windows PC.

Question is which folder should I set as the path in the Star Atlas preferences Star Atlas tab dialog box? Would it be folder U4b which has the 900 "z" binary files in?

Also, should I set the UCAC4 as Catalog 1 and GSC as Catalog 2 or does it not matter which is which?

Thanks
Ian

[fabdev]

Maybe the problem is that the GSC has no stars close to very bright objects(?), but with the UCAC4 this is solved.

Both the u4b and the parent folder will be accepted as valid paths for the UCAC4.

I never used the Python script to fix those stars, because it's related to some stars with high proper motion, which are not interesting for astrometry in any case. I will try in the following days by the way.

It doesn't matter about the two catalogues, but I would enable only the UCAC4 at the end, just clicking on their buttons in the Star Chart.

[iandh2010]

Hi Fabio,
I have now managed to get things sort of working when using UCAC4.

However, even UCAC4 does not have stars close to objects like Messiers. Therefore, even when using the UCAC4 Star Atlas I still could not get a result for the M27.fit example file.

However, when I loaded M65.fit it worked very well, but even I could see the correspondence between the image and the Atlas stars.

Luckily on my setup Nexstar 11" , 2700mm F.L. and ASI294MC camera, I should have have a FOV of 23" X 16"

I have just set the Atlas to Mira which is what I am interested in observing and the UCAC4 Atlas and GSC show Mira in different locations, presumably due to epoch and motion. What is good is that when I hover over the two different images it tells me which atlas the image comes from.

When the Atlas is on M42 the GSC appears to add quite a lot of additional stars, some again are in different locations.

So now I think that it working, just need some of my own images now, if the sky ever clears here in S.E. UK!!!!

When using my one shot colour camera for Photometry should I debayer (RGB Demosaic) the raw image or leave it as raw?

Thanks for your help
Ian

[fabdev]

About Mira, usually the precison of bright stars is not so good.

For precise "DSLR" photometry, (which applies to any GRGB CCD) usually the green or red channel is used, so the image should be demosaiced with the option "Green channel" or "Red channel", see: https://www.aavso.org/dslr-observing-manual

For generic light curves it's possible to use all color information, in this case it's sufficient to remove the bayer dithering (or just demosaic with the option "Gray").

[iandh2010]

Hi Fabio,
Re Mira - its rapidly dimming and was not really visible naked eye but that was largely due to a bright Moon. When I had Mira centred on the camera it was not all that easy to shut the exposure down enough to prevent Mira saturating and at the same time see the other fainter stars that were in the FOV and visible on longer exposures but then Mira was saturating!

I was just experimenting last night as the seeing was not that good, plus a bright Moon. But at least I could see some stars which was much better than the last couple of weeks!

Thanks for your help and advice.

Ian

[iandh2010]

By the way, what is the max. magnitude that gives reasonable results on stars like Mira?

Thanks
Ian

[fabdev]

It depends on the catalog: if the star was extremely saturated on the original plate or image then the accuracy on the position cannot be good. This is why some catalogs do not contain bright stars at all. For astrometry I wouldn't use any reference star brighter than 9.0 mag (by the way, in the Astrometry Window, the rejection based on O-Cs will probably exclude the star automatically).