Struggling with Photometry

[Ian Sharp]

Hi,

I'm a very experienced photometrist but new to photometry in ASTAP. I should say I started using ASTAP for photometry because I have just bought a Seestar and ASTAP worked very well for me with my Seestar S50 Pro files.

However, I've been trying to use ASTAP on some of my regular variables that I process using AstroArt8 on a regular basis and I have had very mixed success. I always feed ASTAP with pre-calibrated files so I haven't had to go through that part of the process.

For example, I tried HL Aur and I went through the whole process successfully. But, when I tried other common variables such as HW Vir, NY Vir, DD CrB I get an error when I go to the AAVSO report screen. The play button detects all of these stars and the AAVSO comparison stars and these show up correctly in the photometry table and also in the AAVSO screen, but when I check the variable it does not get plotted on the graph even though I can see the excellent mag. values in the table. If I try to just grab the report in the clipboard or save to file I get an error message and then the whole program closes. I've also tried manual star selection but this makes no difference.

I have attached some screen shots. I can send you data if you require?

Best Regards
Ian.

[han.k]

Hi Ian,

I found the cause by your screenshots. The comparison stars or one of them is saturated. See the markup in the attached modified screenshot.

The saturation point is set at 60000 as in your screen shot

I next version I will add a red X directly behind the comp/comparison stars.

Does this fix your problem?

cs, Han

[Ian Sharp]

Thanks for your reply,
I don't understand neither the variable nor the comp stars are anywhere near saturated.
Here's a screen shot from AstroArt of one of the NY Vir images.
Cheers
Ian.

[han.k]

I see the low ADU.
Can you attach one of the fits files, so can simulate the problem here running the program in the debugger?

cs, Han

[Ian Sharp]

Hi Han,
Sure here is a zip of one FIT file - let me know if you need more - I could WeTransfer them.
Ian.

[han.k]

The problem is that the filter is 'L'. It expect V, R,G, SI,SG, TG.... See attached screenshot
You could update in all files the keyword FILTER by the menu show in attached screenshot. Was a filter used?

I will improve the messages. It should give a warning.

[han.k]

If it is a luminance filter, so only a block filter for ir and uv then you could renamed the filter value to CV. This stands for clear view. As comparison star you can then only use the Gaia database D80 or D50 since AAVSO does not provide comparison magnitude for clear filter. Check mark in the report window the option "Ensemble D50" or "Ensemble D80".

In tab photometry for each row you should see then two gray icon for clear view. L is not accepted by the AAVSO.

Tell me if this works for you

cs, Han

[han.k]

In next ASTAP version "L" will be recognised as CV and showing a grey icon.

[Ian Sharp]

Thanks Han!,

Yes, that works fo me now - see screen shot.

I use the Luminance filter a lot because I'm interested in getting the exposure down as much as possible to get the best quality eclipse curve possible for later measurement of time of minimum.

I have another question but I'll start another thread.

Thanks for your prompt replies.

Best Regards
Ian.

[han.k]

Good it works for you.

Nice curve.

Comparing luminance/clear view with the V50=Johnson-V could introduce some small absolute errors. If all stars are of the same colour it will be fine. When one or redder or blueish it will introduce an error.

cs, Han